For astronauts, cranking out physics equations to calculate spacecraft trajectories and withstanding the bone-jarring forces of a rocket launch are a snap. But learning how to use the space shuttle's toilet? That's tricky.
To that end, NASA has a specially designed training room at the Johnson Space Center in Houston where astronauts can carefully hone their "technique" before departing on their trip to weightless orbit.
Practice, practice, practice
For NASA astronauts, there are actually two space shuttle toilet stations in the training room a positional trainer (for practice) and a functional trainer (which flushes).
The positional trainer is not a working toilet, but is otherwise an exact replica of the toilet on the space shuttle. The opening in the seat is just four inches wide. (Standard, earth-bound toilets have openings measuring 12 or 18 inches.)
And that's not all. There's a small camera inside just under the rim of the opening and the feed from the camera runs to a monitor just a few feet in front of the seat. Sitting here, space-flyers can make sure that their bodies are positioned so that solid waste will fall through the seat's small opening.
"Alignment is important," said Scott Weinstein, a crew habitability trainer at NASA, as he explained the contraption during a NASA TV broadcast. "If they're not confident that they have good alignment," he said, astronauts can sit down on the seat, flip on the camera, and check to see if they've got it.
When space-flyers have mastered the proper alignment, they can move to functional trainer. This is a working toilet, equipped with the same airflow vents used on the space shuttle. Here, astronauts practice how to eliminate both urine and solid waste.
How the space toilet works
On the shuttle, urine is handled differently than solid waste, so it doesn't go through the 4-inch opening. Instead, a long hose with suction power attaches beside the seat, and each astronaut attaches her or her own funnel for urination to this hose.
Funnels are different for men and women.
Women need to place the top of their funnels directly against their bodies, so the sides of the female funnels need to be vented so that air can flow in when the suction is turned on, Weinstein explained. And women can choose among three funnels with differently shaped tops there are two funnels with oval-shaped tops and one with a circle-shaped top.
Male funnels are simpler. They only come in one shape the top is circular and they do not have venting.
"For men, we do not want them... docking to the funnel," said Weinstein, so male funnels do not need venting at the top to let in air.
Lastly, for paper waste, a separate suction hose on the side of the toilet can be fitted with a larger cup and lined with a plastic bag.
Straps on the foot rest can help to hold an astronaut in place, and there are two thigh restraints on the sides of the toilet that can be swung over the top of the legs to help a person stay down on the toilet. But not everyone uses them.
Before the most recent Atlantis mission , astronauts gathered in the room and compared their techniques for staying in position when they are weightless.
"I stick my hands on the roof," said astronaut Piers Sellers, pressing his hands palm-up over his head.
The thigh restraints are helpful as handles for getting in and out of the toilet, said astronaut Steve Bowen, but he also uses the low roof over the toilet to stay in position.
"You know what I think of? I think of Peter Fonda in "Easy Rider" riding a chopper," astronaut Michael Massimino said of his preferred space toilet position, holding his arms up to grip the handles of an imaginary motorcycle. "That's the right position for me."