Feasability of Interstellar Travel

Great Debates
21

And now to step into the ring once more with Scylla,

Hey, it takes time to write these things and I have to take breaks sometime.

To clear up the old thread stuff (I’m too annoyed at losing my post to hash it out over there again:
With refinements of existing technology a fifty year trip to Alpha Centauri is possible. (Orion coupled by double slingshot around Jupiter and Sun.)

No, that is simply not true. First of all, the ship you described for the trip was NOT an Orion ship, but rather a ship using a fusion drive and ramscoop. No one has figured out how to get significant energy out of fusion in a controlled manner yet, much less how to get significant energy out of natural hydrogen (current work on fusion uses deuterium and tritium, which are not that abundant in the interstellar medium). Ramscoops are pure SF at the moment; collecting unionized hydrogen with magnetic fields across tens of thousands of kilometers is rather energy intensive, and doing so induces a drag on your ship.

A 50 year trip could be done with a laser powered light sail, but that would require power generation at something like 3 times Earth’s current output (by your own numbers) for the course of the whole trip. I suppose it’s possible to call that today’s technology, but IMO it’s unreasonable to call something that would require decades of infrastructure building achievable with today’s technology.

The investment needed for any mechanism for intersteller travel is, well, astronomical. When you start tossing around several times the current power used on the entire planet for your ship, it ain’t like picking up a used car.

Then it seems that you’re practically agreeing with me; you’d certainly want to send at least 2 probes to AC first (one cheap one to see if there’s anything there, a followup one to figure out exactly howto plan the mission). Taking your figure of ~100 years, and adding 60 years for the 2 probes (you can make automated probes lightweight so the energy costs are not prohibitive), you’ve already got a figure of 160 years. Tack on your estimate that you’d spend longer designing the ship than you’d spend on the trip, and you’re at 210 years for an interstellar trip.

And you think this will only take 100 years from now? That seems wildly optimistic to me.

Aside from your like of space, for what reason should people be deeply interested in space, especially extrasolar space? I mean, if you’re looking for a cause there are plenty of them on Earth.

Only because it was cost efficient to ship things back from the New World. Gold, spices, cotton, and later industrial raw materials don’t cost that much to ship accross the ocean. Barring a magical new energy source, the huge transport costs mean that any material is cheaper to mine in the solar system than to ship from some other star. You don’t get rich by spending more money to get the same thing.

But if you disagree, please outline for me what economic benefit people on Earth would recieve from colonizing AC. Also, explain why the inhabitants of AC wouldn’t just use the resources locally rather than impovrish themselves shipping things madly back to Sol.

tracer said,

Personally, I’d rather argue with someone who’s not in doubt. Scylla has proved quite willing to go back in forth over the discussion although we both disagree, and that’s much better than someone who says ‘I’m not sure’ and then refuses to say anymore. You don’t learn much from people who are convinced that they are wrong at the outset (which is one reason I avoid religious debates), or from people who will never admit that they are wrong (which is another reason I avoid religious debates).

Kevin Allegood,

“At least one could get something through Trotsky’s skull.”

  • Joseph Michael Bay
22

BigDaddyD,

You seem unaware of the basic physics behind space travel. In an atmosphere, the limiting factor on speed is friction. In space, the only real limiting factor on speed is fuel capacity (and the speed of light limit, but that’s a ways off). Since you specifically said ‘ignoring fuel capacity’, the top speed of an ordinary chemical rocket is only determined by the distance it has to speed up and slow down. The rockets on the shuttle can certainly sustain an acceleration of 1g, and if they were rebuilt for it could sustain such an acceleration for some time.

Since (again) we’re ignoring fuel capacity, you can accelerate to basically any speed you want. Your question is really like saying ‘ignoring cost, how many cars could you buy’? The answer is ‘how many are for sale’.

Just using an Orion drive (not actually built, but designed in the 60’s and not used because of treaties forbidding nuclear weapons in space), and assuming it’s 25% efficient and is made up of 90% fuel by mass, you could achieve 2% of the speed of light, making the trip in only ~186 years.

I think this pretty clearly shows that your figure of 30,000 years ignoring fuel requirements is rather outrageous.

