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XT
12-04-2006, 02:29 PM
In a recent GD thread there was a discussion about whether its possible to use todays technology to take a crew to the nearest star and have some of the folks (or their decendants) arrive still alive and kicking. The general concensus seemed to be that its totally impossible, that technology simply isn't there regardless of the level of effort or resources put to the project.

Myself, I speculated that with a world wide effort and the resources of an entire world (and no time constraints) that its technically possible, though impossible from a practical perspective (since there is no way the entire world would would ever unit to put in such a maximum effort).

I won't get into my idea's on how it could be done...they were mostly shot down as impossible/impractical. Of course, I'm no aero-space engineer or rocket scientist, so my idea are essentially meaningless on this score. I write bad science fiction and my day job is building computer networks. :p


My hypothetical question though is this...given no time or monetary/resource constraints (other than those of the earth itself), and given todays technology (or technologies that may not be here today but WILL be here soon...i.e. no speculative technologies like fusion, but perhaps emerging technologies that just aren't quite ready for prime time but will be soon), are there any folks on the board that COULD come up with a plausable scenerio to get folks to the nearest star alive and kicking?

Constraints are...you have to use either existing technologies or technologies acknowledged as practical emerging ones. You have a budget consisting of every country on earth. Ditto manpower and other resources...anything you need for the project, if it exists on earth, will be made available in whatever quantity you need. Any person or group of people needed will be made instantly available from any country on earth. Time is no constraint...you can take as long as you like to create the ship and as long as you like to send it to the nearest star. Crew size can vary, but lets fix a lower limit of 50 crew members...feel free to send as many more as you like. Risk...doesn't matter. If the probability of the mission succeeding is 1 in a 1000 thats acceptable...1 in a 1000 is certainly better odds that 'impossible'.

Can anyone do it given those parameters? I know there ARE some rocket scientists on the board...what say you? :p

-XT

CalMeacham
12-04-2006, 02:44 PM
the late Robert L. Forward proposed some innovative technologies, including using massive laser-generated photon proppulsion of what he called a "star-wisp" -- a very lightweight non-manned lightsail-type craft with a sensor package that, aside from carrying people, meets your criteria. Since it's propelled by photon pressure, the "engine" stays here, and we can keep it accelerating so that it reaches nearby stars in about a human lifetime. (It's like the craft in "The Mote in God's Eye", only without the pilot and crew)

Q.E.D.
12-04-2006, 02:49 PM
Since it's propelled by photon pressure, the "engine" stays here, and we can keep it accelerating so that it reaches nearby stars in about a human lifetime.
That's nice. But, how do we stop when we get there?

Jake
12-04-2006, 02:50 PM
I think the distance/logistics involved will just be to great for our current technology. Mars? Possibly.

Grey
12-04-2006, 02:55 PM
That's nice. But, how do we stop when we get there?Magnetic sail.

OldGuy
12-04-2006, 03:01 PM
That's nice. But, how do we stop when we get there?

You have a solar sail so you could at least slow down by flying straight towards the star. If that wasn't enough you could perhaps get into some kind of capture orbit. The nearest star system is Alpha Centauri which is a triple star so even if there are no planets, you might be able to do the capture using two or three of the stars themselves.

In some book I read -- I think the Roche's World set by Robert Forward -- they jettisoned the outer portion of the solar sail and let it continue on. This reflected the laser light back at them and the innerportion of the solar sail.

Ludovic
12-04-2006, 03:01 PM
Well, if there's photon pressure going outward toward a star when we are still near Sol, then once we reach the point where the target star is closer, shouldn't the photon pressure work in reverse order, thus slowing it down?

Q.E.D.
12-04-2006, 03:02 PM
Mars? Possibly.
Oh, I don't think there's any "possibly" about it. I'm almost certain that, given nearly unlimited resources, we could send men to Mars. We're not doing it because it's too expensive and impractical. We can still learn a great deal with unmanned probes; there's no reason to send men, yet.

Baron Greenback
12-04-2006, 03:06 PM
Your (lack of) constraints effectively lower the cost of payload to orbit to a trivial amount, so hell yeah. Need a billion tons of iron shielding, a functioning arcology or ten, the ability to manufacture from raw materials even the most complex equipment - fill your boots! We've got all the time in the world, it just needs many flights using current tech. It'd be a huge mass and wouldn't get anywhere particularly quickly, but it'd have a decent chance, likely better than 1 in a thousand.

CalMeacham
12-04-2006, 03:11 PM
That's nice. But, how do we stop when we get there?




1.) well, you could just not stop, and continue on through, or

2.) Forward suggested some methods of turning the craft around using magnetic fields and using light pressure to stop it.



