Interstellar travel; possible or not?

Great Debates
121

CHAOSGOD–

Right, so now I gotta do muliplication?!?

R* = Not a clue as to the rate. I’d be content to limit the discussion to stars presently existent in this galaxy.

fp = For some reason the “more info” didn’t work, but I will say that the fraction is 1/2 x [the percentage of stars not so close to other stars that a planetary system cannot be physically stable over more than “just a few” billion years]. Other points: I presume there are some cases wherein a planetary system might orbit about a multiple star system. (Considering the great number of stars, even very unlikely–but possible–orbital arrangements ought not be ruled out.) A negative factor is that the “solar” wind produced by the local star(s) must not effectively disperse (or de-orbitize through friction) the protoplanetary cloud of particles before planetary formation gets going.

And consider if you will the neglected topic of nonsystemic planets. Clearly proto-star-like clouds can agglomerate into Jupiter-like bodies not able to ignite. Like Jupiter, such bodies may be surrounded by their own systems of orbitters. Furthermore, I hardly think we know enough to rule out SOLID planetary bodies–even stable systems of them–forming in interstellar space. (Note that internal heating could–frequently WOULD–make such bodies more than deep-frozen worldsicles.)

ne = I’d say this amounts to “Was there a span of a billion years or so wherein a significant (cumulative) volume of hydrogen and carbon compounds were inter-exposed, along with other catalyzing conditions, such that complex organic-chemical molecules were produced; and such that said molecules were enduring, and in fair concentration, for many hundreds of millions of years?” It’s not unlikely that conditions allowed some precipitation of organic (not “living”) chemicals on all the large (spheroidal) bodies of our known solar system FOR A TIME. But for the majority of these (ie, most of the satellites; the big 4 asteroids) the archaic atmosphere arising during their formative and stabilizing epochs simply didn’t last long enough. And Mercury’s boiled away too quickly (though–we can’t be sure). But the other eight could conceivably have met the stated condition for life to begin; likewise the larger moons. Distance from the central sun doesn’t faze me per se, given the role played by internal heat. However, I’ll be cautious and guess that 1/2 of 8/9–8/18ths or about 44% of all “planetoidal” bodies had at one time conditions such that protocellular organic forms were able to make a start. How many such bodies is that? I’ll say: 8/18 x 1/3 the number of stars presently existent (in this galaxy).

fl = Where life actually appears, or where it gets beyond the microbial stage before getting snuffed? Mmmmm, how about 1/12th of the preceding?

fi = So you get beyond the microbial, but how far beyond? I’ll start with another 1/12th of the preceding to arrive at flora, another 1/2 to arrive at fauna, another 1/100 to arrive at “advanced fauna” (on the order of chimps, dolphins, felines, canines), and another 1/20 to arrive at “intelligence”. = 1/48000 of fl

fc = I’ll go against my instincts and say, conservatively, 1/2

l = median length, 150 earth-years +/- 50 Yes, you read it right.(But shouldn’t this be expressed as a fraction, not a quantity?)

“…why would they share there knowledget with us? Any contact we make will almost certainly be with cultures millions of years ahead of us. That means we’ll be as interesting to them as a piece of cardboard is to us…”

Well, we DO study microbes.

But why assume that it’s just a matter of “being interested”? I tend to think that the only currency worth anything to a sufficiently advanced “culture” is–raw experience.

IMHO, the universe has existed more than long enough for pan-galactic culture to have developed into something more like a cosmos-wide “mind” than anything we would call a “civilization.” To indulge a whim and contact humanity costs it nothing at all; thus even a vanishingly minute possibility of gain is a sufficient motive for doing so. (And this is setting aside the possibility of God, or gods.)

Then again–perhaps the whole idea is to allow US to initiate the linkup.

122

At present, all we can detect are Jovian sized worlds. NASA has plans to launch a telescope that would be able to detect Earth-type planets around another star. And terraforming a Jovian-type planet would be pretty difficult, if not impossible, even with nanotechnology (which at present, is little more than “vaporware”) as the core of Jupiter is believed to be metallic hydrogen, which is kept in place only by the tremedous gravity of Jupiter. Were someone to start trying to terraform a Jovian-type world, they might have the problem of the core exploding as the mass of the planet was brought down. (But wouldn’t that be spectacular to watch! :cool: )

123

No one ever does those numbers the other way.