Returning to http://www.treasure-troves.com/physics/RocketEquation.html , we see that out final velocity u is equal to our exhaust speed of .01c (which is 25% of the ideal speed for fission of .04c) times the ln of the mass ratio of our ship (10), which gives us a final velocity of ~.02c.

23

Okay, here’s some additional input to stir up the waters :slight_smile:

First of all, I’d like to comment that most of the space travel methods mentioned in this thread and its predecessor are simply not feasible, whether theoretically or practically.

Gravitational Slingshot: No practical effect at all.

Chemical Rockets: Same as above. Forget about it.

Fission/Fusion Rockets: Nearly 0 effect. Both methods require an unrealistic amount of fuel. You can try to scoop up whatever materials you find in space all right, but there is a reason we call it a vacuum, you know :slight_smile: Sorry, no dice either.

Light Sails: Again, the efficiency is simply too low. It’s kind of like pushing a car to the moon with the strength of a fire hose (same physical basis too). I don’t know about magnetic sails, but they’re probably in the same league. Unless we manage to build lasers that are a gazillion times more powerful than those we have today, and also find a way to focus that laser over humongous distances, this method is not going to work.

Warp Drives: Uh huh…

Worm Holes and Space Folding: Yah, I think you’ll have better luck with warp drives…

So know you must be thinking, what are the feasible methods? Well, I’d say there are two. One takes the more conventional approach, while the other borders on sci-fi, but is still more likely to be utilized than warp drives.

Matter & Anti-Matter Annihilation: This is the conventional method. Build a rocket and fill her up with the ultimate fuel. Assuming Proxima Centauri is 4 light years away, a 10 metric ton rocket can make the trip in 10 years (9 for the passengers) with less than 1 ton of fuel. The figures above are conservative estimates with 100% energy efficiency. Take that down by a factor of 4 just to be safe, and you can still make the trip in the same time with less than 4 tons of fuel. Comparatively speaking, this is likely our best bet for long range space travel in the near future; we already posses to the technology to manufacture and store anti-matter after all. I should remind you of course, that you’d still have to find a way not to get smashed by space dust while traveling at relativistic speeds. In addition to that, scaling the manufacture and storage of anti-matter to a realistic scale and creating an engine that could use the energy is still a big problem too.

Zero Point Energy (ZPE) Field Manipulation: Like I said, this is on the border of sci-fi and generally considered wacky material for the mainstream scientists. There is no known method to manipulate ZPE in any useful manner, but there is no proof that you can’t either. Enthusiasts are looking for a source of practically infinite energy here, but it’s not likely to ever become a power source, not to mention becoming a high power one at that. On the other hand, there is speculation that the ZPE field could have something to do with the nature of inertia, gravity, and a large range of other unexplained phenomena. Anyone of these being true would add a whole new dimension to space travel. With all being said, it’s a very very very long shot.

Whew… there you go. Must sleep now…

24

Zor, that is a very IMPRESSIVE list…

Thanks for pissing on the campfire! :slight_smile:

Actually, I would love to know your sources… not to admonish you or debate, but for knowledge.

Thank you.

The most rewarding part was when I got my money!
-Dr. Nick Riviera

25

Hmm… I’d say you can do all the calculations on the chemical/fission/fusion/anti-matter rockest with a general physics text book common to most college students. Light sails and gravitational slingshots could be done with the same source as well. The one sitting on my shelf is “Fundamentals of Physics” by Halliday, Resnick, and Walker, pretty much the standard text book around the globe.

As to warp drives, worm holes, and space folding… there are such popular topics in sci-fi that many scientists have actually came forward to comment on it. Bascially, the agreement across the board is that they aren’t possbile in a long shot. Scientists are usually nice people though, so they won’t try to extinguish your last hope on these matters :slight_smile:

ZPE is just the new fad which no one has stomped into the ground yet. There are quite a few scientists behind this, but hey, even scientists fall to fads too. Here are a few articles from Scientific America…

What the hype’s about… http://www.sciam.com/1297issue/1297yam.html

Column from “Ask the Experts”… http://www.sciam.com/askexpert/physics/physics32.html

Follow up column to the above… http://www.sciam.com/askexpert/physics/physics33.html

Also, if you ever come across some new method of space travel other than those mentioned above, I’d suggest you step back and take a second look. If it involves teleportation in any sense, take another step back :slight_smile: Your next step (not backwards) is as easy as typing a few words into a search engine. If you get more than a million (e.g. warp drives), or less than a hundred hits (i.e. lunatics), or none on educational (e.g. princeton.edu) or government (e.g. NASA, JPL) sites, it’s likely bogus.

