Humans Not Meant for Space

[chrispenycate]

With all the problems to be solved, would it be safe to say, then, that real space exploration is a third millenium thing - but well into the third millenium. It is probably something inevitable, though.

Real space exploration has already started; something isn't unreal simply because it hasn't got very far yet. The exploration of the Earth didn't start with Columbus, but some long forgotten African leaving his own little patch of Rift Valley (It could be argued it started with unicellular life spreading from its point of origin, and all since then has been rediscovery, but they weren't leaving very detailed maps).

And the inevitability depends on the survival, and progress, of the human race. Which is not in any way certain.

building a ring of geostationary space stations in orbit above the equator is well within our current technology. connecting them together to form a ring would be a major task but still within the scope of current technology.

putting the actual elevators in place would be the hardest part and would require timing down to the nano second but would still be possible

Why timing? Since any point on the ring is geostationary, it is not moving relative to the Earth's surface. Obviously, you'd have to build out at the same speed (masswise) as you built in towards the planet; but as long as any point on the ring had its centre of gravity geostationary, it would never tend to move, so wouldn't need tying down.

But with present day technology? Even putting an optimistic percentage of the world's gross industrial production into space development it would take a hundred thousand years to get enough mass off Earth to start building it; far better to build one tower and haul up the mass for the others (better still , collect bits that are already disconnected, asteroids and comets and lumps of planetary rings and nudge them into place, all the while firing off lumps from the moon). We need a lot of mass; even two hundred thousand kilometres of wire would be impressively heavy, and we want to be able to live on this. Not to mention that each ascending capsule is going to pull down on the structure, slowing it down a fraction, so some appreciable percentage of the lifted matter is going to have to be expelled as extremely high speed to maintain stability.

 

[Urlik]

I would guess that if there was a fixed ring in a geostationary orbit, if you connected a tether at one point it could cause the ring to become unstable.
so it would probably require tethers to be connected simultaniously on opposite sides of the planet to prevent the instability.
once tethers are in place, they may act like the spokes of a bicycle wheel and help stabilise the ring

 

[skeptical]

Just a point of correction.
There is no need in a space elevator to 'balance' loads going up with loads going down.

What you would do is extend a little more of the ribbon outwards - away from Earth - than the ribbon downwards. This to ensure that the centrifugal action was a little stronger than the downward pull of gravity. This would ensure that the whole structure was held taut. You could then haul stuff upwards to your hearts content without having to haul the other way to balance it.

Like a lead sinker on the end of a line being swung around your head. If an ant crawls down the line towards your head, it will not pull the weight down at all. The centrifugal action holds the line taut.

 

[chrispenycate]

Just a point of correction.
There is no need in a space elevator to 'balance' loads going up with loads going down.

What you would do is extend a little more of the ribbon outwards - away from Earth - than the ribbon downwards. This to ensure that the centrifugal action was a little stronger than the downward pull of gravity. This would ensure that the whole structure was held taut. You could then haul stuff upwards to your hearts content without having to haul the other way to balance it.

Like a lead sinker on the end of a line being swung around your head. If an ant crawls down the line towards your head, it will not pull the weight down at all. The centrifugal action holds the line taut.

Do the maths. If the centre of gravity is appreciably off the geostationary orbit, outside or inside, it will pull the tower steadily ahead or behind the attachment point. If you don't want it to slowly pull round and down, you'll have to keep expelling reaction mass to keep it upright; not something we really want.

Besides, we're close to the limits of materials science here (beyond the present limits) so a few more tonnes of tension might turn out to be the camel's straw.

 

[skeptical]

Sorry Chris. Not quite correct.
The whole idea is to get the entire space elevator to pull upwards. That is countered by securing it at the bottom. I am not talking of anything massive. Just a slight pull up, (compared to the whole system, a few thousand tonnes is slight!) to keep the whole system taut. This is easily achieved by having more ribbon out from the geostationary point than in, and by having the bottom of the ribbon extremely well secured to massive foundations.

 

[Pyan]

Hmm, I don't think anyone's written a story about demolishing a space elevator… (Brain starts to hum gently.)

IIRC, RAH describes what happens should one fail, in Friday...

 

[chrispenycate]

IIRC, RAH describes what happens should one fail, in Friday...

And there's another one in "Blue Mars". But I'm thinking of planned demolition of an obsolete structure seventy kilometres in – length? Height? Maximum dimension, anyway. Like getting rid of skyscrapers in Chicago, but this one doesn't merely scrape the sky, it goes through it to the other side. And I think I've worked out how to do it, too. Velikovsky would love it.

