I'm aware of the Astro Pi (1, 2, 3, 4) on board the ISS, but have there been any other instances of the RPi in space (Astro or not), for example in cubesats or other spacecraft which contain a functioning Raspberry Pi? Are there any plans to do so?
As of now, it seems two cubesats AAReST and STRaND2 are two raspberry Pi based cubesats. More Info
These cubesats are yet to be launched as of this answer date. Raspberry Pi is built around BCM2835/2836/2837 broadcomm microprocessor. Arm 11 : BCM2835 ARM A53 : BCM2836/2837
Typical specs therefore are 1Ghz processor and 1GB of RAM which is almost magnitude greater than any typical computers in spacecraft. Curiosity rover has 200Mhz clocked powerpc based RAD750.
The tradeoff one has is the reduced reliability. RAM highly susceptible to bit flips and latches. Requires external coating to bear vibration loads, not every component can bear regular thermal cycling of space etc.
But the concept of reliability through redundancy is attractive and cheap, given that even spaceX uses three x86 dual core and operates via majority logic both in falcon and dragon.
Compute Module, is close to industrial grade in specs and definitely could be made LEO environment compatible after some customization. Inbuilt eMMC is nice as lot of cubesat fail due to SD card failure.
If all goes well I may add one more cubesat in this answer fully/partially powered by rpi. ;)
Edit: eMMC is nothing but a single package consisting of flash memory and controller. Basically SD card and controller into one silicon die. More Info