NASA astronaut Lisa Nowak lifted off from Kennedy Space Center aboard space shuttle Discovery last July 4. Like all shuttle astronauts, she was wearing space diapers – in NASA speak, Maximum Absorbency Garments, or MAGs.

MAGs don’t generally get much attention, but this week they ended up in bizarre headlines after Nowak drove 900 miles from Houston to Orlando wearing her diapers – according to police, so she wouldn’t waste any time at rest stops on her quest to hunt down Colleen Shipman, an employee at an Air Force base near the space center.

Nowak faces kidnapping, attempted murder and other charges related to an apparent love triangle involving Shipman and another astronaut.

Judging from Internet references, the MAG has suddenly risen to great prominence – though there’s little mention of it on NASA’s own Web site. (The space agency didn’t immediately return calls seeking comment about the diapers.)

So, how are these “absorbency garments” used? Here’s a primer.

Before the MAG

On early space flights, astronauts had to wear special equipment called a “Urine Collection and Transfer Assembly,” or UCTA, which proved very cumbersome. NASA’s attempts to deal with waste were extensively covered by Tom Wolfe in his classic account of space travel, “The Right Stuff.”

If you want to see it for yourself, moon astronaut Alan Shepard’s UCTA can be seen in the London Space Museum.

Liftoff pressures

MAGs are used during takeoff, space walks and re-entry.

They are especially needed for takeoff, when astronauts can experience long delays while seated with their head back and their legs face upward. Fluid in the body rolls upward, giving the brain the sensation that the chest area is being flooded. This leads to an increased need to relieve oneself.

All astronauts feel the need to urinate before takeoff but taking an actual restroom break is impossible. NASA estimates that astronauts often expel about a liter of urine while in the crouched, legs up position. Many astronauts try to dehydrate a day before takeoff, but the kidneys still produce a milliliter of urine a minute.

When you add the nervousness and excitement of takeoff, the MAG becomes essential.

A 2000 study found that the MAG can absorb up to 2 liters of liquid.

In flight

As soon as the spacecraft reaches orbit, astronauts remove the MAGs and their familiar orange suits and put on regular clothes. The need to urinate greatly decreases.

Spacewalks

Astronauts conducting spacewalks must also wear the MAGs as the walks last five to eight hours, with no opportunity to climb out of the heavy space suit for a restroom break. In online discussions, NASA trainer Lou Carfagno has said that his team packs two MAGs per space walk.

Astronauts put on the MAGs before entering the hatch that leads to the payload bay.

Back on Earth

In creating the MAG, NASA developed sodium polyacrylate, a super absorbent polymer that is now used in baby diapers as well as deodorants.

It’s also used in gardening during droughts, as it absorbs water and keeps it stored in the soil.

Meanwhile, more technological advances in astronaut diapers are expected to emerge as NASA heads for its next big mission – a trip to Mars.