 

[skeptical]

Demolishing a space elevator.

In one sense - easy. The bulk of the elevator is 75,000 km roughly of flexible ribbon. Giant scale to be sure. To remove a ribbon, you wind it up. This ribbon would have to be wound on a giant size spool - easy to build in microgravity given the use of the elevator to lift the prefabricated spool.

The spool might be a skeletal structure of 10 km diameter. Actually, there woud have to be two spools which counter-rotate to wind in both ends of the ribbon.

Once the entire elevator is wound in, getting rid of it is done by attaching a couple of ion drive engines and accelerating it, albeit very slowly, out of orbit till it can fly off to wherever the powers that be dictate it should go.

An alternative method would be to release it at the Earth base. Since the centre of gravity is outside the geostationary point, it will move to a higher orbit - with the trailing end well up from Earth ground level. Then the giant ion drive motors have to accelerate the whole thing to a safe distance. However, this method involves two 36,000 km long trailing ribbons that might be a space hazard. Would we be able to keep it more than that distance from anyone or anything of importance?

 

[Ursa major]

Rather than simply release the elevator and hope it drifts out of harm's way, should something at the outer end be "pulling" on it? (One might, I suppose, use those ion drives from the off, rather than use them later.) I imagine that no one would want to be near** the bottom of the elevator when it's being removed, so it's only one extra hazard***.





** - I'm not going to provide a definition of 'near' in this context.

*** - I'm not going to define the scale of the hazard.

 

[Arwena]

Another problem of space travel - you've got to have someplace to go. Earth exploration - you don't have to carry your whole environment with you, tohugh some people go to places that are simply impossible to live - Antarctica, anyone? No place in the solar system worth going to!

 

[skeptical]

Arwena

There are a number of luminaries, such as professors Stephen Hawking and James Lovelock, who believe fervently that humanity has to seed itself away from planet Earth to prevent the entire species being wiped out in a sufficiently bad disaster.

My own feeling is that this does not have to be on a planet, though undoubtedly some will stay planet bound. I envisage the majority of humanity living in space, in giant habitats or cities, rotating for gravity, and moving from one resource to another. Such a structure could, in theory, be almost totally independent - just mining space rock for metals and raw materials, and taking in water from comets, planetary rings, asteroids etc.

A lot of the SF fans contirbuting here will have heard of Dyson spheres. What you may not have figured is that the best and safest form of Dyson sphere is successive rings of rotating space cities in orbit, rather than a continuous chunk of matter. It also means the dwellers therein have a chance of escape should the proverbial hit the fan. If energy is by then available from nuclear fusion from deuterium, such a city does not even have to be close to the star it orbits for energy.

Even though Earth water is only 0.015% deuterium (as weight percentage of the hydrogen only fraction), there is enough energy there in theory for 1 tonne of water to equal 8 tonnes of crude oil. Assuming water in space has the same deuterium, there is enough in our own solar system to provide humanity with energy for untold billions of years.
I also think that the unexpected will happen, because it always does, and unknown benefits will fall upon all of humanity once enough is known about the environment away from our world.

 

[Granfalloon]

It is rather interesting to me that members will argue over a single concept for several pages when there are several other contenders out there. The most promising one IMO is this:

MagBeam Propulsion - To Mars And Back In 90 Days: Science Fiction in the News

The beauty of this system is that it eliminates the incredibly high masses of fuel, fuel convertors, or hardware of any kind that would be necessary in most applications.

NASA is planning a trip to Mars in roughly 20 years from now, but I suspect that competing technologies may confuse the issue. (who decides what technology to use, or what combinations and proportions thereof?)

One thing is for certain - we cannot rely on escape from the planet as a way to save "humanity". Ever heard the expression "Wherever you go, there you are."? If we expect to get away from the problems we have, we are just going to bring our problems with us. We must first solve the issues we have with pollution by creating clean, renewable energy. We must solve the "over-population" crisis with a policy of equality in education for the entire planet, and we must build a world co-operative system that eliminates the need for wars and/or terrorism. Ha ha! Pipe dreams you say! Maybe, but can you say that my point is not valid? You don't think it is achievable? If it isn't, we are doomed to take our "issues" into space with us.

 

[skeptical]

To Granfalloon

Couple of points.

First : Your magbeam does nothing to fix the major problem, which is getting clear of Earth's gravity well. Or the second major problem, which is to get up and down through the gravity well of Mars.

