Spitzer's Multiple Instrument Chamber contained the cold parts of Spitzer's three scientific instruments: Infrared Array Camera, Infrared Spectrograph and Multiband Imaging Photometer for Spitzer. It also housed the pointing calibration reference sensor, which was part of the pointing control system that helped to make sure the telescope was pointing in the right direction. The Multiple Instrument Chamber was built to be so tight that no light could get through, except the light that was directed onto the instruments by the telescope. The chamber was 84 cm in diameter, and 20 cm high. It had an aluminum baseplate and cover, and was attached directly to the cryostat filled with liquid helium.