Hi All

Here's an interesting figure on what oil companies spend finding new reserves - in 1997 they spent $156 billion. And they've no doubt spent a lot more since. So I wonder what they'd be willing to spend on PowerSats if a proven design and means of orbitting it were developed.

How much cash could a PowerSat make? If it lasted ~ 30 years - a common assumption - and the energy was sold at $0.05 /kW.hr, that's roughly ~ 263,000 hours x $0.05 x 10^6 kW = $13.15 billion per gigawatt PowerSat, with an annual gross return of ~ $438 million/GW. Of course translating that into a PowerSat is another thing.

Old NASA PowerSat designs had ~ 100W/kg power-to-ground mass-densities. Or 10kg/kW or $1350 gross return per kilo of powersat. Hence it had to be orbitted, constructed and maintained for at least less than ~ $1080/kg for a 20% lifetime return. Doesn't look good if we factor in inflation etc. Looks better if we wave 100-year lifespans around, but that takes decades to actually demonstrate.

Newer designs promise ~ 500 W/kg mass-densities, which gives a more attractive ~ $5400/kg (20% return.) I've read of PV cell arrays with potential mass-densities of ~ 2500 W/kg. Such arrays approach realistic costs and good net returns.

If a PowerSat cost ~ $1000/kg to launch & maintain, then to meet the current growth in power demands (364 GW/yr) will require ~ 146,000 tons of PowerSat per year @ $146 billion dollars. Five one-thousand-ton Space Elevators able to orbit ~ 50,000 tons/year could cover this task. Expected orbital prices for an SE are expected to drop to ~ $100/kg with sufficient demand. I'd say an ongoing and growing demand for ~ 150,000 tons of business a year would be sufficient.

Current PV costs might be an impediment. New production techniques are expected to make cells at ~ $0.36/W cost. You can buy light-weight arrays for a mere $1/W. If we can buy them at ~ $0.40/W even better. Space-based PVs because of no diurnal cycle, stronger sunlight and no atmospheric scattering actually get ~ x4 - x5 more power out of a given area of array compared to ground-based.

But we haven't launched even one PowerSat yet. The first gigawatt sat was due in 1995 according to the old 1980 NASA timetable, and we're ten years behind schedule.

Adam