The Space Pen (also known as the Zero Gravity Pen), marketed by Fisher Space Pen Co., is a pen that uses pressurised ink cartridges and is claimed to write in zero gravity, upside down, underwater, over wet and greasy paper, at any angle, and in extreme temperature ranges.
The Fisher Space Pen was invented by American industrialist and pen manufacturer Paul C. Fisher and is manufactured in Boulder City, Nevada, USA. Pens claiming some or all of the same abilities have also appeared on the market from other manufacturers.
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 pressurised 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 pounds per square inch (340 kPa). Operating temperatures range from -30 to 250 degrees Fahrenheit (-35 to 120 degrees Celsius).