Check out [1]. Seems to be a combination of pre-flight calibration tests and in-flight observation of stars and planets with known optical characteristics. [1]

Check out [1]. Seems to be a combination of pre-flight calibration tests and in-flight observation of stars and planets with known optical characteristics. [1] http://www.responsivespace.com/Papers/RS7/SESSIONS/Session%20III/3003_Bauer/3003P.pdf http://www.responsivespace.com/Papers/RS7/SESSIONS/Session%2...