A LIQUID-HE AUTOMATIC COOLING SYSTEM FOR A BALLOON-BORNE INFRARED TELESCOPE

A cooled telescope for astronomical infrared observations at balloon a ltitudes in the range 2-5 mu m was successfully flown on June 12-13, 1 995 from the NASA/NSBF base at Palestine, Texas. A cylindrical cryosta t (42 cm in diameter, 120 cm high), housing the optics and the detecto r, was cooled by using liquid He as the refrigerating fluid. During th e 11 h flight, the temperatures of the detector, optics, and internal telescope subparts were regulated between 45 and 80 K with very good s tability. The cryogenics were controlled by a pressure control equipme nt designed to operate at both ground level and at 40 km altitude. Fur ther thermal stabilization of the focal plane detector array was provi ded by a dedicated servocontrol to obtain a stability of +/- 0.02 K ov er time scales of a few minutes. The main features of the telescope, a s well as on-ground and in-flight performances of the cryogenic system are described. (C) 1996 American Institute of Physics.