Human space travel - prospects?

[kuroyume0161]

The 'Stupid Teleportation topic' thread in the 'Religion and Philosophy' forum reminded me of a particular conundrum that we, as a highly technological society, face.

In the not too distant past, I was very 'starry' eyed about the prospects of humanity venturing out into the universe (to explore strange new worlds, to boldly go...blah, blah). Within the past few years, after careful consideration of the limitations imposed by Einsteinian physics, the physical harshnesses, and difficulties of maintainable resources, I have come to the realization that we are basically stuck here, on Earth, with little chance of going anywhere beyond our rather desolate solar system.

I've mentioned elsewhere that the distance to the nearest star is approximately 24 light years (travelling at light speed, of course). The distances between galaxies is on the order of millions of light years. Worm holes as means to circumvent these vast distances are truly wishful thinking. We have no way to know that two black holes have a connectivity. We have no way to form such a connectivity. We have no way to know how to traverse something where the laws of physics are either pushed to their limits or breakdown completely. EM transmission (teleportation) isn't even tenable. It not only suffers from cohesion and correction issues, but the same ones imposed by Einstein. Even at Einsteinian speeds (light speed), we are inept at traversing even a miniscule portion of our own galaxy in the next million years!

Barring spectacular scientific discoveries within the next century that circumvent these limitations, what are your thoughts on the prospect of humans actually doing viable space travel?

 

[MRC_Hans]

The distance to the nearest star is about 4 light years (ly). Whether that star has planets is another matter, afaik, none have been discovered, currently. The nearest star system is the Alpha Centaury system, which is a triple star system.

Viable space travel does not necessarily involve interstellar distances, we have a quite complex and interesting planet system right at our door-step. Several bodies in the Solar System are at least theoretically colonizable, and there is also the possibility of free-space colonies.

Interstellar travel is also possible, although the timescales involved effectively restricts us to one-way travel, unless we can extend our lifespan dramatically. However, it is thinkable that once planet systems in our vicinity are mapped, expeditions might set out to travel in space for several generations, in the end to colonize new worlds.

All barring some break-through that enables us to circumvent the speed of light limitation.

Hans

 

[David Swidler]

At some point (10 million years? I'm pulling that number our of my fundament) the sun will go red giant on us and fry all life on Earth. Would that make any of the outer planets/moons habitable?

 

[Asolepius]

At some point (10 million years? I'm pulling that number our of my fundament) the sun will go red giant on us and fry all life on Earth. Would that make any of the outer planets/moons habitable?

I think 5 billion years is nearer the mark. I would not worry about what happens to the human race at that stage, we will be long gone. Species rarely last more than 3m years - we have used up 1m already.

But WRT space travel, I am forced to accept that it is very very difficult. The universe is so old and so big that we really should have good solid evidence of other space-faring races by now. We should have seen evidence of their unmanned craft as well, but we don't. Von Neumann proposed in the 40s a replicating unmanned space probe. The argument goes that if such a thing is imaginable, it should by now have happened, given so much time and material. Well, we should put all our effort into developing von Neumann machines. Within a thousand years our galaxy would be full of them - all beaming back data. The ultimate reality TV (but sadly very old programmes!).

 

[MRC_Hans]

I have read about the von Neumann theory before, but I think it has some flaws.

First of all we cannot be certain anybody would make them.

Even if they were made, they might not have succeeded. Like a life-form, their long-term success would depend on their reproduction rate being higher than the attrition rate, and considering space is mostly empty, and most landing places would not allow them to survive, they might soon die out.

Finally, they might exist out there. The galaxy would not fill up within a thousand years, since the galaxy is about 100,000 ly across, and since small probes will move at a very modest speed, they will take milluons of years to propagate across a galaxy, even if they are not seriously delayed en route. But getting across is not enough, they also need time to multiply to an extremely large number to be enough to cover the galaxy.

I think one fascination about interstellar colonization is that we might perpetuate the human race (or its descendants) virtually indefinitely. Won't make one iota of difference for the individual human, of course, except perhaps emotionally.

Hans

 

[kuroyume0161]

The distance to the nearest star is about 4 light years (ly). Whether that star has planets is another matter, afaik, none have been discovered, currently. The nearest star system is the Alpha Centaury system, which is a triple star system.

