First of the Flight Model blocks configured for testing in the calibration chamber. The upper flexible connections from the three CCDs are visible at the furthest part of the unit, and the Power Supply is connected to the left of it. Gold-coated cold fingers above provide a temperature of 153 K at the CCDs while ambient conditions are maintained for the electronics via the structure below them. The cleanliness of the environment during testing is maintained using cold scavenger plates. The light from the optical sources enters through the dark window ahead of the CCDs. To produce the point sources, a lens array is inserted beyond the window to focus five images on each quadrant of each CCD.