From: Henry Spencer <henry@zoo.toronto.edu>
Newsgroups: sci.space.tech
Subject: Re: satellite computer storage media
Date: Thu, 21 Mar 1996 14:36:35 GMT

In article <ekouba-1803961621330001@slip2270.rmii.com> ekouba@rmii.com (Eric Kouba) writes:
>...earth orbiting birds use hardened RAM and ROM, because they need space for
>programs, not historical data.  Most decently funded satellite programs
>can pay for a comm link that can run faster than the on-board computer...
>historical data gets stored on the ground.

Most decently-funded satellite programs would *like* to be able to pay for
such a comm link, but they can't, because none is available.

In low Earth orbit, any particular ground station sees the satellite a
few times a day for a few minutes at a time, period -- a situation that
demands extensive on-board data storage.  Even a large network of ground
stations doesn't cure this, although it helps a little.

In theory, you can avoid this by using a relay satellite.  Unfortunately,
the only existing relay-satellite system -- NASA's TDRS network -- is very
busy and can't support continuous contact with anything less important than
a shuttle flight.  The practical result is much the same:  the satellite
is out of touch for much of the time, and data gathered then has to be
stored on board until the next contact.

If you can think of any magic solution that can be bought with mere money,
I know some people who would very much like to hear about it.
-- 
Americans proved to be more bureaucratic           |       Henry Spencer
than I ever thought.  --Valery Ryumin, RKK Energia |   henry@zoo.toronto.edu