Posted on 02/15/2006 10:24:11 AM PST by Neville72
In January, LiftPort team members deployed a mile-long tether with the help of three large balloons in the Arizona desert (N Aung/LiftPort Group)Related Articles A slim cable for a space elevator has been built stretching a mile into the sky, enabling robots to scrabble some way up and down the line.
LiftPort Group, a private US company on a quest to build a space elevator by April 2018, stretched the strong carbon ribbon 1 mile (1.6 km) into the sky from the Arizona desert outside Phoenix in January tests, it announced on Monday.
The company's lofty objective will sound familiar to followers of NASA's Centennial Challenges programme. The desired outcome is a 62,000-mile (99,779 km) tether that robotic lifters – powered by laser beams from Earth – can climb, ferrying cargo, satellites and eventually people into space.
The recent test followed a September 2005 demonstration in which LiftPort's robots climbed 300 metres of ribbon tethered to the Earth and pulled taut by a large balloon. This time around, the company tested an improved cable pulled aloft by three balloons.
Rock solid To make the cable, researchers sandwiched three carbon-fibre composite strings between four sheets of fibreglass tape, creating a mile-long cable about 5 centimetres wide and no thicker than about six sheets of paper.
"For this one, the real critical test was making a string strong enough," says Michael Laine, president of LiftPort. "We made a cable that was stationed by the balloons at a mile high for 6 hours…it was rock solid."
A platform linking the balloons and the tether was successfully launched and held in place during the test. LiftPort calls the platform HALE, High Altitude Long Endurance, and plans to market it for aerial observation and communication purposes.
But the test was not completely without problems.
The company's battery-operated robotic lifters were designed to climb up and down the entire length of the ribbon but only made it about 460 m above ground. Laine told New Scientist that the robots had worked properly during preparatory tests and his team is still analysing the problem.
Carbon nanotubes In March, LiftPort hopes to set up a HALE system in Utah's Mars Desert Research Station and maintain it for three weeks. Then, later in the spring, Laine says he wants to test a 2-mile (3.2-km) tether with robots scaling to at least half way up.
Laine aims to produce a functioning space elevator by 2018 – a date his company chose in 2003 based on a NASA Institute for Advanced Concepts study, which said an elevator could be built in 15 years. "This is a baby step, but it's part of the process," he says of LiftPort's recent test.
The idea is to build the actual elevator's ribbon from ultra-strong carbon nanotube composites and to have solar-powered lifters carry 100 tonnes of cargo into space once a week, 50 times a year.
Beams and climbers Laine sits on the board of the California-based Spaceward Foundation, which partnered with NASA to put on two space-elevator-related competitions that were the first of the agency's Centennial Challenges programme – the Tether Challenge and the Beam Power Challenge.
The first is designed to test the strength of lightweight tethers while the beam challenge tests the climbing ability and weight-bearing capability of robots scaling a cable. Laine’s team is not competing in the NASA challenges so there is no conflict of interest.
In October 2005, none of the competition entrants performed well enough to claim the twin $50,000 purses. But the challenges are scheduled to take place again in August 2006 with $150,000 top prizes. Nineteen teams have signed up for the beam power challenge so far and three will compete in the tether challenge.
Ben Shelef, founder of the Spaceward Foundation, hopes the competitions will drum up interest and drive technological innovation. He told New Scientist he is pleased to hear of LiftPort's successful test. "A journey of a thousand miles starts with a single step," he says.
Geostationary orbit (a necessity for this to work) is not possible at the poles.
There is no "torque" involved in this setup.
The forces involved in bending a spinning propeller (Atmosphere) are not present in the space elevator concept. A propeller spinning in a vacuum and micro gravity environment would have perfectly straight blades.
There would be no counterbalance needed. You simply need to provide enough energy for the "car" to climb it's way up. We can't do this with a rocket because it's an independent vehicle. There are many ways you could provide power to the car if it attached to a structure.
The same amount of energy is required to lift the payload, but the method of utilizing that energy would be much more efficient than a chemical rocket.
Actually, I believe it does. If it weren't you would need another one at an equal distance form, and on the other side of the equator.
