[nighthawk (OP)]

...and how would efficiency be affected if it was different? I've read on wikipedia that the pressure is only 0.3% of atmospheric pressure, is this true, wouldn't that crush the glass?

[lyner]

The pressure is inwards and a cylinder is a very strong shape ' in compression'.

[graham.d]

There is a lot of misconception about vacuum (or partial vacuum) being somehow an almost infinite force. Even if you could create a perfect vacuum in a container the maximum pressure (on the earth's surface) is only ever 1 atmosphere (about 14.7 lbs/sq in). Similarly, in a pressurised spacecraft this pressure is in an outward direction and it is only a little lower than this in a modern passenger aircraft at 35,000 feet. Aircraft are made quite strong (for other reasons) but spacecraft can be quite flimsy structures to keep weight down.

Compare this 1 atmosphere pressure to what a submarine has to withstand, which can be over 100 atmospheres and, for specially designed submersibles, much more. Even a diver at 10m depth will be doubling the pressure on himself.

As SC says, a cylinder is a strong structure even though the glass is quite thin.