Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: HST mirror distortion
Message-ID: <1990Jun29.171342.2515@zoo.toronto.edu>
Followup-To: sci.space
Organization: U of Toronto Zoology
References: <1062@orange19.qtp.ufl.edu>
Date: Fri, 29 Jun 90 17:13:42 GMT

In article <1062@orange19.qtp.ufl.edu> bernhold@qtp.ufl.edu (David E. Bernholdt) writes:
>...the (possible) effects of the ascent on something so large and
>high precision as the HST mirrors?  Are there special mountings
>(substantially different from those ground-based mirrors) on the HST
>mirror to prevent problems? ...

A great deal of care was taken on this, and concern about it was one
reason why the original plans to bring the thing back down for servicing
were changed.  The aberration problem seems too symmetrical and smooth
(it's practically "textbook perfect" spherical aberration) to be accounted
for that way.

>...their mirror suffered similar troubles, but the design included force
>actuators, which they used to tweak the mirror into focus.  Obviously,
>HST either doesn't include such hardware, or the abberation is beyond
>the capability of the system.  Can anyone say which?

HST has "tweaking" actuators, but they aren't sufficient to deal with it.
They probably *could* deal with minor warping due to launch accelerations
and the like, but they don't have enough authority to correct a mis-shaped
mirror.
-- 
"Either NFS must be scrapped or NFS    | Henry Spencer at U of Toronto Zoology
must be changed."  -John K. Ousterhout |  henry@zoo.toronto.edu   utzoo!henry