The Space Pen (also known as the Zero Gravity Pen), marketed by Fisher Space Pen Company, is a pen that uses pressurized ink cartridges and is claimed to write in zero gravity, underwater, over wet and greasy paper, at any angle, and in a very wide range of temperatures.
The Fisher Space Pen was invented by American industrialist and pen manufacturer Paul C. Fisher and is manufactured in Boulder City, Nevada, United States of America. Paul C. Fisher first patented the AG7 "anti gravity" pen in 1965. Pens claiming some or all of the same abilities have also appeared on the market from other manufacturers.
There are two prominent styles of the pen: the AG7 "Astronaut pen", a long thin retractable pen shaped like a common ballpoint, and the "Bullet pen" which is non-retractable, shorter than standard ballpoints when capped, but full size when the cap is posted on the rear for writing.
Several of the Fisher Space Pen models (the "Millennium" is one) are claimed to write for a lifetime of "average" use; however the product literature states that the pen will write exactly 30.7 miles (approximately 48.15 kilometres).
Standard Space Pen refills can be used in any pen able to take a standard Parker Pen Company ballpoint refill, using the small plastic adapter that is supplied with each refill. Fisher also makes a Space Pen-type refill that fits Cross pens, one that fits 1950s-style Papermate pens (or any pen that uses that type of refill), and a "universal" refill that fits some other ballpoint pens.
The ballpoint is made from tungsten carbide and is precisely fitted in order to avoid leaks. A sliding float separates the ink from the pressurized gas. The thixotropic ink in the hermetically sealed and pressurized reservoir is claimed to write for three times longer than a standard ballpoint pen. The pen can write at altitudes up to 12,500 feet (3810 m). The ink is forced out by compressed nitrogen at a pressure of nearly 35 psi (240 kPa). Operating temperatures range from −30 to 250 °F (−35 to 120 °C). The pen has an estimated shelf life of 100 years.
Uses in the U.S. and Russian space programs 
A common urban legend states that, faced with the fact that ball-point pens will not write in zero-gravity, NASA spent a large amount of money to develop a pen that would write in the conditions experienced during spaceflight (the result purportedly being the Fisher Space Pen), while the Soviet Union took the simpler (and cheaper) route of just using pencils.
Russian cosmonauts used pencils, and grease pencils on plastic slates until also adopting a space pen in 1969 with a purchase of 100 units for use on all future missions. NASA programs previously used pencils (for example a 1965 order of mechanical pencils) but because of the substantial dangers that broken-off pencil tips and graphite dust pose in zero gravity to electronics and the flammable nature of the wood present in pencils, a better solution was needed. NASA never approached Paul Fisher to develop a pen, nor did Fisher receive any government funding for the pen's development. Fisher invented it independently and then, in 1965, asked NASA to try it. After extensive testing, NASA decided to use the pens in future Apollo missions. Subsequently, in 1967 it was reported that NASA purchased approximately 400 pens for $6 a piece.
See also 
- "Is it true that NASA spent thousands of dollars developing a space pen, whereas the Russians just took a pencil?". physics.org. Retrieved 2 November 2012.
- Steve Garber (2010-05-28). "The Fisher Space Pen". NASA History Division.
- Ciara Curtin (2006-12-20). "Fact or Fiction?: NASA Spent Millions to Develop a Pen that Would Write in Space, whereas the Soviet Cosmonauts Used a Pencil". Scientific American.
- "Gene Cernan's Apollo 17 Lunar Module Flown Fisher AG-7 Space Pen... (Total: 1 Items) Transportation: Space Exploration". Historical.ha.com. 2008-03-24. Retrieved 2010-09-14.
- Fisher Space Pen Co.
- The Billion Dollar Space Pen
- Legend debunked (Urban Legends Reference Pages)
- Did Biros really revolutionise writing BBC News 2006-11-23
- NASA Specification for writing instruments 1973-06
- Nasa History
- "Pen Name: Having perfected the ball-point, Paul Fisher wrote a plan to save the world", by Anthony DeBartolo, Chicago Tribune Sunday Magazine, 1991