Reaching for Interstellar Flight

space.com ^ | 12/17/03 | Leonard David

[KevinDavis]

When Star Trek's U.S.S. Enterprise hit the television screen in 1966, the science fiction series had trouble finding its own space and time slot.

Decades later, a similar visionary zeal to seek new worlds and new civilizations is a factual enterprise for a new generation of galactic explorers. They are taking on spacetime and hoping to boldly go where no spacecraft has gone before -- out to far-flung stars and the planets that circle them.

[King Prout]

I'm harboring a (no-fact-based, irrational) hunch that the practical solution for leaving point A and arriving at point B without having to travel for a great deal of time at high sublight velocity will depend on finding a way to exit this sidereal universe and reenter it at the desired destination.

[King Prout]

yes, but is that not exactly what we all do to our progeny anyway?

[Physicist]

Aliens are not people in rubber suits. They are going to have their own (alien) motivations which we may never fathom.

A recurring theme of Greg Benford's novels. "The thing about aliens is, they're alien!"

Indeed, if they are alien enough we may not be able to determine whether the critter in question is truly intelligent or simply a very sophisticated non-sentient animal.

That debate already rages with respect to human beings, and (preemptively) to A.I. systems.

[inquest]

It's either going to be FTL or we're going to have to develop some sort of suspended animation to get people to explore the stars.

Actually, there is a form of near-suspended animation that's within our science, if not necessarily our present technology: It's called going very close to the speed of light. The energy demand would be a tad high, especially for the transgalactic trips, but you could theoretically have the trip take just a few years for the crew, but still last thousands of years from the perspective of everyone else. Still not my idea of an adventure, but some people might want to do it.

[Junior]

Not really. If your kid wanted to be a sailor or an archaeologist he could do that. If you're on an interstellar voyage, there isn't a lot of call for sailors or archaeologists. Your kid would have to be part of the crew whether he liked it or not. He'd never have the opportunity to do what he liked. Albeit, he may like being part of the crew, but there is no guarrantee that will be the case, in which case your kid will lead a miserable, unfulfilled existence and it will all be your fault.

[RightWhale]

your kid will lead a miserable, unfulfilled existence and it will all be your fault.

You're making us feel guilt as parents for kids we haven't had for dragging them on a trip we haven't decided to make into the country that we don't know if we want to see anyway. What if the kid also wants to play trumpet and all we have aboard is violins? Double angst: get started now to eat out your own heart.

[boris]

"We will gradually expand outward in all directions as economic opportunity presents itself. Assuming we can get our ships to move at .1 c and that the population will increase to fill the volume, we will cross the galaxy in 1 million years and occupy every niche suitable for ourselves. Jumping to the next galaxy, M31 I suppose, will never happen. The techniques would be just engineering problems."

You're still not answering me. At 0.1 c it would take over 40 years (a big chunk of a human lifetime) to reach Alpha Centauri. If the nearest solar system with an earth-like planet is 1000 LY away, that is 10,000 years at 0.1 c.

Humans cannot make the trip. Who or what will?

I gave you generation ships (evidently nope), sending frozen sperm and ova for reconstitution at destination (evidently nope too). So by what mechanism do you foresee humans filling the galaxy in one million years at 0.1 c, given the distances and reasonable estimates of human lifetimes? Hibernation? Dubious. So HOW, dammit?

--Boris

[RightWhale]

So HOW, dammit?

Use any tech you want. Use all the tech if you want. Build entanglement transporter gates everywhere you go and then don't worry about trip time. So what if you don't survive a trip to Alpha Cent? You won't survive if you don't go either. I'll let somebody else dig out the list of possible techs from whichever symposium ran it out last time.

[Junior]

Bubba, I just don't see multi-generational ships being feasible -- mostly for the human reasons I mentioned above (I'm not the only one who would raise such objections). However, there is also the difficulty of building a spacecraft that will have to operate away from homeport for centuries without so much as a comprehensive overhaul. And woe betide the crew that runs out of crucial spares...

[boris]

"Actually, there is a form of near-suspended animation that's within our science, if not necessarily our present technology: It's called going very close to the speed of light. The energy demand would be a tad high, especially for the transgalactic trips, but you could theoretically have the trip take just a few years for the crew, but still last thousands of years from the perspective of everyone else. Still not my idea of an adventure, but some people might want to do it."

Let us neglect relativistic effects for a moment.

