Yuki -

I've looked over your lunar observatory thing and I have a number of
comments.  I've tried to categorize them below.

SUMMARY

This section is a D.S.F. Portree-style annotation [if you don't know about
D.S.F. Portree, see http://members.aol.com/dsfportree/explore.htm]
intended for Loren and Nathan to briefly get a picture of what we're
talking about.  If you want a more detailed look, see:
"http://www.its.caltech.edu/~yukimoon/moon/MoonTelescope.html"

Yuki proposes to build a UV/optical/IR telescope on the Moon.  The initial
observatory would provide better performance than the current Hubble Space
Telescope (HST), particularly in terms of clarity.  The Moon is chosen
over LEO (Low Earth Orbit) as a location due to a number of advantages
including lower temperature, longer integration times available, seismic
stability, reduced particle density, lack of Earth [a major IR
source].  Yuki suggests (perhaps optimistically) that with appropriate
maintenance, the telescope could last > 100 years.  Launch is contemplated
on existing vehicles and aperture would be 2-8 meters.

LOCATION OF OBSERVATORY

The Lunar South Pole (LSP) is decidedly the location for this.  With the
availability of local hydrogen deposits (detected by Clementine using
radar, and Lunar Prospector using epithermal neutron counting), LSP is at
present the unquestioned location for a lunar base.  Even excluding the
fact that LSP (and the lower-hydrogen LNP) are the only places where
hydrogen and oxygen are both commonly present on the Moon, thus allowing >
90% of consumables to be obtained on site, it should be noted that
maintaining satisfactory temperature for human existence for periods in
excess of a couple of months is not presently feasible at any location on
the Moon other than LSP or LNP.  (The 1960s Surveyor robotic probes simply
operated hot.)  In fifteen years, when we have a Lunar Base, it will be at
either LSP or LNP - and LSP, due to greater concentrations of hydrogen,
will be the choice.

Once the region of human presence on the Moon is defined as LSP, key
assets should be placed in this region.  For example, if the telescope is
to have lifetime longer than a few years, it should be in a region
accessible to astronauts who will add improved instrumentation to the
device and replace damaged or worn-out parts.  Astronauts might also be
helpful in connecting the telescope to other telescopes to serve as an
interferometer.

Yuki argues in his paper that LSP is preferable to LNP on several grounds,
including the presence of the galactic center as well as the fact that the
southern sky is less well explored than the northern sky.  This matches my
analysis above (which is from a very different perspective!), however I
must note that the galactic center has a selenocentric  (Moon-centered)
declination of only 8 deg S, so we had better be very careful about where
we position the telescope - you might not be able to see the galactic
center from the bottom of a crater!

TO TRACK OR NOT TO TRACK?

>From the LSP we can see half the sky.  Actually, we can see 51% of the sky
because the Moon does not rotate precisely around the axes defined by its
coordinate system (this isn't of any physical significance, it is a
historical freak accident due to our choice of coordinates.)  However, if
we have a non-tracking telescope, we are in bad shape.  Yuki noted this,
specifying the lunar rotation rate of 0.5 arcmin/minute, so that a field
of view of 2.5 arcmin (HST/WFPC field of view) allows 5 minute integration
time.  Even worse, the visible fraction of the sky is reduced to (at
best) 1/2750, or less than 0.1%.  This is probably not scientifically
acceptable.

Thus a tracking mount is needed.

APERTURE

At violet wavelength (4000 Angstroms), I estimate that a  
diffraction-limited 8 meter telescope can achieve resolution of 0.013 arc
seconds.  As a baseline note, this is equivalent to seeing Bridge from the
Moon, or 200 km size features on Pluto, or 1 AU at a distance of 80
parsecs, or 100 AU at the Galactic center.  By comparison, Hubble is a 2.4
meter telescope.  Thus, if we want significantly better resolution than
Hubble (which is diffraction-limited now that the corrective optics
package COSTAR has been installed), we want 4 meter diameter as an
absolute minimum.  8 meters, of course, is better and 10 meters (the size
of Keck) is equivalent to Keck with the new adaptive optics
system.  Scientifically, resolution (and hence aperture) was a major
factor for HST and will similarly be for the lunar telescope.

Thus we conclude that for aperture, the bigger the better.  We are limited
by two factors: launch vehicle fairing sizes (4.5 meters for Space
Shuttle, and 5 meters for the Delta IV-H which is scheduled to start
flying in 2002/03) and payload capacity to LSP (~ 5000 kg for the largest
of today's vehicles.)  Looking at Yuki's tabulated mass estimates, we see
that this would limit us to six meter aperture, so the fairing is the
stronger constraint.  It would appear that a five meter diameter fairing
effectively limits us to ~ 4.8 meter actual primary mirror size, so the
best we could hope for with this system is twice the resolution of
Hubble.  This, it seems, is unsatisfactory.

What is really needed is a vehicle with wide payload fairing and heavy
lift capability.  This is exactly the type of rocket needed to send humans
to Mars, which brings me to my next point.

POSSIBLE IMPLEMENTATION OF DESIGN STUDY

The Mars Society of Caltech/JPL has, as all of you probably know, been
working on human Mars mission designs.  Most recently a concept has
emerged in which a Shuttle-derived launch vehicle with ~ 90,000 kg to LEO
capacity would be developed in combination with a crew taxi (which would
shuttle to and from the Space Station on small rockets such as Atlas), a
lunar lander which would place the crew taxi on the Moon and then return
to Earth, and [later] an Interplanetary Transfer Vehicle (ITV) and Mars
Lander to carry people to and from Mars and the asteroids.  The lunar
lander propulsion system and the ITV propulsion system would have in
common a nuclear rocket providing roughly double the efficiency of
conventional propulsion systems.

The key item to understand here is that this architecture fits perfectly
into the Lunar Observatory idea.  Specifically, it provides (1) a human
presence at LSP, and (2) the capability to deliver the telescope to the
Moon without extensive on-orbit assembly or unfolding of the mirror (which
would make it difficult to maintain the 10-20 nm tolerances involved in
building a UV telescope.)  

I suggest that, if SEDS is serious about pursuing the Lunar Observatory
study (which in my opinion is a very worthwhile undertaking, given that
much has been written about astronomy from the Moon but very little actual
work has been done, and even less about optical wavelength systems), we
should consider the possibility of a joint SEDS/Mars Society project. 
This might be beneficial to both groups.  The Lunar Observatory idea would
have a payload delivery and maintenance system; the Mars Society's
proposed transportation archtecture and human presence at LSP gains an
actual scientific purpose rather than saying, "here is how we would keep X
people alive at LSP for Y days while doing Z Moon walks."  Additionally,
and more fundamentally, we gain a synergy between the various systems (for
example, the heavy-lift rocket can do both human and astronomy
missions) which increases the likelihood of both happening.  This is true
whether or not they eventually use our Mars mission design or Lunar
Observatory design; the point is that the key technologies have a very
non-empty intersection, and that some of the hardware (launch vehicle and
Earth escape propulsion system) can be the same.  The two missions'
benefits may simply add, but the cost does not.  And in any case, the
exchange of ideas that results could be very helpful.  Finally, Derek and
Loren might get along better ...

I'd be interested to hear any comments on these ideas, or any additional
ideas on Lunar Observatory.  After all, even Robert Zubrin, no fan of the
Moon, agrees that it is a great place for astronomy.  And remember:

"If God had not meant for mankind to colonize space, he wouldn't have
given us the Moon."

     - Krafft Ehricke, one of the captured German rocket pioneers who
          helped us beat the Russians to the Moon

- Christopher Hirata