the Limitations of Intergalactic Travel

[eNtRopY]

It seems to me that the limitation of human space travel isn't time but energy. Applying Einstein's theory of relativity, we see that the time dilation effect would allow humans to travel to virtually anywhere in the universe within their own lifetime.

t' = t * gamma,

where, gamma = [1 - (v/c)2)]-1/2.

The problem of course is finding the limit of how much energy is needed to transport a human at high enough speeds for the length of the journey to become reasonable. I suppose that if there were a means of efficiently converted mass into energy then the limit is simply:

E = mfuel * c2.

The energy needed to move the ship transporting the human would of course be:

KE = mship * c2 * [gamma - 1].

So, E > KE tells us how much fuel would have to be consumed.

eNtRopY

[FZ+]

Applying Einstein's theory of relativity, we see that the time dilation effect would allow humans to travel to virtually anywhere in the universe within their own lifetime.
But I think there won't be much of an universe there when they arrive. The time they experience themselves will to t, not t'.
t' refers to the amount of time the observer (with relative velocity v) would see the ship experience with each second of their own time - in this case, the ship would be going slower than the speed experienced by the crew.

And c is still a speed limit relative to whatever destination they are looking for.

[eNtRopY]

Originally posted by FZ+
But I think there won't be much of an universe there when they arrive. The time they experience themselves will to t, not t'.
t' refers to the amount of time the observer (with relative velocity v) would see the ship experience with each second of their own time - in this case, the ship would be going slower than the speed experienced by the crew.


Sure there would be plenty of universe left to see. Remeber that although the traveller's time goes to zero, the stationary observers time is still only distance divided by the speed of light in a vacuum.

For example, in the extreme limit that a spaceship travels to Alpha Centari at the speed of light (which of course would consume an infinite amount of energy), the trip would be instaneous for the traveller but about 4.3 years for the stationary observer.

If you had a spaceship that could travel at speeds nearing the speed of light for extended periods of stationary observer time, I think the best strategy would be to look for baby solar systems and hope that by the time you get there some type of life will have evolved. Of course, the down-side to this is that you would never have the chance to see your friends or family again, as all of humanity as you knew it would be deceased before you even could think about it.

eNtRopY

[eNtRopY]

Originally posted by FZ+
And c is still a speed limit relative to whatever destination they are looking for.

No, c is constant in all reference frames.

eNtRopY

[Labguy]

On topic, but slightly off-topic, I don't think that near-c velocities will EVER be reached by any type of machine ever to be made by humans. Too much development time and way too high an energy requirement.

But, to keep the conversation going, I do think that the "effect" of c or c+ travel will be accomplished if we survive a few hundred thousand years or so. In December, 1903 the Wright brothers made their flight. Less than 66 years after that we landed on the moon. The rate of technological advancement was definitely exponential in the 20th century. Imagine going back in time to MIT in 1970 with a battery powered laptop computer. It would have easily sold for several million dollars.

If and when c+ travel is accomplished, I am convinced that it will be by some method not yet conceived, not even grazing black holes or through wormholes. The movie DUNE may not be too far off as to c+ travel. It will be by space-time "warping", folding, teleportation or some other odd method instead of building a neat ship and cranking up the power.

Any other ideas????

[Janus]

Originally posted by eNtRopY
It seems to me that the limitation of human space travel isn't time but energy. Applying Einstein's theory of relativity, we see that the time dilation effect would allow humans to travel to virtually anywhere in the universe within their own lifetime.

t' = t * gamma,

where, gamma = [1 - (v/c)2)]-1/2.

The problem of course is finding the limit of how much energy is needed to transport a human at high enough speeds for the length of the journey to become reasonable. I suppose that if there were a means of efficiently converted mass into energy then the limit is simply:

E = mfuel * c2.

The energy needed to move the ship transporting the human would of course be:

KE = mship * c2 * [gamma - 1].

So, E > KE tells us how much fuel would have to be consumed.

eNtRopY

Actuallly, the last formula you gave is just basically a modification of the formula from which E= mc² was originally derived:

E = mc²/(1-v²/c²)

Thus mc²(1/(1-v²/c²) -1) gives the value of the kinectic energy of an object moving at v.

The rub is, that in order to actually accelerate your ship through space you have to make use of a action-reaction engine.

In which case, you need to use the relativistic rocket equation

v = c *tanh(Ve/c * ln(MR))

In this case, Ve is the exhaust velocity and MR is the mass ratio (mass of the fueled ship/ mass of unfueled ship)

For a pure matter to energy conversion ship this means that we convert the fuel to photons, which we direct backwards to provide forward momentum.

To determine how much fuel we need to attain any given velocity, we re-arrange the formula to read

MR = etanh-1(v/c) * c/Ve

If Ve = c and we measure v is units of c we can reduce this to:

MR = etanh-1v

To reach .6c you would need a mass ratio of 2 (1 gram of fuel for every gram of payload.)

for .9c, a mass ratio of 4.259
.99c ---------------------- 14.1
.999c--------------------- 44.7
.9999c------------------- 141.4

Etc.

And that's assuming 100% efficiency; every photon produced in the reaction captured and directed straight backward.

[Janus]

Another point:
The mass ratios given in my last post only concern achieving the given velocity in the first place. You will also need to decelerate once you get to your destination.

That mean's in order to come to a stop from .999c you need 140.1 g of fuel for every gram of ship and cargo.

This compounds the problem, because this fuel is part of the payload you have to accelerate up to .999c in the first place. This means it actually takes 19628 g of fuel for every g of payload you actually want to deliver to the end point of the trip, if you are not just planning on doing a fly-by at .999c.

For actual intergalactic travel, consider the following example:

Andromeda is the nearest galaxy at 2,000,000 ly. Let's assume a 3 yr trip. (2yrs accelerating and decelerating and one year coasting.)

This means you would need to attain a velocity of 0.9999999999998749999999999921875c
for the coasting period.

To attain this Delta v you would need a mass ratio of 4000000. This is the mass ratio you would need to decelerate at the end.

Thus you would need 1.6*1013 g of fuel per gram of payload to complete the trip, or just about the mass of Deimos for every 100 kg of payload ( including the empty mass of the ship itself).

[schwarzchildradius]

if mf = mass of the fuel and ms = the mass of the ship, arent you forgetting that the fuel needs to be accelerated? seems like you need a dms/dt in there somewhere, but I ran through it anyway:
mfc2 > msc2(γ-1)
say you were to accelerate mass ms which must include mf at 9.8 m/s2 for a year (3.1563E7 sec)
Alexander's equation for finding relativistic velocity under constant acceleration was:
v = c tanh (at/c)
tanh a combination of exponentials of (at/c)
I found v=2.322E8 m/s or 60% c after 1 year of acceleration, γ = 1.5793
so the mass of the fuel has to be at least 58% the mass of the fuel + ship by
mf = ms(γ -1) if all the mass of the fuel is converted into energy.
and it gets worse from there (infinitely) as you approach c.

[eNtRopY]

Originally posted by schwarzchildradius
if mf = mass of the fuel and ms = the mass of the ship, arent you forgetting that the fuel needs to be accelerated?

No, I didn't forget that.

mship = mfuel + munfueled ship

I was just presenting some very general equations, and I didn't feel like typing out all the details.

eNtRopY

[eNtRopY]

Originally posted by Janus
Thus you would need 1.6*1013 g of fuel per gram of payload to complete the trip

Okay, that's the number I was looking for.

eNtRopY

[eNtRopY]

Does anyone know to what speed a ship could be accelerated if one were to slingshot the schwarzchild radius of a black hole?

eNtRopY

[Integral]

Originally posted by eNtRopY
Does anyone know to what speed a ship could be accelerated if one were to slingshot the schwarzchild radius of a black hole?

eNtRopY


For a body traveling with respect to, say your Black Hole, there are 2 possible non capture orbits. You are either parabolic or hyperbolic, in either of these the velocity of approach = velocity of exit. You gain NO velocity simply by passing near something.

Ok, what is the slingshot that we hear about near Jupiter. The velocity a satilite picks up as it passes near Jupiter is Jupiters ORBITAL velocity. This is the slingshot, not the mere fact that you pass nearby. Thus, the exit velocity of something passing near a BH would depend on the velocity of the BH, with respect to what?

[huxxar]

"If and when c+ travel is accomplished, I am convinced that it will be by some method not yet conceived. It will be by space-time "warping", folding, teleportation or some other odd method instead of building a neat ship and cranking up the power"

I tend to agree with you. I am also thinking that while superluminal is one prerequisite for inter planetary or inter galactic travel, perhaps the nature of our bodies and spacecrafts needs modification. While most physicists will probably laugh at what I am about to suggest, I think we need to convert our physical forms into energy or some type of zero mass substance before long range interstellar travel can take place. That will not only take out the kinetic energy problem as we approach c, but also drastically increases our life span to perhaps a few million years.

I have come across the "Negative Energy" phenomenon postulated by Paul Dirac but didn't really understand it. I wonder how a body of negative energy will behave at c or near c. Perhaps the physicists among us can shed some light on this matter?

[The Dagda]

I think the only way that c will be exceeded is by sidestepping it. Ie bending space, so the distances become closer, hyperspace sounds a little out there but can we bend space so much it "breaks"? if we could get a light year down to a thousandth or a millionth of a light year by bending the space in between, then maybe we'll effectively travel distances faster than would be possible at c or greater. Mind you what do I know, we may in 1 million years just beam ourselves there. Who really knows...

[kkassinger]

well ive been toying with some ideas Quartz when put under pressure generates electricity so all you need to do is have a big chamber with lots of quartz stalagtights placed really close together with just enough space for air to be around them. then you fill this chamber with compressed air. and use the suns gravity (magnetic field) calculate the polarization and duplicate it and broadcast it tword the sun like polls push with no friction and no interfieance once the magnet is shut down it should continue its rate of travel until stopped using another targeted sun. the only thing i struggle with is how to navigate or how to survive the acceleration

[mjacobsca]

The limit on human space travel definitely is not time. As you said, if you managed to achieve the relativistic speeds necessary to reach distant stars and galaxies, your time frame would be slow enough to make it possible. Most likely, the journey would be a one-way trip due to the fact that the human race may not exist by the time you got to your destination, not to mention by the time you returned.

The energy considerations discussed here seem to focus only on fuel requirements from rocket-engine technologies. There are theoretical engines that utilize solar energy to achieve sub-luminal speeds, and require pretty much no stored fuel at all. A ship would have to orbit the sun closely and build up speed for many years to achieve its target goal, but at least it can be done (in theory). And as for slowing a ship down, you could certainly attempt the same method of deceleration on the other end (you'd have to be sure you were nearing another star that was capable of providing the needed energy). Perhaps even a giant parachute could be used, trapping interstellar and star dust to slow the ship down. Again, this is probably theoretical at best, but it doesn't require a moon's worth of fuel on the ship.

To me, the hazards of interstellar space provide another huge hurdle to overcome as well. Imagine running into space debris at 99.9999% the speed of light? The space debris would shred your ship to pieces. Even a molecular gas cloud could theoretically create immense amounts of friction on the ship and tear it apart. Obviously, a huge energy shield of some sort needs to be created to avoid head-on collisions with space debris at near-light speed. And of course, such debris makes a giant parachute a difficult task as well (I assume it would be designed to be destroyed anyway, but still).

If humans could ever manipulate space itself, near-light-speed travel would be much safer. The ship could move slowly, but the space folded in front of it could make it travel many light years without moving through space faster than 15 MPH. Space debris would not pose nearly the same problem in this situation.

We can dream, right?

[kkassinger]

not solar power or orbiting the sun read what i wrote its a quartz generator powering an electromagnet the sun is a giant magnet what happens when you put two north magnets together

[kkassinger]

and a parachute would be pointless at those speeds one it will be torn apart two what is it going to drag against in a vaccum

[Ryan_m_b]

kkassinger and mjacobsca this thread is years old. It's against the forums rules to necropost. If you want to talk about this topic I would advise starting a new thread.