Suppose a trillion civilizations, in the universe have each been expanding for an average of ten thousand years. Suppose these civilizations expand at the speed of light. Suppose further that this state of affairs is more or less constant, with new civilizations replacing fallen ones over the fifteen billion years of universal history. So, where are they?

Well, given that:

(1.5 x 10[sup]10[/sup])[sup]3[/sup], x 4/3 pi = 1.413 x 10[sup]31[/sup] cubic light years in the universal neighborhood.

And these trillion civilizations occupy

4.189 x 10[sup]24[/sup] cubic light years,

the percentage of space occupied by those civilizations is

0.00000296%

Better than a one in a million chance we are inside one of those civilization’s sphere. Almost a three in a million chance.

Tris

124

And how do you propose we accelerate a space ship to near-light speed, and then slow it back down again, without having to bankrupt the economies of every nation on Earth?

As I’ve mentioned before in this thread, even with nuclear fusion propulsion technology, a space ship that could accelerate to HALF of light speed and then slow back down again would have to carry over 6000 times its own mass in nuclear fusion propellants. That’s the way the rocket equation works, folks: doubling your delta-v requires you to square your fuel-to-empty-spacecraft mass ratio. Every little bit faster you want to go makes your fuel requirements pile up really quickly.

This is why even the most optimistic plans for the Orion space craft don’t predict that we can build one that can accelerate to more than about 1/10 of light speed.

125

And that’s exactly why the first interstellar probes are going to be unmanned. Because 6000 times the weight of the payload isn’t that bad if your payload only weighs 5000 lbs.

With water being discovered on the moon, we could probably build a fast interstellar probe today with an Apollo-level commitment (say, 1% of GDP, and 20 years of development). A nuclear-electric rocket, hydrogen propellant mined from water on the moon, and a payload the size of Cassini, with a laser transmitter powered by a nuclear battery.

I’ll bet we could build something like that and get it to Alpha Centauri with a transit time of say, 10 to 20 years. And even with a very powerful laser transmitter, we’d have to accept a pretty low bit rate for data, and it would take another four and a half years for the data to get back to us.

But we won’t build such a probe until we know where to send it, and we won’t know that until we build an array of space-based telescopes capable of imaging earth-like planets. That’s maybe 20 years away, and by then we’ll be even more capable of building such a probe.

126

Actually, on thinking about this - if we’re only building one probe, scrap the lunar mining. We can put up 50,000 lbs at a time on a shuttle, or close to that on an Ariane-5 rocket. Use gravitational slingshots to get the probe up to speed as much as possible, and settle for a slightly longer transit time, and you could do it with 20 launches. A commitment on the order of the International Space Station.

127

We seem to have gone back to forgetting the problem that space isn’t empty; 1 hydrogena atom per cubic metre is nothing at all when you’re travelling at 25 times the speed of a rifle bullet, but at 0.5c, it becomes an enormous problem, adding physical shielding material is probably a completely impractical idea, since it involves extra mass, for which extra propellant will be required (in any case, I think that a shield thick enough to protect the ship for many years would just be unimaginably thick)

Setting up some sort of electromagnetic deflector field would be awfully energy-expensive (you have to move the interstellar matter out of the way very quickly - almost instantly, which means applying oa lot of energy).

If you were unlucky enough to strike something larger (say, the size of a piece of gravel), as 0.5C it’s going to make a very large hole in your ship.

128

Clarke proposed a solution to that problem in his novel Songs of Distant Earth, where they used a shield made out of ice to protect the ship. Even then, the book admitted it wasn’t a perfect solution. (Space travel will always be dangerous.)

129

Okay, so how would Montgomery Scott solve these problems?

130

Something to with transparent aluminum is my guess.

131

The space ship in The Songs of Distant Earth also didn’t carry its propellant energy with it. It used hypothetical zero-point energy, basically drawing upon the quantum vacuum flux of the universe. Clarke didn’t explain how this was accomplished, only that the physicists of the future had “figured it out.”

With unlimited energy to play with, the ship could basically accelerate all of its reaction mass to nearly the speed of light. This cut back on the needed fuel-to-empty-spacecraft mass ratio considerably, thereby allowing the ship to accelerate to relativistic velocities.

Unfortunately, not only do we not know how to access quantum vacuum energy in real life, we don’t even know if it’s possible to access quantum vacuum energy in real life. The best we can hope to do with existing foreseeable technology is an antimatter powered space ship, and even it would need 9 times its own empty weight in matter-and-antimatter propellants to accelerate to 0.5c and then decelerate back down again.

