QUESTION:
What would the HST do if their solar arrays failed?

ANSWER from Rick Fredo on April 23, 1996:
The HST has 2 solar arrays wings, one on each side of the telescope 
body.  Each wing has thousands of solar cells connected in such a way 
that damage or failed of any singel cell, group of cells, or electrical 
connection would not result in a substantial loss of power to the HST.  
Unfortunately, the HST cannot survive without both solar array wings will 
result in insufficient charging of the HST batteries.  This will lead to 
what is called a "power system rundown" and the eventually loss of the 
HST.  The batteries are needed during the time when the HST passes 
through the Earth's shadow (typically 6 hours)