[Philosophaie]

Our fastest manmade craft is New Horizons on its was to Pluto. It is travelling at about 47,000 mph or 412,002,000 miles/yr. One of the closest stars is Alpha Centauri at 2.566E13 miles away. It would take New Horizons 62300 yrs to reach it at this rate. Maybe with larger rocket engines or a constantly accelerating Ion engine could faster speeds be reached but deacceleration must be perfect. Finally there is the problem of interstellar gas and debris that could destroy a spacecraft travelling at thousands of mph.

[mjacobsca]

kkassinger and mjacobsca this thread is years old. It's against the forums rules to necropost. If you want to talk about this topic I would advise starting a new thread.

The mobile version of the site doesn't show post dates on the thread when I clicked on it. How am I supposed to know when it was originally posted? And what is necroposting? I've never heard the term before?

[Ryan_m_b]

The mobile version of the site doesn't show post dates on the thread when I clicked on it. How am I supposed to know when it was originally posted? And what is necroposting? I've never heard the term before?

No worries, on the actual site you can see the date on the side (august 2003). Necroposting is when you post on a thread that hasn't had posts on it for years.

[Chronos]

This is my main objection to the Fermi paradox. The galaxy is not rife with technologically advanced alien colonies because space travel is prohibitively resource intensive.

[Cosmo Novice]

This is my main objection to the Fermi paradox. The galaxy is not rife with technologically advanced alien colonies because space travel is prohibitively resource intensive.

For all we know the galaxy may be rife with technologically advanced civilisations.

This argument is only taking into account "technically advanced civilisations" in the context of our understanding. This effectively bypasses one of the objections to the Fermi paradox - saying that the galaxy is not rife with technolgically advanced life is a little misleading, there are in fact many objections to the Fermi paradox and I personally believe that resources is one of the least valid objections. Essentially once any sufficiently advanced civilisation achieved non planetary manufacturing facilities resource objections become less valid - although Chalnoth I must grant that I think in the early phases

To assume in the meagre time we have been actively looking via SETI would produce results does seem a little naive on humanitys part - assuming the size of the galaxy.

[Chronos]

New physics is always a possibility, but, by physics as currently understood, the energy cost to colonize a planet orbiting alpha cenauri [our nearest known neighbor] in less than about 50,000 years would require a fuel payload around a lunar mass [at e=mc^2 conversion efficiency]. That appears to be a formidable technological challenge. I concede there may be civilizations capable of such feats, but, suspect they have also found alternative ways to satisy their ambitions.

[Ryan_m_b]

New physics is always a possibility, but, by physics as currently understood, the energy cost to colonize a planet orbiting alpha cenauri [our nearest known neighbor] in less than about 50,000 years would require a fuel payload around a lunar mass [at e=mc^2 conversion efficiency]. That appears to be a formidable technological challenge. I concede there may be civilizations capable of such feats, but, suspect they have also found alternative ways to satisy their ambitions.

I'm curious as to how this has been worked out? Aside from working out the hypothetical energy needed for the rocket I doubt we can make legitimate estimates of how much energy a colony would cost to construct bearing in mind we have no technology we would need to build a colony.

We can tick off things a colony would need (industry, agriculture, patial terraforming) but we have no idea how to do those things nor how much energy we would need.

[Zentrails]

The limit on human space travel definitely is not time. As you said, if you managed to achieve the relativistic speeds necessary to reach distant stars and galaxies, your time frame would be slow enough to make it possible. Most likely, the journey would be a one-way trip due to the fact that the human race may not exist by the time you got to your destination, not to mention by the time you returned.

The energy considerations discussed here seem to focus only on fuel requirements from rocket-engine technologies. There are theoretical engines that utilize solar energy to achieve sub-luminal speeds, and require pretty much no stored fuel at all. A ship would have to orbit the sun closely and build up speed for many years to achieve its target goal, but at least it can be done (in theory). And as for slowing a ship down, you could certainly attempt the same method of deceleration on the other end (you'd have to be sure you were nearing another star that was capable of providing the needed energy). Perhaps even a giant parachute could be used, trapping interstellar and star dust to slow the ship down. Again, this is probably theoretical at best, but it doesn't require a moon's worth of fuel on the ship.

To me, the hazards of interstellar space provide another huge hurdle to overcome as well. Imagine running into space debris at 99.9999% the speed of light? The space debris would shred your ship to pieces. Even a molecular gas cloud could theoretically create immense amounts of friction on the ship and tear it apart. Obviously, a huge energy shield of some sort needs to be created to avoid head-on collisions with space debris at near-light speed. And of course, such debris makes a giant parachute a difficult task as well (I assume it would be designed to be destroyed anyway, but still).

If humans could ever manipulate space itself, near-light-speed travel would be much safer. The ship could move slowly, but the space folded in front of it could make it travel many light years without moving through space faster than 15 MPH. Space debris would not pose nearly the same problem in this situation.

We can dream, right?

That's all true but what would really kill you would be the electromagnetic radiation pointed at you, blue shifted to enormous energies.

You could use a space ship made of an enormous piece of ice and that would shield you from most hazards, but eventually EM would get you.

Assuming short cuts like worm holes are impossible to exploit, the only solution is to transcend physical form.
I'm hoping that's what will happen when I die.

[Nabeshin]

That's all true but what would really kill you would be the electromagnetic radiation pointed at you, blue shifted to enormous energies.

You could use a space ship made of an enormous piece of ice and that would shield you from most hazards, but eventually EM would get you.

Yeah, I did a calculation that found an upper limit of about a 30ly journey (assuming you accelerated half the way at 1g, then decelerate) traveling in deep space before the blueshifted radiation exposure begins to show immediate physiological side effects.

[Labguy]

No worries, on the actual site you can see the date on the side (august 2003). Necroposting is when you post on a thread that hasn't had posts on it for years.The term "necro" simply means dead.

[JaredJames]

The term "necro" simply means dead.

Yes?

Necroposting is the term used here for revivng a dead thread.

[sophiecentaur]

I think that, rather than it being 'outward thinking' and adventurous, the preoccupation with space travel as the 'final frontier' is very limited and unimaginative. Space just isn't the wild west.
There is a vast expanse of investigation possible which is far more interesting and rewarding to anyone with the imagination to see. We could start with our Minds, then the Earth. Both fields are here and now and low cost. No limits on the intellectual demands either. Quad biking around the Universe is so passee.

[Zentrails]

I think that, rather than it being 'outward thinking' and adventurous, the preoccupation with space travel as the 'final frontier' is very limited and unimaginative. Space just isn't the wild west.
There is a vast expanse of investigation possible which is far more interesting and rewarding to anyone with the imagination to see. We could start with our Minds, then the Earth. Both fields are here and now and low cost. No limits on the intellectual demands either. Quad biking around the Universe is so passee.

True - and the oceans are largely unexplored and a large percentage of life on earth is in the form of strange bacteria miles underground.

[Zentrails]

Actuallly, the last formula you gave is just basically a modification of the formula from which E= mc² was originally derived:

E = mc²/(1-v²/c²)

Thus mc²(1/(1-v²/c²) -1) gives the value of the kinectic energy of an object moving at v.

The rub is, that in order to actually accelerate your ship through space you have to make use of a action-reaction engine.

In which case, you need to use the relativistic rocket equation

v = c *tanh(Ve/c * ln(MR))

In this case, Ve is the exhaust velocity and MR is the mass ratio (mass of the fueled ship/ mass of unfueled ship)

For a pure matter to energy conversion ship this means that we convert the fuel to photons, which we direct backwards to provide forward momentum.

To determine how much fuel we need to attain any given velocity, we re-arrange the formula to read

MR = etanh-1(v/c) * c/Ve

If Ve = c and we measure v is units of c we can reduce this to:

MR = etanh-1v

To reach .6c you would need a mass ratio of 2 (1 gram of fuel for every gram of payload.)

for .9c, a mass ratio of 4.259
.99c ---------------------- 14.1
.999c--------------------- 44.7
.9999c------------------- 141.4

Etc.

And that's assuming 100% efficiency; every photon produced in the reaction captured and directed straight backward.

I think the only practical method of interstellar space travel available to us right now would be propulsion by solar sail.

One of the problems a self-propelled space ship would have would be the lack of a light source to power solar panels, so not only would that craft have to carry fuel for propulsion, but also to power the on-board life support and navigation systems.

If we could direct the sun's rays using a gigantic parabolic mirror that would be one solution to two problems, powering the electrical system of the ship by conventional solar panels and at the same time providing photons for acceleration. You'd have to have some means of preventing the beam from diverging somehow.

The mirrors would have to be orbiting the sun also, or they'd just fall into it. I think it could possibly be done with one way mirrors that do not revolve in the slightest, but that would be still be pretty inefficient. There's probably an elegant way of doing it.

There's also the problem of: how do you decelerate when you've reached your destination?

You could aim tangentially for a star that is already moving away just the right way and "catch" up with it, but that would be tricky.

I've often wondered if the SETI project shouldn't look for signs of directed star energy pointed our way to power alien craft towards us. It's the opposite idea of a completely enclosed star with all it's energy being utilized for something.

If you could force the entire output of a star into a tightly focused beam, that would make solar sails a pretty good way to go.

[Ryan_m_b]

I think the only practical method of interstellar space travel available to us right now would be propulsion by solar sail.

One of the problems a self-propelled space ship would have would be the lack of a light source to power solar panels, so not only would that craft have to carry fuel for propulsion, but also to power the on-board life support and navigation systems.

If we could direct the sun's rays using a gigantic parabolic mirror that would be one solution to two problems, powering the electrical system of the ship by conventional solar panels and at the same time providing photons for acceleration. You'd have to have some means of preventing the beam from diverging somehow.

The mirrors would have to be orbiting the sun also, or they'd just fall into it. I think it could possibly be done with one way mirrors that do not revolve in the slightest, but that would be still be pretty inefficient. There's probably an elegant way of doing it.

There's also the problem of: how do you decelerate when you've reached your destination?

You could aim tangentially for a star that is already moving away just the right way and "catch" up with it, but that would be tricky.

I've often wondered if the SETI project shouldn't look for signs of directed star energy pointed our way to power alien craft towards us. It's the opposite idea of a completely enclosed star with all it's energy being utilized for something.

If you could force the entire output of a star into a tightly focused beam, that would make solar sails a pretty good way to go.

Who get's to control this interstellar death ray? You're talking about terrawatts of power constantly focused on one little point. Beyond that it would be almost impossible for the ship to cool down, it isn't going to a perfect mirror so it is going to absorb some of the energy. It's not going to be able to radiate that heat fast enough if it's constantly being hit by a laser.

The ship itself is going to have to be tiny which is a problem, manned interstellar missions would require a habitat capable of carrying a fully sustainable ecosystem as well as the millions of people required to supply all the specialised labour a modern civilisation needs.

Designing a hypothetical 1kg Starwisp (http://en.wikipedia.org/wiki/Starwisp) is a huge challenge, let alone some sort of manned habitat.

[Lsos]

Assuming that the human mind is simply a manifestation of the laws of physics and not something supernatural, it’s just a matter of time before we can reduce it’s contents into digital information. Once that happens, the idea of moving around large masses through space (living or inanimate) will be obsolete. All you’ll need to do is send some sort of “seed” assembly plant to a distant planet, and the rest of what you need, including ourselves, we “transport” by radio.

Again, assuming that our minds are not outside of the laws of the universe, this IS NOT science fiction, but simply a matter of time AND the most practical solution.

If we do indeed have some sort of “soul” outside this plane of existence, then it’s just a matter of time before we somehow utilize that plane to travel to the stars :)

Either way, we’re going!

[Ryan_m_b]

Assuming that the human mind is simply a manifestation of the laws of physics and not something supernatural, it’s just a matter of time before we can reduce it’s contents into digital information. Once that happens, the idea of moving around large masses through space (living or inanimate) will be obsolete. All you’ll need to do is send some sort of “seed” assembly plant to a distant planet, and the rest of what you need, including ourselves, we “transport” by radio.

Again, assuming that our minds are not outside of the laws of the universe, this IS NOT science fiction, but simply a matter of time AND the most practical solution.

If we do indeed have some sort of “soul” outside this plane of existence, then it’s just a matter of time before we somehow utilize that plane to travel to the stars :)

Either way, we’re going!

I strongly object to the notion that it is "simply a matter of time", especially when you make an assumption. When it comes to mind uploading I am disturbed by how prothetic and religious people become about it.

