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Skyhook Robot Passes 1000 Foot Mark
JhohannaVH writes "MSNBC.com is running a story about yesterday's successful test of the Space Elevator!! Maybe it will become a reality after all." From the article: "This week's testing involved a 12-foot (4-meter) diameter balloon. Safety lines held by team members kept the balloon from floating away. The ribbon dangling from the balloon was made of composite fiberglass, with the robot lifter running up and down the tether ... During the day, the highest altitude reached by the balloon/ribbon/robot combination was 1,000 feet (305 meters). 'It gives us complete confidence that the mile goal is well within reach,' Laine said. Laine said that the Federal Aviation Administration has been very supportive and helpful in orchestrating their test flights. "
Centripetal acceleration
It's kinda annoying to see every space elevator article attract a swag of ill-informed comments that get modded as insightful. Please go read question 4 of the FAQ.
the ribbon recovers for the same reason that it stays up in the first place. Centripetal acceleration is acting on the counterweight pulling it outward, and the lost angular momentum is replaced very quickly (essentially as fast as it is lost). The ribbon will never lose enough angular momentum to even deflect a single degree, let alone fall. The extra angular momentum is stolen from the Earth's rotation; we will have to worry about this effect slowing down the Earth and making the day longer if we ever decide to ship Australia into space.
How we know is more important than what we know.
sp. Centrip/e/tal. And technically, it keeps it down.
Thrusting from the bottom is expensive. It requires extra weight to be carried as fuel (or a Big Friggin' Laser). You could instead adjust the counterweight position at the top so that it begins to move away from the Earth by itself. There is some fine-balancing involved, naturally.
"To an extent, Mr. Swartz is correct: As payloads are moved up and down the elevator, the ribbon is distorted, and it would move the counterweight. Nevertheless, looking at the travel time and the relative masses of the climbers, the ribbon, and the counterweight, we find that the distortion is extremely small and would be quickly corrected because of the forces that are felt by the ribbon and the counterweight. The rotating Earth supplies the needed angular momentum through the anchor and the ribbon. The rotation also provides all the restoring forces required--no rockets are needed to move the counterweight. The best way to look at this may be to think of the space elevator as a pendulum. If you pull the ribbon from its normal position--rising straight up from Earth--the forces will always pull it back."
--Brad Edwards
I have been following the progress of research concerning space-elevator for some time now. The LiftPort Group of companies working towards a space-elevator are making a great deal of progress. See here and here for more LiftPort specific information. Slashdot reported on the faa approval of their high altitude tests several days ago -- refer to that thread for some interesting discussion. Check here and here here for several reports concerning the viability of the elevator -- be sure to check the NIAC pdf. Also, Blaise Gassend has a great collection of information. Finally, though carbon nanotubes are still in their infancy (its been a little over 12 years since they were discovered) - their theoretical tensile strengths are perfect for use in the construction of a space elevator tether. This recent development spells a rosy future, and many innovations yet to come.
Gigabytes have been written on the subject. Look it up yourself.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
Actually battery power wouldn't hold out. Current idea is to beam power through lasers. This technique is known to work well with fixed points but could produce problems if tether bends and sways with wind like it did in this test.
As I understand it, most of the fuel that you expend in a standard launch is there to make sure that the rest of the fuel can make it high enough to finally push the payload into orbit.
With a space elevator, you're no longer required to accelerate several dozens of tons (>90% of which is just fuel) up to 7 miles/second just to get a 500lb satellite in orbit. The cost savings would be huge.
Now granted, you'll still have to haul some fuel up the elevator, but it's like the difference between climbing the stairs to reach the top of the Empire State Building vs. jumping to the top from street level in one bound.
You're stupid. Centripetal acceleration is towards the center of the circle. It's the acceleration of the changing direction of the velocity vector (which keeps turning towards the center).
The centripetal acceleration that keeps us on Earth is due to gravity.
As I understand it we're talking about a carbon fiber composite ribbon. You certainly couldn't run an entire circuit through it. If it were pure carbon fiber you could probably run half the circuit through it, but the polymers holding the fibers together would probably make this impractical.
The weight and resistance of a wire are proportional to it's length. The resistance of a wire is inversely proportional to its weight.
You understand this thing is going to be, perhaps 30,000 miles long, right? That's a 60,000 mile circuit when the lifting vehicle is at the far end (as for a moon or Mars mission).
Weight and line loss would be two problems.
-Peter
a break in the line isnt all that catastrophic. It wont fall to earth or spontaneously combust. All that happens is you have a sever in the line. the balanced mass ratio will keep it from flying away, or falling to earth. It will remain mostly stationary.
