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Last week you had the chance to ask electrical engineer and L5 society co-founder Keith Henson about space colonization, his solar power satellite project, and his run-ins with Scientology. Below you'll find his answers to your questions. Microwaving power to Earth from space
by Anonymous Coward

If the beam becomes misaligned and strikes Iowa, how do you stop the entire state from exploding into a massive popcorn volcano?

Henson: Sorry to disappoint about the popcorn, but it can’t happen. The transmission needs a guide beam to phase the wave front. Lose the beam and the power scatters into the entire half space in front of the antenna. Also, the power inside a microwave oven popping popcorn is around 10 kW/m^2. The beam from a power satellite is under 0.3 kW/m^2. Sunlight is around a kW/m^2.



Cost per KWh
by Rob Lister

What is the cost per KW for the build/deployment and resultant cost per KWh for the end user?

Henson: If you are going to do power satellites at all, they have to undercut coal or there is little point in doing them. If you go through the levelized cost of electric power for a no-fuel power source, the capital cost can’t exceed $2400/kW for 3 cent per kWh power. That undercuts coal, which costs around 4 cent per kWh. Because the cost of power to the end user includes a lot of fixed distribution cost, the retail cost to households probably will not change a lot, but it won’t go up either. Also it puts a cap on transport fuel because we can use cheap electricity to make cheap gasoline.

The investment to set up the parts pipeline to GEO is probably around $60 B (not counting Skylon). The financial model shows the whole capital investment paid off in less than ten years.



Minimum cost
by Winged Cat

By focusing only on $ per kW or $ per other unit, you seem to be ruling out consideration of $ per mission or $ per step, thus requiring $billions to be spent up front on technology that has only been proven in the laboratory. This is roughly as difficult as trying to kickstart a fusion reactor using nothing more than a matchbook.

Have you given any thought to demonstration missions, or realistic paths to funding that might eventually unlock enough money for the full system as you describe it? ("Government funding" not being a realistic path, given their demonstrated history with regard to projects that might actually give cheap power to the masses. This applies to any government large enough to fund this - such as US, EU, Russia, or China - though the exact means by which each one has demonstrated it wouldn't fund this, except to sabotage it and thereby waste the energy of those who might otherwise build this for real, varies by government.)

If not, why not? That's as much a part of the problem that needs solving here as the technology, and you've shown you can solve the technical side.

Henson: I have thought a lot about demonstration missions. Sorry to say, but they don’t make sense, at least not if you are trying to use expendable rockets. For less than the cost of one full sized demonstration power satellite, you can set up the low cost transport system and build half a dozen. That recently (last few days) might have changed. There may be a reason to build a 1/8th scale power satellite using a 25 GHz transmission beam. It’s to power the LEO to GEO leg of the transport system, but it would also demonstrate that power satellites work. It also looks like it will cost much less than the alternate, a $15-20 B, 8 GW transmitter on the ground at the equator.

As for why not, convincing governments or private investors to build any part of this is a different skill set. Be delighted to have you (or anyone) help. And thanks for the compliment.



What "wear and tear" factors are relevant
by ShieldW0lf

Could you give a general overview of what the wear factors are for your system, how long you would expect a satellite to last, and what the post failure plan would be?

Henson: PV type power satellites degrade because of radiation damage to the cells. That’s predictable but it might not be as bad as what we have seen on communication satellites. If you build many power satellites, and that’s the only program that makes sense, then the satellites capture the trapped particles in the Van Allen belt. When you start talking about hundreds to thousands of power satellites at 32,500 tons each and a total of 3 kg of protons trapped in the belts, you can see that the trapped particles are going to be soaked up rather fast. There is also a proposal to drain the belts.

If we build thermal power satellites, then there will be a lot of turbines, steam or possibly supercritical CO2. How the bearings will work in space is unknown, but the forces are so small that we could use noncontact bearings. Seals are harder. The levelized cost calculations included 10% per year maintenance based on the cost of the original parts. Thermal power satellites also require steady patching of micrometeorite holes in the radiators.

There is no reason I can think of why a power satellite would last less than several decades. For worn out power satellites, the assumption is that we reprocess the material into new ones. Mass in GEO is worth $200/kg, and it costs much less to reprocess mass than to haul up new materials. If the program comes about, there would be a substantial industrial and human presence in GEO, perhaps upwards of 10,000 people.



Why geosynchronous orbit?
by Anonymous Coward

Has anyone considered using a semi synchronous orbit with multiple receivers around the world to provide electricity to places at peak times (4pm to 8pm) when electricity is more expensive? I'm curious about the economics of it all.. e.g. how much down time would such a system have (as it's over the pacific say), what's the price of a receiving station, what's the comparative peak vs base load price of electricity? Would the sun still be visible to a satellite in semi synchronous orbit that can beam to a place on earth at 8pm (I imagine so) etc.

Henson: Addressing the economics, electricity is a commodity, especially base load power. Market goes to the lowest cost producers. Power satellites are cheaper than ground solar in close to the ratio of their utilization (i.e., fraction of the year they are selling power). Ground solar plants sell power about 20% of the time, vs space-based upwards of 90%. The problem with orbits other than GEO is the low utilization when the power satellites are in a bad location to deliver power. The last thing a utility wants is a big intermittent power plant.

If we build space-based solar power at all, it has to be 3 cents a kWh or less, otherwise the project just does not happen. Since the power uses no fuel and costs 3 cents a kWh, then run half the time it would cost 6 cents a kWh. That’s the same price as gas turbines used for intermediate and peaking loads. In a mature market, off peak power might be worth 2 cents a kWh to make hydrogen. The hydrogen plants are not efficiently used, but there is no reason they should be expensive, which is to say $200/kW or less. The effect of a 2-cent diversion market for power over the base load reduces the cost of intermediate power used half the time to 4 cents (6 +2)/2.