Now I do agree that the mind is an emergent property of the brain and that in principle it should be possible to replicate this through computation, even if it is revealed that human psychology is contingent on an exact replica of a brain (that includes a simulation of an exact replica) which in turn is contingent on an exact replica of a human body which in turn again is contingent on an exact replica of a habitable environment.

If we ever determine how the brain gives rise to mind
If we ever determine what the fundamental components of a brain that give rise to mind are
If we ever develop instruments capable of scanning at a resolution of these fundamental components
If we ever invent methods to simulate this process on a different substrate
If we ever build a substrate good enough to run those simulations

then yes we could in principle mind upload but it is mightily foolish to make an assumption that these things are non-trivial and will be about in "a matter of time". You're making an assumption that there will be no undiscovered show stoppers.

You also get to the problem of how do transport the necessary infrastructure to your target destination? Sure a robot body might be more durable than a human one and require less support (i.e. an ecosystem) but how do you get it to your destination? How do you transport the necessary industry?

The only problems mind-uploading solves is to do away with the need for a biosphere and to speed up transport once a base is established at a destination.

[Lsos]

Obviously any forecast into the future comes with assumptions, and nobody is in any position to argue what will happen in a hundred or 500 or 1000 years.

I'm basing my assumptions on the exponential speed that human progress is moving at, and on the fact that making a human mind IS possible...after all, it's already been done.

I do realize that how hard it will be to replicate and copy at will is another story altogether....

As for transporting the infrastructure, I believe by the time we jump over the mind-uploading issue (IF we jump it) then this will be the smallest problem.The technology to move large masses at ridiculous speed has already existed for decades, except the will and the economic incentive has been lacking.

[Ryan_m_b]

Obviously any forecast into the future comes with assumptions, and nobody is in any position to argue what will happen in a hundred or 500 or 1000 years.

Yet you are trying to do that

I'm basing my assumptions on the exponential speed that human progress is moving at, and on the fact that making a human mind IS possible...after all, it's already been done.

Contrary to popular (*cough Kurzweil) belief if you claim that technology changes exponentially you actually have to provide some evidence that this is actually occurring.

As for transporting the infrastructure, I believe by the time we jump over the mind-uploading issue (IF we jump it) then this will be the smallest problem.The technology to move large masses at ridiculous speed has already existed for decades, except the will and the economic incentive has been lacking.

What technology? Interplanetary propulsion hasn't even been viably invented yet let alone interstellar!! If you are going to make claims you are going to have to back them up with evidence. This is a science forum and using the caveat "I believe" isn't good enough

[JaredJames]

I'm basing my assumptions on the exponential speed that human progress is moving at

That doesn't mean anything.
As for transporting the infrastructure, I believe by the time we jump over the mind-uploading issue (IF we jump it) then this will be the smallest problem.

You've taken two completely separate technologies and used them to judge the advancement of each other. This doesn't work. Even if we managed to upload a mind, that has absolutely no bearing on space travel and certainly doesn't make it "the smallest problem".
The technology to move large masses at ridiculous speed has already existed for decades

Has it really? Perhaps you'd care to share it with the rest of humanity?

[Zentrails]

Who get's to control this interstellar death ray? You're talking about terrawatts of power constantly focused on one little point. Beyond that it would be almost impossible for the ship to cool down, it isn't going to a perfect mirror so it is going to absorb some of the energy. It's not going to be able to radiate that heat fast enough if it's constantly being hit by a laser.

The ship itself is going to have to be tiny which is a problem, manned interstellar missions would require a habitat capable of carrying a fully sustainable ecosystem as well as the millions of people required to supply all the specialised labour a modern civilisation needs.

Designing a hypothetical 1kg Starwisp (http://en.wikipedia.org/wiki/Starwisp) is a huge challenge, let alone some sort of manned habitat.

Yep, that would be correct for a narrow beam, but most of the solar sail designs I've seen call for a solar sail that is hundreds of miles in diameter and a beam that is much larger in diameter than that. They usually suggest the beam be generated by some kind of gigantic laser.

The biggest problem with that, IMO, is how do you attack the sail to the ship without using cables that weigh more than the ship itself?

If the beam were approximately the apparent size the sun is from our earthly vantage point, sure it would heat the heck out of anything trying to use it and wouldn't be practical for solar sail use.

I'm more interested in what such a beam would look like if it were beaming right at us from an alien solar system.
I'm guessing it would probably look like a nebula, assuming it is not laser generated light.

[Zentrails]

Has it really? Perhaps you'd care to share it with the rest of humanity?

Yeah, I could use some help moving my piano. LOL

[Ryan_m_b]

Yep, that would be correct for a narrow beam, but most of the solar sail designs I've seen call for a solar sail that is hundreds of miles in diameter and a beam that is much larger in diameter than that. They usually suggest the beam be generated by some kind of gigantic laser.

The biggest problem with that, IMO, is how do you attack the sail to the ship without using cables that weigh more than the ship itself?

If the beam were approximately the apparent size the sun is from our earthly vantage point, sure it would heat the heck out of anything trying to use it and wouldn't be practical for solar sail use.

I'm more interested in what such a beam would look like if it were beaming right at us from an alien solar system.
I'm guessing it would probably look like a nebula, assuming it is not laser generated light.

Even if the sail is hundreds/thousands of km2 it is still going to need a fantastic amount of energy focused on it, terrawatts of it. Shine that on a planet and you can burn cities away one by one.

Heating problem still applies here, the sail cannot radiate the heat away from it so it will just cook over time.

I've yet to see any paper discussing how solar sails can be used for interstellar transport that do not hypothesise starwisp designs.

[Lsos]

Yet you are trying to do that


I got the impression that forecasting the future is pretty much what this thread is about, so I chimed in with my vision. I do recognize that perhaps I did overstep the boundary of how much we're allowed to speculate. My apologies.


What technology? Interplanetary propulsion hasn't even been viably invented yet let alone interstellar!! If you are going to make claims you are going to have to back them up with evidence. This is a science forum and using the caveat "I believe" isn't good enough

I was talking about nuclear pulse propulsion, which was seriously being considered in the 50s and 60s. Due to the violent nature of this type of propulsion, instead of being a disadvantage, a large mass was actually a design necessity. The main reason why this method of propulsion was dropped was not an engineering, but a political one. This I'm pretty sure is within the scope of this discussion.

[JaredJames]

I was talking about nuclear pulse propulsion, which was seriously being considered in the 50s and 60s. Due to the violent nature of this type of propulsion, instead of being a disadvantage, a large mass was actually a design necessity. The main reason why this method of propulsion was dropped was not an engineering, but a political one. This I'm pretty sure is within the scope of this discussion.

I assume you've calculated how much nuclear fuel you'd have to carry to accelerate to a high speed (0.5c+)? I also assume you've factored in how much fuel you'd have to carry to accelerate the fuel itself?

Here's a hint, it's not as simple as people here seem to like making out when they drop this particular technology into the discussion.

Like I said, I believe ryan has pointed out on numerous occasions how much matter/antimatter it would take (that being one of the best sources) and that's not some reasonable amount.

[Ryan_m_b]

Like I said, I believe ryan has pointed out on numerous occasions how much matter/antimatter it would take (that being one of the best sources) and that's not some reasonable amount.

It does seem like I repeat myself on these space threads doesn't it? So once more, quoting myself...

It always boggles my mind when people express opinions suggesting that NASA worked out space travel decades ago and that all it would require is some investment and a bit of polishing off and we'll be skipping around the galaxy like true space cadets. Space travel is hard.

Antimatter/matter propulsion has the highest specific impulse that we know of. With a 1:1 ratio of fuel (itself a 1:1 mix of antimatter+matter) to ship we get a specific impulse of a megasecond. That means the ship can thrust at 1g for roughly 10 and a half days reaching a speed of ~10,000,000 mps which is 3.3% of the speed of light. To get to near 100% you would need thirty times this but remember you need to decelerate at the other end, that gives you a 60:1 ratio of fuel to ship if we use Am/M. Now Project Orion proposed using nuclear bombs but these can only match Am/M if the following few hypothetical were met;

The entire mass fissile material is converted to energy
-- It isnt, of all the uranium only ~2% undergoes fission. Of this only a half of a percent is converted to energy. Little boy, the Hiroshima bomb, contained over 60kg of uranium but only a penny's worth converted to energy. This means you need to pump up that ratio from 6:1 to 6,000-60,000:1

The bomb's mass is entirely fissile material
-- It isnt, most of the bomb is casing/primer etc. I can't find the exact figures with a brief google but it would be reasonable to assume that only 1-10% of the bomb is actually fissile. this pushes the ratio further to 60,000-600,000:1

The whole energy of the explosion hits the back of the ship
-- It won't, for a 1,400miles3 ship if we make it a cube that makes a ship ~11 miles on the side with each face 121miles2. If the explosion occurs 30 miles from the ship (about the recommended for Orion) then only 0.4% of the energy will hit the ship (the energy radiates as a sphere, the ship obscures a small part of this). This again pushes the ratio to 1,500,000-15,000,000:1

Aside from the horrendous fuel requirements there's a tendency for people to assume that all the other issues are just minor details when in actual fact all areas of space colonisation are extremely non-trivial. For an interstellar colony ship you need to;

Create a sustainable biosphere for the ship
--We have very little idea how complex ecologies work here on Earth let alone how to recreate one that is immune from ecological disaster.

Create an environment capable of growing food
--Same problem as above yet with the added problem of a ship biosphere being a small closed system. In addition a wide diversity of foods combined with the appropriate bacteria to fill up our guts (which contain 1kg of vital gut flora).

Pack a fully capable industrial system into a colony ship
--Many industrial complexes run over tens of km, add up all the wide variety of industries across the world plus the infrastructure and put it all in one place. In addition you need to redesign all of it to have near 100% recyclable capability (remember that closed system?)

Pack a fully capable work force
--In today's high-tech and diverse society there are literally 10s-100s of thousands of different specialities. Provide enough people in the profession to staff each job plus enough to train the next generation and the total number of people in the workforce? You're looking at a figure measured in the 10s-100s of millions of people

Design a long-term stable socio-economic system
-- Societies on Earth don't exactly have a track record of long term-stability. An interstellar trip could take 100s-1000s of years. The vehicle isn't going to be analogous to a captain and his crew, it's more like rolling up an entire country's population building a wall around it and then sending it off alone. Remember a single failing point and the whole mission is gone

Solve all of those problems without invoking magic wands of super-nanotech, AI and robots and then you can play space cadet.

Sorry for the long rant but it's a pet peeve of mine when people blindly assume that manned space exploration/space colonisation is easy then pretentiously claim that it's only reason X that we can't do it.

[Zentrails]

Even if the sail is hundreds/thousands of km2 it is still going to need a fantastic amount of energy focused on it, terrawatts of it. Shine that on a planet and you can burn cities away one by one.

Heating problem still applies here, the sail cannot radiate the heat away from it so it will just cook over time.

I've yet to see any paper discussing how solar sails can be used for interstellar transport that do not hypothesise starwisp designs.

It's my understanding that solar sails have already been experimented with on a small scale in space (described as "partially successful") and larger solar sail experiments are in the planning stages. Not for interstellar travel, but for travel to the outer planets.

Solar sails rely on conservation of momentum, so they don't necessarily need to absorb a photon to work. It's better to use a highly reflective surface, which won't heat up as much.

The sail will certainly radiate heat away like any black body radiator. As the object gets hotter, more total energy is emitted. The question of heating up depends on whether the absorbed heat is greater than the emitted heat. I'm sure an equilibrium would be reached at a relatively low temperature, depending on the intensity of the beam, of course, otherwise the solar sail would have to be designed by a pretty lousy engineer.:wink:

Wiki has a pretty good summary of the pros and cons of solar sails:
https://secure.wikimedia.org/wikipedia/en/wiki/Solar_sail

It's probably our best option considering only today's technology for any possible interstellar travel (unmanned with exceedingly small cargo weights) assuming the Orion Propulsion system is never pursued.

[Cosmo Novice]

It does seem like I repeat myself on these space threads doesn't it? So once more, quoting myself...

Can I just say that rant was brilliant. It was great to read something I have been thinking for a long time when I hear these arguments.

