Linux has become the operating system of choice for NASA's laptops when it comes to the International Space Station. The ISS has been using Windows XP, though the majority of its ground-based support systems on Earth are reportedly Linux-based.
Specifically, the ISS astronauts will be using computers running Debian 6. Earlier, some of the on-board computers had been using Scientific Linux, a Red Hat Enterprise Linux (RHEL) clone. While not the newest version of Debian, Debian 7 has just been released, Debian is nothing if not well-tested and reliable.
While Linux has been used on the ISS ever since its launch (PDF link) and for NASA ground operations almost since the day Linus Torvalds created it, it hasn't seen that much use on PCs in space. "Things really clicked," said Chuvala in an interview, "after we came to understand how Linux views the world, the interconnectedness of how one thing affects another. You need that worldview. I have quite a bit of Linux experience, but to see others who were really getting it, that was exciting."
The laptops that were upgraded belong to the station’s OpsLAN. The crew use the OpsLAN to perform day-to-day activities, such as viewing stock inventory, controlling scientific experiments, or checking their current location. Presumably the laptops used to run bespoke Win32 apps on Windows XP, and now those apps have been re-written to work on Linux — hopefully they’re not being emulated in WINE. To get the astronauts and cosmonauts up to speed, they will be trained by the Linux Foundation.
Not only are the computers being witched to linux, but the first humanoid robot in space, R2, is also reportedly powered by Linux.