Nor is it necessarily the best approach to the journey from Earth to Mars and back. There is a theoretically possible orbit - very eccentric - that will carry a space craft across Earth's orbit, to Mars orbit, and back. There is one long transit period and one shorter. The shorter takes six months from Earth to Mars and the reverse as well.

One of the proposed methods for long term, regular, travel between Earth and Mars is to throw a 'space castle' into this orbit. It will be big and heavy, rotating for artificial gravity, and carrying a thick shell of water or polyethylene for protection against cosmic radiation. It needs to be accelerated into orbit just the once, and will thereafter continue that orbit indefinitely.

Of course, it is still necessary to accelerate to meet the space castle, and decelerate when leaving it. But only a small and cramped space craft is needed for the acceleration/deceleration phases. And the long journey is done in comfort on board a very big habitat.

Obviously, this will not be how the first people get to Mars. It will be a solution for later, more regular voyages, since it will take an awful lot of energy and acceleration to get the big clunker into that orbit. It might take 20 years of acceleration using ion drive motors. Or possibly your magbeam system.

On the problems of planet Earth. I think it goes without saying that the problems on planet Earth will remain there. We do not solve all our problems by getting a relatively few people into space. However, those in space are our species insurance policy. If something happens to destroy the population on Earth, there are still people in space. Examples might include asteroid strike, nuclear war, gamma ray burster not too far from Sol (if our space colonists are far enough away in another solar system, they would survive), war using genetically modified viruses etc.

This is a long term insurance policy, since we are unlikely to have self sustaining colonies off Earth for some hundreds of years, and around other solar systems for some thousands. However, some people think it is important to work towards that goal, even if it takes a long time. After all, in biological time, 10,000 years is just a blink of an eye.

On the very long time scale, our sun will swell and overheat the Earth enough to make it uninhabitable in a few hundred million years, and swallow it completely in about 4 to 5 billion. Hopefully, well before then, humanity will be all through the Milky Way galaxy.

 

[AE35Unit]

Can anyone explain to me exactly why one needs to travel at the escape velocity in order to get into space? Is it not possible,once high enough,to push throu the atmosphere,and what would happen if it was tried?

 

[skeptical]

AE

It is theoretically quite possible to get to space without accelerating to escape velocity. For example : if the space elevator existed, with a 75,000 km ribbon out into space, you could climb that ribbon as slowly as you liked. Of course, you would be accelerated by the ribbon, since it rotates around the Earth at once each 24 hours. In fact, you would have kinetic energy 'put into' you equivalent to escape velocity, with that energy taken from the rotational momentum of the Earth. By the time you reached the end of the tether, you would be travelling at almost 3 km per second tangential to the Earth. If you let go the tether at that point, you would be flicked out into deep space.

However, for normal space travel, you need an energy input equivalent to acceleration to escape velocity. For example : if you used enough energy to simply climb to 100 km on a rocket, you would then fall back to Earth. To orbit at 100 kms, you need 'sideways' speed sufficient to avoid that fall. To get that speed, guess what velocity is required?

 

[Granfalloon]

To Granfalloon

Couple of points.

First : Your magbeam does nothing to fix the major problem, which is getting clear of Earth's gravity well. Or the second major problem, which is to get up and down through the gravity well of Mars.

Granted, but since we've already proved we can do that, It would simply (I say simply, not easily) be a matter of getting the propulsion beams into orbit.

And how do you know that the Mag beam cannot be used to get a craft to escape velocity? Do you have the research to back up a statement like that?
(I don't have any proof that it would, I'm just curious)

On the problems of planet Earth. I think it goes without saying that the problems on planet Earth will remain there. We do not solve all our problems by getting a relatively few people into space. However, those in space are our species insurance policy. If something happens to destroy the population on Earth, there are still people in space. Examples might include asteroid strike, nuclear war, gamma ray burster not too far from Sol (if our space colonists are far enough away in another solar system, they would survive), war using genetically modified viruses etc.

If the scenario plays out the way it has been described previously in this thread (i.e. only the elite or military being the ones to survive), I'm sorry to say that I don't believe they are the best candidates to carry on the species. I actually consider those folks to be the least evolved mentally, emotionally and spiritually. They would need to take a few geeks with them to have any hope of long term survival.

This is a long term insurance policy, since we are unlikely to have self sustaining colonies off Earth for some hundreds of years, and around other solar systems for some thousands. However, some people think it is important to work towards that goal, even if it takes a long time. After all, in biological time, 10,000 years is just a blink of an eye.

