NASA astronaut Greg Chamitoff takes center stage in this amazing spacewalk photo taken by crewmate Mike Fincke (visible in the reflection on Chamitoff's spacesuit visor) using a fish-eye lens and digital camera during a May 27, 2011 excursion outside the International Space Station.

Astronauts who have gone on space walks consistently speak of space's extraordinarily peculiar odor.

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. [Video: What Does the Space Station Smell Like]

But astronauts don't dislike the sharp smell of space, necessarily. NASA astronaut Don Pettit described it this way after a mission back in 2003:

"It is hard to describe this smell; it is definitely not the olfactory equivalent to describing the palette sensations of some new food as 'tastes like chicken.' The best description I can come up with is metallic; a rather pleasant sweet metallic sensation. It reminded me of my college summers where I labored for many hours with an arc welding torch repairing heavy equipment for a small logging outfit. It reminded me of pleasant sweet smelling welding fumes. That is the smell of space."

The interior of the International Space Station smells a little more mundane. Pettit, who recently returned from a second six-month-long mission on the ISS, told SPACE.com, "[The ISS] smells like half machine-shop-engine-room-laboratory, and then when you're cooking dinner and you rip open a pouch of stew or something, you can smell a little roast beef."

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