RSS Feed
June 13th, 2010 
Clint I’ve been saying it for years – hell, it is an integral part of Space Inc., the spec pilot I wrote for the dramatic television series set in the current civilian space race. Space based solar power could be the thing that takes us to space.
The news obsessing with the oil spill in the Gulf of Mexico created an opportunity that someone at the National Space Society took advantage of to create a nice graphic to drive home a salient point.
I found it on the NSS blog entry Space Solar Power is Unspillable and figured to pass it on… even though the “space solar is five times the power of Earth-based solar” line makes it look like the energy from the sun is five times greater in orbit than it is on Earth. In fact a clear sky at noon attenuates only about 25% of the solar energy.
That “clear” and “at noon” are where the power differential shows up.
There are only so many days without clouds, dust, volcanic ash, smoke, smog and fog… at least down here, up in GEO is is always sunny and cloudless. Well, not always sunny. The availability of the sun in GEO is actually more like 23/7 than 24/7… but that is a lot better than the losses incurred on the surface. Down here, the sun is only visible on average of 12/7 and that “12” varies from a best of about 75% at noon on down to that sunset/sunrise of <1% – as compared to the space based solar panel that gets 100% for all but the hour or so per day that it is in the Earth’s shadow.
It is the overall collectability of the energy that may be considered to be “five times” Earth-based solar- which is good but it still takes a pretty big array of solar panels to replace one of those fossil or fissile burning power plants- and big means heavy.
The cost of getting a kilogram on a GTO (Geosynchronous Transfer Orbit) is about $20,000 depending on what you launch with. Then you have to burn some of that mass to stabilize it into a GEO (Geostationary Earth Orbit) so that it remains properly positioned over the rectenna on the Earth’s surface.
Space X is on target to cut that significantly with their Falcon 9. They are offering to put a 4,680 kg payload in a GTO for $51 million… or about half what it is with the various Ariane, Delta or Atlas rockets. Their Falcon 9 Heavy is being designed to launch 19,500 kg to a GTO and may well cut the costs in half yet again – maybe $5,000 per kilogram to GTO. The cost would also have an inverse relationship to the number of flights – so more launches would mean a lowering of that cost yet again.
Even a reasonably optimistic forecast of $2,000 per kilogram would mean tens of billions of dollars when we are talking about launching the infrastructure for a space based solar array able to generate the 4GW that can come from a good sized coal or nuclear power plant.
The estimates for the weight of 4GW capable array of panels and the supporting infrastructure are quite preliminary but they start at about 4 million kilograms on the low end. If that was all launched from Earth, we’re looking at $40 billion which is not competitive with the $8 billion or so to get the same energy from nuclear power.
Now let’s look out five years to the Falcon 9 Heavy and it still takes over 200 launches and costs around $20 billion. I’m sure if I someone called up Elon and said they’d buy 200 launches they would get a discount… although it still wouldn’t be cost competitive.
But what happens when most of the material is already there and we just have to launch a couple dozen Falcon 9 Heavies to get the equipment up there to take advantage of it?
What if someone took that first step and went out to retrieve an asteroid into Earth orbit? An stony asteroid that is about 40 meters in diameter would come in at something like 150 million kilograms. They usually run 18% silicon so we’re looking at roughly 27 million kilograms of solar panel raw material. Fabricating that much silicon into solar panels and you could build six 4GW solar power satellites.
So if a mission like that could be done for $7 billion to go get the asteroid and another $30 billion to build the six powersats then we are talking the tipping point for space based solar power generation. Maybe the tipping point for becoming a space faring civilization because when that asteroid starts running low, there are thousands more NEAs where it came from… and the second one will be a lot cheaper than the first.
If you are willing to go to it and do the processing in situ before shipping the refined materials back, one near Earth asteroid call 1036 Ganymed (not Jupiter’s moon Ganymed) is about 32 kilometres in diameter. That is about 17,000 cubic kilometres of raw material massing 33,000,000,000,000,000 kg.
Since 1036 Ganymed is a S-type asteroid that 18% silicon means about 5,940,000,000,000,000 kg of raw silicon. With that one asteroid, we could build solar power satellites that generate millions of terawatts.
We won’t build million terawatt solar arrays any time soon because, even ignoring the cost of doing it, the entire planet only uses 15 terawatts right now.
Someone could make hundreds of billions of dollars giving the world cheap and abundant energy. This would allowing billions of people to lift themselves out of poverty and hardship to enjoy the standard of living that the developed nations rightfully don’t want to lose.
Or the governments can cap and trade the developed nations back down to join in the suffering of those billions in poverty and hardship – and without cheap energy, none of us will have a way to climb out of it.
Caveat lector, this is napkin engineering and is not meant to be a definitive set of calculations that can be taken to the bank to get a loan for $7 billion to go capture 40 metre nickel-iron asteroid – but it is meant to spark interest in those who can spend the millions of dollars it would take to do the definitive calculations that can then be taken to the bank for that $7 billion loan.
Posted in 
About 200 Billion watts per second… just saying.
