In Short Sharp Science*, a Science blog from New Scientist, Paul Marks discusses using a Space Elevator to facilitate the creation of Space Solar power satellites.
Peter Swan, a member of the Board of Directors of the International Space Elevator Consortium (ISEC) is quoted:
“Half the cost of everything you put in space is down to the launch cost,” former spaceflight engineer Peter Swan told the International Astronautical Congress in Glasgow, UK, in October 2008. “The economics of space-based solar power don’t work with current launch costs. So we have to figure out how to do it without chemical launch.”
Long-time readers know that I’m personally skeptical of Space Solar Power (SSP) ever being more than a niche-application provider of power; there’s just too darn much stuff you have to put into space to supply more than an insignificant amount of our planet’s needs. But if your serious about SSP, then I think you have to be a supporter of the concept of a Space Elevator; nothing else has a chance of being scalable to the order of magnitude necessary to make the idea of Space Solar Power feasible (IMHO, of course)…
I understand your skepticism about power satellites. I don’t even think they will fill a niche market. They are an all or nothing solution to the energy problems facing the human race. All if they can undercut every other large source of power, nothing if they can’t.
If you take penny a kWh as your target (low enough to make synthetic gasoline for a dollar a gallon) then the installed cost for a kW has to be $800 or less (ten year payback of capital).
For 4kg/kW and half the cost being transport to GEO, then the lift cost has to get under $100/kg. That’s probably not possible for pure rockets no matter what the scale.
A moving cable space elevator (if we had the cable) takes 15 kWh/kg. At a penny a kWh, that’s 15 cents, so there is nothing in the physics that requires high lift cost. Even beamed power would only cost $1.50/kg, assuming 10% efficiency.
But the capital cost is likely to excessive. A moving cable lifting power sat parts at 100 tons per hour (about the smallest materials flow that makes sense) uses a 1.5 GW motor. At 10% efficient, a laser setup to lift that much would draw 15GW, and cost $150 billion. The losses present some serious heat problems.
There is another way to get under $100/kg. A low performance rocket that pops a 50 ton laser stage up to 260 miles. A 4GW output (8GW input) ablation propulsion laser then gives it the velocity (taking 1000 seconds) to enter GTO.
Takes half the laser for climbers and you don’t have to build the tether. (You do have to build low performance rockets smaller than a 747 and launch them every 15 minutes.)
I am a major fan of moving cable space elevators, they are just so elegant and efficient from an engineering viewpoint. But I can’t see how you can make a case for climbers given that half that much laser would support the same traffic model.
(The one who helped found the L5 Society)