I understand that without the magic of a "super force field and FTL drive" that space exploration on an interstellar scale may be impossible - now or in any future. Due to the many points you mentioned.

It may be that such technologies will never exist to this capability and I do not agree with the whole technological development exponentiality. The other side to that coin is that eventually the scientific developments humanity makes may be merely refinements of existing knowledge, in fact to me that stands more to reason.

As a side thought, I have always thought this is the main theoretical refutation to the Fermi Paradox, with the sideline being the assumption of radio technologies and assumed detection - assuming cosmic timescales and probably limited use, not to mention algorithms and encryption and CMB in all directions.

Thanks for the laugh and insight into the fuel consumption numbers.

[Ryan_m_b]

It's my understanding that solar sails have already been experimented with on a small scale in space (described as "partially successful") and larger solar sail experiments are in the planning stages. Not for interstellar travel, but for travel to the outer planets.

Solar sails rely on conservation of momentum, so they don't necessarily need to absorb a photon to work. It's better to use a highly reflective surface, which won't heat up as much.

The sail will certainly radiate heat away like any black body radiator. As the object gets hotter, more total energy is emitted. The question of heating up depends on whether the absorbed heat is greater than the emitted heat. I'm sure an equilibrium would be reached at a relatively low temperature, depending on the intensity of the beam, of course, otherwise the solar sail would have to be designed by a pretty lousy engineer.:wink:

Wiki has a pretty good summary of the pros and cons of solar sails:
https://secure.wikimedia.org/wikipedia/en/wiki/Solar_sail

It's probably our best option considering only today's technology for any possible interstellar travel (unmanned with exceedingly small cargo weights) assuming the Orion Propulsion system is never pursued.

With regard to your Project Orion claim I refer you to my above post.

IIRC Solar sails are potentially good for either supplementing normal propulsion on a probe or good for very tiny masses. The effect you allude to whereby the sail must receive less energy than it can radiate is why solar sails would be terrible mechanism for transporting anything above a starwisp (http://en.wikipedia.org/wiki/Starwisp) and even then there are horrendous engineering difficulties. Quoting from the wiki article you linked the most efficient solar sail design yet comes from Drexler whose thesis states his design would only be 50-80 times better than existing, not a huge difference when you consider that simply enlarging the sail would produce the same effect.

Laser powered sail probes may be good when we want to send a few grams to the next system at both horrific expense and severe danger (a gigawatt laser with interstellar range pointed at your town is enough to ruin anyone's day) but they are not a practical solution to manned space exploration.

Can I just say that rant was brilliant. It was great to read something I have been thinking for a long time when I hear these arguments.

I understand that without the magic of a "super force field and FTL drive" that space exploration on an interstellar scale may be impossible - now or in any future. Due to the many points you mentioned.

It may be that such technologies will never exist to this capability and I do not agree with the whole technological development exponentiality. The other side to that coin is that eventually the scientific developments humanity makes may be merely refinements of existing knowledge, in fact to me that stands more to reason.

As a side thought, I have always thought this is the main theoretical refutation to the Fermi Paradox, with the sideline being the assumption of radio technologies and assumed detection - assuming cosmic timescales and probably limited use, not to mention algorithms and encryption and CMB in all directions.

Thanks for the laugh and insight into the fuel consumption numbers.

No problem :smile: it's a pet peeve of mine. I find it fascinating to discuss space travel more so when we stick to reality than when we start with the proposition "if we had magic technology X". It clashes with my other pet peeve, Ray Kurzweil and his exponential change arguments. It really is disturbing when intelligent people propose that we will have an extraordinary technology by X year and base their reasoning on, what is essentially, Moore's law. It really is staggering.

As for the Fermi paradox it always struck me that there are three conclusions;

1)We lack the capability to detect interstellar civlisations
2)No other tool using species has evolved in our galaxy
3)There is something prohibitive about interstellar travel

Option one is impossible to falsify without discovering a civlisation so we can leave it out, option two is interesting because it points to the rarity of such phenomenon. Option three is the only one we can actually investigate and it really is fascinating. Aside from the huge engineering hurdles to overcome there's also the little matter of the devastating potential of an interstellar war fought with relativistic weapons...

[Cosmo Novice]

As for the Fermi paradox it always struck me that there are three conclusions;

1)We lack the capability to detect interstellar civlisations
2)No other tool using species has evolved in our galaxy
3)There is something prohibitive about interstellar travel

Option one is impossible to falsify without discovering a civlisation so we can leave it out, option two is interesting because it points to the rarity of such phenomenon. Option three is the only one we can actually investigate and it really is fascinating. Aside from the huge engineering hurdles to overcome there's also the little matter of the devastating potential of an interstellar war fought with relativistic weapons...

Couldnt agree more.

1) Probably true.
3) Probably resource/technology/total non human rational that does not envisage space travel (this is not assuming a primitive race) etc etc..
2) *Negated by 1 and 3.

*Although I think given the vastness of our galaxy their are probably pockets of life, a very small percentage per star, and then a small percentage of those whose environment is suitable for multi-cellular development, and then a very small percentage of those developing into societal analogues, then developing similar radio technology to humans and probably (on comsological timescales) existing only for a small amount of time.

Well to be fair the dinosaurs did OK. Personally I think they will prove to be more the more succesful species on a history of our planet in the far future. All highly speculative of course :)

[Zentrails]

With regard to your Project Orion claim I refer you to my above post.

IIRC Solar sails are potentially good for either supplementing normal propulsion on a probe or good for very tiny masses. The effect you allude to whereby the sail must receive less energy than it can radiate is why solar sails would be terrible mechanism for transporting anything above a starwisp (http://en.wikipedia.org/wiki/Starwisp) and even then there are horrendous engineering difficulties. Quoting from the wiki article you linked the most efficient solar sail design yet comes from Drexler whose thesis states his design would only be 50-80 times better than existing, not a huge difference when you consider that simply enlarging the sail would produce the same effect.

Laser powered sail probes may be good when we want to send a few grams to the next system at both horrific expense and severe danger (a gigawatt laser with interstellar range pointed at your town is enough to ruin anyone's day) but they are not a practical solution to manned space exploration.

No problem :smile: it's a pet peeve of mine. I find it fascinating to discuss space travel more so when we stick to reality than when we start with the proposition "if we had magic technology X". It clashes with my other pet peeve, Ray Kurzweil and his exponential change arguments. It really is disturbing when intelligent people propose that we will have an extraordinary technology by X year and base their reasoning on, what is essentially, Moore's law. It really is staggering.

As for the Fermi paradox it always struck me that there are three conclusions;

1)We lack the capability to detect interstellar civlisations
2)No other tool using species has evolved in our galaxy
3)There is something prohibitive about interstellar travel

Option one is impossible to falsify without discovering a civlisation so we can leave it out, option two is interesting because it points to the rarity of such phenomenon. Option three is the only one we can actually investigate and it really is fascinating. Aside from the huge engineering hurdles to overcome there's also the little matter of the devastating potential of an interstellar war fought with relativistic weapons...

I agree with you about the looney Orion Propulsion idea, although it resulted in a damn good book written by Freeman Dyson's tree-house living, canoe-building son.

Solar sails are a very tough engineering problem, but at least they would get a constant acceleration from a reasonably non-divergent light beam. I think the heat problem would be insignificant as long as it doesn't melt the sail. The heat would radiate out in both directions, so the net momentum changes would cancel out.

What I envision is a space based extremely powerful EM rail gun for initial propulsion, with the solar sails unfolding and used after that. Like you, I don't think it is possible, with today's technology, to use it with anything but very small, unmanned probes.

Enlarging the sail would require more (and longer) tether lines, so there would be diminishing returns from that. If the ship has a supplementary on board propulsion system that would require the tether lines to be non-compressible as well as having good tensile properties.

That's also something that would be required by a "space elevator" cable. You won't get that using carbon nano-tubes as the cable raw material, which seems to be the consensus material of choice by "space elevator" believers.

Your 3 conclusions are all negatives and negatives cannot be proven, but are probably all true, but I would suggest that:

1) We probably can detect an alien civilization, but only if that alien species is purposely trying to contact us by sending a signal they know we will detect.

2) There may be intelligent species in our solar system that don't require tools and/or could be so different from us that we don't even recognize them as living beings.

3) Probably true, but that may only apply to manned interstellar travel.

There is one more possible way to achieve manned interstellar travel, that I've thought of:

Use spacecraft made of huge chunks of ice that feed water into a nuclear reactor heat exchanger, heating the water to insane temperatures, then letting it blow out of a rocket-like nozzle.

In order to reduce the amount of nuclear fuel you would need for the manned craft, you could first launch many similar, but much smaller unmanned craft with a nuclear propulsion module, giving them an initial velocity using space based EM rail guns.

You have them programed to burn just enough fuel to get to a particular velocity, then shut everything down. The unmanned crafts would have no radiation shielding and just enough electronics to control the reactor and navigation system.

After all the unmanned crafts have launched, launch a manned craft using the same rail guns to get the thing going initially, but unlike the unmanned craft, at accelerations that humans can survive.

Then, the manned craft "catches up" with each unmanned craft one by one, with the unmanned craft accelerating to make the manned craft's velocity. Then the manned vehicle rendezvouses with the unmanned craft and scavenges the remaining fuel and ice from them - or maybe just switch reactor modules.
It would still have to go significantly slower than the speed of light to keep the crew alive.

The crew would have to be in suspended animation for most of the voyage.
There have been some animal studies that suggest you can do that using H2S, IIRC.

I agree with you about Ray Kurzweil, although he seems to be right about a lot of things.
He has been quoted as saying that if he can live 50 more years, he expects aging to be completely eliminated, resulting in nearly limited life-spans.
(We can't get past that "heat death" thing, though, without moving to another universe.)

[mjacobsca]

Previous posts have discussed "mind uploading". I think it is more likely that we will send cryogenically frozen embryos across the vastness of space, and "grow" them when they reach a suitable destination, then feed them knowledge from endless video feeds when they wake. We'll have to keep them asleep while they grow, except for language lessons. We already freeze embryos today, so I see no reason why this couldn't be done, in theory. We'd have to protect the biological organisms from harmful radiation during the journey, we'd have to supply them with seedlings to grow food, and we'd have to build robots that could do construction work to build habitats and start crop growth. There are nearly as many challenges here as there are in building colony ships that travel for centuries with populations on board, but when the Earth becomes uninhabitable, we might resort to anything to save our species. Personally, I'd sign up for a colony ship with a 100,000 year journey ahead of it, but that's just me.

[Zentrails]

Previous posts have discussed "mind uploading". I think it is more likely that we will send cryogenically frozen embryos across the vastness of space, and "grow" them when they reach a suitable destination, then feed them knowledge from endless video feeds when they wake. We'll have to keep them asleep while they grow, except for language lessons. We already freeze embryos today, so I see no reason why this couldn't be done, in theory. We'd have to protect the biological organisms from harmful radiation during the journey, we'd have to supply them with seedlings to grow food, and we'd have to build robots that could do construction work to build habitats and start crop growth. There are nearly as many challenges here as there are in building colony ships that travel for centuries with populations on board, but when the Earth becomes uninhabitable, we might resort to anything to save our species. Personally, I'd sign up for a colony ship with a 100,000 year journey ahead of it, but that's just me.

Better yet, why not just send a DNA synthesis machine (programed to synthesize various genomes) to an alien planet that has the necessary raw materials to construct viable human DNA, then add it to embryos that had the DNA removed from the start?

That way you avoid the DNA damage that likely would occur from long term interstellar travel. You'd also have to figure out a way to do that with the mitochondrial DNA.

[Ryan_m_b]

The idea of a Von Neumann probe capable of building and raising humans counts as a magic technology in my books, as I said earlier it's more interesting when we leave out AI because it completely changes what we are talking about. If you posit strong AI and self replicating tools there's very little that can't be done.

