Jumpstarting

Future Energy and Jumpstarting Space Energy
by Dave Dietzler 2009

Call me a pessimist, but I prefer to be called a pragmatist. I feel that we will not wean civilization off of fossil fuels for a long time. We will use oil until it is all pumped out of the ground, use natural gas until it is depleted and continue to burn coal. Global warming, climate change and sea level rise is inevitable. We will have to retreat from the beaches, islands will be lost, rainfall patterns will change and irrigation systems will be necessary in places where the rains were once reliable, harbors will have to be rebuilt by raising docks and moving warehouses inland or putting them up on stilts and dykes and sea walls will be built in many places. All this will cost trillions of dollars. At the same time every effort will be made to conserve, build more efficient vehicles and buildings, tap winds and solar, expand the use of nuclear fission, tap tides and geothermal, and convert sewage and trash to biofuels or burn them directly. Even so, we will continue to burn fossil fuels for many decades and increase atmospheric CO2 levels.

The holy grails of space solar energy and nuclear fusion are many decades away. There will be severe environmental damage by the time these clean energy sources become available. At least the damage will then stop and the Earth will begin to heal. We can't save the Earth with a crash space energy program. Why? Consider this. It would take one thousand 10 GWe powersats about 10 km by 10 km in dimensions to deliver 10 TW and we will need 50 TW in all forms of energy by 2050 at present rates of growth in energy demand and production. We just are not going to get those one thousand powersats over the next 40 years and even if we did they could only supply 20% of the world's energy and the rest would have to come from ground based sources.

We can't stop global warming, climate change and sea level rise with space energy, but if we could jumpstart the industrialization of the Moon and orbital space and get a powersat building program going as soon as is possible we could wean civilization off fossil fuels sooner rather than later and save billions of dollars, countless lives, prevent resource wars and save a vast number of other species.

To jumpstart a breakout lunar and space industrialization strategy we will need money, and there won't be any money to get the program going until the world comes out of its present recession. Will governments and international cooperation finance a space energy industry project? Will the Saudis with all their oil wealth buy stock in private space commercialization enterprises? Will the oil companies forsake more offshore oil platforms for powersats? I do not know.

I do know that we need cheap rocket launchers and Space X corporation with its Falcon rockets and Dragon crew and cargo capsules might succeed by producing rockets that can orbit payloads for something like a third the price paid with present rockets like the Delta or Atlas V. We also need to figure out how to use lunar materials, land a seed of habitat, robots and machinery, and grow that seed into large industrial complexes, mines and mass drivers as well as construction space stations at L5. I've written much about how we might do that. Another thing we have to figure out how to do is actually build solar powersats.

Most SPS designs consist of an aluminum frame with silicon solar panels and a microwave beaming system. I think we can design better powersats that are smaller and more efficient as well as cheaper and faster to build, or build fewer of them. While the microwave beaming systems based on high power radar systems will probably be the same, the powersats I envision use titanium frames rather than aluminum frames, because titanium is easier to produce on the Moon and titanium has a better strength to weight ratio than aluminum, thus a titanium frame of equal strength would be less massive. They will use reflectors to focus energy onto molten salt filled boiler tanks. They will be similar to power towers except that they will be constantly pointing at the Sun. They will use upported argon gas to drive the turbogenerators, so the turbines will not scale or corrode. Another possibility is that Stirling motors will be used. With waste heat space radiators exposed only to the 10K temperature of outer space heat engines will approach nearly ideal Carnot efficiency. Instead of 100 watts per square meter with silicon solar panels these solar thermal systems will produce 250 watts per square meter if they are only as efficient as ground based power tower systems and 1000 watts per square meter if we can reach nearly ideal Carnot efficiency in space. At 1000 watts per square meter a 10km by 10 km powersat will generate 100 GWe instead of 10 GWe and we'd only need one hundred of them instead of a thousand to generate 10 TW or 20% of civilization's energy demand in 2050 CE. The only drawback is that turbogenerators are heavy sophisticated machines that require more maintenance than silicon PVs and lunar manufacturing capability would have to be up to this complex high tech job unless it turned out that it was economically feasible to rocket the turbogenerators up from Earth and build the powersat frame, reflectors, boilers, argon tubes and waste heat radiators with lunar materials, presuming that these would be more massive than the turbogenerators, but within the range of manufacturing jobs that could be done on the Moon and at the L5 construction space stations. Stirling motors might be simpler therefore easier to build than turbines and they could be more reliable and require less maintenance. Power to weight ratios must also be considered when deciding whether to use Stirlings or turbines.

O'Neill's original design was for a 10 GWe powersat using solar thermal systems rather than silicon PVs that amassed 80,000 tons and was made mostly of aluminum. What if the titanium frame only amassed 50,000 tons? Since there is about 2% titanium in the mare regolith we would have to mine 2.5 million tons of regolith to get 50,000 tons of titanium with ideal recovery rates. That would be a pit one kilometer square about a meter and half deep; not an enormous mining job at all. For 100 powersats we need to launch with mass drivers five million tons of titanium and O'Neill figured we could build a mass driver capable of launching six million tons of raw regolith every year. O'Neill and his colleagues wanted to refine all the regolith at L5 and build a 10,000 man space colony. I think we can dispense with the space colony and use small manned space stations with smaller crews supervising robots teleoperated from within the construction space stations and by Earthside crews rather than using massive amounts of human labor in space. Instead of raw regolith most of which would be unusable materials as far as powersat construction is concerned, the regolith should be refined on the Moon and only the necessary metals launched to L5. The mass driver cargo modules could even contain preformed tubes and struts for the frame and rolls of foil or sheet metal for the reflectors. At the L5 construction space stations the only task would be assembly of parts prefabricated on the Moon.

The 10km x 10km powersat would not consist of one colossal reflector, one giant boiler and one huge turbogenerator or Stirling motor. It would consist of modular subunits each with a foil or sheet metal reflector about 300m x 300m and a turbogenerator or Stirling that produces about 90 MWe. There would be 1,111 subunits. These would be produced by high speed automated mass production systems at the L5 space stations. Since there are only 8760 hours in a year, there would have to be many assembly stations going simultaneously. These would all be wired into perhaps 100 microwave transmitters generating 1GW beams each. The powersat would need attitude control flywheels to keep it tracking the Sun and station keeping might be done with VASIMR drives using abundant lunar oxygen or magnesium (b.p. 1200 C, but lower in the vacuum) for propellant. The powersat would be an incredibly complex work of space engineering. If this is ever done, and not one but 100 powersats are built, they will be some of the greatest marvels of engineering ever created.

The sooner we get the space energy program going, the more we can do to minimize environmental damage on Earth. We can't solve all of our energy and environmental problems with space energy, but we can reduce the intensity of coming disasters from sea level rise to resource wars.

Note: A 100 GWe powersat selling electricity for ten cents a kilowatt hour would earn $87.6 billion dollars in one year! 100,000,000 kWe*8760 hours/year*$0.10 per kWhr. = $87.6 billion per year. That would mean a more rapid return on investment. The power would be beamed down to rectennas in remote deserts as close to the equator as possible then transmitted via superconducting cables to populous regions.