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NASA Still Wants Space Elevator
Jerry Smith writes "The Guardian reports 'Each of the groups that will gather in New Mexico is competing to win a NASA prize set up to encourage entrepreneurs to start development work on the technology needed to create a space elevator.' It still might take a while though, progress is slow, so slow."
FTA: As New Scientist magazine reported last week, the best performing robot last year managed an ascent of only 12 metres up a cable before it stalled, while no material came close to meeting the standards needed for building a space elevator.
Hopefully won't be too hard beating that, my mindstorm robot can do better!
How would the stress of a plane hitting it compare to the stress of just being there in the first place and not breaking under its own weight?
The debates purely academic of course - NEVER GONNA HAPPEN.
They won't waste time and resources to create a folly, this principle is a worthwhile venture (if it can be pulled off).
Once you get one tether you can send runners down it with additional strands.
It would be strengthened and grow like a pearl from an initial seed.
The problem is getting that seed line up there.
liqbase
Most likely, the cable would break, the 99.999% of the cable above the impact point would start to drift upwards, and the 0.001% of the cable below the impact point would fall harmlessly to earth. It would then be a bit of a chore to repair the cable, but not impossible. Fortunately this wouldn't happen, because the cable's base station would be located somewhere in the middle of the Pacific ocean, in the middle of a no-fly zone several thousand miles in diameter. For a crazy pilot to get to the site of the cable, they'd have do evade detection by radar for several hours, and avoid getting shot down by the SAMs or military aircraft whose sole job is to guard the cable against this sort of attack.
Now a question for you: What happens when a plane runs into the Space Shuttle during launch? It only takes on crazy pilot.
I don't care if it's 90,000 hectares. That lake was not my doing.
The variables that need to be addressed are vast. Aside from the material needs I wonder if they are addressing the IT needs. The quickly changing variables such as adjustments from the moon gravity to atmospheric disturbances to maintenance and repair will require great models and this thing will need an amazing nervous system to detect problems before they bocome disasters. BTW: Where will the lower parts of this thing fall when there is a disaster?....
I doubt we will ever see a space elevator. Not only is it incredibly difficult to create. The article clearly states that this technology is nowhere near and it would probably take at least a decade to create, if not two. By the time this is actually a reality - which is unlikely going to happen within 30 years - we will probably have way more efficient space travels as even commercial space tourism has started to kick in as well.
Point is, it would probably not take long before such elevator would be completely useless due to its slow speed and low capacity.
Full Tilt
According to the article, the satellite involved would be in geostationary orbit. OK, but the Centre of Mass of the entire system is not. Isn't the centre of mass of the orbiting body what determines the altitude of the orbit?.
Furthermore, no matter how light the elevator system structure is, may I presume that its mass is greater than 0? Thank you, I will.
The cable will apply drag >0 to the satellite. Any deceleration at all and its no longer in geostationary orbit. Oops.
Uh, since the whole purpose of this thing is to lift stuff into space, and again taking the liberty of assuming that the mass of this stuff is >0, then each and every time we hoist something up the tube, the distribution of mass shifts again, and thus the applied drag will be affected.
I'm not a rocket scientist, but...
Does not the altitude of an orbit depend on the velocity of the orbiting body? If the altitude is the fixed variable (in order to remain geostationary), then what do you adjust when an additional force is applied to to the satellite by hoisting mass upward? This additional force will be "felt" by the satellite as if it were increased mass of the Earth. Lifting mass up pulls the satellite down.
I think that the formula is something like T^2= R^3*(4+PI^2)/(G*M) Where:
T is the orbital period,
R= the radius of the orbit as meassured from the earth's centre,
G is the gravitational constant, and
M is earth's mass
Only way out I can see is to have a body up there so massive that the entire elevator structure plus payload is insignificant. Won't be cheap getting something like 23000 mi up.
Hoping to hear the scoop on orbital mechanics from a real rocket scientist...
-Slithy
>Most likely, the cable would break, the 99.999% of the cable above the impact point would start to drift upwards,
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Umm, no. Real answer: It depends, and none of the answers are good. See also:
http://www.mit.edu/people/gassend/spaceelevator/b
The whole idea of the space elevator is that it's kept up by being weighted on the end. Think about holding a peice of string with something heavy on the end and spinning around. The string doesn't need to support it's own weight, it just has to be strong enough not to snap.
