Will a Ballpoint Pen Work in Space?
The launch of the SpaceX Falcon 9 on May 30, 2020, helped to renew interest across America for space exploration. This spectacular event has generated a lot of important internet searches like "how do astronauts go to the bathroom in space" and "will a ballpoint pen work in space?" I won't elaborate on the first question. But, the answer to the second question is a resounding "maybe." Why? Ballpoint pens, even beautiful, handmade ballpoint pens, are designed to work under the influence of something rather lacking in space--gravity! But, a second factor is also at work inside the pen.
So, how does a ballpoint pen work? When you're holding a pen normally with the tip down, gravity and capillary action deliver the ink to the tip and on to the paper. In capillary action, molecules in liquids are strongly attracted to solid surfaces as well as each other creating a "pull" along the liquid. This pull can be seen in action even against the force of gravity (for a short distance) by dipping a strip of paper towel vertically into water. In a pen, the liquid ink "pulls" itself along through this molecule to molecule attraction along the solid surfaces of the ink cartridge. However, just like the paper towel, when you're trying to write upside down in bed, capillary action can't overcome gravity forever and your pen stops working. Returning the pen to its normal position, ink gets delivered with a gravity assist to the tip where it encounters a small metal ball made usually of steel, brass, or perhaps tungsten carbide. When the metal ball rolls across the paper, ink is continually delivered off the ball to the paper in a measured way. If you've ever used a deodorant (of course you have, I mean a "roll-on"), the delivery system is kind of like that.