The famed
Astronaut Pen is manufactured by the Fisher Space Pen Company, and was invented independent of the space program. The pen works because it relies on
gas pressure to provide
ink to the ball point rather than
gravity. Because of its
clever design, the pen writes at all angles in
extreme cold and heat,
underwater, and in
zero gravity. The closed design of the pen also gives it a estimated
shelf-life of 100 years, but just in case, they provide
refills in ten different
colors.
The ink cartridge is pressurized with nitrogen gas hermetically sealed at nearly 50 PSI, features a tungsten carbide ball point in a stainless steel socket, and is filled with a thixotropic ink which is liquified by the shearing action of the ball point.
The astronauts from the Mercury and Gemini projects had been using pencils because a suitable pen had not yet been invented. After experimenting with the Fisher pen, NASA chose the design for use in the space program. Beginning with the Apollo 7 mission, Fisher Astronaut Pens have been on every manned U.S. space mission, and were also used by cosmonauts on Mir, while it was still functioning.
This dispels another piece of Internet humor:
During the heat of the space race in the 1960s, the U.S. National Aeronautics and Space Administration decided it needed a ball point pen to write in the zero gravity confines of its space capsules. After considerable research and development, the Astronaut Pen was developed at a cost of approximately $1 million U.S. The pen worked and also enjoyed some modest success as a novelty item back here on earth.
The Soviet Union, faced with the same problem, used a pencil.