The Limitations of Intergalactic Travel

[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 http://en.wikipedia.org/wiki/Antimatter_rocket" 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

 

[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 ). 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 traveling 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 traveling 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

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 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.