Space Solar Power For Launch Loop

The space solar power community offers numbers like 7 kg per kilowatt in orbit for space solar power, solar energy converted to <10 GHz microwaves and beamed to Earth. This is built on a chain of optimistic assumptions, and assumes launch costs much cheaper than the current $20,000/kg to GEO, but still using rocket thrust. Too many oughta works is a not oughta work.

A launch loop can launch 5000 kg payloads into GTO (Geosynchronous Transfer Orbit) vastly cheaper than any ground-launched rocket. Low thrust propellant-thrifty electric engines (such as VASIMR) can raise perigee and circularize the orbit of a geosynchronous power satellite, which can be used to feed more power and increase the launch rate of a launch loop.

Starting with a 500 MW thermal power plant, perhaps 300 MW will be needed for deflection magnets and drag losses, leaving 200 MW to power launches. A 6 tonne sled plus the vehicle launched into GTO might result in 2 tonnes of SSPS mass delivered to GEO after a sequence of orbit raising manuevers and construction assembly steps.

5° Inclination

The first "low mass" launch loops will be perhaps 5° south of the equator, to avoid January storms. This means they will launch into 5° inclined orbits. At first blush, this is a problem, since a geosynchronous SSPS is sometimes 5 degrees farther south in the sky, limiting the northern footprint. However, some inclination is good, so that the huge transmit energy of the SSPS does not blind receiver dishes pointed at communication satellites in equatorial GEO orbits. This will require significant angular spacing above or below the crowded GEO orbit. SSPS satellites will probably need to shut down or reduce power as their orbits pass through the equatorial plane. It is better if they pass through the equatorial plane quickly, perhaps using that time for brief maintenance, calibration, and generation of station-keeping thrust.

The 5° inclination means some fraction of the satellites cannot reach as far to the north, while others can reach farther. If they switch between northerly and southerly ground rectennas (pulsed power helps with this) as they cycle north to south in a 24 hour cycle, the whole constellation of SSPS satellites can provide complete coverage farther to the north, while still providing maximum overlapping coverage for equatorial customers (where most of the world's population lives).

So ... no inclination change to equatorial, unless the destination orbit is for a comsat feeding fixed-direction ground dishes. Those comsats will be important, but not a large fraction of the total launch market.

SSPS launch, construction, and deployment

Highly elliptical orbits are relatively cheap with the launch loop; indeed, they can be cheaper than low orbits, because raising perigee from 100 km loop altitude to a low drag 500 km perigee requires less delta V at apogee. Here is a sequence of steps to launch, assemble, and deploy an SSPS to a 5° inclined circular geosynchronous orbit:

period

radius

altitude

v apogee

delta V from below

hours

km

km

m/s

m/s

stage

1389.1

vertical elevator to west station

10.485

6478.0

100.0

1586.8

9855.9

launch from the loop

10.615

6878.0

500.0

1628.4

41.6

safe perigee

11.967

10959.4

4581.4

1975.0

346.6

construction Orbit

23.934

42164.2

35786.2

3074.7

1099.7

GEO delivery

268.2

plane change? maybe not needed

Elevator and Loop Launch

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Rapid Thrust to Safe Perigee

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Slow Thrust to 12 hour Construction Orbit

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Construction

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Slow Thrust to GEO delivery

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Plane Change?

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