>>11400661You really can't, the issue for animals with blood comes down to it decomposing when there is no air pressure. Gasses bubble out of the mix, certain properties are changed, etc. You might be able to engineer an organism to be partly resistant, ie doesn't pass out in a few seconds, but it wouldn't be what you're thinking. It'd be more like "oh shit get back inside everything is pain".
Pressure suits specifically aren't the only way, they're just easy to build. A human could survive in space with a properly built compression suit, facemask, and a sealed portion at the groin. It just replaces the compression causes by air with mechanical compression. The difficulty comes in building one people can move in.
