QUESTION: 
What type of computers are used to receive and process the information 
from the Hubble Space Telescope ?

ANSWER from Bill Crabb on april 26, 1996 :
Many computers are used to process HST data. Onboard the telescope itself
we have three main computers as well as a few additional microprocessors. 
The three main computers are called the NSSC-I, the DF224, and the PSEA. 

The NSSC-I (NASA Standard Computer I) manages the science instruments.  
It controls the commanding to the instruments and controls their data 
output.  It talks to the DF224 to set up the vehicle slews required to 
position the target in the instrument's apertures.  It also monitors the
instruments for problems.

The DF224 (which if you're really interested stands for Digital Fixed 
point 2s complement 24bit computer) is the Hubble's main computer.  The 
DF224 is a 70s-vintage computer.  During the First Servicing Mission we 
added an 80386 processor and additional memory to the DF224.  The 386 is 
the same processor many of you have in your computers at home or in 
school.  In the 1999 Servicing Mission we plan to replace the DF224 with 
a more advanced 486 computer.  The DF224 is responsible for pointing the 
telescope at its target and keeping its position steady while the science 
instruments take pictures or spectra of it.  If you have more questions 
about how the HST is positioned, read Tony Cruz's answer to that 
question. The DF224 also formats data for transmission to the ground and 
processes many of the commands from the ground as well.  Another 
important function the DF224 performs is called safemode processing.  The 
DF224 constantly monitors the spacecraft systems and if something goes 
wrong will take the appropriate action, which often means safemode.  In 
safemode, the DF224 configures the spacecraft to a safe condition where 
the problem can be isolated and corrected.

So what happens if the DF224 itself develops a problem?  That's where the 
PSEA (Pointing Safemode Electronics Assembly) comes in.  The PSEA is 
affectionately known as the back seat driver.  It constantly "listens" to 
the DF224 and if stops "hearing" from it, the PSEA takes control and puts 
the HST in safemode.

On the ground we have hundreds of computers.  Here in the control center 
we have many different types of computers to process the spacecraft data. 
 Our main system is based on DEC VAXes and MicroVAXes.  We also use 
sophisticated workstations from IBM, DEC, and Silicon Graphics to analyze 
the data and to plan the mission.  Most of us have Macintoshes or PCs on 
our desks that we use every day.  These machines are all networked 
together.  The HST Science Institute is primarily responsible for 
processing the science data.  They use similar computers to perform their 
functions.  The control center was originally built in the mid 1980s.  
NASA is currently redesigning the system (the Vision 2000 project) to use 
more powerful computers and take advantage of newer technologies and conce
pts such as artificial intelligence.