Mining Bitcoin on the Apollo Guidance Computer

Alasdair Allan
3 min readJul 9, 2019

In the lead up to the 50th anniversary of the Apollo 11 landing this year, we’ve seen a growing interest in the artefacts and technology used during the lunar exploration programme, including the well publicised collaboration between Adam Savage and the Tested team, and the National Air and Space Museum to build a life-sized replica of the Apollo egress hatch.

Other retro-computing enthusiasts are fascinated with the computing of the era, including the Apollo Guidance Computer (AGC), with one team working to restore an AGC that was never flown. Discarded by NASA after vacuum testing of the lunar module (LTA-8) ahead of crewed flights, this computer is now the worlds only working Apollo Guidance Computer.

Of course, once you have a working Apollo Guidance Computer, obviously the next thing you need to do is getting it mining Bitcoin?

Output from the Bitcoin mining program, displayed on the Display/Keyboard (DSKY). The display shows part of the Bitcoin hash in octal. The DSKY is a modern replica, hooked up to the genuine AGC. (📷: Ken Shirriff)

“The Apollo Guidance Computer took 5.15 seconds for one SHA-256 hash. Since Bitcoin uses a double-hash, this results in a hash rate of 10.3 seconds per Bitcoin hash. Currently, the Bitcoin network is performing about 65 EH/s (65 quintillion hashes per second). At this difficulty, it would take the AGC 4×10²³ seconds on average to find a block. Since the universe is only 4.3×10¹⁷ seconds old, it would take the AGC about a billion times the age of the universe to successfully mine a block.”—Ken Shirriff

The restoration team, consisting of Ken Shirriff, Mike Stewart, Carl Claunch, Marc Verdiell, has a history with both with retro-computing, and the Apollo Guidance Computer. Ken Shirriff is well known for restoring an IBM 1401 mainframe—which also dates from the 1960s—and using it to mine Bitcoin. While Mike Stewart is the creator of an FPGA simulation of the Apollo Guidance Computer, Carl Claunch hand built a replica of the Apollo DSKY, and Marc Verdiell is well known for his work on vintage teletypes.

The Apollo Guidance Computer powered up. The cover is off, showing the computer’s purple wire-wrap wiring of the backplane. We built the interfaces that are plugged into the front of the computer. At the back, vintage core rope simulator boxes are visible in the core rope slots. (📷: Ken Shirriff)

It’s also not the team’s first experiment with ‘absurd’ Bitcoin mining, with Shirriff having mined Bitcoin by hand using pencil and paper with a hash rate of 0.67 hashes per day.

Bitcoin mining on the Apollo Guidance Computer. (📹: Ken Shirriff)

Now only a couple of weeks away on July 20th , the 50th anniversary of Apollo 11 landing is surrounded by any number of special events. However with the date fast approaching it’s really great to see other work, including the creation of a virtual Apollo Guidance Computer, that’s been done around the programme over the last decade or more starting to get a lot more publicity.

Apollo Guidance Computer emulation running on a Palm Centro back in 2009. (📹: Dean Koska)

If you want to learn more about the Apollo Guidance Computer restoration project Ken Shirriff’s blog has a lot more, including details of the AGC’s core memory and the woven core rope permanent memory. You can read about the Virtual AGC on its the project site, and download it from the repo, or if that’s not going to be enough you could always build your own working replica of the Apollo Guidance Computer, and pick up a DSKY on Kickstarter.