[imjoshdean]

Yeah, it's dead simple, google "space pen cartridge" and you'll see. Also, I've not had the pen leave stains when using it.

[Luc]

omegant seems to think you're refilling the cartridge, rather than replacing it.

[omegant]

Yep that was my initial impression, I checked the site and the cartridges are quite inexpensive. I'll buy one to try.