SPS & Beamed Energy Propulsion

On the subject of launching SPS's from Earth...

Darel Preble of the Space Solar Power Workshop -
http://www.sspi.gatech.edu/ - sent me some notes he had as responses to
claims against SPS in Zubrin's "Entering Space". We've posted them here:

http://www.altenergyaction.org/mambo/index.php?option=com_content&task=view&id&&Itemid=2

In particular Preble quotes a pre-2000 NASA estimate of 42,000 tonnes
installed for a 5 GW SPS; that's 8 kg/kW. I've seen lower estimates
elsewhere, but it would very likely not be less than 1 kg/kW.

So for just one SPS we may be talking about lifting 5,000 to 40,000
tonnes (if we ever do launch such a thing from Earth). If that was all
we were doing, what would be the most economical way to do it? With
current commercially available vehicles (i.e. not Proton or Shuttle),
the limit is about 25 tonnes, so this would be 200 to 1600 launches (or
more, depending on how we get it from low earth orbit to
geosynchronous). Preble quotes launch costs of $100/kg that would make
this affordable, but the lowest costs now available are more like
$2000/kg (Elon Musk is shooting for about this). So existing vehicles
would put the launch budget at $10 to $80 billion. Even $10 billion in
capital costs is a little high for a competitive 5 GW power plant.

If, instead of just buying rockets, $5 billion was spent on R&D and
deployment of new systems to cut launch costs in half, you'd be even or
ahead. Construction of the first space elevator was estimated (the NIAC
study) at $7 to $10 billion, to cut costs to geosynchronous orbit to
about $1000/kg - that would almost work. If it could actually be built.

How much would a functional beamed propulsion system likely cost, in R&D
and first deployment, to start launching real payloads to orbit? If you
can do it for well under $10 billion, it just might work.

Of course, we don't want just 1 SPS - hundreds this size will be needed,
if they're to make any significant impact on world energy. The masses
involved will vastly outweigh anything else launched to that point;
that's why use of in-space materials (like from the Moon) makes sense -
if we ever get to that point SPS will be a major driver for all aspects
of launch vehicle and general space technology development. But getting
to hundreds of them has to start with the first one, and we have no
market payback to drive those developments if we can't even get that
first one up with near-term technology. Which probably means launching
from Earth with reusable chemical rockets...

Arthur