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I think I know who was in the spacesuit.
This is my best guess and will probably change a kajillion times before we know. Please don't laugh at my "Eureka!" moment if you've already figured it out; sometimes I'm slow. Feel free to poke holes in my theory if I'm missing something.
( Snipped for possible spoilers. I expect any comments will also be filled with spoilers. If you don't want to be spoilered, don't read. )