Employ common sense. If it’s too good to be true, it probably isn’t. Anything worthy of discussion is sure to make news on more reputable sites. I might be painting a pretty blight picture here, but that’s unfortunately how things are in life. Trust me, I’d embrace warp drives if I believed they could work too :slight_smile:

26

Yeah, but I’m working on a Perpetual Motion Machine of the first kind.

Once it’s patented, we’re outta here!

Wolf 351, here we come.

27

Uhhhggg!

This is twice people have said you can’t get any significant velocity out of a gravitaional slingshot.
Nothing else, no backing it up, no why this is true. Nothing. Just a blatant ignorant and false statement.

I on the other hand went and bought a book describing the subject (God, I sound pompous! But so what?) It is not difficult to increase your velocity tenfold around Jupiter and a hundredfold around the sun. If you take a “standard” Orion spacecraft, burn towards Jupiter at 1g and do a screaming dive towards the sun at 1g, you can head out of the solar system at .05c.

In fact the only thing that’s stopping you from picking up more velocity is the amount of g force you must sustain. My example, which I got pretty much straight out of the book hits you with 18gees and is probably pushing it. The equations are not simple. they were developed by an acknowledged aerospace expert. I had to rely on a table he produced. His results are generally accepted by the scientific community. If you disagree then go read the thread, check out my source and order the text of the report and check the math out for yourself.

I would say a thousandfold increase in velocity is significant, and it gets you to AC in under 50 years. Not that this particularly matters because we won’t be doing anything like this anytime soon.

The laser sail recquires 1/3 of a terrawatt applied over a two month period only, and that gets you to AC in about 14 years.

Though technologically possible, neither of these things is practical until we have significant space infrastucture, and right now we don’t.

Riboflavin:

Let me state that there are no immediate quantifiable economic reasons why we should go to mars.

This doesn’t mean that there aren’t any good reasons.

100 years from now people will not remember this generation for the way we handled abortion rights, gun control, welfare, or any of a dozen other major issues, that we as a societ are so concerned with.

I simply hope that we’re not remembered as the generation that could have gone to Mars, but didn’t.

Basic Science is its own reward. We didn’t go to the moon because we were looking to make advances in microelectronics that would eventually carry us into the computer age, but that’s what happened.

It will likely be the same for Mars.

There’s the fact of the frontier. If a society isn’t growing it’s dying. Surely History has taught us that. What new frontiers await us on earth?

Look at the Chinese of the 11th Century. They had the technology and the capability to explore the world by ship, and they chose not to and stayed at home instead. Now most of South America speaks a version of Spanish. Had the Chinese chosen differently it’s likely that the Chinese language would be as ubiquitous a s Spanish is today. Instead they stayed at home and were conquered by the mongols.

A frontier society is a strong motivator for innovation. Doubtless there is little of an immediate commercial use that can be sent back from Mars, but I think it’s incredibly shortsighted to believe that the technological innovations to be gained by the enterprise won’t be worth it.

Finally, the natural resources of the earth are finite. We simply must have the infrastucture in place to replace these resources (perhaps from Asteroids,) Otherwise we stagnate and die.

Carl Sagan said it well “All civilizations either become space-faring or extinct.”

Again 6 Billion dollars is the price for Mars Direct. That’s one aircraft carrier. It’s less of an investment in todays dollars than it was to put a man on the moon. It’s a smaller percent of GDP than funding Colubus was for Spain (by the way funding Columbus is what Queen Isabella is remembered for today, Indeed it’s what Spain in the 14th century is remembered for.) How can we afford not to do it?

28

I’ve given a lot of thought to this idea – not so much interstellar flight in anything close to the foreseeable future, but just practical interplanetary flight.

