It's not really a bad idea, provided there are no orange-bellied parrots in the way. The real fun is when you have to explain to greenies that yes, it's really solar power, and yes, it's also thermonuclear.

I like the idea of a separate organisation dedicated to this technology, as it's clear none of the existing organisations can do it. Set it in motion, get it done before the bloat sets in. Also like the idea of the solar-electric HEO ferry -- anyone have a link to an artist's perception of it (a real one I mean)?

Seeing as you seem to be a big fan of this 50% you speak of.. here's another one for you: at night, solar panels on the ground receive no sunlight whereas, get this, in space they do. Now, whereas I'm plenty doubtful of your claims to the use of 50% I'm pretty certain of the almost 50% split between day and night.

Of course, I'm more of the belief that solar power satellites will not be practical until we have off earth resources to build them from and, as such, low tech heat exchange designs are a better solution than high tech solar panels as we might actually have a chance of making low tech stuff in space in the near term.

Douglas Adams - "Mostly Harmless"
- The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong it usually turns out to be impossible to get at and repair.

Lets build in some redundancy shall we? (Just in case.)

I think you covered the list pretty well but corrosion is also a factor that space should mitigate. Well, mostly aside from the wandering bit of space debris.

I haven't RTFA, probably won't, but I'd like to throw in the additional suggestion we look into Von Neumann devices to build most of the components on a lunar base. (Earth first, and strip-mine the moon later.)

Indeed - and because of the potential for unparalleled amounts of energy that are possible with more and more direct forms of solar energy extraction, new things become possible. Dark matter-based energy storage systems and/or weapons become closer to practical, matter fabrication factories manipulating atoms using nuclear interactions (think renewable nuclear fuels), all kinds of uses for the astounding amounts of energy we can't practically transport directly back to earth, but have flowing out at all times. New kinds of engineering and uses for high-energy physics.

That's the enormous potential lying just out there, and also something that almost justifies the apprehension that one can feel about nuclear weapons. Dark matter weapons would be to a nuclear weapon as a nuclear weapon is to fireworks. Of course, that's the same kind of problem that exists with any kind of space travel - anyone can get ahold of a big enough rock and manipulate existing forces send it towards anyone else to pose the kind of threat that would also make a joke of existing nuclear weapons.

But we can't stop threats - they come from nature just as much as they do from man. Learning how to face such danger is much more valuable than refusing to ever touch such ostensibly 'dangerous' forces. And I'd much rather have 10, then 100, then thousands of earths able to start up, rather than stagnating ourselves just to force this one earth to hold our entire future potential. Of course, that isn't the real choice we have either - in almost everyone's ideals, we should care for ourselves, care for eachother, and expand to be a peaceful force of diverse enlightenment rather than spending all our resources on war and revenge. We should care for our world, while we embrace the dangerous potential around us, so that we can grow to a point where the potential danger doesn't have to be so terrifying.

Ryan Fenton

First off, putting them somewhere other than Earth orbit is silly - yes, you can get more energy from the Sun, but how do you transmit it to Earth? The microwave (or whatever) beam will also fall of with the square of the distance.

And how exactly do you keep the power beam locked onto the target, when the target is on a sphere rotating once per day?

Putting them in equatorial geostationary orbits is *much* simpler. You'll lose a small amount of generating time each day (while the station is in Earth's shadow), but if you schedule as much of your maintenance as possible during this time, the effect is minimal.

And maintenance *will* be required, for the foreseeable future. Someday we may be able to build solar cells that don't need to be periodically replaced, but not today.

Furthermore, it's been noted that Earth orbit is "halfway to anywhere in the solar system" (attributed to Heinlein). So we'll need serious orbital capability to build these things, regardless of where we put them.

If you really lose 50% in transmission *and* 50% in receiving the case is harder to make - most estimates seem to have higher numbers for overall system end-to-end efficiency, but of course nobody's buit one yet.

Actually, I'm quite sure someone has built an earth bound a set of devices capable of comparable beam energy density to a proposed orbit power system. IIRC, the efficiency of the receiving antenna can be around 90%, not sure about that of the transmitter.

Personally, I'm sure an array of heat engines could provide more power density than currently comparably priced solar panels, it's silly to pass them up.

And how are you going to transmit that energy from space through clouds ?

FTA: "...then beamed toward a reference signal on the Earth at intensities approximately 1/6th of noon sunlight." Seems like they're intending to beam the energy back in a coherent, but rather diffuse beam to a large rectenna, rather than a tight, high intensity laser blast as is often assumed. Does this make sense? If the beam sent down to Earth is only 1/6th of the intensity of sunlight, what's the point? If this is true though, then the bird-slaughtering potential of SBSP is a misunderstanding. It'd also reduce concerns about it being used as an Akira-style orbital laser cannon.