I have been following this for some time... Here are a few links for ya.l Study
http://www.isr.us/Downloads/niac_pdf/contents.htm
LiftPort Group. Company wants to beat NASA.
Reference Site
Place a curse on the RIAA/MPAA
and a rather good image (I use it as my wallpaper)
http://www.mondolithic.com/06Gallery08.htm
I don't understand why you think loading or unloading would take weeks, unless you're comparing it to the current processes which involve special packaging to handle the vibrations of rocket liftoff, which would be largely unnecessary with an elevator.
With an average speed of 50km per hour, it would take about ten hours to get to 500km, which could be a waypoint for transfers to other LEO objects. Getting out to 35,000km would take much longer at that velocity (about a month), but even if the cars were limited to such speeds in the atmosphere the speed could probably be accelerated once at least past LEO since friction and turbulence from the atmosphere are no longer any significant issue. At 500km per hour, it would take about a three days, and I'm sure there would be plenty to do along the way. If they can pull off 500km per hour average from the base to LEO, that keeps the travel time to about 40 minutes, which while twice as long as my commute is something I can handle on a frequent basis.
As to powering the unit, a nuclear plant would probably be used to start, and then eventually large solar arrays at differing points along the stretch would come into use, taking over the primary power duties while the nuclear plant remained as a backup.
Finally, the cost comparisons are hard to do. VoidEngineer threw out a trillion dollars as a construction price, but there are some estimates that come in much, much lower, especially since construction would take place at or near the equator -- as little as $20 billion, once the cable technology is there. I don't buy into something that low at this point, but I doubt it would be as high as the price VoidEngineer tossed out, which he said was an arbitrary number. Launch costs right now are significant; for LEO, a Russian Proton can put 44,000 pounds for ~$2000 per pound, the shuttle costs about $8000 per pound, and a Pegasus can cost $15,000 per pound. It's believed by some that it will be nearly impossible to get rocket-based costs below $1000 per pound to LEO with even the biggest launch vehicles. OTOH, a space elevator may be able to take loads into orbit for $100 per pound or less, with eventually dozens of trips per day depending on how it's built.
So let's say it's $100 billion to build, and $10 billion to maintain per year. For the first ten years ($200 billion), it would need to move 200 million pounds to make $1000 per pound. That's an average of about 55,000 pounds per day, or one fully-stocked shuttle launch. But that's not necessarily just putting things up; it can also bring things down, including rotating crews, satellites in need of maintenance that can't be done in space, retrieval of scientific experiments, and perhaps eventually even raw materials from the moon. However, the more trips that are made, the more infrastructure is in space, and the more there will be to do, including adding to the elevator's schedule, further depressing the price. The numbers here are, as with VoidEngineer's, completely arbitrary, but they show how quickly the costs can flatten out.
You can never go home again... but I guess you can shop there.
The SE is a rock on the end of a very, very long string, being whirled around by the Earth's rotation. That's what keeps it up -- what's sometimes called centrifugal force. Pulling inward/downward on the string doesn't cause the rock to fall; if the rock is whirling fast enough, it won't even be pulled down, and when you stop pulling, the rock is still there. There's no real notion of "center of mass" of the SE as a whole. The majority of the mass is well above GEO.
The "rock" will actually be all the construction machinery that was used to build the SE, a few hundred machines that climb it and add a tiny bit of material all along its length while they're going up. They will have a total mass of about 650 tons and be at an altitude of 100,000 km. The CNT ribbon will have a mass of about 950 tons. We'll be able to send up a 20-ton climber with a 13-ton payload every four days, or a 10-ton climber with a 6.5-ton payload every day. (Gravity falls off so quickly that a given climber is down to 50% of its weight when it's 2600 km up. That's what makes it possible to send up smaller climbers more often than you'd expect.)
If you accelerate something to escape velocity, it does exactly that: escapes the gravitational attraction of the Earth and never comes back, unless it's decelerated by some unspecified means. And escape velocity at 11km height means it will be burned to ashes very quickly, remember the Columbia. With our current technology level, building a ship that can fly at escape velocity at 11km height is much more difficult than building a space elevator.