Even if it didn't, the satellite does however need to be directly over the equator. And for every degree off the equator the anchor point was, it would add a great deal of length to the "cable". It just wouldn't make any sense not to have it on the equator.
To put it another way, we're not concerned with it's efficiency relative to a counter balanced elevator in a building, we're concerned with its efficiency relative to chemical rocket propulsion. Over which it would be a HUGE improvement.
I'm not sure where that number comes from. But you would want it ABOVE the standard GS orbit to provide tension to the "cable".
If you had it exactly at GS orbit, and tensioned the "cable",(effectively increasing the "gravity" acting on the satellite) you'd pull it out of orbit. In the final configuration, the cable would be holding the satellite in an orbit that would otherwise not be possible.
The main idea is to get the space vehicle or satallite past the majority of earths gravity field. Once your 100 miles out its basically zero, and would take alot less fuel to escape earths atmo, or to go to an even further radius.
Ofcourse there would be a counterweight on the end of the elevator (which is basically a rope), that would be needed so when you pulled on the end the rope won't pull down. The weight on the end would have to around the size of the max load you'd want to carry up the ladder. Otherwise the force of the load would cause the rope to accelerate towards earth. Basically you want more torque, its what keeps it in the sky.
You don't need to worry about terrorism because once you get one of these working, it will be much simpler to just drag another up, keeping it attached to earth as you go up. Kind like climbing some rocks, getting the first rope up is hard, but you can bring another rope, and tie it off when you get to the top.
It also doesn't need to be at the equator because you can just angle the wire, theres no reason why it has to be perpenducular to the surface of earth.
The only sci fi part of this is finding a reliable material that will hold for many years, and all that is, is some engineering. If you gave Newton the rope and a way to get it up there, he could have built this thing, thats how old the theory is behind this.
See post 107.
ping
I'm going to have to disagree with you on this. Other than practical reasons (length of cable), I'll try my best to explain.
By having the tether not on the equator, you'd be introducing a "side load" of sorts. The orbiting mass will tend to move away from the center of mass of the object around which it is orbiting until it reaches equilibrium with the forces holding it in orbit, in this case, gravity, and the cable. An angeled cable under tension, would pull the orbiting mass in the direction that would reach the maximum distance from the center of the earths mass, or the length of the cable as it would radiate directly from the center of the earths mass.
Thus you would be using the cable to alter the center of mass around which it orbits, by altering the forces acting on it. For example, if you attached the cable North of the equator, and began to tension it, you'd would pull the orbiting mass to a geosynchronous orbit at some point North of the equator. While it would be theoretically possible to achieve this type of orbit, it simply would not be practical.
The satellite would need to be put in a stable GS orbit in order to tether it. Once that is done, the cable would be tensioned to pull it to it's new stationary orbit. At the same time the satellite velocity would need to be adjusted to compensate for it's change in altitude, as it would be pulled towed the center of the new equilibrium point which would be a tighter circle, so the velocity would need to be increased to maintain it position over a particular longitude. This would require a vastly greater amount of energy than simple leaving it over the same GS spot, and nudging it outward after it was tethered. Once past the geosynchronous altitude the natural centrifugal forces would provide the energy needed to continue to move it outward until the desired tension is achieved.
There. Did I totally butcher that explanation? Anyway, there it is.
Beware terrorists in hot air balloons with scissors!
It's going to be a lot of trouble to build a ribbon that is up to the strength and lightness necessary. If it gets snipped, it will flop down on the earth like a strip of adding machine paper, not hard enough to crush anything but quite possibly causing havoc with shipping and/or traffic.
Need to think.
Therein lies is the reason it wont work off the equator. By tensioning the cable you would by necessity increase the forces holding it in orbit, thus pulling it closer to the center of mass. It cannot maintain orbit if if decreases velocity as it gets closer to the center of mass. The forces of the cable would have to equal the forces of gravity until the object, the cable, and the center of mass of the Earth reach a triangle of equilibrium.