It turns out that one "gee" (32.2 ft/s/s) is 1.032 light years/year/year. So if you accelerate at one "gee" for one year, you are pushing "c" and have traveled about half a light year. Consider one kilogram of mass so accelerated.

Its kinetic energy (neglecting relativistic effects!) is 4.89x10¹⁷ joules. A year is roughly pi times 10⁷ seconds, so you need about 1500 megawatts, running full-tilt for a year to push your kilogram. To account for losses, let's call it 2000 MW.

The problem is now: I have a kilogram. I plan that some of it should be payload. So my power plant--assuming I am going to take it with me--must weigh much less than a kilogram and occupy a small volume. I'll say 100 grams and a few cubic centimeters.

This is equivalent to taking two 1000 megawatt nuclear generating stations and compressing them into the mass and volume of a few sugar cubes.

Or perhaps shoving the Sun into the Rose Bowl.

Scale your kilogram/sugar cubes up until you hit "Enterprise."

So. At present, and for the foreseeable future, human beings are too puny/ignorant/whatever--to perform such an engineering feat. Indeed, the mind dispairs when trying to imagine how it might be done. At least mine does.

[boris]

"Use any tech you want. Use all the tech if you want. Build entanglement transporter gates everywhere you go and then don't worry about trip time. So what if you don't survive a trip to Alpha Cent? You won't survive if you don't go either. I'll let somebody else dig out the list of possible techs from whichever symposium ran it out last time."

This strikes me a circular reasoning/begging the question. You blithely assume some magical technology will make it happen and then "the rest is left as an exercise for the student."

Makes me recall that cartoon: "...then a miracle occurs..."

--Boris

[RightWhale]

Right. I don't see it happening that way. First, there is no hotel with fresh sheets waiting at the destination. Second, the undertaking would be so huge that it would take the entire world product for several years to assemble the expedition. Third, the planet would have to certifiable to believe there could be any positive result from this, not to mention ever hearing from the expedition again.

We'll reach the nearest stars okay, and possibly get deep into the galaxy. Most likely it will be by a process of economic expansion, moving outward stone by stone until the stones are so distant they aren't from the solar system, but from the next star system, then we'll work our way in toward that star.

[PatrickHenry]

The energy demand would be a tad high, especially for the transgalactic trips, but you could theoretically have the trip take just a few years for the crew, but still last thousands of years from the perspective of everyone else. Still not my idea of an adventure, but some people might want to do it.

Assuming the engineering problems can get worked out, that's the way it will be done. From the passengers' viewpoint, so what if the trip takes a few years? Captain Cook's voyages took that long, and the English navy always had people willing to go (well, some seamen had to be coerced). The only problem then -- the biggest problem -- is economics. Who would pay the enormous cost for what is essentially a one-way voyage on a one-time-only starship? If it were a round-trip, then how does it work out for you economically if you come "home" several centuries after you left?

[RightWhale]

Right. I don't see the need to travel to the next star. So I am not going to worry about the tech that makes it possible, nor am I going to worry about the psychic health of those intrepid settlers. The moon is enough for now, although I would, as I mentioned, volunteer to go to Deimos to set up the base for eventual Mars settlers.

[RightWhale]

If it were a round-trip

One thing about space exploration. We have to get past the concept of round-trip. If we're going into space, we're going and not coming back. No more of this Apollo kiss and run.

[PatrickHenry]

The moon is enough for now ...

Speak for yourself. For me: The moon is not enough!

[RightWhale]

The moon is not enough!

Santa might bring the moon. Santa might even bring Mars. Won't hurt to ask for some stars while we are on the subject, although where are you going to store them?

[boris]

"Assuming the engineering problems can get worked out, that's the way it will be done."

See my response at #190. For fun, add relativistic effects and see how truly awful those 'engineering problems' become.

--Boris

[citizen]

Put me on the space ping list, please.

[inquest]

In addition to his main point, boris also brought up a valid point that I hadn't thought of: Gravity.

As he pointed out, 1g= ~1 ly/yr/yr. If I'm not mistaken, to get to a speed where it appears for the crew that they're going 1000c (1000 ly/yr), the energy requirement would be roughly the same as for going that apparent speed using Newtonian calculations. In addition to the fact that finding such an energy source would be quite a challenge (perhaps if there's some way to convert interstellar hydrogen to antimatter and then let 'er rip?), the acceleration from the crew's perspective would either have to be 1g for 1000 years, or 1000g for one year, or something in between. So some form of artificial gravity would have to be discovered in order to compensate for that - which of course our science has yet to give us any clue as to how to do.