Posted on 06/25/2004 2:21:35 PM PDT by Junior
WASHINGTON - President Bush (news - web sites) wants to return to the moon and put a man on Mars. But scientist Bradley C. Edwards has an idea that's really out of this world: an elevator that climbs 62,000 miles into space.
Edwards thinks an initial version could be operating in 15 years, a year earlier than Bush's 2020 timetable for a return to the moon. He pegs the cost at $10 billion, a pittance compared with other space endeavors.
"It's not new physics — nothing new has to be discovered, nothing new has to be invented from scratch," he says. "If there are delays in budget or delays in whatever, it could stretch, but 15 years is a realistic estimate for when we could have one up."
Edwards is not just some guy with an idea. He's head of the space elevator project at the Institute for Scientific Research in Fairmont, W.Va. NASA (news - web sites) already has given it more than $500,000 to study the idea, and Congress has earmarked $2.5 million more.
"A lot of people at NASA are excited about the idea," said Robert Casanova, director of the NASA Institute of Advanced Concepts in Atlanta.
Edwards believes a space elevator offers a cheaper, safer form of space travel that eventually could be used to carry explorers to the planets.
Edwards' elevator would climb on a cable made of nanotubes — tiny bundles of carbon atoms many times stronger than steel. The cable would be about three feet wide and thinner than a piece of paper, but capable of supporting a payload up to 13 tons.
The cable would be attached to a platform on the equator, off the Pacific coast of South America where winds are calm, weather is good and commercial airplane flights are few. The platform would be mobile so the cable could be moved to get out of the path of orbiting satellites.
David Brin, a science-fiction writer who formerly taught physics at San Diego State University, believes the concept is solid but doubts such an elevator could be operating by 2019.
"I have no doubt that our great-grandchildren will routinely use space elevators," he said. "But it will take another generation to gather the technologies needed."
Edwards' institute is holding a third annual conference on space elevators in Washington starting Monday. A keynote speaker at the three-day meeting will be John Mankins, NASA's manager of human and robotics technology. Organizers say it will discuss technical challenges and solutions and the economic feasibility of the elevator proposal.
The space elevator is not a new idea. A Russian scientist, Konstantin Tsiolkovsky, envisioned it a century ago. And Arthur C. Clarke's novel "The Foundations of Paradise," published in 1979, talks of a space elevator 24,000 miles high, and permanent colonies on the moon, Mercury and Mars.
The difference now, Edwards said, is "we have a material that we can use to actually build it."
He envisions launching sections of cable into space on rockets. A "climber" — his version of an elevator car — would then be attached to the cable and used to add more lengths of cable until eventually it stretches down to the Earth. A counterweight would be attached to the end in space.
Edwards likens the design to "spinning a ball on a string around your head." The string is the cable and the ball on the end is a counterweight. The Earth's rotation would keep the cable taut.
The elevator would be powered by photo cells that convert light into electricity. A laser attached to the platform could be aimed at the elevator to deliver the light, Edwards said.
Edwards said he probably needs about two more years of development on the carbon nanotubes to obtain the strength needed. After that, he believes work on the project can begin.
"The major obstacle is probably just politics or funding and those two are the same thing," he said. "The technical, I don't think that's really an issue anymore."
http://www.mit.edu/people/gassend/spaceelevator/center-of-mass/index.html
Ok, here's another page, that I found fascinating and enlightening, and it proved my intuition correct! CG slightly beyond geo.
But if you don't get off at geo, then you need to be really sure that the cable won't snap while you are on it. Because beyond that point, if anything goes wrong with the elevator, then you are in serious trouble. At least don't put a space station at the anchor.
1) Concept by ex-Air Force folks to build air breathing craft with large JP-4/LOX rocket in the tail. Concept drawing looked very much like an old British Vulcan bomber. Craft would launch from Edwards area and cruise on turbojets to an existing military area off the Washington State coast. It would hit a military tanker loading up on JP-4 (far more than it would normaly be able to get off the ground with). LOX is carried from takeoff. It would aim south, ignite the rocket, and go suborbital, re-entering military airspace off the California coast. At apogee of the flight at perhaps 300k feet and several mach, it would open large doors in the top not unlike the Shuttle, and kick out an upper stage that would continue into orbit. Performance of the vehicle is perhaps only a bit higher than the X-15 was. So it's very do-able. The advantage is in the ability to carry an upper stage internaly, and eject it during the 2-4 minutes it spends in "space".
2) Basically similar idea to No 1, but rather than carry air breathing engines for takoff, would be towed by 747/C5 class aircraft. Idea was tested by towing an F106 with a C141 a few years ago.
Those are two of the ideas that stick in my mind. There are others with exotic scram jet mid stages that should be considered too. I believe that the material science has been figured out, if you use Shuttle style tile thermal protection. These tiles have been bashed in the media, but I believe they would work fine as long as you don't put them next to a large external tank and accelerate the stack to hypersonic speeds exposing them to extreem shock waves in the space between shuttle and tank, and bashing them with FOD.
There are other ideas, but it's too late to think of them right now, and I think the above are the best.
There is Pegasus, with over 100 successful satellite launches, similar idea. They even used that to test the scramjet. While you wouldn't see all the ideas in use all at once, they are in use.
Circumference of earth ~ 24,000 miles
Circumference of elevator orbit ~ 206,809 miles
Speed of base (24 hour rotation) ~ 1,000 mph
Speed of platform (24 hour rotation) ~ 8,617 mph
The platform is 62,000 miles above the earth's surface. If the elevator cars travel at 100mph, they will still take almost 26 days to travel the ribbon. Delta-V will average out at just over 12 m/h2. I think that will be manageable.
RADIUS of elevator orbit ~ 65,829 miles
Circumference ~ 413,615 miles
Orbital velocity ~ 17,233 mph
Delta-V over 26 day period ~ 26 m/h2
My bad.
"The platform is 62,000 miles above the earth's surface. If the elevator cars travel at 100mph, they will still take almost 26 days to travel the ribbon. Delta-V will average out at just over 12 m/h2. I think that will be manageable."
The mass that balances the cable is at the top (65,829 miles), but the only point in the system that is in true orbital motion is the geosynchronous orbit point, 22,236 miles up.
If this is an elevator to orbit, then we will ride it to the geosynchronous point.
The higher portion is just for balance. (The center of mass should be at the geosynchronous point). So the upper part could be shortened by using more mass. (a captured asteroid).
See "Fountains of Paradise" by Arthur Clarke 1979, where this is laid out in some detail.
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