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Benford on Space Exploration
gid-goo writes "Gregory Benford looks at what we should do in the aftermath of the Columbia accident. Is the shuttle, or the International Space Station for that matter, useful? Or just payola to aerospace interests and a means for keeping Russian rocket scientists employed?" Benford's comments about the necessity of a closed biosphere and of some way for astronauts to stop muscle and bone loss are far more insightful than the usual discussions about where our space exploration priorities should lie.
According to this article mentioned earlier on Slashdot:
I code, therefore I am.
The main part of the Benford's article is that the primary problem of space travel is dealing with the lack of gravity to maintain human bone and organ health.
Cats spend up to 20 hours a day sleeping and yet still manage to stay fitter than most human gymnasts.
Purring creates vibrations through the cat's body helping to maintain muscle and bone density.
Transducers in an astronaut's suit could produce similar resonant vibrations. These vibrations could simulate the stresses of g-forces by rapidly moving the astronaut a very small distance back and forth.
Sorry I didn't connect the dots for you in the original post.
- A new spaceplane, designed for crew. See the Orbital Space Plane [orbital.com].
Wings add greatly to the weight, and there are lots of tradeoffs, like high landing speeds. Arguably adding wings to the Shuttle killed Columbia, certainly it was a wing failed, and the tiles are necessary because of the aerodynamic shape required, and the slower reentry that wings impose/allows, leading to overall higher heat load (compared to Apollo, Shuttle has to cope with a somewhat lower temperature but for much longer).A new technology, reusable launch vehicle. See the Space Launch Initiative [slinews.com].
The SLI has been cancelled.
Continuing with the Prometheus Project [space.com]. We fucked up when we stopped persuing NERVA/Rover [astronautix.com].
Prometheus is a development of a nuclear power plant for space use; it is for ion drives. NERVA will not be supported under this program.
Mars. Need I say more? [nw.net] I'd also like to see a space elevator persued, but I don't know that we have the tech yet. Then again, I haven't looked into it that much either.
It seems doable with hardly much more technology than we have right now. Scaling up the production of carbon nanotubes to production of tonnes rather than milligrams is required, and a demonstration of a few percent more strength, and a reasonably large wodge of cash- about $15 billion ;-)
-WolfWithoutAClause
"Gravity is only a theory, not a fact!"This article on spacefuture.com has a pretty good analysis of what centripetal forces we should be looking for in deciding to build a rotating space station. It takes into account not only the physics, but also the effects of this artificial gravity on humans (since there is a significant effect due to Coriolis forces that make it behave differently from natural gravity).
The escape velocity of Mars is 5.03kps as compared with Earth's 11.2kps escape velocity. That figure is based on its gravaty.
As for the atmosphere, here is more info out of a Newsletter from the Coconino Astronomical Society about what is in the atmosphere and how they know. You may want to read the whole letter at http://www.lowell.edu/cas/news/2002_sep. pdf (warning! it gets boring fast).
In order to determine if a gas is retained by a planet, the following formula is used.
Escape velocity of molecules = the square root of (2 times Boltzmann's constant times the effective temperature / molecular weight times the mass of the hydrogen atom).
The escape velocity of Mars is three miles per second. Therefore, Mars has carbon dioxide and no water vapor in its atmosphere. Carbon dioxide has a molecular weight of 44; water has a molecular weight of 18. Obviously, water vapor requires much less energy to escape the Martian gravitational pull than carbon dioxide. Hydrogen and helium molecules are not present in any of the inner planets because of their atomic weights of one and four, respectively
Laika! But she was kind of a bitch.
Really - Valentina Tereshkova, the pilot of Vostok 7. The only thing remarkable about Sally Ride (or other "female firsts") is that women in the west were prevented from pursuing that field for so long. The Soviet Union had no shortage of flaws, but they were more equal-opportunity than the West.
And actually I rather dislike the story of Laika. She was sent to her death (an unpleasant one, slow suffocation, dehydration, or burning up) and they knew they had no way to get her down. The Americans weren't much better, killing lots of monkeys and chimps. At least by the time they actually managed to get a primate in orbit it was late enough that they were also able to land it safely. Maybe there's a message there about prematurely putting humans in space...
