Question

why ball pen is not used in space or why it wont works in space.​

Answer 1

because in space there is zero gravity

Answer 2

Unlike most ballpoint pens, Fisher's pen does not rely on gravity to get the ink flowing. The cartridge is instead pressurized with nitrogen at 35 pounds per square inch. This pressure pushes the ink toward the tungsten carbide ball at the pen's tip. The ink, too, differs from that of other pens.