[extropy-chat] Space elevator numbers V

[Keith Henson]

The way you justify a space elevator (which is going to be expensive) is 
power satellites.

Now if you have an elevator, you want to take up power sat parts as densely 
as you can because of the high speed run up through the atmosphere.  And in 
the early stages you need the loads to be fairly small, a ton or a few tons.

Power sats are mostly huge areas supporting photo voltaic cells and/or 
reflectors.  The best way I can see to make the supporting beams is to 
bring up kilometer coils of sheet metal, run them through roll formers, and 
stretch them to make them straight.

A 0.2 mm by 1.5 m by 1 km roll of Invar weights close to 2.5 metric 
tons.  Punched out holes will reduce the weight to a ton.  After passing 
through a roll former you get a beam with the cross section of a bracket 
character.  Why Invar?  Think eclipses.

If one ton beams are placed at 10 meter intervals, the level one main 
structure masses 100 tons per square km.  Level 2, the photo voltaic 
surface, the reflectors, and the transmitter will about double that.

A production rate of a 5-10 Gw power sat every 5 days is daunting.  I am 
assuming a "dry dock" construction area built out of the same kind of 
beams.  There would be 500 beam spinners on each end, each with a magazine 
of at least 5 rolls of sheet metal.  The beams would be pulled out at 
walking speed and spliced to generate the underlying 5 km by 5 km 
surface.  There is nothing I can see that would prevent the "keel" of a 
power sat from being constructed in a day.

For connections between the main layer of beams and the cross beams, I 
believe spot welding (the same process used in forming car bodies) would be 
best.

One of the tricky problems might be keeping the vacuum hard enough around 
the power sats in GEO.  Hard vacuum is an excellent insulator, but it does 
not take much gas to make it into a serious conductor.  Voltage to the 
transmitting antenna might run 10,000 volts.  That not hard to build up in 
series photo voltaic cells across the 5 km width of a power sat 
collector.  But at 10 Gw, it is a *million* amps.  A high powered arc is 
going to vaporize any material, generating gas and a cascading failure.

Much thought will have to be given to this problem.  It might be that the 
satellite output would have to be shorted (which does not raise the current 
much because of the internal resistance of the cells), the satellite 
pointed away from the sun, the short removed and the satellite faced back 
to the sun, a process which would take the power sat off line for hours.