As for cryogenic freezing we are still a long way off that being possible (if it is for long periods of time). Though I will admit that studies in that field are getting better, but its a world away from freezing a dog for a few hours to freezing a human for hundreds of thousands of years. Then you still have the problem of building a vehicle that can last, needing the technology to build an ecosystem from scratch, packing an industry onto the ship etc etc

[sophiecentaur]

Had there been an Internet at the time, I could imagine that discussions about the Philosophers' Stone would have gone along the above lines.
Would we not be fundamentally limited by human nature, at least as much as by Physics? Few governments can get voted in on the basis of projects taking more than a decade at the most. Just Who is likely to want to put off their present enjoyment in order to fund a project taking hundreds or thousands of years? And who would it all be for? Great great great grandkids?
Even Wormholes and the like are not going to let bodies through. Possibly communications though.

[Cosmo Novice]

The ideas of Von Neumann probes are interesting for our cosmic exploratory development. Tehnologically advanced genocidal Von Neumann probes may also be the answer to the Fermi paradox - which I find an amusing idea.

As this thread seems open to speculation I will throw in my two penneth. *IF* we are to ever actualise interstellar travel then it may be entirely necessary for technology to provide an extended degree of control on the physical Universe. Such as the ideas of advanced Alcubierre Drives, contained singularities and post physical evolution. All of which are highly speculative and may be impossible to realise.

I do not think anything we can currently develop or technically create (such as solar sails, ion propulsion etc) or even when these technologies have been refined, that they will provide realistic interstellar travel.

[sophiecentaur]

The VN Probe sounds a bit like inventing a new bacterium. This could evolve, all on its own, and decide to put an end to Humanity, on the grounds that we are an absolute shower and a blot on the Galaxy. Shooting ourselves in the foot or what?

[Ryan_m_b]

The thing is if we ever invent VN probes we would drastically change the parameters of what we are talking about.

VN probes, by definition are self-replicating machines. If we still wanted to colonise space we could send some to the moons of a gas giant and get them to dismantle all of them before using the mass to build millions of O'Neill cylinders. Into all of these cylinders we put different ecologies and study them to discover which one works best. Using this super-experiment we could crack the problem of building a sustainable environment by observing what works and what doesn't (without danger to human life or Earth's ecosystem)

There's really no need to go interstellar from that point because we can just live in millions of habitats orbiting the sun, the increased surface area allows populations so large we'd have to use standard form.

VNs seem a silly idea for space colonisation because you don't actually get to colonise anywhere, nobody leaves your planet you just make another planet full of humans. Though even if you did manage to build some sort of fantastical universal constructor (http://en.wikipedia.org/wiki/Universal_assembler) capable of being packed into a small enough mass to be sent interstellar you would still have to crack the problem of designing an AI to raise the children on the other end. Children do not develop from passive media (i.e TV). They need interaction, specifically human interaction. If we ever overcome the hard problem of consciousness (http://en.wikipedia.org/wiki/Hard_problem_of_consciousness) we might begin to see how we could go about making an AI but until then we're stuck where we are.

[Zentrails]

I do not think anything we can currently develop or technically create (such as solar sails, ion propulsion etc) or even when these technologies have been refined, that they will provide realistic interstellar travel.

Impractical might be a better word than unrealistic or maybe economically/politically unfeasible.

[Ryan_m_b]

Impractical might be a better word than unrealistic or maybe economically/politically unfeasible.

Very impractical. Looking at the numbers on the Spacecraft Propulsion (http://en.wikipedia.org/wiki/Spacecraft_propulsion#Table_of_methods) article of wikipedia current solar sails produce 9 newtons per thousand square metres at a distance of 1 AU (~300watts per metre). Working off of those numbers to propel a 1 tonne probe at 1g would require a sail 1km2.

As I said a suitable investment in resources might help us send interstellar probes via beamrider but no manned.

[Cosmo Novice]

Impractical might be a better word than unrealistic or maybe economically/politically unfeasible.

Socio and economic feasibility are generally what I was referring to. I stand by unrealistic - the reason I stand by unrealistic as opposed to impractical are that impracticalities automatically assume possibility, I refute that the technological examples I gave (Solar sail, ion propulsion etc) will realise interstellar capability. If interstaller technologies are ever theoretically proven (technologies beyond what currently exists) then I am happy to refute my comment and agree with impracticality.

Although really this is just semantics :)

[Ryan_m_b]

the reason I stand by unrealistic as opposed to impractical are that impracticalities automatically assume possibility

Totally agree. Something can be technologically impractical whilst still being totally unrealistic

[Lsos]

It always boggles my mind when people express opinions suggesting that NASA worked out space travel decades ago and that all it would require is some investment and a bit of polishing off and we'll be skipping around the galaxy like true space cadets. Space travel is hard.

Antimatter/matter propulsion has the highest specific impulse that we know of. With a 1:1 ratio of fuel (itself a 1:1 mix of antimatter+matter) to ship we get a specific impulse of a megasecond. That means the ship can thrust at 1g for roughly 10 and a half days reaching a speed of ~10,000,000 mps which is 3.3% of the speed of light. To get to near 100% you would need thirty times this but remember you need to decelerate at the other end, that gives you a 60:1 ratio of fuel to ship if we use Am/M. Now Project Orion proposed using nuclear bombs but these can only match Am/M if the following few hypothetical were met;

The entire mass fissile material is converted to energy
-- It isnt, of all the uranium only ~2% undergoes fission. Of this only a half of a percent is converted to energy. Little boy, the Hiroshima bomb, contained over 60kg of uranium but only a penny's worth converted to energy. This means you need to pump up that ratio from 6:1 to 6,000-60,000:1

The bomb's mass is entirely fissile material
-- It isnt, most of the bomb is casing/primer etc. I can't find the exact figures with a brief google but it would be reasonable to assume that only 1-10% of the bomb is actually fissile. this pushes the ratio further to 60,000-600,000:1

The whole energy of the explosion hits the back of the ship
-- It won't, for a 1,400miles3 ship if we make it a cube that makes a ship ~11 miles on the side with each face 121miles2. If the explosion occurs 30 miles from the ship (about the recommended for Orion) then only 0.4% of the energy will hit the ship (the energy radiates as a sphere, the ship obscures a small part of this). This again pushes the ratio to 1,500,000-15,000,000:1

Aside from the horrendous fuel requirements there's a tendency for people to assume that all the other issues are just minor details when in actual fact all areas of space colonisation are extremely non-trivial. For an interstellar colony ship you need to;

Create a sustainable biosphere for the ship
--We have very little idea how complex ecologies work here on Earth let alone how to recreate one that is immune from ecological disaster.

Create an environment capable of growing food
--Same problem as above yet with the added problem of a ship biosphere being a small closed system. In addition a wide diversity of foods combined with the appropriate bacteria to fill up our guts (which contain 1kg of vital gut flora).

Pack a fully capable industrial system into a colony ship
--Many industrial complexes run over tens of km, add up all the wide variety of industries across the world plus the infrastructure and put it all in one place. In addition you need to redesign all of it to have near 100% recyclable capability (remember that closed system?)

Pack a fully capable work force
--In today's high-tech and diverse society there are literally 10s-100s of thousands of different specialities. Provide enough people in the profession to staff each job plus enough to train the next generation and the total number of people in the workforce? You're looking at a figure measured in the 10s-100s of millions of people

Design a long-term stable socio-economic system
-- Societies on Earth don't exactly have a track record of long term-stability. An interstellar trip could take 100s-1000s of years. The vehicle isn't going to be analogous to a captain and his crew, it's more like rolling up an entire country's population building a wall around it and then sending it off alone. Remember a single failing point and the whole mission is gone

Solve all of those problems without invoking magic wands of super-nanotech, AI and robots and then you can play space cadet.

Sorry for the long rant but it's a pet peeve of mine when people blindly assume that manned space exploration/space colonisation is easy then pretentiously claim that it's only reason X that we can't do it.


I don’t understand how everyone can so easily dismiss the nuclear-pulse propulsion idea, especially in this thread which is obviously open to some off-the-wall concepts.

ryan_m_b, you’re the first source I have ever met that for one reason or another doesn’t accept the Orion Propulsion idea. No offence, but I’m sure you understand that to me, all the other sources are going to be more credible than you.

I am left with simply digesting the above dissertation you made. Again, no offense, but it appears like both an incomplete AND cherry-picked collection of data designed purposely to maul nuclear-pulse propulsion, but not necessarily reflect reality.

For example,

“of all the uranium only ~2% undergoes fission”. This is perhaps true for the Hiroshima bomb…the first ever bomb of its type not only used, but tested. The second bomb used was 10x more efficient, and modern bombs, boosted by fusion, are much more efficient than that.

“only 1-10% of the bomb is actually fissile”. Again this is perhaps true for the very oldest designs, but I’m sure modern ones are much better designed than that. Just a few years after Hiroshima they could make bombs two orders of magnitude lighter with the same yield.

“If the explosion occurs 30 miles from the ship (about the recommended for Orion) then only 0.4% of the energy will hit the ship (the energy radiates as a sphere, the ship obscures a small part of this).” ~30 meters was the recommended for Orion. The bombs were shaped charges which directed almost all the available energy at the pusher plate.

“With a 1:1 ratio of fuel (itself a 1:1 mix of antimatter+matter) to ship we get a specific impulse of a megasecond”. This part I can’t don’t understand because I have no idea how this alleged matter/ antimatter propulsion system is supposed to work. The only thing I can figure out is that it’s incredibly inefficient, as matter/antimatter annihilation produces enough energy which, if fully harnessed, could move a 1:1 ship not much slower than the speed of light. This matter/antimatter propulsion harnesses only a small fraction of the available energy. This leaves many possibilities, including that it’s more inefficient, or perhaps similarly to the Orion concept, and therefore it’s likely that it has the same sources of inefficiencies (if not more) as those outlined above. This would mean that they were calculated twice.

And then, of course, nobody says that the spaceship has to be 1:1 fuel to payload. 1:1 is damn good. Hell, some modern commercial jet liners do that.

I don’t have time to go through all the numbers and see for myself if Orion is feasible, but I hope you can understand how an armchair space cadet such as myself will, for now, continue to take their word for it, and not yours.

[Ryan_m_b]

“of all the uranium only ~2% undergoes fission”. This is perhaps true for the Hiroshima bomb…the first ever bomb of its type not only used, but tested. The second bomb used was 10x more efficient, and modern bombs, boosted by fusion, are much more efficient than that.

I hardly cherry picked data, I used what I had. Even if it was 10 times more efficient we still aren't talking on the order of 100% efficiency.

“only 1-10% of the bomb is actually fissile”. Again this is perhaps true for the very oldest designs, but I’m sure modern ones are much better designed than that. Just a few years after Hiroshima they could make bombs two orders of magnitude lighter with the same yield.

Again I am unaware of a nuclear device where the fissile material accounts for the majority of the mass.

~30 meters was the recommended for Orion. The bombs were shaped charges which directed almost all the available energy at the pusher plate.

Are you kidding? A nuclear explosion 30 metres away???? Do you have any links for that? How small would the explosion have to be not to destroy the ship/flood it with radiation and yet provide useful thrust?

“With a 1:1 ratio of fuel (itself a 1:1 mix of antimatter+matter) to ship we get a specific impulse of a megasecond”. This part I can’t don’t understand because I have no idea how this alleged matter/ antimatter propulsion system is supposed to work.

Here's the wiki article on antimatter rockets (http://en.wikipedia.org/wiki/Antimatter_rocket) and here's a NASA article (http://science.nasa.gov/science-news/science-at-nasa/1999/prop12apr99_1/) outlining the Isp

The only thing I can figure out is that it’s incredibly inefficient, as matter/antimatter annihilation produces enough energy which, if fully harnessed, could move a 1:1 ship not much slower than the speed of light. This matter/antimatter propulsion harnesses only a small fraction of the available energy. This leaves many possibilities, including that it’s more inefficient, or perhaps similarly to the Orion concept, and therefore it’s likely that it has the same sources of inefficiencies (if not more) as those outlined above. This would mean that they were calculated twice.

Sorry but how did you work any of that out? A moment ago you mentioned not knowing anything about how antimatter propulsion would work yet now you are claiming that the specific impulse of antimatter is somewhere close to 30megaseconds (close to what you would need to get "not much slower than the speed of light"

And then, of course, nobody says that the spaceship has to be 1:1 fuel to payload. 1:1 is damn good. Hell, some modern commercial jet liners do that.

