Lunar vs. orbital astronomy

Fair questions. I was merely parrotting what I have read in several
articles regarding the desirability of emplacing radiotelescopes on the
farside of the Moon. Such articles are not difficult to find; if I
remember correctly, there are some in the Space 1996 and Space 2000
proceedings. Whether or not, as you suggest, a thin aluminum baffle in
HEO could provide an equivalent amount of shielding as the Moon does for
radiotelescopy, I frankly do not have the technical knowledge myself to
discern independently.

Jay Huebner: You teach astronomy, so why don't you opine on this issue?

Regarding constellations of satellites... I'm interested in your comment,
"achieving stability in orbit (which NASA seems to think they should be
able to do)". Is there some NASA study or paper that indicates that constellations
of satellites for interferometry is very possible (p.s., URL would be
appreciated; thanks)?

Ron
******

"Combs, Mike"
12/17/01 11:02 AM
Please respond to spacesettlers

To: "'spacesettlers@yahoogroups.com'"
cc:
Subject: [spacesettlers] Lunar vs. orbital astronomy

From: rmenich@... [mailto:rmenich@...]

I think that there are different answers for different types of
astronometric observations. Sren Nielsen pointed out the advantage of
positioning a radiotelescope on the farside
of the Moon --- it would be shielded there from electronic interference
from Earth. The farside of the Moon is optimal for such an observatory,
much better than an orbital location.
How so? The orbital dish needs an aluminum baffle, but how does the
construction of this compare with the difficulties of construction much
further away from Earth? The farside telescope has 50% of the sky blocked
by the moon. And if it's an Aricebo type array, it can't even be pointed
at all of that remaining 50%. The orbital dish can always be pointed
directly at any point at any time for any length of time. The orbital
dish can be reached from Earth for less delta-V, which means lower
construction costs and lowered costs for maintenance. If the lunar
surface array is solar powered, it may remain inoperative for at least a
portion of the lunar night. The orbital array could be solar powered
continuously. On the moon, we can probably build dishes several times
larger than Earthly gravity would allow. In orbit, there's no reason why
monolithic dishes the size of nations couldn't be built.
Long-base interometry is another example of a type of astonometric
observation for which the Lunar surface is a superb site. There is very
little seismic activity on the Moon, thus providing a very stable
platform. Achieving this type of stability with a constellation of
satellites might be doable, but more challenging than just using the Lunar

surface to provide that stability.
So the question that must be answered is which is more challenging:
achieving stability in orbit (which NASA seems to think they should be
able to do), or constructing the observatory at the more distant location
of the moon?

Regards,

Mike Combs