Fourth Quarter 1995

Further analysis of the cryostat conceptual design resulted in relocation of the closed-cycle cooler to the top plate of the vacuum jacket. The cold structure is now mounted on fiber-glass trusses attached to the top plate. [This arrangement avoided having very rigid (and massive) sides to the vacuum jacket and reduced the moment of inertia of the instrument on the telescope.] An FEA analysis of internal instrument flexure required changing the large optical table into smaller and more rigid box structures. to meet the flexure budget.

A detailed study of the cryostat cooling concept confirmed that the best approach was to use a closed-cycle cooler to cool a radiation shield which enclosed a liquid-nitrogen-cooled optics box. It was also decided to use external motors rather than cryogenic motors.