Keith Wood wrote:

David Woolley wrote:

In article <2tkff7F20kr42U3@uni-berlin.de>, Knoppix User
<knoppix2004@hotmail.com> wrote:

I have not read anything about new Hubble but I wonder. Is it wise to
send another telescope on space? I mean look at the price of Oil? How
about adding one to the ISS?

I believe the reference was to the use of adaptive optics to compensate
for atmospheric scintillation (star twinkle) and achieve better than
Hubble results with earth based telescopes.

Pure fantasy.  Only telescopes in space can produce wide-field
diffraction-limited images every time.  The resolution of HST has been
surpassed from the ground at optical wavelengths for some time via
Adaptive Optics, but AO works only over a very small field, still requires
good atmospheric conditions and requires a suitable guide star very nearby
(or an artificial one, which few observatories have).  AO doesn't work
through clouds, and can only operate at night.  Advances like
multi-conjugate AO and tomography will improve the FOV, but will still be
unable to image the Eagle Nebula in one exposure.

    I am not an astronomer much less into telescope engineering but I am certain there are several on earth now that are better than Hubble. How many does it take to compensate for "wide field, every time" in terms of cost. The lastest 'binocular' one to go on line was something like $120M and maintenance does not require a shuttle launch but a van. How much did Hubble cost even in then year dollars? How much will it cost to get a few more years out of it? What does one shuttle launch cost today? If on the order of $120 million how about another binocular telescope instead?

    It would be different if fixing Hubble this one interim time would keep it available for decades like Palomar but price it in dollars per year. That is, how many tens of millions of dollars per year will it cost?

Much of the advances in our understanding of the famous extrasolar planet
HD209458b has come from spectra taken with HST at Ultraviolet wavelengths
(Lyman-alpha). Earth's Ozone layer prevents observations shorter than 310
nm.  Ground-based telescopes have tried for the easier Sodium absorption
lines seen during the exoplanet's transit, but even mighty Keck failed to
extract the Sodium lines from Earth's own Sodium spectrum with enough S/N
to provide a reliable measurement.  For HST, the Sodium was a cinch, and
went on to detect Hydrogen, Carbon and Oxygen.

    And no one is going to argue there are things much better done abover the atmosphere and there is a replacement tailored to exactly that planned for launch in 2009 or so. But NASA has finite resources, finite dollars. Fix Hubble, delay the replacement or delay something else.

Oh, and don't forget about eta Carinae:  Since the primary star's dense
wind extinguishes much of its own far-UV luminosity (Hillier et al. 2001),
and because the companion star is probably an O-type star, our only hope
of directly detecting the companion is in the UV with HST.

The cost effectiveness of Hubble's impact is clear:  HST's annual
operations cost in 2002 was 2% of NASA's total budget, yet it accounted
for 33% of all NASA discoveries.

    A cynic can use that to suggest NASA should be cut back so it is only in the telescope business.

The National Academies: "The Hubble Space Telescope is arguably the most
important telescope in history."

    As was once Palomar as was once ... you get the picture.