Re: HST question
The main mirror is flawed, but in a perfect way, so to speak.
Meaning, it was easy to correct it (once on the spot, of course).
I'm sure the WFPC2 camera has a mirror that corrects the flaw of the main one and all the other instruments must have this too (except the FOC which was there since the beginning).
The Costar is a box loaded with small mirrors that are moved into position.
Many moving parts means higher chances for malfunction.
And Costar does take the place of a scientific instrument.
Raoul