The next time you see a picture or broadcast of astronauts in space, take a look at their wrists. Chances are good that you'll see not one, but two, or even three wristwatches. Astronauts have a lot to keep track of in space.
Astronauts have a choice of four watches that are certified to fly in space, says Stephanie Walker. Stephanie Walker is a subsystem manager for flight crew equipment at Johnson Space Center. These watches can be purchased at retail stores. "The certification process assures that they can perform and not self-destruct in the vacuum of space. With pressure variances and temperature extremes, watch components may expand, rupture, or crack, causing a potential hazard to the crew." Many materials are safe on Earth, but in space they may emit gases. These gases can contaminate the space atmosphere. This would cause a strain on the air recycling and purification systems.
"The old standby watch is the Omega® Speed Master watch," says Walker. Omega was made famous by Apollo astronauts as they conducted space walks. It was first used in space by Walter Schirra when he orbited the Earth six times in the Sigma 7 spacecraft in 1962. "It's a constant favorite even though it has a standard face with hands instead of a digital readout. It's basic and simple, and many pilots and commanders prefer it because they can time their maneuvers accurately with it."
The Omega X33 Chronograph is a more sophisticated watch. It has analog and digital displays, and several timers. The Casio® G-Shock features a digital face and several timers. This is helpful when working on precise projects.
The new watch for astronauts is the Timex® Ironman. This cutting-edge timepiece sells for less than $100. It has a light-emitting diode (LED) port to synchronize up to 10 alarms to the calendar of a personal computer, stores 38 telephone numbers, identifies messages, displays the time in two different time zones, and comes close to serving as a wrist computer, Walker says.
An astronaut can even request to wear a personal watch from home. It will be logged in as crew member personal property. However, it cannot be worn during space walks or launches. "Personal watches can't be worn in the launch suit," Walker says, "because the suit is designed to automatically pressurize in the event of an emergency. That pressurization may cause the watch to rupture.
Wearing several watches helps astronauts with priorities and some experiments that require precise timing. The Shuttle is on Central Time, while the ISS time is measured in Greenwich Mean Time. At the same time, the astronauts' families at home are on various local times. Several watches help keep track of all the different time zones.
There are other watch-like devices worn that reflect the work being done on a particular experiment or project. The Actilight watch, for example, measures light intensity, body movement, and sleep quality.
Unless it's a personal watch brought from home, all NASA-issued watches are government property. They must be turned in once astronauts return to Earth. Astronauts are permitted to check the watches out before launch. They take them home to familiarize themselves with how the watch works or to program data into the memory.
"Once you know what to look for, it's fun to notice how astronauts use their watches, like when they walk out to the launch pad, for instance," Walker says. "If you see an astronaut with a white band on the wrist area, that means he or she is wearing a watch. That wristband protects the launch suit from being scuffed by the watch. And, astronauts who do wear a watch on the outside of the launch suit need to use a band extender; otherwise, the watch would never fasten around that thick, bulky suit."