Humans Not Meant for Space

[skeptical]

The space elevator must be able to withstand impacts by micrometeorite or space debris. This is the reason I suggest it may take the form of a ribbon. A wide enough ribbon will still hold together after tiny and ultra-high velocity projectiles fly through it.

Imagine a space elevator with a total length of twice 36,000 kms, which uses a cable rather than a ribbon. And then a large space object cuts through the cable higher than the geo-stationary point! All of a sudden the space station plus more than 36,000 kms of cable starts to fall to Earth. There is net angular momentum, which means it would not all fall to the same spot. Instead, 36,000 kms of massive thrashing cable would encircle the globe. It would be a disaster on a scale unprecedented since the KT asteroid struck!

Obviously, a wide ribbon structure, resistant to cutting by meteors and space debris is essential.

I do have one question, though. Does anyone have any idea how the ribbon could be placed so it does not move by twisting and contorting, with waves running up and down its length? It is normally an inevitability with ultra long cables or ribbons. Any unevenness of the movement of any part of it will trigger such contortions.

 

[Parson]

All proving that there is a lot more difficulty to a space elevator than simply the materials necessary to extend from earth to space, something we presently do not have. All of this leaves me skeptical of Skeptical's 100 year estimate.

 

[Pyan]

Oh, I don't know, Parson. Try looking at it another way, and compare the transportation systems and vehicles we have now to those of 1908...

 

[skeptical]

Yet another space elevator difficulty.
There is a zone above the Earth where, due to the magnetic fields of our planet, radiation is concentrated to a point where it will rapidly become lethal.

With the space shuttle and similar vehicles, this is not a problem, since they pass the lethal zone so quickly, and little damage is done. However, what of a space elevator carriage, which would appear to travel much more slowly? The passengers would be exposed to seriously damaging radiation.

My own feeling is that we will need magnetic levitation to get the carriage moving fast enough. It would have to be damn fast anyway, bearing in mind that it has to travel 36,000 kms to the geostationary point. However, what if humanity develops the technology for a space elevator, but fails to develop magnetic levitation and high speed levitation transports to the same degree?

I see all these difficulties as engineering problems rather than basic science, and hence potentially solveable. However, we should not kid ourselves that a working space elevator will be easy.

 

[Urlik]

the van allen belts wouldn't be such a problem as the carriages could be shielded (unlike conventional rockets) as the mass of shielding on the upward bound carriages would be countered by the mass of shielding on the downward bound carriages

 

[skeptical]

Re radiation shielding

There was an article on this in Scientific American a few years back. The best shielding is conferred by water or some other compound with lots of hydrogen atoms. With water, a thickness of 3 metres (10 feet) is required to give adequate shielding effect. I rather doubt that the operators of the space elevator will want to have their carriages lifting walls three metres thick with the massive amount of weight that entails.

There has been proposed an alternative shielding system using magnetic fields to divert charged particles away from the vehicle. Whether this is achievable remains to be seen.

 

[Ursa major]

I rather doubt that the operators of the space elevator will want to have their carriages lifting walls three metres thick with the massive amount of weight that entails.

If, as Urlik has said, a carriage going up is balanced by one coming down, the weight of the water is not that a big problem.

 

[chrispenycate]

If you built a superconducting Faraday shield incoming charged particles (the only ones to be trapped in the Van Allen belts) would cause eddy currents producing a force proportional to, and in the opposite direction to, the velocity of the particle, and the square of its distance. While this couldn't stop incoming particle it could slow them to manageable energies.

 

[skeptical]

Urlik

How do you plan to use a descending vehicle to balance one that is ascending. With a 36,000 km long cable?????

chris

The SciAm article I read had no such simple solution. They proposed a magnetic system, but admitted that such technology does not yet exist. Perhaps in 100 years???