Oops. Sorry, you are correct. Wrong number there. Nonetheless, we can't even travel at a significant portion of lightspeed. One can accelerate to a significant portion and then decelerate the other half, but it would take probably 8 years (or many more) to arrive at that nearest star.

Viable space travel does not necessarily involve interstellar distances, we have a quite complex and interesting planet system right at our door-step. Several bodies in the Solar System are at least theoretically colonizable, and there is also the possibility of free-space colonies.

I don't deny our ability to explore our own solar system. But even this is a momentus task. Six months to mars, without gravity and exposed to radiation and micrometeors, is supremely perilous. And any notions of colonization are without merit. Mars, our best hope, might require thousands (if not millions) of years to become viably habitable (through some form of terraforming).

Interstellar travel is also possible, although the timescales involved effectively restricts us to one-way travel, unless we can extend our lifespan dramatically. However, it is thinkable that once planet systems in our vicinity are mapped, expeditions might set out to travel in space for several generations, in the end to colonize new worlds.

Nah. I don't think so. We can shoot off the odd robotic probe, but the required resources for human interstellar travel would be 'astronomical'. The only way humanity can accumulate the needed wealth of material and construct the needed means of such transport would be with the assistance of millions (if not billions or trillions) of nearly sentient, totally autonomous machines (to literally stripmine the solar system). Don't expect any interstellar colonization attempts for another two to five thousand years - yes, barring some fantastic means to circumvent lightspeed.

 

[brettDbass]

There are a large and ever-increasing number of known extrasolar planets. Most of those discovered have been very close to hom in the grand scheme of things - that's how we've been able to spot them at all!

princeton.edu/~willman/planetary_systems/


Give that above a www and it links to a table of known extrasolar planetary systems. It doesn't show their distance from the sun as far as I can see, so you'll have to just trust me on that bit

 

[kuroyume0161]

There are a large and ever-increasing number of known extrasolar planets. Most of those discovered have been very close to hom in the grand scheme of things - that's how we've been able to spot them at all!

princeton.edu/~willman/planetary_systems/


Give that above a www and it links to a table of known extrasolar planetary systems. It doesn't show their distance from the sun as far as I can see, so you'll have to just trust me on that bit

Yes. The techniques to resolve extra-solar planetary systems are improving quickly. Most of the discovered systems are of very large, most likely gaseous, planets.

As exciting as these discoveries are, these potential places of exploration are far beyond our feeble human primate hands.

 

[brettDbass]

Yes. The techniques to resolve extra-solar planetary systems are improving quickly. Most of the discovered systems are of very large, most likely gaseous, planets.

As exciting as these discoveries are, these potential places of exploration are far beyond our feeble human primate hands.

All true.
At current rates of progress It shouldn't take many more genrations before we have discovered many more Earth-like planets (although at least one is known to date) and, more crucially, before we have invented the means to get there within reasonable time scales too.
The biggest hindrance is the natural resources such a large-scale operation would demand.

Nevertheless, am I hinting that perhaps the answer to the initial question might be a tentative "yes, we can do it"?
Quite possibly so.

 

[CurtC]

Finally, they might exist out there. The galaxy would not fill up within a thousand years, since the galaxy is about 100,000 ly across, and since small probes will move at a very modest speed, they will take milluons of years to propagate across a galaxy, even if they are not seriously delayed en route.

OK, so let's say they take ten million years to cover the galaxy. If they are out there and are less than ten million years old, that would mean that some other civilization developed these things within ten million years of our being able to detect them, a mere 0.1% of the time our galaxy has existed.

I think that's the basis of the argument that they aren't there - the unliklihood that another civilization came of technological age at virtually the same instant in time that we did.

 

[chance]

The resources required to take humans into space are such that I think long distance/time voyages can only be practically accomplished robotically and our human component reduced to AI. There may be a possibility for very long very slow voyages using generation ships.

 

[elgarak]

"There is no strife, no prejudice, no national conflict in outer space as yet. Its hazards are hostile to us all. Its conquest deserves the best of all mankind, and its opportunity for peaceful cooperation many never come again. But why, some say, the moon? Why choose this as our goal? And they may well ask why climb the highest mountain? Why, 35 years ago, fly the Atlantic? Why does Rice play Texas?

