QUESTION:
If the Hubble breaks how long does it take to fix it?

ANSWER from Andy Doherty on May 13, 1996:

>     This question has two answers.
>     
>     The first answer is a couple of days for big items that break. The 
>     second answer is several years when an item that breaks needs an 
>     astronaut to replace it.
>     
>     With the Hubble, there is great need to make sure that it is available 
>     to the astronomers as much of the time as is possible. The make sure 
>     that it is, the Hubble was designed with redundancy. Redundancy 
>     provides for a backup in case something breaks. For many items on 
>     Hubble we have 2 items that can do the same thing. That way, if the 
>     first one breaks then the second one can do the job. Switching from 
>     the primary unit to the backup unit can take anywhere from a couple of 
>     seconds (it is done automatically by the Hubble) to several days when 
>     the ground controllers must change the configuration.
>     
>     If the item must be replaced by an astronaut, then several years of  
>     planning must be done to train and prepare for a Shuttle mission. The 
>     replacement item is carried into orbit in the Shuttle payload bay. The 
>     astronaut will take out the old item and then install the new one.
>     
>     An example of this is the tape recorders we use to record science data 
>     on the Hubble until it can be sent to the ground. In January 1996, one 
>     of the three recorders we have jammed and quit working. We are using 
>     only two recorders right now and on the next mission in February 1997 
>     the one that broke will be replaced.
>