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Old August 21st 18, 07:23 PM posted to sci.space.policy
Bob Jenkins
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Default Towards routine, reusable space launch.

On Monday, August 20, 2018 at 4:37:29 PM UTC-7, Alain Fournier wrote:
On Aug/20/2018 at 6:47 PM, wrote :

OB space elevators. If there's any asteroid mining going on, you could have climbers go up and down, put heavier cargo in them going down (from mining), and use the weight differential to power the up-climbers. No lasers required.


And how will you transfer the energy from the climbers going down
(descenders) to the climbers going up. This is not a regular elevator
with a cable moving around a pulley. The cable has to be tapered, so if
it is mobile it is difficult to keep the thickest part at geosynchronous
altitude and the thinnest part near the ground. It isn't totally
impossible to do if you have multiple sections with pulleys between each
section. But it makes a very difficult engineering project much more
difficult.


Alain Fournier


Two cables, one up one down, with occasional spacers in between, and C-shaped cars centered on the cables but missing the spacers. Down-cars use regenerative braking, generating electricity, which you run along the spacers, to power up-cars like a rail gun. Neither side should actually touch the cable. I haven't tried to measure how much heavier down-cars have to be than up-cars for this to work out. Cars are reloaded at either end then transferred to the other cable.

Another thing, once you're out of the atmosphere (or the thick part of the atmosphere), up-cars should accelerate to as fast as feasible (and down-cars, the reverse). That way cars are much further spaced above the first 5km or so, so don't add as much total weight, so you can afford to have more of them, plus you reach geosynchronous orbit in hours instead of weeks.