OTOH, if you want to put something in orbit around the Earth, then you should give it orbital velocity, which means it should have a very high tangential velocity around the Earth. You cannot do that with a vertical tower, unless that tower reaches the synchronous orbit altitude of 36000km, which is the whole idea of a space elevator. Remember, velocity is a vector. It has both magnitude and direction. If you want to reach orbit, it's useless to throw something straight up with a high speed, because it will fall straight down.
Well, you may say, let's make the top of the tower curved, so the ship will be accelerated tangentially. Do the math. Find out how big the curvature radius must be so that the ship isn't subjected to deadly accelerations in order to convert that vertical velocity to orbital, i.e. tangential, velocity. That math has been done even before artificial satellites reached orbit. I have an old book, "Flight in Cosmic Space", written in 1952 by Russian scientist Ari Sternfeld, where he analyzes, among other concepts, the idea you have proposed. A practical accelerator to send a ship into space would have to reach a 100km height and have a curvature radius so great that it would be several thousands kilometers in length.
Seeing as how the price to Geosynchronous orbit will be measured in cents - the price of getting cargo to an equatorial base is negligible.
Storm are not problem either - because you do NOT build the thing and attach it to an island. You build it on a floating platform, and the platform is powered. When a storm comes, you simply drive the thing in the opposite direction. The platform can move a coupel of hundred miles to avoid bad weather. This has already been thought of - and the math/engineering works just fine.
How many escape pods are there? "NONE,SIR!" You counted them? "TWICE, SIR!"
They tried to simulate it... it depends. If it breaks in the upper part, the cable will (literally) tie the Earth many times, but it shouldn't do much harm (they say). Not even killing people under the cable.
here and very iteresting here.
I only wonder how could such event be interpreted in countries without much civilisation... a cable you cannot break and without and end. Woah.
This is only tangentially related, but I thought /.ers would enjoy seeing this space elevator concept video, made by my friend Alan Chan. He's done special effects for LOTR and Harry Potter, so the production values on this video are much nicer than your standard NASA flick.
There is also a very good companion article on IEEE Spectrum, and a fun interview explaining how it was made (short answer: lots and lots of Lightwave).
No, I'm not getting paid to promote this or anything, I just enjoy sharing it with friends/family, and thought a few of you would like it as well. Alan Chan's a ridiculously cool guy, I mean anyone who could make a short film entitled 12 Hot Women and get people to play it at pretentious movie festivals... wow.
Well, I can think of two reasons: (1) an elevator would be more fail-safe... i.e. if you ever need to shut down the lasers, your elevator car comes to a halt, puts on the brakes, and waits for the lasers to start again, whereas a free-flying vehicles would fall to its destruction. But more importantly, (2) it's not clear to me how a free-flying externally powered craft would work. How is the received laser power to be converted into upward acceleration? If it's done by boiling reaction mass off the bottom of the craft and shooting particles towards Earth somehow (i.e. rocket-style), then we're back to the original scaling problem of having to lift additional mass. A Space elevator solves the problem by giving the craft something to pull against, so it can just use an electric motor to lift itself. I'm not saying it can't be done -- as you say, the energy is there -- I just don't see how.
Why the hell would we lift raw mass out of our gravity well when there is so much of it available in much shallower wells?
Seems like there is a bit of a chicken-and-egg problem there: you need large manufacturing facilities in space in order to make all that stuff from raw materials up there, but the large manufacturing facilities are far too heavy to lift into space.
I don't care if it's 90,000 hectares. That lake was not my doing.
There's the idea of laser launch - instead of providing the energy to vapourize propellant with chemical reactions, you aim a laser at the spacecraft to do the job.
Secondly, there's a variety of space tether schemes that don't go all the way down to the surface; instead, they dip down to an altitude and relative velocity where they could be met by hypersonic rockets. These have the rather large advantage of not requiring super-nanotubes. here is a NASA-funded study on the idea.
And, of course, there's always Project Orion - explode nuclear bombs beneath a gargantuan steel plate to push the thing along...but somehow I don't see that one getting approved any time soon
Any sufficiently advanced technology is indistinguishable from a rigged demo
--Andy Finkel (J. Klass?)