I'm not sure putting our priorities on designing the next shuttle is what's really needed since it is basically a truck to LEO. In retrospect, in the early 70's NASA would have been much better off ramping up production and building scores of Saturn V's, a hundred Saturn 1B's and a few dozen Skylabs. With 20/20 hindsight, big dumb boosters were probably the best way to go three decades ago and that probably still holds true today. Who knows, maybe we still would have lost 1 out of 50 Saturn launches as well, but at least would have a lot more interesting stuff everywhere between LEO and the Moon for the same money.
For me I'm much more interested in spending the bulk of NASA's limited budget on interesting payloads that leave LEO rather than developing trucks to deliver the payloads to LEO. After all, 60's technology was fine for getting us to LEO and the Shuttle isn't going to take NASA to Mars.
Since the beginning of the shuttle program there were plans for a shuttle derived unmanned heavy lift vehicle that basically looked like a huge boxcar strapped to the side of the external tank. The only recoverable parts were the engines themselves, which would parachute to Earth after entering the atmosphere with an ablative heat shield. I believe that with most of the weight of the shuttle structure, wings, and crew cabin removed, such a booster would have had nearly the capacity of the Saturn V. It seems that such plans could be resurrected and within a year or two we have a heavy lift vehicle that can take advantage of economies of scale for shuttle solid rocket boosters and external tanks which I believe, ironically, are the cheapest parts of the shuttle. NASA can then use the proven Soyuz (thank you very much Russia for keeping the rocket and capsule assembly lines going) to get human crews into orbit until some suitable replacement is made.
Once NASA again has heavy lift capability it can then concentrate on truly interesting payloads that can take us to Mars and beyond. I'll cry if NASA does get the go ahead for a Mars mission and comes up with a scheme where dozens of shuttle missions (either the remaining three vehicles or next generation shuttles) are required to build the spacecraft in orbit from small components.
Here's a good paper on the subject. It's a 15mb pdf, but worth the download.
In it, a good many of the technical problems are solidly examined, and reasonable solutions are proposed.
The approach presented is to launch an initial spool of very thin cable into geosynchronous orbit. This spool will be some thousands of kg in mass; this won't be *that* much harder than putting up a communications satellite. Then you lower that cable down to earth (and raise spool-unreeling spacecraft up past geosynch. as a counterweight), and you have a sort of "mini" space elevator that can haul up a mere 1200 kg. A series of climbers then ascend, each epoxying on a new layer of cable. Continue for 2 years, and you have a cable that can carry up as much as the shuttle. Continue for 5 years, and you have one that can lift a million kg.
All the solutions to the technical problems will require lots of research/testing to truly overcome, so it'd likely still be decades away, even with full effort. And that's also assuming the cable itself can be built.
I think that's the paper's main weakness, actually: its reliance on finding an epoxy to construct the cable with, that will allow the overall cable strength to be similar to the inherent nanotube strength. The proposal calls for 3-cm lengths of carbon nanotube to be assembled into the cable (in a mostly flat ribbon shape) with the epoxy. This is because such lengths of carbon nanotubes have indeed been produced, and the paper is trying to go with known technology as much as possible.
Now it seems to me that finding an epoxy strong enough to hold on to the fibers would require finding a substance with nearly as much strength as the fibers themselves. Otherwise, the epoxy will fail when the load becomes great, and the fibers will just slip out. A strong rope does you no good if you can't hold onto it!
Though perhaps there's something about epoxying materials from fibers that I don't understand. Anyone? Anyone? Bueller?
The terrorist-threat angle is another concern. Though a terrorist attack would presumably occur at the low end of the cable, which would have minimal effect on the earth.
The main environmental risk is that of the cable breaking at a high point, possibly at the counterweight. The paper say that if this happens, "About 3000 kg of 2 square millimeter cross-section cable ... may fall to Earth intact and east of the anchor." It goes onto say that further study/simulation is necessary to determine the full threat.
So again, for me, I'm not so sure that the epoxy technique of cable construction will work. We may have to wait until we have enough nano-scale control to be able to construct the cable with full-cable-length nanotube, finely interwoven. Of course, once we can make nanotubes like that, a lot of other possibilities for space travel may open up.
"Orthodoxy is unconsciousness" - Orwell
- It would be a money sink that would never pay back its construction costs - a tax money sink, because no commercial firm could ever get investment funding (not this side of AD 3000 anyhow).
