You all have to think that this zombie apocalypse may have 2 causes:
1) Religious one: if so, when the cosmonaut will die, he'll turn.
2) Scientific: if so, he most probably was not affected and will not turn while orbiting into the space. Yet, if his corpse will be intact (impossible) when the shuttle will crash into the world, then his corpse will reanimate.
Don't know which is more sadder..to die in a world full of reanimated corpses or to be alone in the space and see the world you once used to live in dies...