Future of Space Elevator Looks Shaky 486
lurking_giant writes "In a report on NewScientist.com, researchers working on development of a space elevator (an idea we have discussed numerous times) have determined that the concept is not stable. Coriolis force on the moving climbers would cause side loading that would make stability extremely difficult, while solar wind would cause shifting loads on the geostationary midpoint. All of this would likely make it necessary to add thrusters, which would consume fuel and negate the benefits of the concept. Alternatively, careful choreography of multiple loads might ease the instability, again with unknown but negative economic impacts."
I call bullshit! (Score:3, Informative)
The coriolis effect is not a real force. It's an illusionary effect that happens when you have a moving point of reference. As to solar winds and stuff; can you be a little less vague. Let's say for a 10 meter thick cord, white color, how much force would be imparted on the cable over its length? Is the concept currently economical? No, and that's hardly news. Is it unstable and unworkable? Well... if you're pinning your conclusions something that doesn't actually exist to answer that, I think you might have a problem.
ACC already covered this... (Score:3, Informative)
...,kind of, sort of, in Fountains of Paradise.
In that novel he proposed timing the departures of loads for a space elevator on Mars. Not to damp oscillations, in this case, but to cause them. By timing the oscillations correctly, the elevator would oscillate out of the way of the moon Phobos, which orbits lower than the Martian geosynchronous orbit.
Re:Fixed thrusters rockets (Score:5, Informative)
Ion drives need physical fuel as well as power... they just are a lot more efficient than traditional chemical-reaction drives. This is because they accelereate the fuel to near-lightspeed, maximizing the reactionary force per kg of fuel. (force is a combination of the mass expelled and the speed of which it is expelled... the faster the exhaust, the higher energy per kg of exhaust).
So, you'd still have to haul up fuel, just not as much as with chemical rockets.
MadCow.
Re:A solution to coriolis force (Score:4, Informative)
if the top of the elevator isn't in geo-synchronous orbit, the elevator has to be a free-standing structure. You can only put stuff in geo-synch on the equator...
Good luck with that!
Re:Scary stuff (Score:2, Informative)
Having read the article... (Score:5, Informative)
Their big objection seems to be not that the forces on the elevator are unmanageable but that oscillation could lead to payloads being released into orbits that are "10 km" too high or too low, or that the oscillation could put the elevator in the path of a satellite. Correcting that would require thrusters.
For the first, surely you could simply time your release with the oscillation, to get into the orbit you want. Even if you couldn't, the space elevator would be good for putting things in geosynchronous or interplanetary transfer orbits. The cost of a bit of propellant to correct a +- 10 km error is pretty minor compared to getting into one of those orbits in the first place.
For the second, thrusters to purposely oscillate the cable to allow it to dodge out of harms way are a pretty standard part of any space elevator proposal. That is, the ability to move the cable a little is a desired, even necessary part of its design.
Re:I call bullshit! (Score:5, Informative)
You are right, but you are wrong. The Coriolis effect is very real, but it is not force in the strict sense.
The gist of the point in the article is that as a payload is moved up the elevator, it must be accelerated to the side, since the upper portions of the elevator are moving circumferentially faster than the lower portions. The force required to accelerate the payload must come from the elevator itself, causing small displacement of the elevator. The use of the term "Coriolis effect" is not strictly wrong, though it is somewhat sloppy.
The internet makes playing "telephone" boring (Score:5, Informative)
The "Space Elevators are unstable! The concept is doomed!" Slashdot summary would have been much more thrilling if there wasn't a link to the "Space Elevators are tricky! There might still need to be tiny final orbital adjustments!" New Scientist article, and even that would have been more exciting than the "Space Elevator dynamics is modeled by these stable but undamped equations! Sending multiple payloads up in the right phase causes the minor Coriolis-induced wobbles to cancel out!" Acta Astronautica article.
You people with your damn hyperlinks are ruining journalism. It's getting so a guy can't even wait breathlessly for the News At 11 anymore to find out what common household product might be Killing Our Children.
Re:there goes another dumb jet pack idea (Score:4, Informative)
At 2G the entire way, that rail would have to be 1600km long, and would have to rise >20km into the atmosphere to prevent annihilation by friction.
Even at 4G, the track would have to be 400km long.
Frankly, I am not sure that this project would be any more realistic.
These seem like the least of the problems (Score:3, Informative)
You forgot Apollo 1 (Score:3, Informative)
From Wikipedia:
The first failure resulted in the deaths of three astronauts, Gus Grissom, Ed White and Roger Chaffee, in the Apollo 1 launchpad fire.