I think one resource we often overlook are the near-Earth asteroids that cross both our orbit and that of Mars. I believe it is well within the engineering capabilities of our society as it stands to mount an expedition to a sizable asteroid, using a trajectory sufficiently hyperbolic that the change in direction and speed at the point of ‘crossover’ would be safe/endurable, with the added bonus that, in the event of a miss, the mission craft would eventually loop back and make rescue possible.

Assuming crossover went as planned, the mission could use the nickel-iron content of the asteroid as the reaction-mass for a mass-driver that would permit some degree of ‘steering’, and a method of slowing the mission craft as it neared Mars and separated from the asteroid.

29

George:

Good point, but it is actually tougher to do than a trip to mars. Mars has water and permafrost as well as oxygen. This means we don’t have to lug all the fuel or oxygen for the return trip, but pick it up on Mars.

The asteroids don’t have any water or gases to make use of, so it makes a mission to one of them actually tougher.

30

http://www.discovery.com/news/archive/news20000120/brief1.html?ct=388e0fba

The above link will show why I think the key is to learning more about “black holes” and “ripples” and “worm holes”

The actual displacement of a vehicle from one place to another may be possible with aide of these “occurances”.

You cant travel faster than light, so see how you can travel around it? or without it as a factor?

31

The problem with “worm holes” is two-fold.

First, the theory of “worm holes” only predicts that they would be very small at their “center”. To travel through them with a starship we would have to prop them open. How exactly you would do this is completely unknown, but certainly it would require a tremendous amount of energy.

Second, the force of gravity inside the worm hole would, as I think Hawking put it, turn your astronaut into astronaut pate thanks to tidal forces. The gravitational forces that would create a worm hole would be tremendous, it is completely unknown how you would protect a starship from being torn/stretched apart.

Granted, it is possible to say IF we could do these two things then we could travel using worm holes, but that’s a huge if. Certainly with our level of science it is equivalent to impossible.

32

Scylla said:

Earth’s resources are finite.

That’s a whole other debate, but let me just say that this is false. While there IS a finite amount of material here on Earth to use, human ingenuity will prevent the complete depletion of these resources. History ahs proved this time and time again.

It’s not how you pick your nose, it’s where you put the boogers

33

Could the creation of “counter gravitational” shielding be used to repel the crushing forces from the outside?

A la Trieste on the dive into Marianas Trench in 1960’s…?

Better yet travel at a speed at which you arent subject to forces of gravity.

Like a jet plunging towards earth, you have momentary weightlessness and loss of gravity. Now accelerate that in a linear direction?

-N

34

Actually, IIRC, a worm hole would require a ton of negative energy. We can’t figure out how to create enough negative energy to even open a worm hole that a needle could fit through let alone one the size of a ship.

But once we do, man, that is going to be cool.

I think my only hope to see it happen in my lifetime is if aliens give us the technology, like in “First Contact.” I think I’ll just go play the lottery.

35

The bigger problem is to create a stable worm hole, and most physicists suspect that it can’t be done.

The slightest disturbance ( a spaceship ) would probably collapse the wormhole and destroy the ship or hurl it into elsewhere and elsewhen.

The second possibility doesn’t sound too bad until you realize that there’s no way to predict the outcome.

36

Big Daddyo:

Since when has human history proved that we don’t use up all our resources? Clearly, it proves the opposite.

Anyway, I agree with you. Human ingenuity will solve this problem by determining that the easiest and most accessible resources exist in the asteroid belt between Earth and Mars. Later it will be complex hydrocarbons from gas giants.

37

What Mr.Z says is right. It, in fact, is a huge amount of negative energy (I just finished checking Hawking’s book, not to check you but I was going to come back and post with more specific information) or as Hawking put it, some kind of “exotic” material.

As for using counter-gravitational forces, the problem there is that since the worm hole is created by immense gravity in the first place using counter-gravity (if there is such a thing) would almost undoubtedly collapse it.

Newton, don’t get me wrong, I certainly am not saying scientists shouldn’t examine the possibility. That is the core of a good scientist. But certainly, right now, the theory doesn’t look possible that worm holes will be the mode of interstellar transportation. I am sure somebody said the same thing about cloning at one time, so who knows what the future will bring.

