Re: ATM 8" in space, Hubble vs. interferometer

[Peter C Chen <chen@stars.gsfc.nasa.gov>]

Hi folks:
        As someone who has been advocating a telescope on the Moon for the past
few years and is actively developing the technologies for it,  I thought
I'd put in my 2 cents worth.

        An 8" in orbit is no match against the Hubble Space Telescope, UNLESS THE
8" IS ON THE MOON.  The reasons are:
1.  The Hubble is of course much bigger and can collect more light (say
150X).  However it is in low earth orbit and has an orbital nighttime (time
in Earth shadow) of around 45 minutes.  This limits how long it can
integrate on an object.

        On the other hand, nighttime on the Moon is around 15 days or about 350
hours  (give or take a few for terminator crossings).  The 8" can therefore
integrate for roughly 500 times longer.   With zero read noise detectors
that can accummulate for a long time (we are developing those), the
increased observing period more than compensates for the smaller aperture.

2.  The Moon offers an absolutely stable platform.  A pair of 8"
telescopes, separated with a baseline of 100m to 1 km and coupled by fiber
optics, can resolve its theoretical limit of 0.001 arcsec or better.  This
is the kind of performance required to resolve planets around other stars.

        Theoretical limiting resolution of the Hubble is somewhere around 0.04
arcseconds (visible).  Orbiting telescopes wobble, and it is an extremely
challenging technical problem to keep them steady enough for imaging or
interferometry.

        Our goal is to put a pair of 1-2 meter telescopes on the Moon to do
imaging, spectroscopy, and optical interferometry.  We all know of the many
spectacular things that the HST has done and is doing.  Try to imagine what
a comparable telescope (or interferometer pair) can do if it were placed on
the Moon.

        We have a website at http://snoopy.gsfc.nasa.gov  unfortunately it has
been down for the past couple of weeks.  Should be back up again soon.

Cheers,
P.C. Chen