Computer scientist Ken Shirriff programmed an Apollo Guidance Computer to mine bitcoin. This was the onboard computer developed to navigate NASA’s Apollo spacecraft and control their engines during missions to the Moon. It weighed about 70 pounds and had roughly 4 KB of RAM. This particular unit never flew in space. Its owner had bought it from a scrapyard in the 1970s after NASA discarded it. Shirriff wrote custom code to make the 1960s machine perform SHA-256, the calculation used in Bitcoin mining. One calculation took 5.15 seconds, implying approximately 10.3 seconds for Bitcoin’s double hash. At the network difficulty in 2019, he estimated that finding a new block would take, on average, roughly a million times the age of the universe. His demonstration used a block that had already been mined. The computer reproduced the calculation; and never did earn bitcoin.