To me, the obvious solution to this problem, given 100 years to develop a better system, is high speed magnetic levitation technology. We will need this anyway, to get people to their destination in a reasonable time frame. Imagine rising the space elevator at 100 km per hour? To get to the geostationary destination would take 15 days. Not, in my opinion, acceptable. However, raise your speed to 1000 km per hour - very possible with maglev - and you get there in 1.5 days.

The reality is that such a journey would start slow, as you moved through atmosphere for the first 100 km, and then accelerated as you moved into vacuum, and as gravity declined. Maximum speed with an advanced maglev system, in vacuum, and with a somewhat reduced gravity, could be many thousands of km per hour. Decelerating again could use EM braking, and generate electricity.

 

[chrispenycate]

So, what would stray fields from your acceleration coils do to the Van Allen belts? Accelerate them with the capsule or create turbulent regions.

And "magnetic levitation" is for horizontal rails, not vertical ones; what you are creating is a vertical linear accelerator, possibly with magnetic bearings. I will assume that some form of mechanical brake in the event of power failure.

And how do you power the coils, anyway? Thirty six megametres of electric wire is going to introduce serious power losses unless that cable was superconducting, particularly as it has to be relatively high frequency alternating current, and quarter-wave transmission is practically guaranteed.

 

[skeptical]

Chris

Those are good questions. I am not an engineer, so I probably cannot really answer them. I will give it a shot anyway. I am arrogant enough to pontificate from ignorance. If it comes out idiotic, I am sure you will correct me.

1. Effects on the radiation belts. I would hope this would be irrelevent. If you went quickly enough, as with today's space shuttle, the radiation should not be a serious import.

2. Your correction on maglev is warranted. Yes, magnetic bearings, and a vertical lifting force. I am insufficently expert to detail how this might be structured, but I can see no theoretical barrier given some advanced and clever engineering.

3. Mechanical brakes would pose a difficulty at the speeds we are discussing. If the vehicle was ascending, gravity would slow it. If falling, perhaps a parachute system might be appropriate. Once the movement was slowed sufficiently, a mechanical brake might finish the job. Alternatively, perhaps the vehicle might have a generator on board able to generate a magnetic brake.

4. Power losses. A good point. Yes, superconducting may be the answer, especially with another 100 years technological progress. I wonder also if it is possible for the vehicle to supply the power needed? Either the vehicle could have a generator on board (nuclear??) or else receive power by microwave beam. If coils in the ribbon were activated by induction from the vehicle, would that be sufficient?

Incidentally, I hope no-one takes the 100 year estimate too seriously. I have read estimates of 20 years, 50 years, and 100 years from different sources. I think 20 is ridiculously optimistic. 100 years should do it. However, it will not matter, from our viewpoint if it takes 1000. We are none of us going to see it anyway, and even 1000 years is infinitesimal compared to biological, geological or astronomical time. It is only one tenth of the time span since humans learned agriculture, so it is not a real major even in terms of human history.

I sometimes like to speculate on the future of humanity. When I do, I like to think in time spans of thousands of years or more. This changes things quite considerably. Predictions over decades are inevitably inaccurate. Predictions over long time spans at least means no-one can prove me wrong!

 

[ktabic]

With water, a thickness of 3 metres (10 feet) is required to give adequate shielding effect. I rather doubt that the operators of the space elevator will want to have their carriages lifting walls three metres thick with the massive amount of weight that entails.

Well that could be a problem except:

Imagine rising the space elevator at 100 km per hour? To get to the geostationary destination would take 15 days.

People without water die in about three days. So you need to provide water. And if the shielding can also be used as the water supply, you are solving two problems at once. The passengers will also need other stuff, like food, oxygen, space to move around in, entertainment, bathrooms. 15 days in a carriage with no showers? That is going to stink.

Not, in my opinion, acceptable. However, raise your speed to 1000 km per hour - very possible with maglev - and you get there in 1.5 days.

