The Great Solar Power Debate continues! --
NB: M. V. Smith is the person who led the Pentagon's space-based solar power study last year.
(See "Space Based Solar Power As an Opportunity for Strategic Security", available here in pdf format.)
M. V. Smith's comments reflect his personal opinions and are not officially endorsed by the US Government, the Department of Defense, or any associated organization.
I am constantly barraged by skeptics and those who want SBSP to be an evil Pentagon plot for the purpose of championing its defeat. This makes conspiracy nuts feel clever and useful.
The DoD will never own or operate SBSP satellites for the simple fact that energy production and delivery to customers is outside of its lawful mission assigned to it under Title 10 US Code. SBSP can only be done in the civil or commercial sector, but NASA does not do energy, and our Department of Energy does not do space. So, we are stuck. As you know, the Pentagon simply wants to be an anchor customer for whomever fields SBSP systems. In fact, the Pentagon does not care who by whatever national registration fields SBSP, we simply want to be a paying customer.
The smallest size rectenna that has been discussed is over 16 kilometers in diameter with the space-based transmitter over a kilometer. This keeps the signal intensity on the Earth less than the energy you'd receive in the noonday sun.
There is also the option of using laser broadcasts of energy from space to Earth. This does create an intense beam that will require no-fly zones in the downlink path. Positive control can be preserved by having a UN licensed and encrypted laser on the ground make a permanent contact with the satellite that in turn directs the downlinking of the energy to the approved collection site. This will be a matter for the commerical company and its country of registration to work out with the ICC within the UN framework.
Finally, if this were a weapon, I would simply build it and not tell anybody about it. As it is, we've let everybody in on this non-secret.
Perhaps ironically, I am very hopeful that China and India will be the first to field SBSP systems because they need safe, clean energy more than the West.
As for terrestrial solar and wind systems beating SBSP, well, sure. That would be nice, but ground based solar, wind, and hydrogen might someday produce 30% of today's demand. Unfortunately, the demand is increasing logarithmically, so we will still be in a quest to field other new sources of safe, clean energy. There still won't be enough energy to go around. Yes, SBSP is a long way off, but we have to start somewhere to find entirely new sources.
The real problem is human overpopulation.
That said, it is possible to cut the Earth's population by several billion if our other alternative energy sources don't provide enough, but I don't think Ray Wright wants to go there -- neither do we.
By pursuing SBSP and other alternative energy sources -- and pushing them into the commercial sector for all international audiences -- the DoD is trying to avoid resource wars in the future. Preventing such wars is not only a matter of national security, but of international security as well. It also offers an opportunity for real wealth creation, jobs, and environmental benefits as well.
This is the exact opposite of the Evil Empire trying to build a Death Star without anyone noticing. This is a matter of America, who largely defended Europe during the Cold War against Soviet expansion, and who now defends the world's oil supply coming out of the Middle East (where the US currently gets less than 11% of its petroleum supply, on its way down to 4%) trying a new and innovative method to help ween the World off petroleum by suggesting another alternative energy source.
Your thoughts, good Sir?
Some interesting discussion here.
Ray does have a point about the infrastructure needed to haul the bulk of an SPS up to geostationary orbit, but whether it's a problem or not depends on (a) how it's done and (b) where the material comes from.
If you have a fully reusable craft like Skylon, with a LEO-GEO transfer vehicle, then the major costs are the SPS materials and the fuel, rather than having to include the cost of a booster for each flight.
However, these costs could be reduced by not having to ferry the materials up from Earth. A mining facility on the Moon, providing the silicon and aluminium for the main structure, would mean that the delivery costs, using a Lunar Orbit-GEO transfer vehicle, could be much less. The high-tech parts would still be brought up from Earth, but the main bulk could be transported at a much reduced cost.
In fact, if a mass-driver was used on the Moon, then after the capital costs, the running costs (i.e. the cost of transport from the Moon) would be almost zero.
Of course there is still the option of using the asteroids, but a mass-driver would probably not be practical due to the higher rotation rate, so we'd have to produce fuel from the asteroidal materials, or use ion propulsion, as it wouldn't matter if it takes a long time to reach GEO.
This all comes back to O'Neill's vision of the space colonies being built from off-Earth materials, and using it for manufacturing the SPS units. In fact in that scenario, the land-based rectenna was intended to be about 7 miles across giving an area nearly 8 times that of a 4-km diameter array, and presumably a lower power transmission factor.
Whilst I'm happy to promote these scenarios for making use of the resources of space, I do admit that it still requires a base infrastructure that allows some cheap and frequent access to space in order to kick-start the whole thing. This is why I'm so pleased about the financial support that Alan Bond is getting which is allowing him to make such good progress with Skylon.
By the way, I presume you have seen the statement from Mike Griffin that China could be on the Moon before the US.
Back in 2004, when the US plans to get back by 2020 were first announced, I did say that I was sure they'd like to be back by 2019 (for obvious reasons), and also that what might spur Congress to action (though I suspect NASA would prefer not to rush) would be a statement of intent by China ...
22 July 2008
Jerry Stone FBIS FRAS
Freelance Presenter on Astronomy and Space Exploration
Chairman, The Space Education Council
STEMNET Science & Engineering Ambassador
Many thanks for your comments, which I'll post in the next Astronautical Evolution.
I'm a little wary about the idea of a mass driver on the Moon, because I understand it would be need to be quite a large-scale structure which has to be engineered to fine tolerances. The reason why I prefer bringing asteroidal water back as a feedstock for propellant manufacture is that it seems to be relatively low-tech -- and if that water is used as reaction mass in a low-thrust engine as John Lewis suggested, then it's even simpler to visualise.
The question is not, what is the ideal solution, but which solution is likely to appear first. Certainly, once a lunar engineering industry is established, then mass drivers will be on the agenda, but by then I would hope that a large scale astropower industry to serve Earth will already be in operation.
Regarding China, I've not heard or seen anything that might suggest they have any plans to send astronauts to the Moon. Their launch rate of one flight every couple of years is slower even than the Shuttle!
23 July 2008
I do completely agree that if some form of fuel can be resourced, then it is likely to be a much simpler setup than the construction of a mass driver. I think I may be looking too far into the future!
I'd suggest there are two choices: water as a direct reaction mass, or electrolysing it to produce hydrogen and oxygen, though again that needs another level of complexity to liquify the gases.
"The question is not, what is the ideal solution, but which solution is likely to appear first" -- You're quite right, and the likely answer is:
1) Water as reaction mass
2) LH2 & O2 propellant, or methane, depending on just what type of asteroid is involved
3) Mass drivers
As for China going to the Moon, don't take my word for it -- here's what Mike Griffin said last week, and here's what they said in 2006, and this story from last year showed what other technology they're working on.
24 July 2008
Much is made of the "astronomical" costs of lifting solar power satellite elements to GEO from Earth, and thereby deducing that it cannot be done.
We need to be remember
1/ That many proponents and studies of SPS have explicitly based their proposals on using extraterrestrial raw materials for the bulk of SPS construction ( >95%), with only robots, some humans, basic mining equipment, and small but vital sophisticated components coming from Earth itself.
2/ That for a number of reasons, within 20-25 years or so, there are expected to be lunar bases, and quite possibly NEO missions, from several major powers, not to mention great advances in nanotechnology. Maybe not the West so much as India, China, and Japan.
By a possibly happy coincidence, this period just about ties in with the expected need for solar power/hydrogen to start replacing fossil fuels on an interesting scale.
We may yet end up with SPS not from foresight or vision, but, as is often the way with great human advances, pure opportunism!
1 July 2008
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