Path: utzoo!utgpu!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!mcsun!unido!mpirbn!p515dfi
From: p515dfi@mpirbn.mpifr-bonn.mpg.de (Daniel Fischer)
Newsgroups: sci.space.shuttle
Subject: Re: Recovering HST from orbit
Message-ID: <1614@mpirbn.mpifr-bonn.mpg.de>
Date: 7 Feb 91 16:02:41 GMT
References: <6814@harrier.ukc.ac.uk>
Reply-To: p515dfi@mpirbn.UUCP (Daniel Fischer)
Organization: Max-Planck-Institut fuer Radioastronomie, Bonn
Lines: 24

In article <6814@harrier.ukc.ac.uk> sss3@ukc.ac.uk (S.S.Sturrock) writes:
>..some other reason why the HST was not just recovered and the mirror replaced.
>Is it because the Shuttle would not be able to land safely with the added
>weight, or maybe it could land but would be so damaged that it could not
>be re-used?

It's not the weight issue: initially the HST was designed to be returned
periodically with the STS, but this plan was dropped already many years ago.
Among the reasons were the vibration loads of touch-down, but to my knowledge
the principal objection was the cleanliness of the mirrors: any dirt(+) would
severely compromize the UV reflectivity. Ironically this same concern has also
contributed to the terrible chain of mistakes at Perkin-Elmer and NASA: they
simply didn't dare to do all possible tests with the precious mirror(s) in
fear of contamination. Whether this was a key factor is not clear, but the
Allen Report mentions it as a contributing cause.

(+) One might ask: hey, why is the STS payload bay supposed to be dirty? But
then again, the last Shuttle mission had almost to be terminated because of
excessive dirt in several systems... One would have to put a sack around the
HST in orbit before berthing it, but even then exhaust from the OMS and RCS
could hit it (question to Henry at all: how much pollution does a Shuttle
typically produce in its vicinity dyring an orbital rendezvous, like when
they captured LDEF a year ago? Did they find traces of the thruster exhaust
on the satellite?).