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. Not content, Fisher continued experimentation until he perfected a refill that would flow only when needed. Fisher's development couldn't have come at a more opportune time. The space race was on, and the Fisher cartridge worked in the weightlessness of outer space. Beginning with the October, 1968 Apollo 7 mission, astronauts began using the Fisher AG-7 Space Pen in orbit.