From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: HST Servicing Mission Scheduled for 11 Days
Organization: U of Toronto Zoology
Lines: 35

In article <1rd1g0$ckb@access.digex.net> prb@access.digex.com (Pat) writes:
>How will said re-boost be done?
>Grapple, HST,  stow it in Cargo bay,  do OMS burn to high altitude,  
>unstow  HST,   repair  gyros,  costar install,  fix solar arrays,
>then return to earth?

Actually, the reboost will probably be done last, so that there is a fuel
reserve during the EVAs (in case they have to chase down an adrift
astronaut or something like that).  But yes, you've got the idea -- the
reboost is done by taking the whole shuttle up.

>My guess is  why  bother with  usingthe shuttle to reboost?
>why not  grapple,  do all said fixes,   bolt a small  liquid  fueled
>thruster module  to  HST,   then let it make the re-boost...

Somebody has to build that thruster module; it's not an off-the-shelf
item.  Nor is it a trivial piece of hardware, since it has to include
attitude control (HST's own is not strong enough to compensate for things
like thruster imbalance), guidance (there is no provision to feed gyro
data from HST's own gyros to an external device), and separation (you
don't want it left attached afterward, if only to avoid possible
contamination after the telescope lid is opened again).  You also get
to worry about whether the lid is going to open after the reboost is
done and HST is inaccessible to the shuttle (the lid stays closed for
the duration of all of this to prevent mirror contamination from
thrusters and the like).

The original plan was to use the Orbital Maneuvering Vehicle to do the
reboost.  The OMV was planned to be a sort of small space tug, well
suited to precisely this sort of job.  Unfortunately, it was costing
a lot to develop and the list of definitely-known applications was
relatively short, so it got cancelled.
-- 
SVR4 resembles a high-speed collision   | Henry Spencer @ U of Toronto Zoology
between SVR3 and SunOS.    - Dick Dunn  |  henry@zoo.toronto.edu  utzoo!henry
