Other attributes
Hubble accommodates five science instruments at a given time, plus the Fine Guidance Sensors, which are mainly used for aiming the telescope but are occasionally used for scientific astrometry measurements. Early instruments were replaced with more advanced ones during the Shuttle servicing missions. COSTAR was a corrective optics device rather than a science instrument, but occupied one of the four axial instrument bays.
Since the final servicing mission in 2009, the four active instruments have been ACS, COS, STIS and WFC3. NICMOS is kept in hibernation, but may be revived if WFC3 were to fail in the future.
Advanced Camera for Surveys (ACS; 2002–present)
Cosmic Origins Spectrograph (COS; 2009–present)
Corrective Optics Space Telescope Axial Replacement (COSTAR; 1993–2009)
Faint Object Camera (FOC; 1990–2002)
Faint Object Spectrograph (FOS; 1990–1997)
Fine Guidance Sensor (FGS; 1990–present)
Goddard High Resolution Spectrograph (GHRS/HRS; 1990–1997)
High Speed Photometer (HSP; 1990–1993)
Near Infrared Camera and Multi-Object Spectrometer (NICMOS; 1997–present, hibernating since 2008)
Space Telescope Imaging Spectrograph (STIS; 1997–present (non-operative 2004–2009))
Wide Field and Planetary Camera (WFPC; 1990–1993)
Wide Field and Planetary Camera 2 (WFPC2; 1993–2009)
Wide Field Camera 3 (WFC3; 2009–present)
hubble
