The cartridges of conventional ball point pens are open to permit ink to be fed to the point. The secret behind the Fisher Space Pen lies in the unique design characteristics of the ink and the high manufacturing tolerances of the ball point and socket. The ink is fed to the ball point by gas pressure permitting the pen to write in any position. An additional benefit of the closed design is that it keeps the pen from drying out giving the Fisher Space Pen an estimated 100 year shelf life. 

Although renowned for the invention of the anti-gravity pen for space travelers the Fisher Space Pen also has proven track record here on earth. Due to its unique design and reputation for writing in extreme conditions the Space Pen has become the pen of choice for the United States air force, law enforcement agencies, undersea explorers, mountain climbing expeditions, ski and snowboard teams or anyone else demanding a high degree of reliability from the equipment they select. The Space Pen has even been chosen for a few less extreme "celebrity" appearances. Space Pen users know the value of owning a product that routinely performs beyond their expectations. In addition to being durable the Fisher Bullet pen is also attractive and has been displayed in the New York Museum of Modern Art - cited as an outstanding example of industrial art. 

In the 1950's there were dozens of ballpoint models, and nearly every one took a different cartridge. In 1953 Fisher invented the "Universal Refill" which could be used in most pens. It was a good seller, since stationary store owners could reduce their stock of assorted refills. 
Not content, Fisher continued to work on making a better refill. After much experimentation he perfected a refill using thixotropic ink-semisolid until the shearing action of the rolling ball liquefied it-that would flow only when needed. The cartridge was pressurized with nitrogen so that it didn't rely on gravity to make it work. It was dependable in freezing cold and desert heat. It could also write underwater and upside down. The trick was to have the ink flow when you wanted it to, and not to flow the rest of the time, a problem Fisher solved. Fisher's development couldn't have come at a more opportune time. The space race was on, and the astronauts involved in the Mercury and Gemini missions had been using pencils to take notes in space since standard ball points did not work in zero gravity. The Fisher cartridge did work in the weightlessness of outer space and the astronauts, beginning with the October, 1968 Apollo 7 mission began using the Fisher AG-7 Space Pen and cartridge developed in 1966. 

Oh yes boys and girls, ladies & gentlmen it's here and its the penultimate gadget (don't worry I've all ready slapped myself in the head for that gag). 
The Fisher Spacepen.