The comparisons to his novel Rocheworld[/B] (in its various incarnations ) is appropriate in some ways, but I want to emphasize that Forward -- who worked a long time at Hughes Research Lab and later founded his own R&D firm, [i] Forward Enterprises (he had the name for it, in more ways than one) -- put this forward not as part of a science fictioon work, but as a doable piece of engineering. He presented and defended it at AIAA meetings.

Stranger On A Train
12-04-2006, 04:03 PM
Link to the referenced thread. Since I already expounded in great detail the technical concerns I have regarding the feasibility interstellar transit using existing technology, I won't reiterate here except to say that it is well and beyond existing capability and experience.

I don't doubt that at some point--assuming that we aren't wiped out by natural disaster or apocalytic warfare--if will be feasible to travel, if slowly, to another system. Given unlimited time, as the OP posits, we will develop technologies that make the exisiting capabilities look as primitive as steam power. But current technology, even assuming an unlimited budget (of which there is no such animal), will not get you to another star system, and the schemes presented by the OP in the previous thread have crippling technical problems for which there is no plausible solution.

Stranger

Polycarp
12-04-2006, 04:49 PM
There are a number of options, each requiring extensive refinement of existing technology -- but no brand-new technology.

1. The Universe Ship. Build a humongous artificial planetoid in orbit around Earth -- something that will sustain human life indefinitely. Setting up a stable ecology is no small matter; just getting enough raw materials to orbit to build the thing is an enormous task. Decide what all is needed on this monstrosity. Equip it with Shuttle-like SSTO landers. Give it enormous engines capable of moving that enormous mass. Then get volunteers to man it -- male and female. They'll spend the rest of their lives on board it, have children who will do likewise -- but sooner or later it will arrive at another stellar system, with a living crew aboard to explore it.

2. Bussard ramjet. This is a vessel able to "refuel" itself en route from the vacuum. Essentially you construct a ship capable of getting up to a certain fraction of the speed of light, at which point the concentration of dust, ions, etc., in space becomes "thick" enough to be collected (by an electromagnetic field trap) and used as fuel or propulsion mass. (To get an idea how this works, consider how much harder it appears to be raining/snowing when you're driving at freeway speeds than when you're standing still.) Again this is not a simple matter: you need to devise reliable equipment suitable for the initial acceleration and for generating the "net" to collect the particles. But the technology exists in its infancy today; it merely requires refinement.

3. Ultra-Efficient Fusion Drive: We can achieve controlled fusion today, but at barely a theoretical breakeven level (as much energy produced as goes in to generate the conditions for fusion) -- nowhere near an "economic breakeven" level needed to build the things for power generation. And at that, only a few percent of the theoretical E=mc2 energy content of the deuterium-tritium-tralphium fuel is available. But if we can somehow improve the efficiency of a fusion generator to a very high percentage of theoretical energy, use anything for reaction mass and accelerate a ship of any arbitrary configuration to a high percentage of light speed. Advantage: relativistic time dilation -- the time it would takefor such a trip as measured on board the ship shrinks. At 0.7 c you are travelling one light year per ship's year; at higher speeds yet, the apparent speed for a given distance measured in light-years drops to a fraction of the years light takes. (From a rest perspective, of course, it's significantly longer -- but that doesn't matter to the people on the ship, except for permanently distancing them from the people back home.)

4. Light sail vessel. Already described by others. Uses the pressure of solar (and stellar) radiation, and/or monumental lasers, for propulsion. Supposedly there are also "leave your motor at home" type devices using MHD as well, but I don't even pretend to understand how they might work.

All these require extensive refining of technology but no new breakthroughs. Obviously an FTL vessel, if possible, will require entirely new theory, something that turns Einsteinian physics into a special case as Einstein's insights did to Newtonian physics.

With existing technology, allowing only minimal refinements, the only plausible way to reach the stars is with an unmanned StarWisp type probe.

Stranger On A Train
12-04-2006, 05:03 PM
Well, if there's photon pressure going outward toward a star when we are still near Sol, then once we reach the point where the target star is closer, shouldn't the photon pressure work in reverse order, thus slowing it down?JHere's an old thread where we discussed how solar sails work. Solar sails by themselves are good for maneuvering the inner system, but aren't terribly efficient once you get further out and beyond the orbit of Saturn you might as well just get out an push for all the good it will do. The limiting case is the ratio between the photon flux and the mass of the sails; once the ratio gets too small, the performance is less than the influence of other factors.

Dr. Forward's idea about the starwisp (http://en.wikipedia.org/wiki/Starwisp) is interesting but his assumptions about the performance were flawed, and in any case it is both way beyond our current capabilities (a 10GW maser, 50000km focusing lens) and not scalable to the size necessary to transport a useful habitat-sized payload. Forward proposed other solutions involving the use of a powerful laser or laser array (deceleration was performed, as previously indicated, by separating the reflector into a forward free floating section and a section remaining mounted to the spacecraft) but the feasibility of this, even given the requisite technology and throughput, is highly questionable.

