PowerPC. Cool. inconsistent though. odd. they're using a 486 in the Hubble. That's the upgrade. when it first went up, the computer was a Rockwell leftover from the Apollo program - with hardly any memory (I think less than 100kB) and complete with a couple of reel-to-reel storage devices. Oh yeah - and a mirror with the wrong shape.
All computers on space vehicles are relatively primitive. They select a processor, build an OS, and don't change it even if the launch is 4 years or more away.
The space shuttle runs on an Intel 486; this is a recent upgrade from the original 286 processor used well into the 90's.
Early space programs were usually done with no computers whatsovever (ie not even on the ground at mission control); the very first computer installed in a space vehicle was the custom-made IBM (58 pounds, 19" long) in the 1965 Gemini capsule. Astronauts were told to consult the computer but ignore it's results if they differed from manual calculations. They did just that, landing 60 miles off target; the computer's advice would have had them off target, but much closer than 60 miles.
Like many specialized or embedded uses, you don't need much in the way of fancy processor architecture, speed, or memory to make a ballistic missile land on a dime half a world away. Computationally, that is a much simpler task than running System 7 on a 10-year old Mac. The first 2 original operational computers were designed to do such calculations (one in the UK, to decipher Nazi encryption, the other, in the US, to calculate artillery trajectory) and did them well.
RAD 6000 doesn't refer to a specific chip I can find, but does point to a Radiation-Hardened embedded chip common in military applications, probably made by Motorola. That doesn't necessarily mean a PPC chip ever used in a Mac.
Control-click (to save) or click to view the PDF link if you want to know too much about it RAD-technology roadmap.