From: Frederick.A.Ringwald@dartmouth.edu (Frederick A. Ringwald)
Newsgroups: sci.space
Subject: Re: SPS fouling astronomy (long)
Date: 18 Aug 92 01:18:53 GMT
 <1992Aug12.044959.19501@dartvax.dartmouth.edu> 
 <1992Aug13.175839.24133@cfa.harvard.edu> 
 <1992Aug15.224819.15041@dartvax.dartmouth.edu>  
 <roelle.714081429@uars_mag>
Organization: Dartmouth College, Hanover, NH

In article <roelle.714081429@uars_mag>
roelle@uars_mag.jhuapl.edu (Curtis Roelle) writes:

> Are there really persons out there who believe a fair assessment of
> the physical universe can be made by restricting our view to the
> celestial cones around Earth's polar regions?

I'm fond of the Milky Way myself, but I'm not *too* worried about its
imminent demise at the hands of SPS. Much of this thread shows that SPS
is a very advanced concept, and maybe necessarily so (although no one
so far has picked up on the idea of making them out of gossamer, the
whole satellite resembling a gigantic net of fine wire; this idea is
only partly stolen from Freeman Dyson). I think we've seen clearly that
many problems need to be solved if SPS is going to become economically
feasible. In the meantime, competing technologies may not be standing
still. A breakthrough in superconducting cable (either solve the flux
creep problem in the new kind, or perfect an inexpensive manufacturing
process for the old kind), or improvements in hydrogen combustion
technology, are only two examples what might solve the energy storage
problems that ground-based solar and wind power now have. So might a
breakthrough in nuclear fusion technology, although if you like hard
problems to solve, this is the field for you. You can start with the
basic plasma physics, one problem being the equations are linearized,
although high-order effects often dominate the observed behavior of
real plasmas. Another problem is that we really don't have enough
observations of the behavior of real plasmas, and there is little
funding to do it; I know several young experimental plasma people who
used to be interested in fusion, but have now defected to space
physics. Then there's the first-wall problem, and of course the heating
and confinement problems. Maybe if they started all over from scratch,
with magnetic bottles...

Of course, breakthroughs being breakthroughs, they're unpredictable,
and so by definition you can't count on them for anything in advance.
But, SPS itself will require it own breakthroughs in space launch and
operations technologies. For example, anything the Space Shuttle now
carries has to be worth about its weight in gold, to be profitable
(that's $4e8/65000 lbs, or about $400/oz). This isn't so bad, though,
since some things, such as communications satellites, are worth more
than this (and the photons streaming through their channels are
massless). It will be interesting to see if space manufactured
materials, such as pharmaceuticals, can beat the transportation costs,
although they too will have competition from the ground; adapting the
technology from film recovery from photo reconnaissance satellites
might help in bringing things down. DCX may also help, but space flight
will still be much more expensive than jet travel, and while jets are
fine for passengers and FedEx packages, they're still very expensive
for bulk freight. So, there's an incentive to develop extraterrestrial
resources, such as lunar concrete for construction. But current
estimates (all sketchy) for a Moon base are in the range of $100-500
billion. This is more expensive than even the Apollo project, which was
carried out in the best of economic times and even then widely
criticized as too expensive. But of course, the Apollo project did not
have making a profit among its primary goals. So, there's an incentive
to automate as much as possible, and to develop less expensive
technologies for getting lunar material into space, such as
electromagnetic mass drivers and powdered aluminum/oxygen rockets.
Industrial processing will need to be worked out in the space
environment, where air, water, and human supervision come at a premium.
There may be advantages in readily available solar energy, hard vacuum,
and microgravity, although there may be liabilities, too, such as
radiating waste heat away from a large structure. (Sound familiar?)

SPS is also not without its own unique problems. Microwave power
transmission presents safety problems, and terawatts of transmitted
power may well generate enough static to interfere with
telecommunications, not to mention cause the demise of ground-based
(i.e., inexpensive) radio astronomy. Laser transmission, at various
wavelengths, has problems with clouds and atmospheric water vapor,
which you might be able to get around by putting the receivers on large
balloons, but these present problems, too. (There aren't too many large
balloons, these days. But there used to be. Many of them crashed.)

I don't know about you, but this is beginning to sound like epicycles
upon epicycles to me. When I was little, I heard a lot about the "world
of the future": but if there's anything I've learned about the future,
it's that it always comes out a LOT different from how you think it'll
come out. We don't have jet packs or flying cars, which even if they
were practical, would probably be noisy and dangerous. But we do have
personal computers, which are perhaps much more wonderful, especially
for a kid who really hated adding up long columns of numbers (and
really hated typing, too). The Cold War is over, too, something I
certainly never expected to live to see.

So don't worry about the demise of the Milky Way. It's already taking a
beating in every city in the world! And if it becomes profitable to
construct SPS, it'll happen; if not, then not. This whole argument has
taken on the air of a SETI debate: every contingency entails multiple
uncertainties and lots of assumptions. This concept is just plain too
advanced: the only way to get away from lots of the uncertainties is to
try to run experiments (e.g., for SETI, do radio searches, or
orgin-of-life laboratory experiments, or searches for extrasolar
planets). I think I've had enough, for now!

P.S. At the South Pole, there is some interesting astronomical work
going on. When the weather is clear, a solar telescope takes
measurements of the Sun used to probe its interior by analyzing
pressure waves in its surface, in a manner not unlike seismology;
helioseismology, it's called. The South Pole has an important
geographic advantage: the last I heard, the longest uninterrupted run
they had was eight days long. This makes for tasty frequency
resolution, the best so far. Then there's the cosmic ray project, to
analyze waves in the interplanetary medium. (They wanted to hire me to
take care of it, but I turned them down. Living at the South Pole would
be fun, for three weeks, but they wanted me to stay for 53 weeks!
Anytime anyone razzes me about this decision, I say "Well, there's a
job open: why don't YOU do it?") There's also a high energy gamma ray
instrument, and interest in infrared instruments, to take advantage of
the high altitude and dry air, at least one being a cosmic background
experiment, to follow up on the COBE results. There's even talk of a
2.5-m class optical telescope, mainly for time series work such as
asteroseismology, although it'll have to deal with the aurora and with
the normally just-awful weather.