[ExI] China SPS by 2025

[Keith Henson]

David Lubkin wrote:

snip

> I still have my copies of the GAO reports studying Solar Power
Satellites from forty years ago

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> If they meet the 2030 goal, how soon before they can field a gigawatt facility?

Some things have not changed in 40 years or more.  Between the
atmospheric window for microwaves and the physics (diffraction
optics), the minimum practical size is still around 5 GW   Neither is
likely to change, though you do see some people proposing the rectenna
to be put on a StratoSolar type platform at 20 km.

The interest in China is driven by the reductions in cost to LEO that
reusable rockets allow.  For a given target power cost, the capital
investment is about 80,000 times as much.  So, 3 cent power would
require an investment of no more than $2400/kW.

The rectenna is estimated to cost $200/kW, the parts around $900/kW.
The lift cost is dependant on the specific power.  The best estimate
for that is currently 6.5 kg/kW.   Given the investment limit, that
sets $200/kg (to GEO) or, if you can build in LEO and selt-power them
up, $100/kg to LEO.

Power satellites have never been technically hard to do.  They are
very hard to make them work economically.  I spent the last ten years
working on the economics.  It depends on progress by Reaction Engines
and SpaceX.

Keith