Of course it doesn't have to be 1:1 but that's a good reference to the efficiency of a propulsion system hence why specific impulse assumes it. You may wish to still believe in Orion but you could at least look into it yourself, especially with the things I've discussed that are nothing to do with propulsion.

[JaredJames]

I don’t have time to go through all the numbers and see for myself if Orion is feasible, but I hope you can understand how an armchair space cadet such as myself will, for now, continue to take their word for it, and not yours.

Recommend you read through this: http://en.wikipedia.org/wiki/Project_Orion

The numbers just aren't enticing.

[Lsos]

Are you kidding? A nuclear explosion 30 metres away???? Do you have any links for that? How small would the explosion have to be not to destroy the ship/flood it with radiation and yet provide useful thrust?"

A fraction of a kiloton was my understanding. The wiki page provides a range of numbers ranging from 25-60 meters, as well as pretty much every other link I've seen. I'd be interested in where you got the miles figure from...would an atomic bomb do anything more than give you a sunburn from 30 miles away?

Sorry but how did you work any of that out? A moment ago you mentioned not knowing anything about how antimatter propulsion would work yet now you are claiming that the specific impulse of antimatter is somewhere close to 30megaseconds (close to what you would need to get "not much slower than the speed of light"

I just used E=mc^2 and then calculated velocity from the resulting energy. Of course I realize that neutrinos and gamma rays and the whole "action-reaction" thing will make the whole process inefficient. The point I'm making is that the antimatter rocket in question already took these inefficiencies and more into account, perhaps overlapping or completely encompassing the sources of inefficiencies which you went over again with Orion. And perhaps it would have it's own problems that Orion wouldn't. The links you showed don't lead me to believe otherwise.

Of course it doesn't have to be 1:1 but that's a good reference to the efficiency of a propulsion system hence why specific impulse assumes it. You may wish to still believe in Orion but you could at least look into it yourself, especially with the things I've discussed that are nothing to do with propulsion.

Of course. I just brought that up to underline the fact that Orion was never meant to be 1:1.

JaredJames, I have looked at that link as well as many others. For 60s technology using fission, I'm still impressed, and I still haven't seen anything that makes me think it wouldn't work.

[Ryan_m_b]

Well I'm happy to change my stance on the basis of the distance. I can't actually find the link I got mine from.

What do you mean by calculating the resultant velocity from E=mc2? Are you trying to go directly from mass -> energy -> momentum? I still fail to see why you think an antimatter rocket would be less efficient than Orion.

The fact still remains that project Orion (and for that matter Daedalus) were both concepts, not fully worked blueprints. They little more bearing as a realisable product as Da Vinci's drawings of a helicopter. Note that I'm not saying that nuclear fission/fusion are not potentially good propulsion technologies, I'm objecting to the notion that we've got it pretty much all figured out.

[qraal]

Well I'm happy to change my stance on the basis of the distance. I can't actually find the link I got mine from.

What do you mean by calculating the resultant velocity from E=mc2? Are you trying to go directly from mass -> energy -> momentum? I still fail to see why you think an antimatter rocket would be less efficient than Orion.

The fact still remains that project Orion (and for that matter Daedalus) were both concepts, not fully worked blueprints. They little more bearing as a realisable product as Da Vinci's drawings of a helicopter. Note that I'm not saying that nuclear fission/fusion are not potentially good propulsion technologies, I'm objecting to the notion that we've got it pretty much all figured out.

Orion is described in great detail, sufficient to begin construction. They fully intended to build it, but the Test Ban and Outer Space Treaty ended hope of using it in a civilian role. But the fission version was insufficiently energetic for an interstellar mission. Dyson did a sketch of that in a 1968 paper, but that's as far as that got.

Daedalus was more than a concept. The ignition system is described in great detail in the original reports and the rest of the vehicle was deliberately designed using known or near-term technology. The only "futuristic" parts were the computer system and the need for gas-mining Jupiter via gas-core nuclear rockets.

Alan Bond & Tony Martin, who led the Daedalus study, went on to design World-ships for interstellar colonization. They would've been immense, with cruise speeds of just 0.005c, but propelled by gigaton nuclear pulse units ignited by accelerator driven ignition units. Gargantuan but not inconceivable if O'Neill-style space colonies became the normal habitats of much of humanity. Definitely not "near-term" but not a big techno-stretch.

[sophiecentaur]

I think you are taking the term "detailed design" here a bit more literally than can be justified.
The very best one can hope for here would be broad feasibility studies as no enough is known of the practicalities.
Aamof, there are two ways in which 'efficiency' affects design. The amount of energy actually involved in refining 'fuels' and building the unit is highly relevant and should not be dismissed when considering feasibility.

[Lsos]

What do you mean by calculating the resultant velocity from E=mc2? Are you trying to go directly from mass -> energy -> momentum? I still fail to see why you think an antimatter rocket would be less efficient than Orion.

Yes, that's what I did....mass-> energy -> velocity....if just to establish a theoretical limit and compare it to the figure given in the article. What I gathered is that the article is being conservative.

Why would an antimatter rocket be less efficient? I'm not saying it would be less efficient, just that it might have similar (or more) sources of inefficiency. The article explained nothing about their antimatter concept, other than that antimatter could be used as a fuel. This leaves us to speculate all we want. First thing that comes to mind is that simply containing the antimatter could be a 1x - ?100000x larger pain in the *** than encasing some uranium. For all we know they're just using the antimatter to heat water and throw it out the back. They really gave us nothing to work with. The article wasn't informative at all and seemed like they shot from the hip to arrive at the specific impulse figure. Not only that, but their very own estimate for antimatter specific impulse was only 100x better than fission. It seemed designed for nothing more than to incite interest, and certainly not as a foundation from which to invalidate Orion.

Note that I'm not saying that nuclear fission/fusion are not potentially good propulsion technologies, I'm objecting to the notion that we've got it pretty much all figured out.

Ok I'll go with that. It seemed like you were dismissing the very concept as hogwash, but maybe it was necessary to balance out my overly optimistic vision.

[Ryan_m_b]

Ok I'll go with that. It seemed like you were dismissing the very concept as hogwash

Oh no no no, far from it. In my view nuclear propulsion could be a good way of achieving interplanetary travel, however there are potentially better technologies (e.g VASIMR) than lobbing a radiation inducing, EMP producing nuclear bomb out of the back of your ship.

My peeve is the idea that there are firm blueprints to how to build these things, lot's of work has been done on the idea but its nowhere near the stage where we have a "Project Orion kit, just add money!".

On the subject of colonising off Earth we have the collection of troubles I outlined that are nothing to do with propulsion (i.e establishing a biosphere, industry, society) etc. There is a perception I regularly come across that all we need to live in space is better rocketry, but there's so much more left to do!

but maybe it was necessary to balance out my overly optimistic vision.

Maybe you can counteract my pessimism :tongue2:

[Lsos]

On the subject of colonising off Earth we have the collection of troubles I outlined that are nothing to do with propulsion (i.e establishing a biosphere, industry, society) etc. There is a perception I regularly come across that all we need to live in space is better rocketry, but there's so much more left to do!

Yes this is a problem that I didn't even want to touch. We can't seem get along on the whole planet, and have been (are?) not far from destroying the entire thing. A colony spaceship? No...I don't see any solution except figuring out how to kill everyone on board and reviving them at the destination.

[sophiecentaur]

I think you should be taking into account just how much water you would need in order to get hold of enough Deuterium / Tritium for all this Fusion Fuel. It may be fun to talk of 'concentrated' fuel for a starship but is it actually available? Have you considered the practicalities???

[qraal]

I think you should be taking into account just how much water you would need in order to get hold of enough Deuterium / Tritium for all this Fusion Fuel. It may be fun to talk of 'concentrated' fuel for a starship but is it actually available? Have you considered the practicalities???

Deuterium is being separated in bulk from bottled water in China because of the supposed health benefits of depleted water. Off-world there are several sources with higher H/D ratios than Earth - comets, Mars, probably the Moon too. Tritium is next to useless as a starship fuel but small amounts might be worthwhile to act as a trigger, but it's difficult to make and store. Helium-3 would be a good fuel if it were more available, but mining the Gas Giants is about the only way to access it, unless a clever way of capturing it from the Solar Wind can be figured out. The Moon is often touted as a source, but a lot of regolith would need to be baked to get small amounts.

So, yes, the practicalities are being considered by at least some starship designers.

[sophiecentaur]

What has the drinks industry in China got to do with the availability of deuterium? Deuterium constitutes about 0.03% of naturally occurring Hydrogen (afaik).
The overheads for producing enough fuel by extraction would be a bit high,no? And the other sources are a bit speculative too.

I haven't yet heard of a proposal for serious inter-stellar propulsion that would not cost an awful lot of money. I seem to the only one who is questioning who will be prepared to spend / waste their hard earned Earthbound income (in the form of a tax or a 'charity donation') to pay for some enthusiastic group to set off on one of these one-way expeditions. I haven't heard of a fund to send holidaymakers up on the Virgin ship because, not surprisingly, people want to spend their own money on themselves unless given a pretty damned good reason.
What would be the reason that you could give them? Survival of the species, general interest, a rosy glow? I should have thought that a technology capable of sending starships all over the place would be be capable of improving many more lives on projects that would get more votes. Or are we suggesting that this could be achieved under a totalitarian regime?

This is, of course, a fascinating discussion topic but, really chaps, we can't be serious about it can we?

[qraal]

SophieCentaur
I understand your skepticism, but I am quite serious about it. One direct benefit is the simple fact that what can power starships can equally power cities on Earth. That would pay for starships many times over if they could be propelled by relatively abundant fuels.

Deuterium is one option which isn't excessively rare. Consider a probe needing ~1,000 tons of it. By mass deuterium is about 1/27,000th of water, thus processing ~27,000,000,000 litres is enough to tank up the probe. That might sound like a lot, but how many billions of litres of water are drunk in China per year? We're talking 0.027 cubic kilometres. That sounds like a lot less doesn't it? There's 1.35 billion cubic kilometres of ocean on Earth alone.

The Moon is estimated to have at least ~600 million tons of water in a few small polar craters, probably enriched in deuterium like it is in comets and any environment that light hydrogen can be preferentially lost from. I'd hazard there's at least ~1 million tons of deuterium available on the Moon.

[Wonderbread]

the Limitations of Intergalactic Travel

This is a new design for Gyroscopic Inductance circuit for DC current
production using the gyroscope itself as the induction circuit for
long term space flight. It will produce Direct current from a
gyroscope functioning in a zero gravitational field as an inductance
circuit. The two non-permeable gimbals armatures rotate around a
permanent inner magnet 180 degrees out of phase from one another
giving 360 degrees of a full rotation that allow a 100% duty cycle
when precession occurs. A north and south alignment on the spherical
inner permanent magnet rotates around the central centrifugal spin
axis witch doubles as a rotor flywheel. I have been working on the
proto type for 15 years now utilizing nano carbon fiber as the coils
in the inductor circuit; they are imbedded into the gyros non-
permeable gimbals in a zigzag pattern un-like the coils in an
induction circuit. Magnetic couplers between the gyroscopes parts
reduce further fatigue on the motor parts and reduce friction. There
are strategically placed permeable alloys in the gimbal armatures when
pulsed with DC current create magnetic field areas that interact with
the rotor for start, stop and homing of the gimbals. if gravitational
interference occurs in space flight a dc pulsed circuit 90 degrees
adjacent from the rotor flywheel controlled with small pulses of
current to control initial spin and braking on the central rotor while
motor functions are restored as needed, This design has several viable
applications for aro space industry. If solar panel deployment fails
or damages to solar panels this is a solid backup for running the
system operations of satellites and communication and instrumentation,
imaging instrumentation devices for space flight

[sophiecentaur]

SophieCentaur

. .
Deuterium is one option which isn't excessively rare. Consider a probe needing ~1,000 tons of it. By mass deuterium is about 1/27,000th of water, thus processing ~27,000,000,000 litres is enough to tank up the probe. That might sound like a lot, but how many billions of litres of water are drunk in China per year? We're talking 0.027 cubic kilometres. That sounds like a lot less doesn't it? There's 1.35 billion cubic kilometres of ocean on Earth alone.

. . . ..