We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard, because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win, and the others, too." - JFK, 1962

Regarding travelling outside our solar system, I advise anyone the reading of the RAMA series by Arthur C. Clarke, who at one point majored in physics and math. In the series, thanks to relativistic effects, several characters manage several interstellar trips within their lifetimes, with moderate speeds, and returning to a still recognizable earth with living relatives (albeit in spaceships of alien origin).

Yes, space travel is hard. It is a technological challenge, but I do not see unsolvable problems. We have the technology now. Let's start. We, as humanity, have to do it anyway at some time in the future. The gratification will be infinite.

 

[shecky]

I think humans are pretty tied to Mother Earth. To the point that the term, "Mother Earth" is almost literal. I regretably doubt humanity has any real chance of ever truly colonizing other planets, unless we could find/create one that's damn near identical to Earth. Sure, we may be able to send people to places like Mars for long periods of time. But I suspect being forced to retreat there, say, in the event of Earth's demise, would be a very dismal prospect for those who do so. Unless Mars were somehow terraformed, I'm not sure I'd want to face that fate.

As Hans points out, should we somehow manage to overcome the speed/distance problems, perhaps there would be some promise.

 

[kuroyume0161]

The moon shots took nearly fifteen years of dedicated and well-funded research (after the creation of NASA) and a humungously large chunk on the NDP. And that is only three days at moderate speeds both ways.

This isn't even the problem just of human physical limitations and requirements for long-distance space travel, it is about limitations imposed by the laws of physics on top of that.

Victor J. Stenger, Professor of Physics and Astronomy and a Fellow of CSICOP, makes the unassailability of these problems rather clear in his "Marooned on Spaceship Earth" article (no link, but certain that is either linked from his site or easily found at CSICOP's). And I agreed with these prior to reading it.

The first and most pressing problem for any space travel beyond the Moon is artificial gravity. Study after study and finding after finding of long-term effects of microgravity show this: 'no gravity, no long-term space travel'. It decreases bone and muscle mass (including the heart) and impacts physiological functions all in adverse ways. So far, we only know three ways to create gravitational acceleration:

1. A large mass (about the size of Earth's would do).

2. Constant angular velocity (imparting constant linear acceleration towards the center of rotation).

3. Constant Linear acceleration.

The first appears to be so far beyond our wildest imaginings as to be perposterous.

The second has merit, but in order to avoid certain affects, the radius of rotation must be extremely large. This means a very large rotating platform. Most propose something several miles in diameter at minimum. That's a massive structure to fly through space.

The third could be accomodated if the travelling incurs a constant acceleration toward the destination's halfway point and a flip with constant deceleration from there. This would require some pretty amazing precision (since you could end up wisking past your destination or needing to do several years of the bad velocity travel). Um, how many probes have landed right on the money on Mars?

Space travel isn't hard. It's almost unsolvably hard. This is just one of a long string of problems and look at the issues. I'll keep adding to this list (plus some new ones) as I continue posting.

 

[Jyera]

Is it sensible to venture far awy from earth?

Too near the sun and the water in the human body will boil.
Too far away from the sun ... will the human body freeze?
Will there be too little sunlight for a solar energy system to maintain the operation of the ship and humans?

I'm under the impression that earth is unique. We are just the right distance away from the sun for water to be able to exist in all three stages (water, ice, gas) on the planet.

 

[epepke]

The first and most pressing problem for any space travel beyond the Moon is artificial gravity. Study after study and finding after finding of long-term effects of microgravity show this: 'no gravity, no long-term space travel'. It decreases bone and muscle mass (including the heart) and impacts physiological functions all in adverse ways.

The first thing we have to do is find out how much acceleration is required to maintain health. This is a good reason to go back to the Moon. It might turn out that 2m/s^2 plus resistance training is enough to maintain reasonable health.

The second has merit, but in order to avoid certain affects, the radius of rotation must be extremely large. This means a very large rotating platform. Most propose something several miles in diameter at minimum. That's a massive structure to fly through space.

The best solution I've seen for this is to have the crew compartment on a long tether connected to the engines, so the engine unit would pull the crew compartment providing linear acceleration. When the system is coasting, the engine unit and crew compartment would be set spinning. There are no insurmountable problems with this. The chief problem would be to keep the reaction mass from frying the cable or the crew compartment, but that could be handled by having the engines point at a slight angle. It might even be an advantage, as if the engines were hot (in the sense of radioactive), it would be nice to keep them far away. Going from dragging mode to revolving mode has non-obvious details, but we have good computers.

