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 = m_fuel * c².

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

KE = m_ship * 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 = m_fuel * c².

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

KE = m_ship * 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 = e^{tanh-1(v/c) * c/Ve}

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

MR = e^tanh-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.

m_ship = m_fuel + m_{unfueled 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 spacecraft s 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 I've 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 traveling 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 traveling 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 spaceship 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 spaceship 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 = e^{tanh-1(v/c) * c/Ve}

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

MR = e^tanh-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 spaceship 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 spaceship 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 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 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.

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.

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 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 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 successful 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 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 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.)