How many of the billions of litres consumed in China are, at present, being treated for deuterium removal and how much does the process cost? My point is that the numbers involved in these proposals are all massive and the associated cost is proportionally high. I, personally, can't envisage a society or technology in which the costs will not be outrageous. Hence I say that people will just not be prepared to pay for someone else's space flight. Where is the possible advantage in it?
I have quite a pessimistic view of the future, in fact. The basics of society revolve around small, 'tribal' grouping and an inverse power law of concern for one's fellow creatures applies.
Humans are quite incapable of getting this planet sorted out, even, so I can't think how anyone could think that they have any chance or even inclination to undertake any such project with its inevitable timescale of hundreds of years and the need for unbelievable levels of cooperation.
Perhaps, in a nightmare future society, run by advanced computers, which could conceivably not have the short-termism that humans exhibit, such projects could be 'inflicted' on their human charges. But why would they need humans any more."I'm sorry Dave, I can't do that" would be the outcome. . . . . . .

[Ryan_m_b]

How many of the billions of litres consumed in China are, at present, being treated for deuterium removal and how much does the process cost? My point is that the numbers involved in these proposals are all massive and the associated cost is proportionally high. I, personally, can't envisage a society or technology in which the costs will not be outrageous. Hence I say that people will just not be prepared to pay for someone else's space flight. Where is the possible advantage in it?
I have quite a pessimistic view of the future, in fact. The basics of society revolve around small, 'tribal' grouping and an inverse power law of concern for one's fellow creatures applies.
Humans are quite incapable of getting this planet sorted out, even, so I can't think how anyone could think that they have any chance or even inclination to undertake any such project with its inevitable timescale of hundreds of years and the need for unbelievable levels of cooperation.
Perhaps, in a nightmare future society, run by advanced computers, which could conceivably not have the short-termism that humans exhibit, such projects could be 'inflicted' on their human charges. But why would they need humans any more."I'm sorry Dave, I can't do that" would be the outcome. . . . . . .

I agree. The expense of such a project is massively prohibitive and doesn't bring anything back. The only argument for why such a thing is an investment that I can see is if we crack the problems of building and maintaining a biosphere we will be able to maintain the one we have on Earth a lot better.

As for the rest any technology needed for interplanetary space travel or space colonisation would be a huge investment but even if we did spend that much money it would have far better applications at the bottom of the gravity well.

[Lsos]

I'm not sure about deuterium production, but it sure doesn't sound any more difficult than mining and then enriching Uranium. I never did the cost analysis but sending rockets into space is not all that cheap either, and it's very possible that using deuterium as a fuel would make economic sense, if nothing else.

You're probably right though in thinking that people won't go for spending a large portion of the GDP on a spaceship just for the hell of it. There usually needs to be some kind of spark, such as WWII for making the atom bomb, or the Cold War for going to the moon. The trigger might be societal or it might be something extraterrestrial, such as huge asteroid which eventually WILL come, if we can wait long enough. For something like that, building a risky, costly, radiation-spewing spacehip might be the only option.

[Ryan_m_b]

The trigger might be societal or it might be something extraterrestrial, such as huge asteroid which eventually WILL come, if we can wait long enough. For something like that, building a risky, costly, radiation-spewing spacehip might be the only option.

This is one of the biggest fallacies that the subject of space colonisation receives (no offense intended Lsos! I've stated this before too :smile:). If we ever need to leave Earth because it is about to become uninhabitable then we are going to need some sort of space based colony (perhaps in orbit or somewhere else in the system) and this colony is going to require us to;

Create a sustainable biosphere for the ship
--We have very little idea how complex ecologies work here on Earth let alone how to recreate one that is immune from ecological disaster.

Create an environment capable of growing food
--Same problem as above yet with the added problem of a ship biosphere being a small closed system. In addition a wide diversity of foods combined with the appropriate bacteria to fill up our guts (which contain 1kg of vital gut flora).

Pack a fully capable industrial system into a colony ship
--Many industrial complexes run over tens of km, add up all the wide variety of industries across the world plus the infrastructure and put it all in one place. In addition you need to redesign all of it to have near 100% recyclable capability.

Pack a fully capable work force
--In today's high-tech and diverse society there are literally 10s-100s of thousands of different specialities. Provide enough people in the profession to staff each job plus enough to train the next generation and the total number of people in the workforce? You're looking at a figure measured in the 10s-100s of millions of people.

Now assuming that a freakish world wide effort pours most of the world's GDP into the project and comes up with a complete toolkit of these technologies (never mind the industrial needs). Why would we use it for a space rocket? Why would we not just fix the biosphere?

If the disaster is an asteroid or something would it not be easier to deflect it? If not (for some reason) why not just put backup habitats in orbit that can come down and terraform the Earth using these technologies? Rather than build fleets of rockets to boost a space habitat bit by bit to orbit why not build domed cities here or under ground? No bottleneck of a gravity well there.

I know it sounds pedantic but I cannot think of any solution to a disaster that would require us to star trek across the universe.

[sophiecentaur]

If we want (or are forced to find) somewhere else to live then the most economical alternative to Earth would surely be another structure in orbit around the Sun.
@ryan m b
I totally agree that the problem of dealing with a possible collision would be far better solved (cheaper and shorter timescale) by deflecting the threat than by launching a lifeboat.

I think the main problem that the 'enthusiasts' have is the naive picture that they have of a Star Wars / Star Trek Universe in which we can all hop from place to place (and back again) within some sort of galactic community and in the same sort of timescale that Earthly travel takes place. What they are really proposing is something far more radical than the early colonisation of the New World from Europe. There is no chance of return to Earth. There is no community. There would be no knowledge of how the experiment had fared, except to later generations. There would be no benefit for the people remaining on Earth. S why propose it????

[Ryan_m_b]

If we want (or are forced to find) somewhere else to live then the most economical alternative to Earth would surely be another structure in orbit around the Sun.
@ryan m b
I totally agree that the problem of dealing with a possible collision would be far better solved (cheaper and shorter timescale) by deflecting the threat than by launching a lifeboat.

I think the main problem that the 'enthusiasts' have is the naive picture that they have of a Star Wars / Star Trek Universe in which we can all hop from place to place (and back again) within some sort of galactic community and in the same sort of timescale that Earthly travel takes place. What they are really proposing is something far more radical than the early colonisation of the New World from Europe. There is no chance of return to Earth. There is no community. There would be no knowledge of how the experiment had fared, except to later generations. There would be no benefit for the people remaining on Earth. S why propose it????

Absolutely. People like to apply analogies to these things compared to the colonial times. The reality is colonial travel was orders of magnitude easier; a wooden boat cost nothing to a nation, society's labour force wasn't as specialised and when they got where they were going there was local resources to easily exploit and a habitable ecosystem.

Star trek et al have confused the issue with this whole concept of a space "ship". For manned interplanetary travel one day we may build a vehicle that can take a small group of astronauts for a few months but anything taking colonists (or going interstellar) would be the equivalent of rolling up a New York into a cylinder and lobbing it through space.

And as I've said, any technology developed that allows us to build space colonies could be better used on Earth, for nearly any reason normally given to space.

[Lsos]

If the disaster is an asteroid or something would it not be easier to deflect it? If not (for some reason) why not just put backup habitats in orbit that can come down and terraform the Earth using these technologies? Rather than build fleets of rockets to boost a space habitat bit by bit to orbit why not build domed cities here or under ground? No bottleneck of a gravity well there.

I should have been more clear...this is exactly what I had in mind, deflecting the asteroid :). For a reasonably sized space-mountain, nuclear propulsion would probably be the best, if not only shot at deflecting it.

This would mobilize us to build the thing. Once (if) we succeeded at deflecting the rock, the technology would already have been tested and proven, at which point pursuing it further for exploration or to show up the Chinese or the Americans or whatever would make more sense.

But yeah, I’m pretty sure if we all of sudden were faced with having to build a space-ark and leaving the earth….we’d be fu*ed.

[Kenneth w]

Seems to me that in the case of travel to andromeda, to travel there in 3 years would entail traveling at millions of times c. Andromeda is over 2,000,000lys away.

[Lsos]

Seems to me that in the case of travel to andromeda, to travel there in 3 years would entail traveling at millions of times c. Andromeda is over 2,000,000lys away.

Doesn't seem any more impossible than traveling at 1x c :)

[Ryan_m_b]

Seems to me that in the case of travel to andromeda, to travel there in 3 years would entail traveling at millions of times c. Andromeda is over 2,000,000lys away.

If you were travelling at (roughly) .9999999999999999c then you would cross the distance in 2-4 years. Of course to someone back on Earth 2,000,000 years would have passed.

And Kenneth, it is impossible for objects with mass to travel faster than light.

[qraal]

If you were travelling at (roughly) .9999999999999999c then you would cross the distance in 2-4 years. Of course to someone back on Earth 2,000,000 years would have passed.

And Kenneth, it is impossible for objects with mass to travel faster than light.

More like 0.999999999998875 c, but what's a few 999s between friends. The only problem is that high gamma-factors need high accelerations to be reached in a short amount of tau-time (ship time), so flying to Andromeda (2.55 million ly at last count) in 3 years of tau-time means an acceleration of at least ~11 gees and a peak speed of 0.99999999999999766c. That means flying just 0.7 microns per second slower than light, which is probably not healthy because the CMB is blue-shifted to gamma-ray frequencies and an intensity of 666 MW/sq.metre.

[Ryan_m_b]

More like 0.999999999998875 c, but what's a few 999s between friends.

Blame excel, apparently getting beyond too many .9s makes a number 100 :tongue:

The only problem is that high gamma-factors need high accelerations to be reached in a short amount of tau-time (ship time), so flying to Andromeda (2.55 million ly at last count) in 3 years of tau-time means an acceleration of at least ~11 gees and a peak speed of 0.99999999999999766c. That means flying just 0.7 microns per second slower than light, which is probably not healthy because the CMB is blue-shifted to gamma-ray frequencies and an intensity of 666 MW/sq.metre.

I've always known that blue shift would be a problem but I've never seen any figures behind it. Thanks!

[shashankac655]

When I see people talking about intergalactic travel i feel that more than it being an impossible thing(with current technologies or those that may occur in the near future) to do, i feel it is actually unnecessary ,if humans are indeed capable of becoming a multi-planet species or a space faring species we don't need to travel to other galaxies. If we avoid extinction when we are limited to earth and then if want to find other alternatives to the sun and earth there are plenty of stars in our own galaxy and may be plenty of rocky habitable planets too in the habitable zone around it's star,they may be not as habitable as earth but at least close to what mars can offer. Currently we may know about a few hundred to a 1000 exo-planets of which most of them are gas giants like Jupiter and Saturn but astronomers are coming across rocky planets more and more, by looking at the number of stars in our galaxy, the planets may be several times this number but still our galaxy is also a big thing stretching across hundreds of millions of light years but we may not have to travel from one end to the other.

Developing radically new and powerful propulsion technologies may be the most important factor and we will definitely require huge leaps in developing artificial intelligence too and others.How fast or slowly these technologies are going to be developed depends on it’s level of necessity (if it is not at all necessary it may not happen at all). Ultimately everything comes down to what is necessary(or how much necessary) and what is not.

I think the real limitation of intergalactic travel or space travel in general is the lack of necessity for it right now( not because of the limitations of our intelligence or as a species or anything else) , adventurism and curiosity are two ways to unleash human potential but the ‘will to survive’ is the greatest of them all and only it will allow us unleash our true potentials (our biology may limit us from doing so unless our survival itself is in question) i.e we are not going to go extinct if don’t build human settlements outside earth starting from today or tomorrow or if we don’t try to travel to other galaxies, just like evolution cannot progress if a particular mutation does not produce more off springs i.e nature doesn’t care for our ambitions or curiosity it is only concerned about our survival.
(this is purely my opinion and it may be wrong but I have tried to be as realistic as possible with my extremely limited knowledge about these things.)

[Ryan_m_b]

When I see people talking about intergalactic travel i feel that more than it being an impossible thing(with current technologies or those that may occur in the near future) to do, i feel it is actually unnecessary ,if humans are indeed capable of becoming a multi-planet species or a space faring species we don't need to travel to other galaxies. If we avoid extinction when we are limited to earth and then if want to find other alternatives to the sun and earth there are plenty of stars in our own galaxy and may be plenty of rocky habitable planets too in the habitable zone around it's star,they may be not as habitable as earth but at least close to what mars can offer.