But at a higher cost, both financially and energy. The reason for building a space elevator is to make launching stuff into space cheap. It's not worth making small carriages (except for special purposes), since you are trying to reduce costs of getting stuff into orbit, so you go large. The more stuff you can move at once, the cheaper it becomes. But large increases energy costs, and fast increases energy costs. Which is what you are trying to avoid in the first place.

 

[Parson]

Oh, I don't know, Parson. Try looking at it another way, and compare the transportation systems and vehicles we have now to those of 1908...

Point taken. However, at least in transportation, we are not looking at a quantum leap in technology. The cars and planes and yes, even rockets we had in 1908 ran on basically the same principles we use now. AND there was a tremendous economic engine driving the production of the incremental increases which have added up quite nicely in the 100 years. At this point there is no economic or philosopical engine driving a sky hook so incremental increases in the technology needed will be much slower, and to move a "big rock" in to tether it to takes the kind of thrusters which need that "quantum leap."

 

[AE35Unit]

Someone on another forum is arguing that our lack of progress is due to the Van Allen Belt:

I`d like to think the landing was real, chances are that it is, but a few things have always niggled at me since i was a kid
1. From the moment Kennedy made his "putting a man on the moon" speech,the technology required was astounding and unheard of, yet it took less the 10 years to do
2. The Van Allen belt ! ! even todays shuttle expeditions steer well clear of it, due to its massive radioactivity. To pass through it you`d need lead shielding at least 3ft thick, at the time of the Apollo mission the radiation was it its highest for decades ! !

These 2 points alone make you wonder a bit, and i have`nt even gone into the rest of the "accelerated technology"..... ie, space suit, lunar module, camera film (van allen belt) again ,,,, etc etc etc
No matter what the cost, it was a race the Americans could`nt contemplate loosing

Just how much of a brake to progress in Space travel is down to the Van Allen Belt? And isn't there more than one?

 

[skeptical]

Interesting article in New Scientist

Scramjets promise space travel for all - space - 22 July 2009 - New Scientist

This discusses the intermediate between current space shuttle type technology and the space elevator. It may be possible to design a space craft that takes off from an airport on standard jet engines, accelerates to speed and switches to scramjet engines which might make mach 10, and achieve very high altitude, before finally switching to rocket engines to achieve orbit.

Since carrying oxidiser for rockets is enormously expensive in weight (80% of the fuel load of the shuttle), and since jets and scramjets use atmospheric air, this approach will both cut the weight of the spacecraft, and its cost per launch, but also increase payload. Perhaps a flight into orbit may be affordable for the ordinary person within our lifetimes.

 

[chrispenycate]

Not, I fear, within my lifetime.

The main advantage of a jet over a rocket is reaction mass; the rocket has to carry everything it must expel for conservation of momentum, the jet collects it from its environment. The minor losses due to extra friction and changeover from jet to rocket operation should be easily compensated for by this difference, even if I would like to apply the first takeoff thrust with a linear accelerator to conserve all possible fuel for high altitudes, where it is most effective (yes, you're right, I like linear accelerators)

Have you considered laser launchers? Nor reuseable craft, no, and possibly not for passengers, but possibly a good way of getting enough mass up to geostationary to start the counterweight.

Oh, and on the tower, I've got up to:

Chris

Those are good questions. I am not an engineer, so I probably cannot really answer them. I will give it a shot anyway. I am arrogant enough to pontificate from ignorance. If it comes out idiotic, I am sure you will correct me.

I, on the other hand, am a bit of an engineer (you noticed?) and actually knew Laithwaite, the father of magnetic drive technology. So yes, there is no real problem in adapting to vertical operation; I'm just so used to splitting nits (should that be picking hairs?) that I pointed it out. I'm now preparing my paper on "the long-term effects if ionising radiation on the stability of molecular bonds in carbon monofilaments". Slightly more seriously, would we need to protect the entire cable (all right, ribbon, whatever. It we're planning to send up capsules the size of ocean liners, which is fine by me, the difference is irrelevant, anyway; it's a tower) from radiation to prevent it from degenerating over the centuries?

