Posted by Ed Cheng on December 21, 1999 at 11:16:33:
In Reply to: Hubble computer posted by David Hardy on December 21, 1999 at 10:50:14:
> In the Hubble fact sheet it says that the present Hubble computer is
> based on the Intel 60386 and will be upgraded to 80486. Why was this
> done ? Wouldn't a Pentium be better ?
The original equipment on Hubble is a computer called the DF-224. It is a
very old 8-bit computer with 64K CORE memory. It has proven very reliable
and works well but obviously it does not have much more processing capability
than most modern calculators.
During the First Servicing Mission in 1993, we installed a 386-based
coprocessor for the DF-224 which provided some redundancy and memory.
However, the DF-224 is still the main computer.
A significant amount of effort is put into ground-based scheduling and
commanding for Hubble because of limited computing capability on board.
Our plan is to replace the DF-224 with a 486-based computer so that the
increased processing capability can be used to reduce ground processing
complexity and cost.
Why a 486 instead of a Pentium? It takes many years to develop a processor
for flight in space. We call it a 486, but that just means that the
architecture and coding is similar to a 486. The electronics that implement
the computer are very different from a commercial PC. These parts need to
be specially engineered to be resistant to radiation and other hazards
in space. Thus, there is a time lag between when a commercial product is
successful and when we have a space-qualified version. Of course, if we had
a space-qualified Pentium, we would use it!
Even the 486 provdes a dramatic improvement (20X) in computing power
and memory (6X). Besides, there are many more people who know how to write
good code for a 486 than a DF-224!