I suspect there are plenty of intelligent life forms who are well aware of our existence. Well aware enough to stay well away from us for now. I don't think there is as much need for an "insurance policy" as there is a need for humanity to mature to the point that it can handle the responsibility of the technology they are toying with.

On the very long time scale, our sun will swell and overheat the Earth enough to make it uninhabitable in a few hundred million years, and swallow it completely in about 4 to 5 billion. Hopefully, well before then, humanity will be all through the Milky Way galaxy.

Hopefully by that time, we'll be hanging tight with the sentient folks who escaped from Beetleguise.

 

[skeptical]

Granfalloon

Re Magbeam. I just read the reference. No suggestion of using it to lift people off the Earth. In fact, it is logical to assume it cannot, since gaining orbit is the most difficult part of the whole exercise, and needs immense thrust. There are all sorts of ways of accelerating away from Earth, once in space, ranging from standard rockets, to ion drive, to laser thrusters, to solar sails etc. However, no-one has yet come up with a practical and safe method of lifting into orbit apart from brute force rockets. Perhaps in the future we may be able to do so, but not yet.

On your idea of advanced aliens waiting for us - I have my doubts. However, that is a topic for another thread, perhaps under the title of 'the Fermi Paradox" (google it).

 

[chrispenycate]

Like the magbeam, but there are a couple of minor difficulties they have glossed over, (or actually ignored, in that article)

Action and reaction are equal and opposite, so while the plasma generator is pushing the spacecraft forward, it is pushing itself back with equal or slightly greater force. If you reuse it for a number of missions, it's not only going to need to be minimum an order of magnitude more massive than the craft it's propelling, it's going to have to spend half its time firing backwards, to maintain station. And it needs reaction mass. Even if the plasma does come out considerably faster than any chemical reaction can provide, it's still a long way from light speed, and there are no reletavistic advantages to be gained. So, capturing and compressing solar wind, or regular fuel tankers hauling it in from somewhere? Linearly accelerated packets of lunar regolith (you can make plasma from anything) aimed close, and caught in nets?

While the plasma generator will only work in fairly hard vacuum, you could lift spaceplanes into orbit with a tangential beam through the upper atmosphere giving them the final boost. You could definitely use it to power the tugs pulling mass from LEO to geostationary, taking over from the laser launcher at the top of its trajectory or keeping the ferris wheel spinning (I had a look at the "into orbit" problems quite a long time ago, in this:

http://www.sffchronicles.co.uk/forum/35007-the-first-step-into-orbit.html

post, meaning to follow it up with in system drives and ultimately interstellar technology, but ultimately there was little enough interest it didn't seem worth going on.

 

[AE35Unit]

However, for normal space travel, you need an energy input equivalent to acceleration to escape velocity. For example : if you used enough energy to simply climb to 100 km on a rocket, you would then fall back to Earth. To orbit at 100 kms, you need 'sideways' speed sufficient to avoid that fall. To get that speed, guess what velocity is required?

But I still don't see why? You're at the thin barrier between earth and space,just give a little push and you're thru!

 

[chrispenycate]

Can anyone explain to me exactly why one needs to travel at the escape velocity in order to get into space? Is it not possible,once high enough,to push throu the atmosphere,and what would happen if it was tried?

Look, you accept the law of conservation of energy, right? Escape velocity (actually "escape speed" would be more accurate; the direction vector is reasonably irrelevant. As long as it's not straight towards the planet) is the speed that would be attained by an object falling from infinity to a point on the planet's surface, assuming there wasn't any atmosphere to confuse things. All potential energy converted to kinetic. So, to escape from Earth's gravitational pull, we need this much kinetic energy to convert into potential.

Often people say "out of the Earth's gravitational field" for the astronauts spacewalking round Hubble, or the international space station. Of course they aren't. Earth's field continues a lot further than that, holding the moon in place, making measurable perturbations in the orbit of Mars… Technically, it extends to the limits of the universe, but it's below noise level before we leave the confines of the solar system, dropping off as the square of the distance. Those astronauts are omitting falling down to the planet because they have a secondary vector sideways so the planet is no longer there when they fall on it (frequently inaccurately referred to as "centrifugal force"), which velocity they share with all the objects around them, in comfortable stability. This doesn't give them enough energy to climb out of the 'gravity well', just to avoid falling any further down. The sum of their kinetic energy and potential energy for any stable situation is a constant, and to get any further out – say a quick trip round the moon – you have to add more kinetic energy, which means more momentum, which means more reaction mass.

TANSTAAFL