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
It was also decided to use external
motors rather than cryogenic motors.