I really liked my Fisher Space Pen, the key attribute being its size: it fit comfortably in the side pocket of my jeans. After I lost it, I really liked my second Fisher Space Pen too. After I lost that one, I thought for a minute before buying another. Did I really care about anything but the size? Had I even once used my Space Pen to write underwater or in the cold vacuum of space? No. To the tune of $15 a pop, did I want to go $45 in the hole to Fisher? No. So here's what I did:
Got myself a dozen of these Bic pens (something like $0.35 each):
Took one apart and cut off around two-thirds of the barrel (cut through the "d" in the "med USA" part of the label):
Lined up the ink sleeve with the remaining part of the barrel to see how much I'd have to remove, then snipped it off (even cutting through the inky part, I've never had any leakage - YMMV):
Assembled, it's as small as a Space Pen, and not as smooth and shiny, so it's less likely to slide out of your pocket (and if it does, who cares?):
With the cap on the back it's long enough to hold comfortably, even with big hands:
I've gone through four or five of these, and have never had a leak. Even though you lose some ink when you trim 'em down, they still last for a good long time.
True, the next time I'm on a top secret mission and my nemesis tries to kill me slowly in a vacuum chamber and my only hope is to write a note on a piece of paper and hold it up to the plexiglass telling my trusty sidekick how to turn off the machine I'll be completely hosed, but I'm willing to take my chances.