Stranger

Otara
12-04-2006, 05:18 PM
I found Starwisp on Wiki. Its proposed weight was 16 grams, and even with that is considered to be an 'enormous challenge'.

Critiques were also listed:

http://en.wikipedia.org/wiki/Starwisp

Otara

Otara
12-04-2006, 05:19 PM
Curses!


Otara

Chronos
12-04-2006, 06:28 PM
The conditions of "using today's technology" and "given unlimited time" are fundamentally at odds with each other. For instance, it would be very useful, in constructing our starship, to have ready access to space. We could take a few millenia to build a space elevator cable, 10 cm at a time (we have the technology to do that much, right now). Or, we could spend a few decades or a century refining nanofiber technology, and then spend a year or two building the cable with the new, refined technology (which has the added benefit that if we want to use nanocable anywhere on our ship itself, we can make that quickly, too, rather than waiting another millenium). Which of these options is more realistic?

John DiFool
12-04-2006, 07:49 PM
Advantage: relativistic time dilation -- the time it would takefor such a trip as measured on board the ship shrinks. At 0.7 c you are travelling one light year per ship's year; at higher speeds yet, the apparent speed for a given distance measured in light-years drops to a fraction of the years light takes. (From a rest perspective, of course, it's significantly longer -- but that doesn't matter to the people on the ship, except for permanently distancing them from the people back home.)

A fun little toy for calculations like the above:

Relativity Calculator (http://www.1728.com/reltivty.htm)

Stranger On A Train
12-04-2006, 08:07 PM
2. Bussard ramjet. This is a vessel able to "refuel" itself en route from the vacuum. Essentially you construct a ship capable of getting up to a certain fraction of the speed of light, at which point the concentration of dust, ions, etc., in space becomes "thick" enough to be collected (by an electromagnetic field trap) and used as fuel or propulsion mass. (To get an idea how this works, consider how much harder it appears to be raining/snowing when you're driving at freeway speeds than when you're standing still.) Again this is not a simple matter: you need to devise reliable equipment suitable for the initial acceleration and for generating the "net" to collect the particles. But the technology exists in its infancy today; it merely requires refinement.As discussed briefly in the previous thread, the Bussard ramjet has some serious technical drawbacks that may make it unusuable for interstellar flight and almost certainly unsuitable for living cargo. Aside from the fact that moving at large fractions of c would be immediately hazardous even when intersecting a dense cloud of hydrogen (much less the smallest speck of solid matter) you are going to have to operate an enormously powerful magnetic field. Variation in the constituants of the interstellar medium from which you are drawing fuel/propellent will play havoc with your confinement system. Drag on the field will limit top speed, which despite what certain science fiction authors have written, is probably no more than a few percent of c at best. It also has problems with regard to deceleration; you still have to carry enough fuel do decelerate from low range ramjet speeds to orbital speeds, and the trick of diving down into the sun only works if you assume very high thrust and efficiencies (and a lifesystem that can withstand a heavy dose of radiation); otherwise, you shoot out of the system in a hyperbolic orbit and keep going.

I wouldn't classify the Bussard ramjet as being completely impossible, but it's far more than an existing technology that requires refinement, and it's possible that it would be completely unworkable, especially for an organic payload.

Stranger

Napier
12-04-2006, 10:33 PM
>and given todays technology (or technologies that may not be here today but WILL be here soon...i.e. no speculative technologies like fusion, but perhaps emerging technologies that just aren't quite ready for prime time but will be soon)

My vote - this restriction pretty well shoots it. And the restriction is weirdly misplaced, too, as others point out. The biggest help with advancing time will be technologies that aren't even speculative yet.

Less that 0.2 millenia ago, Sadi Carnot revolutionized the understanding of thermodynamics in a publication that escaped major notice until after his death - and even so, in his publication stated that heat engines create mechanical power without actually consuming any of the heat. At this time the fact that magnets can generate electrical current was unknown. In just a few more millenia, how different - how *magical* - will technology have gotten? Would you challenge Burt Rutan to build an around-the-world airplane without using any electricity or thermodynamics, or CFD or CAD or polymers or aluminum or gasolinte or...???

Napier
12-04-2006, 10:38 PM
...Well, OK, you could withold the gasolinte, I guess...

Triskadecamus
12-04-2006, 11:04 PM
The path to the stars proposed is the actual path to the stars.

Do everything you need to do to have a chance to actually get someone there first.

That will be about a thousand years. Or perhaps longer.

It will include building and maintaining population centers in space. That is just one major step. It includes a half billion other smaller steps. It will have social, and military, and scientific consequences, both foreseen, and unforeseen. It has to come first, because we need to know that multi-generational populations can survive in space. There is no other way to know that, than to do it.

