Based on what we have now, and what is in development; no super-heroes, death rays or figments of a favoured imagination - the Laws of Physics are sacrosanct.
"... the appearance of a man in t-shirt and jeans on the outside of the spacecraft is alarming, so he tends to stay inside." I repeat - The Laws of Physics are sacrosanct.
Mary-Jo and Ash begin a space-walk, but it does not last long - he sees something that did not come from Earth. Then she is stranded in space. Stuart goes to her rescue but has he got everything he needs? No navigation equipment, not even a properly constructed spacecraft - in fact not even a spacecraft; just a rocket engine and some frame-work.