132

For the first point, we can send unmanned supply ships along with them so they will get a head start. For the second, one only has to look at the relationship between Europe and America. But more importantly, humanity gains the massive advantage of not being all on one planet.

133

TRACER:

“…As I’ve mentioned before in this thread, even with nuclear fusion propulsion technology, a space ship that could accelerate to HALF of light speed and then slow back down again would have to carry over 6000 times its own mass in nuclear fusion propellants…”

Bah!

As far as we know so far…What is the composition of the matter a vehicle is likely to encounter in interstellar travel?

What I’m really interested in is: how much of it (as a percentage) is ionized?

Imagine a mile-diameter, flattened hoop-shaped vehicle. It travels in the direction of its axis. From its fore-edge, we extend, mmm, several tubular “poles” forward of the ship, along our line of travel. These poles have diameters of a few inches. Perhaps, at their fore-tips, we connect them to a ring of similar diameter, which is parallel to the plane of the ship itself. Or perhaps the ring is superfluous. In any event, we use these poles as liquid-helium-cooled electromagnetic field generators. The field acts like a sort of “lens,” sweeping the ionized particles toward the center AND accelerating them aftwards–which in turn provides a forward thrust. They pass through the middle of the ship-hoop, not touching it. Furthermore, I wonder if they wouldn’t tend to collide-with, and thus impart momentum to, nonionized particle, sweeping them out of the path of the “hoop”.

IANA physicist–painfully obvious, I’m sure–but wouldn’t the Lorentz Contraction increase the energy-density of the field, making it corresponding more forceful? It really would become like a “shield”.

And now that I think of it, if the ship is gaining mass, wouldn’t it have correspondingly a greater “invulnerability” to particle impacts? (Remembering that we have here an accelerating frame…)

Or–Lasers produce a measurable recoil. A bank of rear-pointing lasers (or masers, or x-raysers, or gammasers) could produce a continuous thrust of 1-G…if you have enough power. But I’d be surprised if some exotic power source were required.

A variant on the hoop-ship: a needleship…one mile long, 25 feet in diameter.

134

Just stick a few guys on a space station, then launch them off into deep space using a rail gun.

They’ll make it sooner or later, but weather or not they will make it is a matter of conjecture.

135

How about we take the entire Chicago Cubs team, put them on a spaceship, and then have them throw baseballs out the back for acceleration?

Sure, it’ll take them a couple of hundred thousand years to get anywhere, but the Cubs are used to waiting long periods of time to achieve anything.

136

  1. Spend 20 years and billions of dollars on design studies.

  2. Submit proposal to Congress. Proposal is rejected as too expensive.

  3. Proposal is vastly scaled back, given highly optimistic cost estimates, and resubmitted. Key senators in states with aerospace industry get it passed.

  4. Scaled back design is further altered to cut short-term development cost at expense of long-term goals.

  5. Cost overruns force NASA to ask for more money to complete project. More money obtained since otherwise investment of billions would be for naught.

  6. Project ends up costing 3 times amount that was originally rejected as too expensive by Congress.

  7. Design flaws add further expense for retrofitting and force near-abandonment of project’s entire purpose.

  8. Project completely fails original purpose. Is kept running anyway since the alternative would be the cancellation of the USA’s space program.

  9. Since space program now moribund, NASA funds design studies for ambitious new space exploration program.

  10. goto 1.

137

Sadly, Lumpy, I think you’ve nailed it.

138

How so? Particle accelerators move massive particles to enormous veolocities and you don’t see the inside of these things got big gapping holes.

The force of hydrogen atoms at that velocity is still very low.

139

I may be wrong, but isn’t the whole design concept of particle accelerators steered towards keeping the accelerated particles away from the container?

[back of an envelope]Assuming that the 1 atom per cubic metre figure is a reasonable one, at 0.1c, each square metre of the forward-facing part of your spaceship will be impacted by nearly 30 million particles per second, or over the course of a twenty-year stint at 0.1c, each square metre will have been exposed to the impact of roughly 19,000,000,000,000,000 particles, each travelling at a relative velocity of 0.1c.

What kind of protection would be required for that?

140

RE: Biohazard.

Yep. You cannot detect tiny, worthless planets like Earth through their methods.

By the way…do folks think we’ll get full impulse power (0-.25c in within 30 minutes) or warp drive first?