There’s a popular myth that NASA spent “millions” of dollars developing a pen for astronauts to use in the weightless environment of a space ship — while their sensible Russian counterparts were happy to use the low-tech pencil.  Alas, for all its appeal and plausibility, this is not true.  Initially, astronauts and cosmonauts were both equipped with pencils, but there were problems: if a piece of lead broke off, for example, it could float into someone’s eye or nose.  A pen was needed, one that would defy gravity, write in extreme heat or cold, and be leak proof: blobs of ink floating around the cabin would be more perilous than a stray pencil lead.  A long-time pen maker named Paul C. Fisher patented the “space pen” in 1965 (which he had developed at the cost of a million dollars, at the request of but not under the auspices of NASA.)  NASA bought four hundred of them at $6 each, and, after a couple of years of testing, the pens were put into space.

That is from Kitty Burns Florey, Script & Scribble: The Rise and Fall of Handwriting.Pen and pencil myths — Marginal Revolution.