QUESTION:
How many batteries does the Hubble Space Telescope have and how big are they?

ANSWER from Andy Dougherty on April 19, 1996:
The Hubble Space Telescope (HST to those of who work here) has 6 
batteries. Each battery contains 22 'cells' (more on a cell later). 
Three batteries are packed into a battery module. Battery modules are 
roughly 3 feet wide, 3 feet deep, and 10 inches tall and weighs about 
475 pounds.

Each battery cell looks like a miniature scuba tank. They are about 4 
inches in diameter and contain nickel and hydrogen. These two 
chemicals react with each other to produce the electricity. The 
electricity used by the HST is replaced by the solar arrays capturing 
energy from the sun. Each battery contains enough energy to power a 
hair dryer for about 6 hours.

I have a couple of question for you to think about - Why does the HST 
need batteries? Why can't just the solar arrays be used to supply 
electricity to HST?