Posted on 02/21/2005 4:38:48 AM PST by nuke rocketeer
President Reagan talked about a "space-plane," which is what I'm talking about. VTOL is fairly standard technology anymore. The Joint Task fighter will have it as does the harrier. Vectored thrust, right? So now we need that on a greater scale, plus the ability to achieve orbit. All the science is there, and it sounds a lot more realistic than a 200-mile high elevator.
True. Science fiction it is and science fiction it will remain.
Has that changed in the recent past?
They are looking for the ability to buy unobtainium with the investors bank accounts.
"Geostationary orbit is at 42,245 km. Most communication satellites are found here, as are an assortment of others that want a constant view of the Earth (early-warning satellites, some weather satellites) or just easy communications in high orbit (some astronomy satellites).
(Source: Scienceword.wolfram.com)
There have been thorough threads on this every year for at least four or five years. It's all there if somebody wants to search the archives.
Exactly, regenerative braking using the potential energy of elevation. Except for a small loss due to machinery inefficiencies, you caouldget back at least 90% of the energy used to put stuff up the elevator. And like another post indicated, parts could be made conducting to take advantage of moving through the Earth's magnetic field.
The fuel requirements for a rocket/jet plane to go to LEO are still enormous. It will never be cheap enough to really make space accessible. I posted the new article on the elevator because I thought it was interesting that there is someone trying to surmount the engineering challenges.
IMHO, the laser launcher is the best near term bet for making LEO cheaper.
Yup. Actually (if you'd research it instead of just insulting it), the line would be about 64,000 miles long to achieve orbital equilibrium. Once we achieve practical production of long nanotubes (about a decade or so), we send up a cable-building satellite to geosynchronous orbit; it spits out a line in both directions, eventually one end touching down for tethering and the other end acting as counterweight.
Once in place, running an elevator car up & down is easy, costing a few bucks a pound instead of tens of thousands of $$$ per pound (i.e.: rocket / space-shuttle cost).
Being able to build it is not really in question now. Those who understand orbital mechanics, strong fiber construction, and creative financing believe it is doable given a large (but not preposterously so) sack of money and a couple decades to develop the technology (a predictable task) and actually build the thing.
The first objection I can see is how any such device would interfer with airline travel,
It's very narrow, not like it's hard to miss. "Don't fly there" zones are not unusual in aviation.
not to mention creating a really big target for would-be terrorists.
That's probably the only viable objection to the whole thing. Mechanically it's doable, financially it's doable, the only problem is its attraction to psychotics - i.e., a security issue.
Even that can be handled. There is a big incentive to secure a relatively small area - not particularly hard. And even if someone did manage to attack it, the damage done would be repairable: fixing the last mile of a 64,000-mile rope just kinda hanging there would just be a matter of churning out a little more rope from what made it in the first place.
Why not design a VTOL vehicle that can acheive multiple-mach speeds, and take off and land on its own power, plus a serious cargo load.
VTOL is kinda irrelevant, especially outside the lowest few feet. HTOL planes work fine. (In prior posts, I was assuming you were talking freaky Star-Trek like no-thrust gravity-neutralizing teleporter-age-technology fantasies.)
Work is being done on fly-to-orbit planes. Cargo capacity just comes with time. NASA just tested a Mach 10 engine, and Virgin Galactic just tossed a reusable HTOL shuttle into suborbital space.
The problem with shuttles is the energy needed to fight gravity without mechanical supports, carry all needed fuel onboard, and achieve orbit in a few minutes. The space elevator solves these problems: fighting gravity _with_ mechanical support (the difference between climbing stairs to the 2nd floor vs. jumping there), energy can be provided electrically from elsewhere (ground or orbit), and you can take as long as you like to climb it (slow energy expenditure easier than fast).
How is that any more outlandish than a 200-mile high elevator?
If your "shuttles" amount to fast-flying planes, the technologies are about equal: not quite here yet, but certainly within reach (Mach 30 engines vs. long carbon molecules). Best thing to do is set up competing systems: induce commercial interests into each, and let them compete until one or both wins.
The thoughts of multi-thousand-mile paved roads, 3GHz computers, and instant global communications technologies - and those available darn near free - were completely outlandish through practically all of human history ... yet now, I bring you a casual message via them. Within your lifespan, a space elevator could easily become common.
Not quite. It has been calculated, and the required strength is about equal to the tensional strength of diamond fibers (a theoretical substance predicted by science fiction writer Arthur C. Clarke). Nifty thing is, carbon nanotubes - a recent invention - are essentially exactly that: diamond fibers, which are being made longer and longer all the time.
Ah, I was a heck of a lot closer than 200 miles. :-)
Not what I heard, but even if what I heard was wrong (always possible), would you want to chance a structure that was EQUAL to the stresses on it? (rather than having a comfortable margin)
Some of the doubters need to visit the website for the company founded by the late Dr. Robert Forward, Tethers Unlimited. The plan is for multiple, mutually supporting cables in case one fails, which is insured by space debris. However, if the cable is cut it cannot fall far because of the cross linking. As for cutting the Earth's magnetic field lines and generating enormous electric power, single walled carbon nanotubes conduct electricity better than copper.
"...so the biggest questions will be about economics and strength of leadership."
The biggest question with any megaproject to advance Humanity is ALWAYS "strength of leadership".
As George-the-1st put it "...the Vision Thing..."
Though for the last 3 decades neo-Luddite neo-Malthusian antihumans love to pretend its all about [UNmoney] economics as their excuse for 'limits to growth' stasis-quo.
Expect immediate cries from the antihumans of "Even if we CAN do it it will 'cost' too much TO do it!!!"
And, in case anyone really cares, 26,249.8 statute miles is 30,207.75 nautical miles.
How does the Rock of Gibralter strike you... we only need to move it to the Equator...
Actually, we anchor it in space... by extending a cable outward from the Geosynchronous point to equal the mass of the cable and cars. Properly engineered the Earthside anchor would not need to be as massive as the Rock of Gibralter.
NO... its even more "outlandish" than that... we would have a 36,000 mile long line reaching up into space, through the geosynchronous orbit point at 22,000 miles, and on out to a point just beyond escape velocity orbital distance where it is anchored.
Airlines would avoid it... give it wide berth. Terrorists probably could not damage it on Earth but might be able to hit it above the Earth by smuggling a bomb into cargo.
The problem with any VEHICULAR method is it takes energy to raise the vehicle in addition to raising the payload. Right now it takes 1000 lbs of fuel to put 1 lb in orbit... mostly because you have to carry a large portion of the fuel to lift the fuel and the rocket.
Not to be to picky here, but subtract the radius of the Earth (~4,000 Miles) from 26,249.8 statute miles to get approximately 22,000 miles above the surface of the Earth... the length of the string.
Hey, good point! Guess I'd better forget about being an engineer when I grow up!
Rock of any variety does not do so well under tensional or lateral shear stresses.
The biggest weight in the world (including the world itself) means little if you cannot attach it.
Carbon Nanotubes can handle the stress.. at this point there this can become reality.. there are obviously technical issues to overcome, but none of them are major.
Basically the only factor that is going to determine if this happens is whether or not it will continue to be funded.
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