How does SOFIA cope with open hull? On the SOFIA aircraft, the aircraft is designed to fly at very high altitudes (higher than what can be achieved by regular 747), with a cargo door open.

https://upload.wikimedia.org/wikipedia/commons/8/8a/SOFIA_ED10-0182-01_full.jpg

I know that oxygen mask are a standard feature for most airliners but:


How is the aircraft designed to handle this situation ?
What about redundancy ?
If there is supplemental oxygen, is it really without adverse effects ? 


pic credits wikimedia
From the picture I can see a bulk head forward of the telescope area. This modified 747SP might have a re-positioned bulk head then. Anything forward of the telescope would be pressurized.

This source confirms, bulk head was moved from the aft to be ahead of the telescope.