Re:Scary stuff (Score:5, Informative)
Serious Alterantives (Score:5, Informative)
In all seriousness, the space elevator gets a lot of press because it's the concept that is easiest for the average person to understand, that doesn't mean it is the only option (or even the best option) to efficiently get stuff into orbit without rockets. I always thought the launch loop made more sense (http://en.wikipedia.org/wiki/Launch_loop/ [wikipedia.org]).
The idea is that the moving parts are what keeps the structure stable, rather than tension or compression. In theory it could be built with today's materials and technologies and could be cabable of launching more into orbit in its first month than has been launched to date with conventional rocket launches.
Then of course, there are the non-traditional rockets such as laser propulsion, where a laser is shined up from the ground to superheat the air in the rockets cone, which, in turn, produces thrust. And of course, my personal favorite, there's always Project Orion. Not the wimpy one NASA is using to get to the moon, I'm talking about the original Project Orion. As in, using thermonuclear bombs to launch a city sized spaceship into orbit.
Comment removed (Score:3, Informative)
Re:Serious Alterantives (Score:2, Informative)
Oh heck, read Heinlein's The Moon is a Harsh Mistress. There you will find a war fought with the use of the catapult, pretty much the same thing as the Launch Loop, and predating it by 20 years.
I could, however, suggest a couple of places to launch Orion from.... :-)
A Rotating Skyhook doesn't have that problem. (Score:4, Informative)
A rotating skyhook (a rotating line connected to a ballast on one end and a payload on the other) wouldn't have that problem.
http://www.nss.org/settlement/L5news/1983-skyhook.htm [nss.org]
But a rocket hook combination makes the most sense right now, it would reduce the launch weight by removing the need for the vehicle to accelerate itself all the way to orbital velocity.
Re:air tube (Score:3, Informative)
No matter what medium you are using for propulsion (Air, C02, or combusting fuel), it still requires the same amount of energy to make the stability corrections (in one case the energy comes from fuel combustion, in the other case, it comes from some sort of air pumps at the ground). The point is, that it still requires a potentially unknown amount of energy to stabilize the thing. Since the *point* of the space elevator idea is to conserve energy, the question becomes, will we actually conserve any energy with a space elevator? Plus, with an 'active' stabilization system like that, there's the posibility of something going wrong (like the air pumps at the ground going out of operation due to power loss or something), causing the whole thing to be destroyed.
Re:Scary stuff (Score:2, Informative)
The resonance effect was considered but they forgot about the human factor.
They assumed that the footfalls of the people crossing would effectively be random, but when people walk close to each other they start walking in time with each other, that was enough to start a small wobble in the bridge, which eventually everyone on the bridge started walking in time with increasing the effect even further.
Re:Scary stuff (Score:3, Informative)
Not much, unless the soot is a problem: it's going to burn up in the atmosphere.
Re:Why hasn't this problem come up sooner...? (Score:3, Informative)
It's accelerated by the tension of the space elevator cable, which is attached to a large counterweight beyond geo-synch orbit. This causes the elevator cable to pull on the counterweight and on the Earth. Eventually the orbital energy comes from the rotation of the Earth, slowing it ever so slightly. The system naturally returns to a state where the elevator cable is perpendicular to the plane tangent to the earth's surface at the attachment point as the counterweight drifts back into a higher orbit via centripetal force.
Corrected Link (Score:3, Informative)
ITYM: http://en.wikipedia.org/wiki/Launch_loop [wikipedia.org]
Re:No energy saved (Score:5, Informative)
So much wrong, so little time...
Sorry, most of your post is factually challenged.
1) Space elevators do not lower the energy required - they just use the energy differently.
2) They do not take you to where the gravity is weak - they take you to the point where the force of gravity (which is essentially unchanged) is balanced by centripetal force (which, being linked to w^2r goes up linearly with distance).
3) Rockets typically take you to about 7.7 km/s (orbit), not 11.2km/s (escape).
4) The energy given to the satellite (assuming the same final orbit) is identical regardless of the launch vehicle/elevator used. What is different is the energy efficiency of the system in putting energy into the satellite:
A rocket sends lightweight propellant in the opposite direction very fast in order to transfer the energy. An elevator sends a huge mass (essentially the entire earth) very slowly in the opposite direction. Since momentum is conserved, the mass x velocity of both systems is the same - but since the Earth masses a lot more than most rockets, the Earth's relative velocity is far lower. This is where the e=0.5*m*v^2 comes in - the "wasted" energy is the energy provided to the Earth or propellant. Earth has a small v, big m - which works better than the rockets big v little m.
