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 able to write in zero gravity, underwater, over wet and greasy paper, at any angle, and in a very wide range of temperatures. Inventors The Fisher Space Pen was created by Austrian Friedrich Schächter and expanded by Erwin Rath. Paul C. Fisher invented the "thixotropic special ink". The pens were manufactured in Boulder City, Nevada. Paul C. Fisher first patented the AG7 "anti-gravity" pen in 1965. Models 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 . In contrast, the standard PR (Pressurized Refill) cartridge is rated to write over . Standard Space Pen refills can be used in any pen able to take a standard Parker-type 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. Technology 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 visco-elastic ink in the hermetically sealed and pressurized reservoir is able to write for three times longer than a standard ballpoint pen. The ink is forced out by compressed nitrogen at a pressure of nearly . Operating temperatures range from . The pen can write without the help of gravity, at any angle. The pen has an estimated shelf life of 100 years. One of the first Space Pen patents is US3285228, which was filed on 19 May 1965. Uses in the U.S. and Russian space programs An urban legend states that NASA spent a large amount of money to develop a pen that would write in space (the result purportedly being the Fisher Space Pen), while the