Marketers of the Space Pen claim that the writing implement can be used in zero gravity, upside down, underwater, over wet paper, at any angle, and in extreme temperatures. The pen, which was invented by American industrialist Paul C. Fisher, uses pressurized ink cartridges to force thixotropic ink through its tungsten carbide ballpoint. Though standard ballpoint pens can be used in space, both the American and Russian space programs use Fisher’s pen. Why is it dangerous to use pencils in space? Discuss