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 precision 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.