It will include creating multiple methods of communicating, and transferring material among the population centers. It will include multiple methods of transferring people among them as well. These populations will either have, or will develop politics. It doesn't matter what sort of scientific wizardry gets them there, once there are more than three of them, they will need to settle differences among themselves, and soon, differences with earthbound authorities.

A crew has to be independent to have any sort of chance of reaching a multi-generational goal. There has to be all the things we have discussed before, and a successful and peaceful revolution among the space born. Without it, no one is going anywhere. No one expected to die aboard ship when colonizing the "New World." Not even penal colonists will board a ship that does not expect to arrive anywhere with them alive.

If you have an independent population, born in space, and always expecting to live in space, the matter is different. But the Earthbound will never be able to rule them. They must be physically independent of Earth, or the plan cannot succeed. If they are independent of Earth, they will not consider themselves to be colonists of Earth. No authority can reach them. It's the definition of the event. Go where no man has gone before. (And where damn few will ever go at all.) Earth's billions will continue to teem. They will consider the colonists irrelevant long before they reach their destination. Leaving at all is the point of no return. But it will take the concerted and sustained effort of a significant majority of those same teeming billions to make it happen.

However daunting the physical factors of the trip seem, they are trivial compared to the social factors. No one on Earth ever gets to benefit from the trip in any non philosophical manner. Even assuring the survival of the race is purely philosophical, from the point of view of the many billions who are not going to be saved, and for most of that time, everyone will know that they are not now, nor ever will be among the elect.

The revolution in space mentioned above is a minor happening compared to the revolution needed on the home world.

Tris
--------------------------------
"We have too many high sounding words, and too few actions that correspond with them." ~ Abigail Adams (1774) ~

msmith537
12-05-2006, 09:18 AM
Risk...doesn't matter. If the probability of the mission succeeding is 1 in a 1000 thats acceptable...1 in a 1000 is certainly better odds that 'impossible'.


Well I wouldn't want to get into something that has a 99.9% chance of exploding. :eek:

Using today's technology to reach another star system with a live crew? Impossible. Not like one out of a billion impossible, but completely impossible.

Since faster than light travel is nothing more than some interesting artifacts of some relativity and quantum mechanics equations, that idea is out.

That means we would have to create some kind of self-contained habitat capable of supporting life for probably a thousand years or more as it slowly drifts towards some distant star. Do you know of any complex machine that can run for a thousand years? How big does this ship need to be to contain 1000 years worth of replacement parts?

Which of course begs the question, what do the colonists do when they get there?

Mangetout
12-05-2006, 09:33 AM
I'm not sure how this can be a GQ; it seems inevitable that it will turn into pretty much a clone of the GD thread that spawned it, but I'll say this:

If some 'free energy' technology can be perfected, or even something that permits us to completely convert matter into energy, then two birds are potentially killed with one stone; obviously one of these is the issue of energy to sustain life support and other shipboard systems, but the other is propulsion - if energy budget is not a pressing concern, then something like a circular particle accelerator could be used to provide thrust - the advantage of this method would be that the propellant is thrown away at the maximum possible velocity, achieving the maximum thrust per unit mass of that finite supply of propellant

Stranger On A Train
12-05-2006, 09:33 AM
Which of course begs the question, what do the colonists do when they get there?Go to XenoDisneyworld?

Stranger

Stranger On A Train
12-05-2006, 09:42 AM
If some 'free energy' technology can be perfected, or even something that permits us to completely convert matter into energy, then two birds are potentially killed with one stone; obviously one of these is the issue of energy to sustain life support and other shipboard systems, but the other is propulsion - if energy budget is not a pressing concern, then something like a circular particle accelerator could be used to provide thrust - the advantage of this method would be that the propellant is thrown away at the maximum possible velocity, achieving the maximum thrust per unit mass of that finite supply of propellantWell, if you can convert matter directly into energy, then you might as well dispense with mass propellent entirely and use high energy photons as your propellent. With the highest possible exhaust velocity (c there's no theoretical limit to how fast you can go; plus, it makes a dandy weapon should you be attacked by large, cat-like aliens en route. Just make sure you don't wave the exhaust around an occuped planet.

This, of course, is beyond highly speculative. Converting mass particles into energy as anything like a going concern is far past conceivable technology.

Stranger

Chronos
12-05-2006, 11:01 AM
plus, it makes a dandy weapon should you be attacked by large, cat-like aliens en route.What do you mean, weapon? I already told you they had absolutely no weapons at all on board!

Seriously, efficient matter to energy conversion is a lot more plausible than an FTL drive (I know of three different ways to do it), but you're correct that it's far past conceivable technology. It's quite likely that we would actually need interstellar travel in the first place to develop any of those three technologies: At least two and possibly all three require the use of small black holes, and it may be that the only way to get those is to go out into the Universe and find them.

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