Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: HST - Repair or Augment.
Message-ID: <1991Feb11.190058.27540@zoo.toronto.edu>
Organization: U of Toronto Zoology
References: <6814@harrier.ukc.ac.uk> <91039.210444NU128479@NDSUVM1.BITNET> <1991Feb10.022414.2365@zoo.toronto.edu> <32iu02bN05Of01@JUTS.ccc.amdahl.com>
Date: Mon, 11 Feb 1991 19:00:58 GMT

In article <32iu02bN05Of01@JUTS.ccc.amdahl.com> haw30@DUTS.ccc.amdahl.com (Henry Worth) writes:
>   Now, as H.S. surely knows :-) , much of the cost and delay
>of recent projects has been due to their relience upon the Shuttle.

While this is somewhat true, the extent of it is much exaggerated.  When
you look hard at the scheduling for HST, in particular, you find that
although its launch nominally slipped several times due to pre-Challenger
shuttle delays, in fact the thing was only barely ready to launch in
spring 1986, and some useful upgrades ended up being done during the post-
Challenger hiatus.  At least until Challenger, the shuttle delays and
resulting cost increases were only just keeping ahead of HST's own delays
and resulting cost increases. :-)

>... So, are we better off repairing the HST, or
>would the HST's lifetime servicing costs significantly offset
>(or even cover) the costs of a follow-on (or even a series) designed
>with today's realities in mind?

As has been pointed out repeatedly in other connections, just because you
save money in one area doesn't mean you get to spend it somewhere else.
HST has already had too much spent on it to just write it off; that would
almost certainly kill any hope of a successor.  Bear in mind that much of
the servicing planned for HST is *not* the result of the mirror screwup
or the solar-array problems.  If you write off all servicing, you probably
write off the telescope after only a few years.  You cannot possibly get
a replacement up there that quickly.  It would take until after the first
servicing visit just to get such a project approved as a major new start.

>   For example: by not servicing the HST and using an ELV to launch
>a follow-on/supplement to the HST we would:
>   > Save the cost of several shuttle flights (big $$$'s). Freeing
>     up those shuttle flights for other purposes would also
>     be of significant value.

Freeing up the shuttle flights would certainly be useful.  However, you
are kidding yourself if you think that big expendables (the HST is *not*
a small payload!) are lots cheaper.  Titan IV, the probable choice, in
its maximum-lift configuration costs $250M+ per flight.

>   > By using an ELV we would also save the cost and complexity
>     associated with man-rating a satellite for shuttle launch and
>     on-orbit servicing.

Using an expendable and abandoning on-orbit servicing are quite
separate issues, please note.  An expendable launch means no chance
of bringing the thing back down or making quick fixes in the event of
a startup problem, but doesn't affect the possibility of servicing
later.

>   > Giving up on-orbit servicing opens up the possiblity of
>     a geo-sync orbit with reduced operating (communications)
>     costs and reduced solar array/battery capacity requirements.

Although it will require better radiation-hardening, since Clarke orbit
is in the fringes of the outer Van Allen belt.  This could be a problem
for the more sensitive detectors in particular.  A still higher orbit
might be desirable.

On the whole not a bad idea, but please note that this is going to
require scaling down the telescope significantly.  Not even a Titan IV
could get an HST lookalike that high.

>   Using a commercial ELV also opens up the possibility of having NASA's
>role reduced to that of a minor sub-contractor providing launch
>facilities ...

Um, what are you thinking of?  NASA has no expendables and is not involved
in launch facilities for them.

On the whole, getting NASA out of the telescope business is probably a
good idea.  But one should not underestimate the hassle and time involved
in that rearrangement of funding.  NSF is not used to funding space projects,
especially big ones.

In retrospect, a series of smaller telescopes funded by NSF and launched by
expendables to high orbit is probably a better way to go than HST, other
things being equal.  But other things are *not* equal.  It would be quite
reasonable to start on such a program now, as HST's replacement, because
it's going to take much of HST's working life to get such a program off
the ground.  It's not a good reason for abandoning HST repairs.

Sure, a determined and well-run program could get results much more quickly.
But nobody is going to fund one.
-- 
"Read the OSI protocol specifications?  | Henry Spencer @ U of Toronto Zoology
I can't even *lift* them!"              |  henry@zoo.toronto.edu  utzoo!henry