– Xochielt Sanchez
Answer by Clayton C. Anderson:
One of my favorite things to do these days is to "piggy-back" on the wonderful –and always technically sound– Quora answers of NASA's Robert Frost. While he gives you the clear and concise "mechanical, text-book" type answer to your questions, I can jump in with some real life experiences. Together, it is my hope that our "tag team" efforts give you some insight that you may not have expected, but can honestly appreciate and enjoy. Hopefully, we are all learning something together!
As a two-time space flier with over 167 days in space (all but 8 on the International Space Station (ISS)), I have definite personal knowledge of the odors existing inside her anodized aluminum hull.
The systems mentioned by Robert typically perform flawlessly, with the crew performing routine maintenance on those systems per the schedule provided by the ground. This, in and of itself, gives us a significantly "odor-free" environment on the ISS. That's not to say we are without smells however. Our standard atmosphere, composed of the very same percentages of constituent gases that we have here on earth, is regulated to 14.7 psi and gives us a shirt-sleeved environment maintaining about 72 degrees F, 55% humidity, with a slight breeze out of the south!
Oleg Kotov, my Expedition 15 Russian crewmate and our Soyuz Commander, liked to stash his used workout clothes above the forward facing FGB (Functional Cargo Block, Russian Module) hatch. This was not my favorite choice for the stowage of sweaty workout gear as there was not a very good chance that they would dry out effectively. I chose to put my nasty shorts/socks/t-shirt onto a handrail in the US segment's Node 1 module. This handrail was near an A/C vent, meaning fresh, cold air would blow across my sweaty laundry for many hours until I donned them –dry as a bone– the next day. Decreasing their ability to generate any "locker-room" odors, that special placement also allowed for our environmental systems to easily soak up my sweat and turn it into drinking water for later!
Food odors were also present, but they didn't seem unusually overpowering to me.
Eating a fish dish often produced the most pungent odor, especially the US version of seafood gumbo. It might take a couple of hours to "purge" that smell from the airflow of the ISS. On shuttle missions, many commanders outlawed the eating of seafood gumbo due to its distinctive, and disliked, smell.
And don't worry too much about the stink from the toilets. The airflow systems there (especially the US segment… not so much for the Russian side) were very effective (the shuttles had the absolute best system for containing poop odors!), pulling the stench quickly and completely into the bowels (from one set to another!) of the ISS where they were absorbed efficiently by filters.
Finally, there is the "smell of space." Oft mentioned by astronauts, in answering insightful questions from folks like you, the smell of space is somewhat hard to describe. Ever distinct –I would know it instantly if I smelled it– it has been likened to smells associated with welding or burning of ozone (now who the heck really knows what that smells like?!). Most noticeable following a spacewalk, when crews and their equipment returned to the inside of the ISS, I remember being able to smell traces of this unique scent for several days following an excursion into the unforgiving vacuum of space.
Keep lookin' up! And thanks to Robert Frost, for his continued, insightful answers.