Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!uwvax!uwmacc!jwp
From: jwp@uwmacc.UUCP (Jeffrey W Percival)
Newsgroups: sci.space
Subject: Re: Space Telescope
Message-ID: <440@uwmacc.UUCP>
Date: Wed, 29-Oct-86 20:21:43 EST
Article-I.D.: uwmacc.440
Posted: Wed Oct 29 20:21:43 1986
Date-Received: Wed, 29-Oct-86 22:48:15 EST
References: <1322@rayssdb.UUCP> <4270002@hpfcla.HP.COM> <363@uwmacc.UUCP> <7240@utzoo.UUCP>
Reply-To: jwp@uwmacc.UUCP (Jeffrey W Percival)
Organization: UWisconsin-Madison Academic Comp Center
Lines: 31

In article <7240@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:
>> There is an earth/moon flag available to the flight software on board,
>> that indicates when the ST is within some small angle of these
>> objects;  the instruments can take action or not, depending on
>> the situation.
>> 
>> You can bet there's a sun flag, too.
>
>Possibly not.  My recollection is that the attitude-control system is
>forbidden to point the ST at the Sun, and won't even point it near the
>Sun unless specially ordered to.  There is also a completely independent
>system, which cannot be turned off, which closes the telescope's lid if
>the line of sight starts to intersect the Sun.
>-- 
>				Henry Spencer @ U of Toronto Zoology
>				{allegra,ihnp4,decvax,pyramid}!utzoo!henry

I'm not sure what the "possibly not" refers to...
There *is* a sun flag, but it is generated differently than
the earth/moon flag.  The sun flag is wired to sensors on ST,
and is set by this hardware system.  The door gets closed,
and the sun flag alerts the flight software.  The earth/moon flag,
however, is uplinked to the HST, and is not connected to any sensor.
The ground software is supposed to compute the earth/moon flag
based on the timeline, and has the responsibility to uplink it
at the appropriate times (and clear it too, of course).

What trivia, huh?

-- 
	Jeff Percival ...!uwvax!uwmacc!sal70!jwp or ...!uwmacc!jwp