So you always have to give the satellite the same energy - there are just different efficiencies of giving it that energy. Space cannons have the problem of needing to give that energy extremely quickly... very difficult indeed.
Re:Perhaps a zepplin? (Score:4, Informative)
Speaking of which, there is an airship to orbit concept that was discussed here a few years ago.
You have two airships, a ground ship and an orbital ship. You put your payload on the ground ship where it ferried to a high altitude rendezvous with the orbital airship. The orbital airship raises the payload farther, to the highest point it can on buoyancy. That point is far below orbit, but the atmosphere there would be thin enough to permit the use of ion thrusters. Ion engines take the airship to orbit: a two week process. To return payloads from orbit the process is reversed.
Personally, I don't think this would ever prove to be practical, but it is possible to imagine it working.
The outfit behind this concept (JP Aerospace [jpaerospace.com] seems to be a volunteer organization of high altitude balloon enthusiasts. They've done a number of spectacular balloon missions, in one case sending a balloon to over 19 miles, or 1/3 of the way to the official "space" line. They don't seem to have done anything in the last year though.
Re:No energy saved (Score:5, Informative)
Earth's gravity is substantially weaker at GSO. GSO altitude is large compared to the Earth's radius.
Space elevators *do* lower the energy that is supplied by the launch system.In a space elevator, the energy for the sideways motion comes from the rotation of the Earth (hence the Coriolis forces on the elevator mentioned in the summary). For GSO, that's less than the energy spent climbing up the gravity well, but it's still not trivial.
For escape trajectories, the elevator looks even more attractive -- once you pass GSO, the ride becomes free, and you gain energy from the dynamics of the system without spending any propellant / electricity / whatever. Time it carefully, and you just "fall" off the end of the cable on the right trajectory.
All of that said, rockets aren't *that* inefficient. For LEO, they can be 10% efficient or better (slightly worse for GSO). That's not great, but there are no proposed methods of getting energy to the elevator car that are all that efficient either, especially when you count electricity generation losses. Given the disparity in capital costs, and the fact that in neither case is the energy cost a noticeable fraction of the budget, I suspect rockets will win out for some time to come...
Re:Serious Alterantives (Score:3, Informative)
The catapult is not even remotely the same as a launch loop. In the case of the catapult, all the energy is delivered from the power supply to the payload at once, and over a very short distance. A launch loop uses its power supply to maintain a loop of masses flying from one end to the other, and adds only minimal energy to each one on each pass. The payload then couples into this giant flywheel. This spreads the load on the power supply out, and also lets the payload take a *much* longer time to accelerate. Try launching a person to orbital velocity in a cannon. The launch loop also solves the problem of how to build something that long and that high, without magical materials.
In short, the only real relationship between the two is that they both use a linear electric motor. The closes relative to a launch loop is probably a Space Fountain [wikipedia.org]. For that one, look to Robert L. Forward instead of Heinlein.
Re:Told you so (Score:3, Informative)
ACC? ... served in the Royal Air Force as a radar instructor and technician from 1941-1946, proposed satellite communication systems in 1945[4][5] which won him the Franklin Institute Stuart Ballantine Gold Medal in 1963.
Re:No energy saved (Score:2, Informative)
A space elevator which uses a counterbalance weight would lower the energy required dramatically.
Once it's built and in place, then the only energy consumed is the energy lost to friction in the pulley at the top as the thing simultaneously raises the cargo, and lowers the ballast weight..
But- lightning will fry it..
Re:Told you so (Score:3, Informative)
So is there anyone looking at the "supergun" concept? or did the idea die out with Bull?
My understanding is that the usefulness of that design is limited because any cargo must be able to withstand such high G-forces.
Re:air tube (Score:3, Informative)
Re:Scary stuff (Score:3, Informative)
You've got to be kidding. Read up here [wikipedia.org] about the Apollo guidance computer systems. They didn't navigate those rockets to the moon by hand or with slide rules.
More alternate approaches (Score:3, Informative)
Of course it's possible to accelerate payloads gradually, using a launch ring [newscientist.com].
Another cool idea: airship to orbit [wikipedia.org]. More [msn.com]. Still more [thespacereview.com].
In any case, we need something beyond standard chemical rockets to get cheap access to orbit.