You’re probably familiar with the famous “space pen” that can write at any angle — and even in zero-g conditions, of course. You’ve probably also heard about how much it cost NASA to develop, and how the Russians just used pencils.
But that’s not quite accurate. The Write Stuff explains:
NASA never asked Paul C. Fisher to produce a pen. When the astronauts began to fly, like the Russians, they used pencils, but the leads sometimes broke and became a hazard by floating in the [capsule's] atmosphere where there was no gravity. They could float into an eye or nose or cause a short in an electrical device. In addition, both the lead and the wood of the pencil could burn rapidly in the pure oxygen atmosphere. Paul Fisher realized the astronauts needed a safer and more dependable writing instrument, so in July 1965 he developed the pressurized ball pen, with its ink enclosed in a sealed, pressurized ink cartridge. Fisher sent the first samples to Dr. Robert Gilruth, Director of the Houston Space Center. The pens were all metal except for the ink, which had a flash point above 200 [degrees] C. The sample Space Pens were thoroughly tested by NASA. They passed all the tests and have been used ever since on all manned space flights, American and Russian. All research and developement costs were paid by Paul Fisher. No development costs have ever been charged to the government.
The space pen’s ink is thixotropic; it’s actually a highly viscous gel within the pen and doesn’t become fluid until released.