 

[MRC_Hans]

Oops. Sorry, you are correct. Wrong number there. Nonetheless, we can't even travel at a significant portion of lightspeed. One can accelerate to a significant portion and then decelerate the other half, but it would take probably 8 years (or many more) to arrive at that nearest star.

And even that would require an impossible amount of fuel, given any propulsion system we can imagine at present. So 80 years is more appropriate (and probably very optimistic).

I don't deny our ability to explore our own solar system. But even this is a momentus task. Six months to mars, without gravity and exposed to radiation and micrometeors, is supremely perilous. And any notions of colonization are without merit. Mars, our best hope, might require thousands (if not millions) of years to become viably habitable (through some form of terraforming).[/quite]Quite right, however, the ideas of a step-sone approach is, at least, somewhat promising: First establish a self-sufficient moon base. Form here the energy requirments to launch Mars-bound ships are much less, then move on from there.

Nah. I don't think so. We can shoot off the odd robotic probe, but the required resources for human interstellar travel would be 'astronomical'. The only way humanity can accumulate the needed wealth of material and construct the needed means of such transport would be with the assistance of millions (if not billions or trillions) of nearly sentient, totally autonomous machines (to literally stripmine the solar system). Don't expect any interstellar colonization attempts for another two to five thousand years - yes, barring some fantastic means to circumvent lightspeed.

well, the amount of ressources available in the solar system is truely enormous, could we exploit it efficiently, but I totally agree that this is an undertaking that not even our great-grand children will even see a serious beginning of.

However, we must realize that, cynical as it seems, wars and hunger are part of the motors for our present world economy, and one requisite for abolishing both is that we find some other motors. Grand-scale space exploration could be one such.

Hans

 

[MRC_Hans]

OK, so let's say they take ten million years to cover the galaxy. If they are out there and are less than ten million years old, that would mean that some other civilization developed these things within ten million years of our being able to detect them, a mere 0.1% of the time our galaxy has existed.

I think that's the basis of the argument that they aren't there - the unliklihood that another civilization came of technological age at virtually the same instant in time that we did.

0.1% ... So that is only three orders of magnitude off. Not much in this connection. Also, developing sentient life takes time; it took about 5 billion years on Earth. So assuming this figure is average, we can knock the first 5 billion ears off the age of the galaxy, since it will not have had sentient life before then. Finally, still assuming they ARE out there and ARE successfully spreading, it could be a very slow process. Perhaps their reproduction rate only just exceeds the attrition rate.

We can speculate a lot, but my main point is that we cannot take the absence of self-reproducing robots as proof that no sentient beings exist or have existed in the galaxy, because several other viable explanations exist.

Hans

 

[brettDbass]

Is it sensible to venture far awy from earth?

Good grief, yes. Have you not seen what a mess we're making of this planet?

Too near the sun and the water in the human body will boil.

Err, right. Ok...

Too far away from the sun ... will the human body freeze?

Well, too far up in the atmosphere of the planet and the body will freeze, yet we've managed a spacewalk or two. I think that's easy to handle.

Will there be too little sunlight for a solar energy system to maintain the operation of the ship and humans?

Every extrasolar system has, by it's very definition, a sun at it's centre.

I'm under the impression that earth is unique. We are just the right distance away from the sun for water to be able to exist in all three stages (water, ice, gas) on the planet.

Ok, enough sarcasm. I see you're probably actually referring to terraforming in these last few posts.

Firstly, there has already been at least one non-gas-giant planet discovered in the wider reaches of the galaxy.
Secondly, life does not necessarily have to evolve around the various states of water - that's just the condition on our planet.
Thirdly, we are indulging in a little fantastical imagination here. I imagine that by the time mankind has developed the superior kind of transportation required for this venture, terraforming technology will also have advanced considerably too. We have already started the relevant experiments after all.

 

[elgarak]

The second has merit, but in order to avoid certain affects, the radius of rotation must be extremely large. This means a very large rotating platform. Most propose something several miles in diameter at minimum. That's a massive structure to fly through space.

So? What's the problem? It's in microgravity, so it doesn't have to be massive, just large.

And what force do you need? 1/6g (Moon)? Less? Let's find out. Means we have to go into space.

The history of manned space flight is a long string of impossibilities, until they were done.