Lunar vs. orbital astronomy Forum: Spacesettlers
Thread: Lunar vs. orbital astronomy
# 2274 byrmenich@... on Dec. 17, 2001, 7:52 p.m.
Member since 2021-10-03
There are a variety of articles on the potential of Moon-based astronomy
located at http://ads.harvard.edu/books/lbsa/toc.html.
"6. Is seismic activity a problem? The Moon is far quieter than the
Earth, with a low Q. At good seismic stations on the Earth, the seismic
noise is less than one A rms; the poor locations have high noise because
of the effects of wind and surf. Lunar seismic activity is not a
concern."
Perhaps both the article and Arno are correct, in that the required
stability of the array depends on the wavelength of radiation being
studied.
A very interesting article there is
http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1985lbsa.conf..301D
on very low frequency radio astronomy conducted on the Lunar surface.
Enjoy!
Ron
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rmenich@...
12/17/01 11:14 AM
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Arno: Thanks for the information. Are some of these studies available on
the Web for perusal?
Ron
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"Wielders, Arno"
12/17/01 11:12 AM
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A long baseline optical / infrared and maybe even radio interferometer
can
not be placed in orbit, only in a stable Lagrange point, due to the very
hard requirements on stability. (Even in Lagrange point the spcaecraft
need
to be stabilised against solar wind pressure using microNewton FEEPs). But
on the Moon the micro seismic environment could play havoc with your
instrument. Note that for optical and infrared interferometry nanometer
stability is required. Even though NASA and ESA have performed studies for
putting interferometers on the Moon, the main conclusion is that putting
them in Langrange points seems to be easier in terms of building and
performance.
Best regards
Arno Wielders (i have worked on VLTI instruments)
rmenich@manu.com
12/17/01 11:11 AM
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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
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"Combs, Mike"
12/17/01 11:02 AM
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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