The long-range effect of power satellites will be to greatly reduce the value of peaking power, essentially to zero. What do we do with the hydrogen? Combine it with CO2 to make transport fuel. That solves the other half of the energy problem.



Space Elevator
by Btrot69

Most of us on slashdot will probably agree that "Economics, Energy, Carbon and Climate" are all one big problem that needs more investment. But the devil is in the details of how to do it.

I'm not an expert on this subject like Henson, but IMHO a space elevator seems just as close to being technically viable as space plane powered by a ground-based laser and microwave power beamed to earth.

Not only that -- a space elevator would be much cleaner and the cables might even be able to double as power transmission lines.And -- since all the good tethering points are in the third world (the equator) it would be a big solution to economic disparities too.

Why does Henson's article not consider the possibility of a space elevator?

Henson: The easy reason is that we don’t have the materials for the cable. I worked on the problem years ago, even figured out how to make a step-taper, moving-cable elevator. I can’t make one work for the Earth. I am not down on elevators; a Lunar elevator out through L1 makes sense with current strong materials such as Spectra. If someone finds material good enough for an Earth to GEO cable, we can then try to solve the other problems with satellites hitting and vaporizing the cable.



We've learned a lot
by Geoffrey.landis

We've learned a lot since the rather naive plans of the 1970s, when space colonization was first proposed by Gerard O'Neill and his students.How are things different now? What's the most important thing we've learned since then?

Henson: The main thing that is different now is the single-stage-to-orbit space plane—Skylon. Space has always been tightly constrained by the cost of launch, $20,000 to get a kg to GEO. The energy cost is under a dollar so there is lots of room to improve. At 10,000 flights per year Skylon should get the cost down to around $120/kg to LEO and with remotely powered electric rockets, the cost to GEO should not exceed $200/kg.

It’s hard to say what is the most important thing we have learned since O’Neill’s days. For me it might be that humans may not leave the Earth in significant numbers, but instead leave reality as we know it (by uploading).

I think O’Neill was aware of the problem, but if you read up on the space-station activities, the fraction of time they spend on maintenance is impressive. I think the solution might be to send up families, and put the kids to work.

If you want to keep up with the progress look here, It used to be low traffic, but activity is picking up. There are a few conferences on the topic and it gets coverage at the International Space Development Conference.



Transportation station
by Jack Dixon

With some of the income and infrastructure from this project, why not use it as a way station for Mars expeditions? Build a self sufficient habitat and inject it into the favorable orbit between L5 and Mars. Then every two years a group of colonists could ride it with very little fuel expenditure to Mars. They would need to park their descent vehicle nearby. Food, water, and radiation protection could be provided in the habitat, with artificial gravity and greenhouse food production managed by a team of robots during the long sector of the orbit.

Henson: I am not a big Mars fan. O’Neill convinced me long ago that planetary surfaces are not good places for a growing industrial society. Still, I have proposed that the charter for the construction company include a “hundredth one goes to Mars” clause. The Mars fans can have a power satellite to move to Mars and use there, or the mass (~30,000 tons) of one in GEO for a Mars mission. This could happen rapidly. Governments could decide that they just have to quit burning fossil fuels and that power satellites are the only way to do it without destroying the economy from high energy prices. If we started building power satellites at 5 per year in 2023, and doubled every year (mostly building more Skylons) then the Mars mission could leave before 2030.



Asteroid Mining
by meta-monkey

Leaving aside the not insignificant economic and safety concerns, I'm interested in the technical feasibility of extracting minerals from asteroids in useful quantities. On earth, we extract minerals concentrated by geological and biological processes that are unlikely to have occurred on an inert asteroid.

What do we know about the distribution of minerals within asteroids, what more do we need to know in order to design machines that can extract these minerals, and what can you speculate about how those machines might work?

Henson: You are correct, other than the Siderophile separation, same that sent most of the gold to the center of the Earth, it doesn’t look like the asteroids had mechanisms that concentrated minerals. There may be exceptions on asteroids as large as Vesta.

We know a lot about asteroid mineral concentrations from the tens of thousands of samples found as meteorites. Most of them would not be valuable if you found them in the millions of tons on Earth.

On the last question, you are in luck! I happen to be one of the few space fans who actually worked in mining. A few years ago I wrote up my thoughts on how to mine a huge asteroid (1986 DA). It is the metallic core of a differentiated asteroid.



So, whatever happened, anyway?
by Anonymous Coward

So, whatever happened to the scientology thing, anyway? I remember reading about what was going on, but I never really heard how it all came out.

Henson: It’s still in process. The cult has shrunk from around 100,000 when they tried to rmgroup alt.religion.scientology to (some say) 10,000. With all the data on the net, they have an awful time trying to recruit new members, and former members sue the cult in an orgy of litigation. After the recent “Going Clear” documentary on HBO, there are now many people saying the IRS should yank the cult’s tax-exempt status. The cult abused the IRS through the courts back in the early 1990s to get that status. The IRS still fears the cult so that’s not likely to happen soon, in spite of huge abuses such as hiring PIs that have no legitimate corporate function. That makes the money spent on them an illegal use of a non-profit funds (inurement). If any ordinary religion did this they would be facing jail time. Of course, the cult has more in common with organized crime than religion.

I got a couple of academic papers out of my involvement. I was trying to figure out why (some) people are so vulnerable to cult attention rewards that they act like drug addicts, for example abandoning their own children. Search for Sex, Drugs, and Cults or just go here. Other papers are here.