I think you'll find radiation to be an interesting additional challenge to add to the mix. That and the relative lack of local oxygen. I get what you're saying though, its a heck of a lot more rational to design and airdrop an algae plant on Mars than to expect oil wells to produce on Mars.

> I think you'll find radiation to be an interesting additional challenge to add to the mix.

Not as much in near-Earth orbit where we enjoy much of the Earth's magnetic field's protection. Astronauts come back with an elevated risk of cancer but not tremendously so.

> That and the relative lack of local oxygen.

Grow some photosynthetic algae too, which'll convert sunlight to oxygen.

I can't tell if you're joking, but photosynthesis rearranges carbon dioxide and water into sugars, releasing some of the oxygen from the water molecules.

And when you burn the algae sourced synthetic kerosene and algae sourced O2 in your rocket engine (or whatever you're doing with it) you'll run out of water. And its dumb to ship unprocessed water up into space if you can use cheap earth based refineries to ship the same weight of highly refined fuel. Keep those heavy refineries at the bottom of the gravity well unless you have a really good reason to hoist them up.

So that was the origin of my idea that this isn't going to scale in space "in general". I'm told Europa has a lot of water, other than the whole lack of sunlight thing, I could see Europa as the "fuel tank of the solar system" in the future. Maybe it could be economically viable to mine comets and turn them into fuel while they're near the sun? Or mine icy asteroids?

I think you're going to overall have more trouble finding water in space than energy.

The problem is that algae is biomass. Thanks to conservation of mass, whatever amount of biomass you bring down from space needs to come from somewhere, and space is famously devoid of mass, let alone anything for algae to consume. That means that the problem of algae farms in space becomes one putting algae food into orbit.

I'm not sure how effective launching literally tons of material into space will be.

Tons is an understatement.

You're forgetting the one plausible energy source, however: the gravitational energy that the biomass has in outerspace. If you could figure out how to capture the energy of millions of tons of material moving from orbit to the Earth's surface, that might be able to provide the large majority of the energy needed to bring it up there in the first place.

I wonder how efficient we could make space elevators.

>> how to transport that energy to where we'd like to use it

I've always thought that a rectenna[1] would be the most efficient way to send power from orbit down to Earth.

> I struggled with the question of how to transport that energy to where we'd like to use it

Lasers

Thus spoke our prophet:

Let me tell you one of my pet peeves: space solar power. Okay, the stupidest thing ever. If anyone should like space solar power, it should be me. I got a rocket company and a solar company. I should be really on it, ya know. But it's like, super obviously, not going to work because, ya know, if you have solar panels - first of all, it has to be better than having solar panels on Earth, so then you say, okay, solar panel is on-orbit, you get twice the solar energy - assuming that it is out of Earth's shadow - but you've gotta do a double conversion. You've gotta convert it from photon to electron to photon, back to electron. You've got to make this double conversion, so, okay, what's your conversion efficiency? Hmm. All in, you're going to have a real hard time even getting to 50%. [The solar cells are better.] It does not matter, put that cell on Earth then. See, that's the point I'm making. Take any given solar cell, is it better to have it on Earth, or is it better to have it on orbit? What do you get from being in orbit? You get twice as much sun - best case - but you've got to do a conversion. You've got to convert it the energy to photons - well, you have incoming photons that go to electrons, but you - you've gotta do two conversions that you don't have to do on Earth, which is you've got to turn those electrons into photons and turn those photons back into electrons on the ground, and that double conversion is going to get you back to where you started, basically. So why are you bothering sending them to bloody space. "I wish I could just stab that bloody thing through the heart." BTW - electron to photon converters are not free and nor is sending stuff to space. Then it obviously super doesn't work. Case closed. You'd think. You'd think case closed, but no. I guarantee it's gunna come up another ten times. I mean, for the love of God.

From: http://shitelonsays.com/transcript/elon-musk-panel-bta-2012-...

I always saw it as a very long-term solution. Once we have the lunar colonies, orbital space stations, asteroid mining, and the economic infrastructure to make interplanetary travel routine, we could begin building out SSP as a practically unlimited source of power. But, for the foreseeable future I have to agree with Musk. Considering how expensive launching stuff to orbit is right now almost any sort of terrestrial solar power coupled with an energy storage mechanism (e.g. pumped hydro, heat reservoirs for solar thermal) would be more cost-effective.

Isn't the point of solar in space, well, space? You get less efficiency, but you are not going to run out of deserts nearly as fast. So the ultimate scale is not limited.

Are we really running out of deserts anytime soon? Isn't the issue more the capital and labor intensity of harvesting energy from sunlight, and transporting that energy to places that actually need it?

Space exacerbates those two issues.

Can't we skip the conversion and use giant optical lenses to focus sunlight onto panels on earth? ;)

No, that doesn't work since the sun is not a point source.

Maybe it doesn't work for lenses but it seems it would work for mirrors: http://www.academia.edu/5185260/SUNBEAMS_FROM_SPACE_MIRRORS_...

Thanks for the good link!

Ok, here they produce 1-sun intensity by having a 10 km mirror at 1000 km height, focusing on a 10 km terrestrial array.

That's a similar angular diameter, 1/100, as the sun, so from the receiver's point of view it can appear as powerful as the sun. I'm surprised that the numbers work out like that.

Maybe you could create a huge "death ray" constellation with 10x solar intensity and whose ground track (all sats in the same ground track) was filled with liquid cooled solar panels. Over the ocean it would just kill everything in its path.