I've been reading Russian Spacesuits and have run into a number of odd useages of words

One I'm still not sure I full understand is thier use of the word casque...

And dictionary gives us:
Casque: The iron casque, the main head defense during the 9th - 13th centuries, was a rounded or pointed steel bowl that fit snugly over the head but was usually worn over a mail coif and arming cap. A strip of steel or other metal was often fitted to the front of the helmet to protect the nose, called a "nasal." Common examples of these helmets can be seen in the Bayeaux Tapestry. They evolved from the Roman legionnaire's helmet and the crude spangen helmets that replaced them as Europe rebuilt following the fall of Rome. During the early years of the 14th century most casques were replaced with bascinets as more defense was sought against arrows and the defense of the neck and head were enhanced.

An example of how they use it in the book:

"The spatial helmet designed for the VSS-type suits (see also Section 2.2) was found to be the nearest match to meet these requirements. This helmet was selected as a prototype for the S-10 and SK-1 space suits (Figure 3.2.1). The helmet was fitted with a large visor in the form of part of a sphere with its upper edge connected to a soft back-of-the-head element made of rubberized fabric. With the helmet open, the visor was positioned above the cosmonaut's head and the soft part was folded behind the head. The helmet interface was located along the lower edge of the visor. The interface incorporated two semi-frame joints coupled to the visor sides near the ears. The helmet was also fitted with two rigid casques, an inner one located between the head and the helmet's soft enclosure and an outer one located above the helmet enclosure. This design was selected to avoid the folded, soft part of the helmet being squeezed between the cosmonaut's head and the seat headrest. With the helmet open, the visor and helmet enclosure fitted between the casques. The casques also protected the cosmonaut's head during ejection and parachute descent. To improve reliability and prevent misting up, the visor was double-glazed with an 8-mm gap between the layers."