The tether would be already equipped with thrusters every now and then to counteract natural wind and gravitational forces and the inevitable inaccuracy of the mass ratio that cause it to shift. These same thrusters can reposition the line after a break occurs, at which point an automated repair robot could patch it back together in moments. I doubt the system would even be down for a day.
Of course, damaging such a line to that extent is difficult because of the strength of the material involved. A plane hitting it would be destroyed, but it would barely scratch the line itself.
If you do some reading into the materials and idea involved, a space elevator is not only feasible, its downright the thing we should be focused on. From an engineering standpoint, once you've the got the material down (we do), and the mass production means ready (we do, just need to construct the plants to make it), its technically much simpler than building volatile fueled rocket launch ships and all their various specialized equipment and facilities, maintenance programs etc.
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The space shuttle costs 450 million dollars per launch. This would cost much more than that, but the upkeep should cost a small enough amount that it might pay off in the long run (Depending upon it's projected lifespan).
In an article by Bradley Carl Edwards in the August 2005 print issue of "IEEE Spectrum", he writes "The estimated operational cost for the first elevator is several hundred dollars per kilogram to any Earth orbit, the moon, or Mars, a drop of two orders of magnitude over the cost of current launch technologies. With the completion of subsequent elevators, the cost would drop even further, to a few dollars per kilogram." So using a space elevator to transport whatever is cheaper than using rockets for transportation.
FalconShould there be a Law?
Moores Law doesn't apply to everything just computer speed
It doesn't even apply to that. It applies to transistor density. And, now more than ever, speed gains aren't directly proportional to transistor density increases.
So your point might even be stronger than you intended it to be.
We currently build transoceanic fiber optic cables that can be completely powered from one end using DC power, with the ocean acting as ground (current technologies require a powered repeater every so often), so we have already built power cables within an order of magnitude of the required length (though the energy it would need to carry would likely be much much higher - a single crawler might use several megawatts continuously)
I would be curious to know how a power cable on a space elevator would interact with the Earth's magnetic field. Would it impart a significant force on the cable? Would the cable need to be shielded?
Alternatively, what are the power generation options in space? Could a nuclear powered crawler be built, and/or could power generation facilities be spaced at regular intervals along the cable?
"Centripetal acceleration" only says it will keep this thing from flying into space, nothing more. Tie a string to a small object and spin it. The centripetal force is the part of the tension in the string pulling the object towards the centre. Centripetal acceleration is the effect of that force that curves the object's trajectory, instead of letting it go in a straight line.
But here's the catch: centripetal force is _strictly_ the component pointing at the centre of the circle. It can't accelerate or decelerate the rotation. The reason you can accelerate that small object on a string is precisely because the string is a little crooked, and it pulls a little forward too, in addition to the centripetal force pointing at the centre.
The apparent force pulling it outward, that they mention there, is called "centrifugal" (runs away from the centre), not "centripetal" (pulls it towards the centre). This one doesn't do anything to keep it from losing angular momentum. Hold your hand still after you've made your object on a string rotate. It's seeming to tug outwards is centrifugal force. Note how the item can slow down due to friction anyway.
And things get even more screwy in a gravity well.
Basically what I'm trying to say is that while I'm sure some actual physicists did some actual calculations for that project, and they probably have a very sound theory of how it regains lost momentum (and how much can it safely lose or gain before that string breaks), that quoted explanation isn't it. It's some handwaving that's as "scientiffic" or "informative" as saying that Santa's reindeers keep it up.
"It's kinda annoying to see every space elevator article attract a swag of ill-informed comments that get modded as insightful."
I feel your pain. I found it slightly annoying too to see your quote of that pseudo-science babble modded as "+5 Informative". No offense, since you're not the one who wrote that, but it's got exactly zero useful information, and doesn't answer the question at all.
I'd imagine that the reason people keep asking is precisely because that handwaving doesn't answer it.
A polar bear is a cartesian bear after a coordinate transform.
It needs to be externally powered (probably by laser or microwave from the ground), it needs to climb *fast* since capacity of the beanstalk is directly proportional to the speed of the climbers. (if the beanstalk can hold 10 climbers and they go 100km/h you can launch one every 2 weeks. If the climbers can do 1000km/h you could launch every 2 days on the same beanstalk.
If you want to use it for space-tourism the climbers must be humongously fast, noone wants to sit in an elevator for a month, not even if the elevator is equipped like a luxus-liner. If you want to climb to orbit in 24 hours you need to climb at 1500km/h. That's not exactly trivial, probably rules out physical contact with the ribbon and nessecitates magnetic levitation or similar.
Oh yeah, and for security-reasons manned climbers probably also need a mechanism for disengaging from the cable and doing some sort of emergency-landing in the event of catastrophic failure of the cable.