The cost is actually quite modest. Figures between $5bn and $40bn have been mentioned. At the lower end of the scale, this is about 15 shuttle launches. At the high end, it's a tiny fraction of the US defence budget. The benefits to the first company or government who does this are the ability to launch satellites at a tiny cost, build further space elevators for (relatively) next to nothing, and in the long term the full exploration and exploitation of natural resources in space.- It would be the worst sort of governmental monopoly, a choke point where everyone must bow and scrape to the groundbound owners, in order to get a lift.
This is certainly true in the short term. In the longer term, many elevators can be built by different companies and governments. (Only the first elevator is expensive - once that's working the others are cheap to build).- It would be The Definitive Terrorist Target - and the bad guys only have to get lucky once. It would be utterly indefensible from a simple kamikaze attack, being so long that no weapons installation could keep cover over its whole length without weighing it down.
The proposal is to have an exclusion zone around of the order of 10-100 miles. It would be extremely hard to fly unnoticed into such an area. Attacks from underneath (submarines, etc) and attacks from people actually travelling on the elevator are harder to deal with. In the end it doesn't matter however. Once one elevator is up, you build more, and you keep a few reels of carbon nanotubes "parked" in space to cover this eventuality and natural disasters.- And it would be a catastrophe waiting to happen, when (not if) it snaps and rains megatons of carbon cable down upon the ground below.
Yes, we've all read Kim Stanley Robinson too. He's a good writer, but not a great scientist. A break in the cable is most likely to happen in the first 20-40 miles (ie. in the atmosphere). So the 20-40 miles of cable drops down - into the exclusion zone which is just a harmless area of sea. The top part slowly drifts off into space. There's even the possibility of repairing a broken cable by lowering more down to earth before it drifts off.Rich.
libguestfs - tools for accessing and modifying virtual machine disk images
Complete bollocks. Specficially, if it cost $20G to build (they say $10G), it need only make $2G/a to handily beat bank loans and stuff as a payback means. So double the $100/kg lift costs to $200/kg, big deal in the face of the $10,000-$30,000/kg it is now. $2G / $100/kg extra profit == 20Mt/a, 55,000t/day, 2300t/hr, a 400t load every 10 minutes.
Need to halve that load? Triple the price instead of doubling it. Or use the elevator to build more, and amortise the costs between them.
And we don't have one now? Go ahead, build your own Saturn V or Energia-Groza, be my guest.
Once they have half a dozen of these up, owned by 3 or 4 countries or consortia (I'd guess USA, EU, China, Russia, India, Brasil), that starts to break down anyway. If Australia wanted to build the first one, that would cost us $10,000 a head. If it built the 8th one, maybe $500 a head and every Australian gets their first 2kg hauled to space for free. If the people living in Perth pooled their gree kilograms, we could loft a 3000 tonne satellite.
Ever tried to hit something a meter wide from 10 km away? With defenses on the elevator shooting back at you and at your shells?
Clearing a corridor 10km wide around this would be no problem, and keeping it clear with SDI technology (near the ground, a perfectly ordinary Vulcan radar-guided cannon would do the job) relatively simple. Can you outfly a laser? Could your aircraft or missile survive several hundred unexpected megawatts of microwaves tuned to some vital dimension? How about a smart remote-targeted crowbar dropping in on you from LEO at mach 20?
Any concievable replacement would be worse.
It would have to be a clever piece of space-junk, smaller than a peanut and yet more destructive than a nuke. You haven't had a look at the design, have you?
If they were kind enough to put the elevator up on the Equator (not necessary, but it helps), it (or more specifically the defenses on it) would actually make a pretty good street-sweeper for the space industry.
That statement just betrayed your complete ignorance of how the elevator would work.
Of the 100,000km length, less than 100km would be in atmosphere. Take what is presumably the worst case: the cable snaps about 50km up. 50km of cable fall to earth, the top 30km or so burning up on re-entry, the balance stays in orbit. That's right, losing 0.05% of the cable makes very little difference to its orbit. Soon the lost 50km is replaced by shipping it out along another cable and unreeling it off the next segment above the damaged one.
But what about the bottom 20km? Even if it were heavy (did you read the line saying `paper-thin?'), it would fall into the ocean. Even if they anchored it at, say, Kununurra (in the far north of Western Australia) and it were heavy, you'd still only lose a stripe of desert a few m wide and 20km long. Big deal.
Now, important step, visit High Lift Systems and RTFM. Then come whinging back here.
Got time? Spend some of it coding or testing