Recently, I visited NASA in Houston. The gift shop was selling "official" NASA space pens. I was tempted to buy one, because they will write upside down. At my job, I sometimes need to take some notes standing up, using the wall as a "desk". But, they were more expensive than the ten cent BIC pens I use for taking notes and unlocking my bike. I got the impression that the gift shop sells quite a few of them though.