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.
I agree.
If we can build a 60,000+ mile elevator, we can build a sturdy 40,000 ft. fence around it.
Yes, but if it breaks near the "middle" (at the point of highest stress), it'll have time to fall several thousand miles in vacuum, building up a *lot* of velocity and energy, before it encounters any atmosphere. Plus there are interesting forces similar to a game of "crack the whip" as it starts to wrap itself around the Earth.
There's a good description of the consequences of this in the science fiction book "Red Mars" (by Kim Stanley Robinson). The falling space elevator (in the book, on Mars and not on Earth) does some counterintuitive but spectacular things as it wraps around the planet 3-4 times.
Furthermore, the point of attachment at the surface would be the *least* catastrophic place for something to go wrong. Even if it were severed completely, it would just hang "loose" (albeit probably drifting aimlessly across several miles back and forth) and the rest of the elevator wouldn't fall. All you'd have to do is grab the loose end, drag it back to the anchor point, and reattach it.
The worst place for something to go wrong would be at the midway point, and it's a lot easier to keep terrorists away from geosynchronous orbit (as long as you carefully screen who gets *on* the elevator itself and with what).
Without seeing the book yet, wouldn't it basically vaporize itself upon hitting the air, freeing the remainder of the loose end which would fly out into space?
Thanks for that layman's explanation. I never quite grasped that before.
No, at least not in the case of Mars (which has a thinner atmosphere, albeit a weaker gravity, so it might balance out). I haven't seen anyone run the numbers for Earth, but the faster it goes before it hits the atmosphere, the farther it can penetrate before it burns up -- with enough speed it could make it to the surface before it's all gone. Plus as the Columbia disaster showed, you'd be surprised how much stuff can re-enter pretty much intact even after undergoing high-velocity re-entry. A further complicating factor is that it could have something like the velocity of a rifle bullet by the time it re-enters (which is *slow* relative to orbital velocities), which would save it from vaporization but still have enough velocity to slice cars and people in half when it hits the surface. So there are a lot of fun physics involved.
As for parts of it breaking off and flying off into space, no such luck -- if it broke in the middle, every portion of the multi-thousand-mile strand would have less than orbital velocity (much less escape velocity), and even if it broke apart the pieces would still crash down independently, or at best circle in elliptical orbits until atmospheric drag eventually caused them to come down anyway sometime in the future, like Skylab. It could be raining hundred-mile chunks for years to come.
Oops, make that 95.2% (40002 / 41002), and change the later mentions of "ten miles" in my post to "one hundred miles". The argument remains the same though, even though I lost a zero after the start of my post.
Rifle bullets are pointy and twist in flight, but would the ribbon necessarily be that way. I'd think it could be made with a dogbone profile (edges looped over on themselves and attached) to mitigate the hazards from falling pieces, and the flat main part be oriented broadside to east-west.
Ah. So that's why rockets go straight up.
Hmmmm. Isn't that what I said? How is that velocity to be obtained? How will you increase the velocity of a 100 tonne object from 1037 mph to 6881 mph?
If you merely lift it along the ribbon, won't the ribbon tend to form a "C" as it tries to increase the horizontal velocity of the rising payload?
And if a counterweight is being lowered simultaneously, won't the ribbon tend to look like an "S"?
Where is the City in the Bubble that was taunted back in the 60's, scientists were saying we would have these futuristic cars by 2000?...
Not scared of Progress - Hate money wasted....
You are missing a point... YOu would be correct if the elevator was built starting at 100 miles up, we are talking about the first 100 miles being effected by the atmosphere and gravity forces. The weight that would be on the object the first 100 miles would still be constant, no matter what the last miles would be. The foundation has to be huge to hold it... there isn't a force outside of earths gravity that will counter weigh this action. Basic Laws of Newton and bernoulli's law. Aerodynamics must be in play, due to being in the atmosphere.
This is a stupid idea.
Indeed it is. By emphasizing WOULD, I was acknowledging that I was wrong on that point, and you were correct. ;)
The question is, how much acceleration in the horizontal direction would you need, and thus, how much stress would you impart to the cable. The answer is, it depends on how fast you gain altitude.
Aerodynamics would not be in play, because even though the payload is accelerating, it is only moving vertically relative to the ground, and relative to the atmosphere. The only aerodynamic forces, other than the winds, would be the result of it's vertical speed.
Novel Space Fantasy, but not an earthly reality
Gives a whole new meaning to the phrase, "Blue screen of death."
So this is why all the satellites we try to send up keep falling back down.
WOW.
You should contact NASA and let them know, before they waist anymore money trying to achieve this technological impossibility called "orbit".
Thanks
The counterweight will be beyond geostationary orbit but moving at an angular velocity relative to the earth the same as an object in geostationary orbit. This will create a centripetal force - like a weight at the end of a string being whirled around - that will create a tension in the cable. If you were to cut the cable once this system is in orbit the counterweight would go flying off into an even higher, less-than-geostationary orbit.
I'm not expert on orbital mechanics, but the concept, at least in theory, is pretty simple and well-understood, and workable. The only real impediments to achieving the goal of a space elevator are practical - producing a cable light and strong enough to be practical, dealing with induced electrical currents and static electricity, actually figuring out to make the elevator climb the cable and reach orbit in a reasonable amount of time, and so on.
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