Thixotropic ink

It all began in the 1960s, at a time when the space race between the world's superpowers, the USA and the then USSR, was at its peak. At that time, space agencies faced enormous problems, among others, with what writing instruments to equip their mission crews on their journeys of exploration. Given the sterile environment on board spaceships, ballpoint pens would be the ideal solution; however, there is a problem with their functionality. To write, they need the force of Earth's gravity, which naturally causes the ink to flow onto the ball while writing. In a weightless state, they simply do not work.

Another major problem was the potential leakage of thin ink from an open or damaged cartridge into the surroundings. For these reasons, astronauts in space had no choice but to use ordinary pencils (Mercury and Gemini missions). Yes, seemingly the simplest and cheapest solution. However, this posed another significant risk with the potential for catastrophic consequences. When using a pencil, there was a danger of breaking the fragile lead and its subsequent uncontrolled floating inside the vessel. If later this stray, electrically conductive piece of lead entered the sensitive instruments' internals, it could cause a short circuit or mechanically immobilize some of their moving parts.

Solving this problem was taken up by Paul C. Fisher and his company Fisher Pen Company in Boulder City (Nevada, USA), who had been involved in the development of ballpoint pens since 1945. So in 1965, after investing one million dollars (!), he presented his patented pen, named AG7 (Anti-Gravity 7) Astronaut Space Pen, to the American National Aeronautics and Space Administration (NASA).

The main advantage of this highly reliable pen with a metal body was its hermetically sealed cartridge with an internal space divided into two chambers by a movable piston. The lower chamber contained a special, highly elastic thixotropic ink (in a solid state when at rest, liquefying at the point of the ball's movement while writing). The chamber above the piston was pressurized with nitrogen at 343 kPa. Thanks to this unique design, the pen was not dependent on Earth's gravity, could write in a weightless state, in any position, on most surfaces, underwater, in oil, and at extreme temperatures from -35 to 120 °C. Moreover, in the event of mechanical damage to the cartridge casing, the thixotropic ink did not freely leak into the surrounding environment but stayed adhered around the cartridge.

In 1967, after two years of thorough testing, NASA decided to incorporate the Fisher Space Pen into its space program. It began its cooperation with the Fisher Pen Company by purchasing the first four hundred units of these pens for the Apollo project, with the Fisher AG7 Space Pen being used for the first time during the Apollo 7 mission, which took place from October 11 to 22, 1968.

Soon, in February 1969, the then Soviet Union took advantage of cooperation with the USA in the Apollo - Soyuz project, purchasing the first one hundred pens and a thousand replacement cartridges for its cosmonauts. Since then, Fisher Space Pens have been part of every manned space mission's inventory, including the most famous one - Apollo 11's first landing of a human on the Moon (July 20, 1969).

As of now, there is no doubt that Fisher Space Pens remain the best pens under the Sun, primarily due to the use of thixotropic ink, which, thanks to its specific properties, practically has no alternative.