Let's watch this test case

>...and there's a certain
> amount of environmental damage from lifting things from earth
>(even ET resource based plans involve some heavy lift).

I wonder how much we could parlay those early lifts into sustainable
orbital infrastructure? The amount of enregy expended to lift into
orbit that evenutally turns into an orbital ability to thereafter
develop SPS with minimal Earth launch requirements. This is what I
refer to as the energy payback.

> I don't think the prospects for SPS are good in the near term,
> simply due to the difficulty of raising that kind of capital for
> such a risky venture.

The achilles heel. I agree.

> As soon as the first SPS nears operation there will be an
> outcry from the enviro-hysteriacs, and the best we can hop for is
> serious delays.

Probably accurate with this prediction too.

> The worst is total shutdown. That's way too much
> investment risk, even discounting technical risk entirely. In the
> longer term SPS will probably at least be tried, but we might have
> decent fusion reactors by then. SPS could be one of those ideas
> that never quite gets its day in the sun (so to speak).

I think that fusion reactors as a concept are easier for people to
accept than SPS. Fusion reactors fall into the same "central power
plant" paradigm whereas SPS is too Sci-Fi for people to seriously
grasp.

Let's hope that this generation is the last in which we hear the
phrase "Fusion power is only a decade or two away" :-)

> One area where SPS
> might find a niche is beaming power on orbit for ion drive orbit
> raising stages. Put all the heavy solar cells and power conversion
gear
> on the SPS, and beam the power to an ion drive tug which lifts
> satellites from LEO to GEO.
>
> ......Andrew

Makes sense to use it for that, but then we re-open the whole can of
worms about how to fund the all of the necessary orbital
infrastructure. SPS ideally serves a highly capital intensive
industry and can reap resasonable profits, but we've already danced
to that tune, haven't we :-)

TangoMan