Together, they make up the Spaceborne Computer, which operates on the open-source Linux system and has supercomputer processing power.
They were sent up to see how durable they would be in space with minimum specialist treatment.
After 530 days, they are still working.
Their return flight was postponed indefinitely, after a Russian rocket fail in October 2018.
And HP senior content architect Adrian Kasbergen said they may return in June 2019 if there was space on a flight “but right now they haven’t got a ticket”.
HP is working with Nasa and Elon Musk’s Space X to be “computer-ready” for the first Mars flight, estimated to take place in about 2030.