Short for Random Access Memory. This is the type of memory people most often think about when it comes to computers. It’s fast and systems tend to have a lot of it so they can do everything from add numbers together to store files. The downside is that it’s volatile, which means that when the power goes out, it loses everything it was storing.

Short for “Real-Time”.

In the software world, this term implies “a lot”. Your hardware, operating system, and flight software all have to be configured and written in a way that minimizes the delay between action and response. It’s non-trivial to get right and maintain because it usually means a lot of the protections of systems offered by Windows and many versions of Linux are removed, giving you more control over the details. Like they say, “With more power comes more responsibility.” But if you need super fast responses, it’s the way to go.

Short for “Real-Time Operating System”. A real-time operating system prioritizes running actions at precise times. This means, for instance, that high-priority events can interrupt low-priority events “instantly”. The supermajority of spacecraft that have an operating system use a real-time version because even milliseconds count when you’re flying 8 km/s. (One millisecond is 8 km of distance.)

For Core Flight Software, real-time options include VxWorks, RTEMS, and POSIX systems. FreeRTOS has also been shown to work. While Core Flight Software runs great on Linux, Linux isn’t real-time by default. However, you can make modifications to it to make it mostly real-time and, in the summer of 2024, they announced they’re working to improve their performance in this area.