Newsgroups: sci.space
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: GEOS-6 dies.
Message-ID: <1989Feb10.192623.12510@utzoo.uucp>
Organization: U of Toronto Zoology
References: <AXrTkzy00UkZI0RUwa@andrew.cmu.edu> <14215@cup.portal.com> <1989Feb9.013228.965@utzoo.uucp> <5352@whuts.ATT.COM>
Date: Fri, 10 Feb 89 19:26:23 GMT

In article <5352@whuts.ATT.COM> sw@whuts.ATT.COM (WARMINK) writes:
>> ... Those bulbs are a notorious
>> reliability problem that is being designed out of more recent satellites...
>
>There must be a good reason why LEDs weren't used - 6 years plus isn't that 
>long ago...anybody know why not?

Semiconductors can take quite a while to become space-qualified, and there
is considerable reluctance to change a design that seems to work all right.
I think it was only in the last few years that it was understood that the
bulbs were a systematic weakness.

Also, don't forget that the bird may have been built well before it was
launched -- it's not uncommon to build a batch of satellites and then keep
the last few on the ground until they're needed.

The more recent encoder designs do use LEDs.
-- 
The Earth is our mother;       |     Henry Spencer at U of Toronto Zoology
our nine months are up.        | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
