Many years ago I read a very bad SF novel in which a 747 was put into space. Seemed pretty silly to me at the time but I always wondered what would happen if you strapped some really big boosters onto a 747 and tried it. According to the web, the cabin pressure in a 747 is set at about 6000 to 8000 feet and the max altitude of a 747 is around 45000 feet. So the hull has to withstand a pressure difference of something like 8.8 psi. This means that if you put it in space, you could have 8.8psi cabin pressure, equivalent to normal air pressure at around 13000 feet. Some ski resorts have peaks this high. I wonder how leaky the cabin is in a 747. In space, you can't compress exterior air and inject it into the cabin so you might have to carry air tanks to replace leaked air. And then there's radiation, but never mind that. Apart from that, seems like it might actually work.