When Americans send spacecraft to explore space, scientists have discovered that they can not use ink pens there. This is due to the lack of gravity in space. The ink inside the pen can not get out through the end hole to flow on paper.
To solve this problem, NASA scientists have made many experiments to make a pen that they can write in the absence of gravity and in unstable weather conditions even at low temperatures below zero.
After these experiments and research, which lasted several years, they finally succeeded in making them the pen required after the cost of huge sums of millions of dollars. When the Russians faced this problem they decided to use pencils.