They can’t smell it while they’re actually bobbing in it, because the interiors of their space suits just smell plastic-y. But upon stepping back into the space station and removing their helmets, they get a strong, distinctive whiff of the final frontier. The odor clings to their suit, helmet, gloves and tools.
Fugitives from the near-vacuum — probably atomic oxygen, among other things — the clinging particles have the acrid aroma of seared steak, hot metal and welding fumes. Steven Pearce, a chemist hired by NASA to recreate the space odor on Earth for astronaut training purposes, said the metallic aspect of the scent may come from high-energy vibrations of ions.
“It’s like something I haven’t ever smelled before, but I’ll never forget it,” NASA astronaut Kevin Ford said from orbit in 2009. [Space Sights and Smells Surprise Rookie Astronauts]
But astronauts don’t dislike the sharp smell of space, necessarily. After a 2003 mission, astronaut Don Pettit described it this way on a NASA blog:
“It is hard to describe this smell; it is definitely not the olfactory equivalent to describing the palette sensations.