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: <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