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Space Spiders to Assemble Satellites in Orbit
Grubby Games writes "New Scientist reports that a JAXA mission to determine whether spider-like robots could construct complex structures in space is set to launch in January 2006. The spider bots could build large structures by crawling over a 'web' released from a larger spacecraft. The engineers behind the project hope the robots will eventually be used to construct colossal solar panels for satellites that will transmit solar energy back to Earth."
It'll get hit constantly... mostly be the junk we've put in orbit. So they'll have to repair little holes. But solar panels work just fine with little holes punched through them.
Things don't tend to fall straight into the sun either -- they travel in orbits. Extremely elliptical orbits might see a fairly large cross section of this thing, but to anything on a more or less circular orbit it's going to be very, very thin.
I don't know if anyone's done the calculations. Better fix that!
Photon pressure force:
F = PA/c
At 1 AU from the sun, P=1400 watts/m^2. For a 1km^2 collector we have A = 1*(1000*1000) = 1 million m^2.
So F = (1400)*1x10^6/3.00x10^8
F = 4.7N
4.7N is almost enough to hold half a kilogram up on the surface of Earth. Divert a bit of the power to some ion thrusters, and you should be fine. You might have to shuttle up some reaction mass every few years, but that mass would be REALLY insignificant compared to the mass of the array itself.
The mass of the array is irrelevant for countering the solar sail effect. You're not trying to accelerate it, you're trying to STOP it from accelerating, so you just have to counter the force being applied to it, which is the same regardless of the mass of the array.
Rigidity shouldn't be a problem -- any sort of solid structure shouldn't have a problem withstanding tiny forces like that.
So let me guess we are going to have a 50ft thick cable floating from earth where these solar panels are located in space
No - the solar array sits in geosync orbit and transmits the collected energy back to a rectenna array on Earth as microwaves using a phased array. This is a pretty safe idea - you transmit a pilot microwave signal from Earth up to the satellite and the phased array on the satellite then uses the wave fronts of that pilot signal to synchronise the wavefronts transmitted by the phased array, so the energy will always be focussed on the source of the pilot beam. If the pilot beam stops transmitting then the phased array on the satellite will simply defocus the energy.
The rectenna array on Earth would also allow sunlight pass through it so it's even possible to use the land under it for growing crops or grazing animals, and in geosync orbit the satellite is exposed to the sun almost all the time.
Previous suggestions for putting large satellites like these in orbit have been to construct them on the moon from local materials - the moon's gravity is so low that you can launch them with a linear mass driver, no rockets required.
IMHO, this technology should be taken seriously to meet our long term energy needs - in the short term I can see fission being a good energy source but over the next 50 or so years I think fusion and orbital solar platforms are the best plan. Sadly, noone seems to want to get their finger out and spend money on this stuff until it's too late and we _have_ to.
http://blog.nexusuk.org