Remember we are going to need a comprehensive understanding of ecology far beyond that of today so that we can terraform (either partially or wholly) these planets to make them suitable. We can't live on worlds that have already evolved life (because the ecosystems would not mesh and we may have superantigenic problems) and lifeless worlds cannot support us.

Currently we may know about a few hundred to a 1000 exo-planets of which most of them are gas giants like Jupiter and Saturn but astronomers are coming across rocky planets more and more, by looking at the number of stars in our galaxy, the planets may be several times this number but still our galaxy is also a big thing stretching across hundreds of millions of light years but we may not have to travel from one end to the other.

Of course it begs the question as to why you need a planet at all. To build an interstellar colony ship you need fantastic knowledge of:

Ecogenesis to maintain both a stable ecology on the ship and build one when you get to where you are going.
Manufacturing because your ship needs to build a new civilisation so it needs on it factories capable of building everything. No small feat as on Earth I suspect such factories would be gargantuan (in addition everything has to be 100% recyclable because the ship is a closed system.
Cogsci knowledge so that issues of social/economical management can be so sophisticated that you are able to build long lived institutions (for a colony mission you're looking at a time scale measured in centuries-millennia and human institutions don't have a good track record of reliably embarking on projects that last longer than themselves)
Propulsion technologies to get there in a reasonable time i.e. centuries-millennia

This confuses the issue because if you've got all of this there is no need to wander into space and colonise other planets at all. An interstellar colony ship is less of a vehicle and more of an island in space. Rather than fly off for millennia you might as well build these colossal ships and put them in orbit around the Sun. Ignoring what specific elements you need if we posit an O'Neill style colony ship 100km long, 20km wide, 1km thick with a mass of ~6e15kg then with the mass of an object such as Ceres (9e20kg) you could make 150,000 ships with a total of 9e8km2 of living space, 6x more than the land surface of Earth.
Developing radically new and powerful propulsion technologies may be the most important factor and we will definitely require huge leaps in developing artificial intelligence too and others.How fast or slowly these technologies are going to be developed depends on it’s level of necessity (if it is not at all necessary it may not happen at all). Ultimately everything comes down to what is necessary(or how much necessary) and what is not.

I would argue the need for the three things listed above is more important than propulsion but I agree it is still important. Note that there are still huge complications with propulsion; even if we posit the creation of something as hypothetically good as an antimatter rocket (1,000,000isp, the best currently speculated with reasonable thrust) you still need an outrageous amount of energy to get anywhere. To boost one of our colony ships described above to .01c would require ~1.8e15kg of fuel (itself a 1:1 mix of matter and antimatter). Double that to slow down at the other end. That amount of Am/M fuel is equivalent to 3.2e32j of energy or 7.2e16 Tsa bomba's (http://en.wikipedia.org/wiki/Tsar_Bomba) (I'd hate to be the enemy of that ship).

I'm confused as to why you think artificial intelligence would help? Sure more intelligent software would help with everything but why do you think it is necessary?
I think the real limitation of intergalactic travel or space travel in general is the lack of necessity for it right now( not because of the limitations of our intelligence or as a species or anything else) , adventurism and curiosity are two ways to unleash human potential but the ‘will to survive’ is the greatest of them all and only it will allow us unleash our true potentials (our biology may limit us from doing so unless our survival itself is in question) i.e we are not going to go extinct if don’t build human settlements outside earth starting from today or tomorrow or if we don’t try to travel to other galaxies, just like evolution cannot progress if a particular mutation does not produce more off springs i.e nature doesn’t care for our ambitions or curiosity it is only concerned about our survival.
(this is purely my opinion and it may be wrong but I have tried to be as realistic as possible with my extremely limited knowledge about these things.)

If you read through the rest of the thread you will see that the "we will survive" idea doesn't really hold for space travel on this magnitude. Firstly the technologies you need to do it are orders of magnitude harder than those needed to keep Earth perfect (i.e. long before you have terraforming technology you have the ability to keep the worlds ecosystem perfect, long before you have propulsion technology you can deflect any asteroids, long before you have the ability to construct the societal models needed for generation ships you have a model for harmonious living on Earth).

The only time I see mankind achieving any of this is when the technologies are developed as a by-product of other scientific research and when the Earth is so much more prosperous than it is today that people are willing to commit resources to this endeavour.

[shashankac655]

Remember we are going to need a comprehensive understanding of ecology far beyond that of today so that we can terraform (either partially or wholly) these planets to make them suitable. We can't live on worlds that have already evolved life (because the ecosystems would not mesh and we may have superantigenic problems) and lifeless worlds cannot support us.
.
I agree


Of course it begs the question as to why you need a planet at all. To build an interstellar colony ship you need fantastic knowledge of…..
This confuses the issue because if you've got all of this there is no need to wander into space and colonise other planets at all. An interstellar colony ship is less of a vehicle and more of an island in space. Rather than fly off for millennia you might as well build these colossal ships and put them in orbit around the Sun. Ignoring what specific elements you need if we posit an O'Neill style colony ship 100km long, 20km wide, 1km thick with a mass of ~6e15kg then with the mass of an object such as Ceres (9e20kg) you could make 150,000 ships with a total of 9e8km2 of living space, 6x more than the land surface of Earth.
…...
I agree with all the points you have stated
Actually I was thinking about the possibility of humans outliving the Sun ,this might be ridiculously far away in the future and may even be impossible that’s why I talked about the need to travel to other solar systems.( i may be wrong)
I fully understand why we don’t have to abandon our solar system just because earth becomes inhabitable and so your suggestion is better than what I thought of but I am not sure how we are going to create gravity in space ship ,I have read about rotating spaceship inside which the centrifugal force can act like gravity and there are other ways like rotating electromagnets and stuff like that but can it really create gravity to the same magnitude as we experience on earth? How fast should the spaceship rotate ?
Is it easy to maintain the speed of rotation?




I'm confused as to why you think artificial intelligence would help? Sure more intelligent software would help with everything but why do you think it is necessary?

Considering such large interstellar ships we will be facing huge problems in maintenance, in such a large ship minute damages can prove to be disastrous.
Such a large ship will be constantly bombarded by tiny space rocks or asteroids travelling at very high speeds but may be the ship’s outer layers will be designed to withstand these collisions but it can’t withstand that forever(after repeated collisions on the same part) and solar winds or flares may overtime cause some kind of damages and even inside the ship somethings may go a little wrong and we may need a super computer to detect minute unintended changes in the ship. keeping an eye on every single miniscule corners of a ship (inside and outside)will be very difficult ,even if we have advanced surveillance systems (like we use in monitoring modern day traffic and security systems etc.) we will still have to depend on the ‘human element’ which may not be safe enough for example: in the Columbia disaster the hole in the shuttle was clearly seen by some people yet the crew were not informed about it and the consequence was fatal ,this kind of human error is something we cannot afford in our interstellar ship.
I don’t know of the possibility of this kind of AI but here it goes:-
We will need some kind of a super software which will make the ship behave like a huge artificial organism (not really an organism but only to a certain extent) which can detect and repair (or at least inform the inhabitants) when somethings go wrong in any corner of the ship or any point on the ship (inside and outside) this will considerably reduce the burden on the ship’s inhabitants and will improve safety.
Surely we can’t think of the interstellar ship to be just a hard and inpenetrable shell, inside which we can have an ecosystem can we? It has to be a lot more complicated than that.



Firstly the technologies you need to do it are orders of magnitude harder than those needed to keep Earth perfect (i.e. long before you have terraforming technology you have the ability to keep the worlds ecosystem perfect, long before you have propulsion technology you can deflect any asteroids, long before you have the ability to construct the societal models needed for generation ships you have a model for harmonious living on Earth).

The only time I see mankind achieving any of this is when the technologies are developed as a by-product of other scientific research and when the Earth is so much more prosperous than it is today that people are willing to commit resources to this endeavour.

I don’t disagree with any of these but the colliding asteroid problem was not what made me to think about why some day space travel or space colonization will become a necessity for humanity.
Harmonious living on earth is possible and appears to be a better thing to do instead of dreaming of space colonization right now, I agree.

I also agree with 2nd paragraph, there are so many things to be done on earth before humans can afford to live in space ,wealth distribution should become uniform and sufficient throughout the world ,scientific temperament and rationality has to cultivated among the masses especially in the developing world where religious superstitions, blind beliefs and discrimination on the basis of caste ,color or gender still dictates the lifes of millions of people.
The developed world should not only find more powerful energy sources (or renewable sources)but also try to put a limit on their consumption of energy and natural resources, for example if the countries in the developing world (with their huge populations)start to consume energy and natural resources in the way countries like the USA is doing right now we will need several earths to sustain humanity and human population has to greatly come down too.

[Ryan_m_b]

If the spin of the ship is big enough it will be barely detectable. I can't find a good calculator at the moment (feel free to google centrifugal calculator and find out how fast things have to spin for yourself) but there has been lots of speculative work done on the subject. The most famous of which comes to mind is Island Three (http://en.wikipedia.org/wiki/Island_Three).

EDIT: Here's a few more useful links
http://en.wikipedia.org/wiki/Artificial_gravity
http://en.wikipedia.org/wiki/Rotating_wheel_space_station
http://regentsprep.org/regents/physics/phys06/bartgrav/default.htm

[Chronos]

Blue shift would definitely be a problem traveling at .999 c. Not to mention random space debris. At that speed even a speck of dust would hit like a mountain.

[tkav1980]

I absolutely love these kind of topics. Being a huge Sci-fi nerd it's right up my alley.

I do have a question for all of the more knowledgeable people on this board. IF you were going to design a propulsion system for a future interstellar space craft how would you do it? Would you start with known technology or try to develop new technology? Is the idea of a "Warp Drive" purely science fiction and the Alcubierre metric no more than an exercise in mathmatics, or a viable basis for where to start from? Finally, What would your estimated timescale be for the development of efficient technology to travel to other solar systems be?

[Cosmo Novice]

I absolutely love these kind of topics. Being a huge Sci-fi nerd it's right up my alley.

I do have a question for all of the more knowledgeable people on this board. IF you were going to design a propulsion system for a future interstellar space craft how would you do it? Would you start with known technology or try to develop new technology? Is the idea of a "Warp Drive" purely science fiction and the Alcubierre metric no more than an exercise in mathmatics, or a viable basis for where to start from? Finally, What would your estimated timescale be for the development of efficient technology to travel to other solar systems be?

You should re-read this thread and pay specific atttention to the earlier posts on propulsion - namely that "warp" drive is purely speculative. Realistic propulsion methods are discussed in this thread.

[Ryan_m_b]

I absolutely love these kind of topics. Being a huge Sci-fi nerd it's right up my alley.

I do have a question for all of the more knowledgeable people on this board. IF you were going to design a propulsion system for a future interstellar space craft how would you do it? Would you start with known technology or try to develop new technology? Is the idea of a "Warp Drive" purely science fiction and the Alcubierre metric no more than an exercise in mathmatics, or a viable basis for where to start from? Finally, What would your estimated timescale be for the development of efficient technology to travel to other solar systems be?

I refer you to post 80, propulsion is the least of your issues. On this subject I strongly agree with SF author Charles Stross (http://www.antipope.org/charlie/blog-static/2009/11/the_myth_of_the_starship.html) that the term "space ship" confuses the whole issue because it conjurs up the notion of a dedicated crew travelling between hospitable environments. In reality any kind of manned interstellar travel is going to be analogous to rolling up a small country inside a cylinder and giving it a slight shove in one direction. This is going to require some particuarly huge leaps in science, technology and especially social sciences because you have to;
Build and maintain a viable ecosystem
Design an ultra-versitile and ultra-diverse industrial complex capable of recycling and manufacturing almost anything
Construct a socioeconomic and political system capable of maintaining a stable society over extremely long time periods with no failure

Technologies such as warp drives are almost totally speculative as they require negative mass and other such possibly non-existant unobtainium. Other technologies such as AI and Von Neumann probes may be possible but are essentially magic right now and can't meaningfully be discussed in this context.