The pen for astronauts! Debuting on the Apollo 7 mission in 1968, Fisher Space Pen has been on every NASA crewed space flight since and have even been utilized by the Russian and Chinese space programs, as well! Their pressurized ink cartridges were developed to write in just about any condition and on almost any surface. Underwater or over grease. In extreme temperatures (-30 to +250 F/-35 to +121 C). Upside down or floating in a gravity-free zone!