I retired from what Bush called The Nucular Bidness a few years ago and I can tell you how the guys down at the plant did it. The scope's final assembly was accomplished inside a plastic bag filled with Nitrogen gas that had first been used to purge the air out of the bag. Grease on all the threads & fittings of course.
The Nitrogen gas? Used to store certain high-grade components in an inert environment and also to shrink-fit parts together. As the (pressurized) liquid Nitrogen is exposed to air, it turns to gas and the expansion super-cools whatever it touches.
You may recall certain gruesome high-school Biology class demonstrations....
Regards, Joe