Personally, I think it will come from space folding on a small scale (i.e. the warp drive) so that you literally don’t need to travel as far. Of course, this is just as impossible as stable large worm holes. :wink:

38

I think I’ll say this the third time just for kicks — Scylla, you can’t get any significant velocity out of a gravitational slingshot :slight_smile: No backing up? You mean you have back up? Show me the equations and we’ll see about it. You have to remember I’m trying to take into account as many realistic factors as I can. I know about Robert Zubrin’s Daedalus project, but I also know he’s about the only one who thinks it’ll work. Also, in addition to the unlikely fuel pick up at Jupiter, and the use of conventional fusion/fission propellants; he still leaves the solar system at a speed of 0.05c (I’m quoting you on that). Now, 0.05c may sound good, except it’s still closer to 0 than the speed we must attain. The problem falls back to the raw acceleration of the spacecraft again. Fusion/fission just won’t cut it.

Okay, enough nitpicking between us. For those of you that want a quick introduction to the problems we face in interstellar travel, I suggest you visit the NASA Breakthrough Propulsion Physics program homepage. There is an introductive tour you can take from the link below:
http://www.lerc.nasa.gov/WWW/PAO/warp.htm

In comparison to all the Star Trek fan links mentioned earlier, this one probably has a bit more foundation. The author of this page is still an enthusiast, so good or bad, he doesn’t quite put the smack down as must as a mainstream scientist would :slight_smile:

If you ever dig up the anti-matter calculations, you’ll see there’s quite a discrepancy between his calculations and mine. I did a little review, and the distinction is likely attributed to difference assumptions in the efficiency of an anti-matter drive, plus other parameters such as acceleration. I still maintain that anti-matter propulsion is still the most likely candidate without diving into the realms of sci-fi. Barring any significant advances in physics, it’s about the only choice we have anyway.

39

Au contraire. Did I say it would be a two-way trip? I imagine we might ‘have old’ waiting for a convenient return asteroid. My idea is just to use it for the outgoing trip. Whether asteroids in space lack any water or gases is still somewhat conjectural, but I didn’t propose it for that reason. (We already know we can build spacecraft capable of millions of miles of flight, even if we’ve only demonstrated it in near-Earth orbits.)

We can still send a robot ship ahead to generate water and fuel for the return trip. However, on the way out, the ship’s crew would have more to do than just twiddle their thumbs; they could study asteroid structure and even, perhaps, mine the asteroid for nickel, sending it back toward Earth to be captured and help defray costs of the trip.

Hey, I’m not Charybdissin’ ya, I swear!

40

Zor:

Since we can only make very very small amounts of antii-matter (a couple of subatomic particles in an acclerator), I don’t think it’s a feasible basis for a star drive at this time.

When we can make a pound of the stuff, and contain it reliably, then it is probably worthy of consideration. Until then, it’s fantasy.

As for the slingshot effect, in the thread Riboflavin links to at the top, I cite the book I got it from, the page number, the report that the data was based upon, and take my figures directly from a chart inside the book. These figures are pretty much agreed upon as fact by the scientific community at large (barring any misinterpretations I may have made, but I was pretty careful.) If you alone disagree with the scientific community at large, than the burden of proof, or at least a reasonable explanation of why you might do so is called for. “Those guys are wrong, and it’s insignificant because I say so” doesn’t cut it.

.05 C is a significant headstart. It gets you there in a hundred years or so. The reason it’s significant is because you are going that fast with the bulk of your fuel intact. Over the next several years you can continue to accelerate and cut your journey in half. There’s your fifty years.

You’ll notice that in this entire thread I have not made reference to any other potential interstellar craft other than Orion and a Lightsail, nor have I mentioned a ramscoop. You don’t need a ramscoop or Dedalus to do AC in fifty years. Just Orion.

A gravitational slingshot is significant. It’s a function of the mass of the body you approach, your speed at approach, how close you approach, and what delta v you can apply at the right moment.

The key limitting factor when we are talking about a slingshot around the sun is how many gees your ship can sustain for how long.

Until you at least attempt to show me a reason why I shouldn’t, I think I am going to accept Zubrin’s and the scientific community’s calculations over your unsubstantiated say so.