Example. Take a helium balloon with two equal length strings tied to it. Letting the balloon float, place the ends of the strings on the ground, and move them apart. The balloon will get closer to the ground. In this example, one string is the cable, and one is gravity. Thus, for the forces of the cable to equal the force of gravity acting on the satellite, the statute would need to be moved closer to the axis of the earth. The velocity would have to decrease in order to keep it over the same longitude, but it would not be able to stay in orbit because of that decrease in velocity.
Geosynchronous orbit is 22,282 miles altitude and 6881 mph. An object on the ground is traveling at 1037 MPH so it WOULD need to add velocity in order to stay over the same relative spot on the ground. Whew. I need sleep.
There are not many clouds 62,000 miles up.
I think the current idea is to use the carbon nanotubes to "dope" other materials. Think re-bar in concrete.
Actually the forces involved in something this massive would be incredible. Don't forget that if it fell (even from halfway) it would wrap itself around the Earth.
The weight to area ratio of this material would probably be similar to that of paper. Meaning that the atmosphere would slow its fall like it would a strip of paper.
This is quite incorrect. 100 miles up from the surface, gravity is still 99.5% of what it is on the surface (4000^2 / 4010^2).
Even a thousand miles up, it's still 64% of surface gravity.
The only reason that objects in orbit at that height are "weightless" is not because there's little gravity there, it's because they're in free-fall. Normally this would result in a quick trip back to the surface and a loud crash, but thanks to their huge lateral velocity, they never land -- by the time they have dropped one foot, they have traveled far enough horizontally that the curvature of the Earth has "lowered" the surface by an equal distance, so those in orbit maintain a fixed height. Rinse, repeat. This is the basic dynamic of any circular orbit. If there were no atmosphere and the Earth were smooth, they could do the same trick six inches off the ground as well (at the appropriate velocity), and still be weightless inside their space capsule despite the full 1G of gravity and the proximity of the surface.
Since a vertical space elevator is "stationary" (relative to its point of attachment on the surface), an object on the space elevator ten miles up (including the elevator cable itself at that point) would still feel 99.5% of its surface weight (minus a negligible amount of "centrifugal" force, but this would be quite tiny at ten miles). Nor would you gain much "free ride" -- if you wanted to leave the elevator at that point and launch off into orbit or outwards towards the Moon or points beyond, you'd have to accelerate a great deal to get there; roughly 99% of what a rocket from the surface itself would have to expend without the elevator.
Additionally, if the space elevator ended at that point (ten miles up), it would come crashing down, as there would be nothing to "hang" it from, nor would a ten-mile-tall ribbon be rigid enough to stand on its own like a radio tower.
The reason that space elevators would have to be thousands of miles tall is so that a) the "top" of the elevator would be high enough that payloads would need only a negligible amount of additional energy to launch into orbit or outwards to the rest of the Solar system, and b) so that centrifugal forces at the end (top) of the elevator would be strong enough to "hold" the elevator vertical. Due to the rotation of the Earth with the elevator sticking straight up from it, basically the outer "half" is being flung outwards (faster than orbital velocity) in a way that provides exactly (or more than) enough force to counterbalance the lower "half" of the elevator which wants to fall (slower than orbital velocity) back down to the planet.
In practice the most efficient way to construct the elevator is not from the ground up, but from a fabrication plant in geosynchronous orbit which makes two separate ribbons of cable, feeding one "up and out" while simultaneously feeding another "down and in", keeping the tidal forces on the plant-plus-cable system in balance so it doesn't drift out of its fixed orbital position. As the final feet of cable are added (still in both directions), the lower string of the cable touches lightly down to the surface and is anchored in place by a crew on the ground, while the outer string reaches its farthest extent out into space in the opposite direction. Contrary to expectations, the portions of the cable under the most tensile stress (and needing to have the greatest thickness of nanotubules) would be the portions in the "middle" nearest the fabrication plant, whereas the portion at the surface and at the farthest end of the outer "whip" would be under the least tension.
"LiftPort Group, a private US company on a quest to build a space elevator by April 2018, stretched the strong carbon ribbon 1 mile (1.6 km) into the sky from the Arizona desert outside Phoenix in January tests, it announced on Monday."
1 down...61,999 to go.
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