The danger of coal - need SPS

I made no assumption of cheap electricity from SPS. The question is can
we replace coal and oil, without too much harm to the economy. The
answer is, we can, but it will take several decades. As far as
profitable business goes for space applications; some private companies
are ready to try things now - but more likely we'll need a few billion
dollars of federal investment first to prove out the technology and lay
the groundwork - as generally has happened in almost every other field
of technology in the past.