In the 1950’s there were dozens of ballpoint models, and nearly every one took a different cartridge. In 1953 Paul Fisher invented the “Universal Refill” which could be used in most pens. Not content, Paul continued to work on making a better refill. After much experimentation he perfected a pressurized refill that writes in freezing cold, desert heat, underwater and upside down. The Fisher cartridge works 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.