It might appear that I am negative towards the project. Not at all; I am a pessimistic follower of St Murphy, as any engineer should be. When you have enumerated all the ways in which a project can go wrong, it's obsolete, so we'd best start now; a century or two might not be enough. But you can't build half a suspension bridge, or half an orbital tower; the thing is built once, and forever, with no real hope of demolishing it, nor repairing errors. (sorry that last was for the elevator, not the bridge)

Power source in the capsule? Well, yes, you could turn it inside out, I suppose, although one of its principal advantages (along with a total lack of moving parts; very Clarkeian) was that all the drive was external, saving weight and complexity. And microwave energy is not an efficient way of powering a linear accelerator- oh, possible, of course, but involving three transformations of energy (microwave to HF electricity, rectified and smoothed then converted into polyphase AC for the drive) and the multigigawatt maser beam is as dangerous as the rockets it replaces; how much would it spread over thirty-six million metres? If aimed down from solar generating panels on the counterwieght, how many birds would be microwave cooked, how many humans have to be evacuated from the danger zone?

Besides, when we are slowing, we want to recuperate those terrajoules of kinetic energy, and use it to power the capsules going the other way, and it is now being captured (due to our inverting the drive structure) inside the capsule. Bad idea, really; batteries that powerful may be invented in the next century, but I don't really want the energy of an atomic bomb in there with me.

Perhaps reading too much SF has oversensitised me to catastrophe scenarios, but we're looking at lots of energy here. If, on the descent, the tower stops pulling energy out of the capsule (braking, if you like, but using the energy, not wasting it as heat) it's going to hit the atmosphere at damn near escape velocity. I think you can write off parachutes as a way of slowing it: a meteor with magnetic bearings. The energy released on impact will be closer to Bikini quantities than Hiroshima, and it will definitely sever the cable/ribbon/tower, leaving the loose end free to wander through the atmosphere; this must not be allowed to happen. Even if mechanical braking reduces the passengers to mush, they were doomed anyway (except in an adventure film).

, which is not all I intended to write, but I'm rather work-intensive these days (nice; I like my work)

 

[skeptical]

Chris

You have some interesting ideas.
I am something of an optimist in relation to human development, in that I think our species is highly innovative and can come up with an amazing array of solutions to problems.

I do not deny the problems, as shown by my earlier posts, in which I detailed some of them. However, I believe we can, with time and sufficient money and ingenuity, overcome such.

You stated :
"But you can't build half a suspension bridge, or half an orbital tower; the thing is built once, and forever, with no real hope of demolishing it, nor repairing errors."

I disagree. Once the first space elevator is built, the next is going to take a fraction of the effort and money. The biggest problem is to get that first 75,000 km cable to the geostationary orbit point. However, once the first space elevator is complete, the cable can winch up its replacements.

Why do you think we would stop at one space elevator? Once we have the first, relative to the progenitor, it would be easy to set up a second, a third, a hundredth (given enough time). If the first shows signs of age, simply wind it up again, and attach an ion drive engine to carry it off into deep space, or recycle its bits. By that time, hopefully, we will have plenty of replacements.

Arthur C. Clarke postulated a structure he called Ring City. A massive tube running right around the Earth, with a thousand space elevators descending to the equator. That is what I call vision!

 

[Urlik]

Arthur C. Clarke postulated a structure he called Ring City. A massive tube running right around the Earth, with a thousand space elevators descending to the equator. That is what I call vision!

an equatorial ring would be an enormous undertaking but may be easier to construct than a single space elevator.

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

 

[chrispenycate]

Build more, certainly; mend or demolish a damaged one? The environment is not propitious. I suspect you have to detach the base and cut off small (perhaps 100 M) segments from the bottom up, as the thing drifts into a higher orbit, unrestrained by tension.

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

 

[Arwena]

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.