HP-65 and NASA/JPL Missions

[Gene Dorr]

I thought it would be useful to summarize an answer to the direct question so folks viewing this thread would have an answer without having to refer to an external source (albeit my own).

The only manned space flight that carried an HP-65 calculator was the 1975 Apollo Soyuz Test Project (ASTP) flight. ASTP was comprised of a Soviet Soyuz spacecraft launched from Baikonur Cosmodrome in the Soviet Union, and an Apollo spacecraft launched from Kennedy Space Center in Florida. Only the Apollo spacecraft carried an HP-65. (In fact two HP-65s were carried on that Apollo flight.)

The calculations that were programmed for the HP-65, and recorded onto a set of 19 program cards, were to (1) produce solutions -- specifically time of ignition, required delta-V (change in velocity), and thrust vector (i.e. direction) -- for 3 different engine firings that were needed to achieve a rendezvous with the Soyuz spacecraft; and (2) to produce pointing angles for Apollo's steerable High-Gain Antenna so that the crew could aim it at the ATS-6 communications relay satellite.

Some sources claim that since the HP-65 was intended simply as a backup for the Apollo Guidance Compter (AGC), that it was never used because the AGC did not fail. This is a vast over-simplification. You can't be in the middle of a time-critical operation (orbital rendezvous) and suddenly switch to a backup source of solutions if your primary source fails. In fact, they used the HP-65 alongside the AGC all during the rendezvous, and compared the solutions from each all along the way. In the post-flight debriefing the crew reported that the two solutions (from the AGC and the HP-65) always agreed with very little deviation.

As for the antenna pointing function, I've been unable to find any evidence that it was actually used in flight. There were other sources for that data that may have been sufficient.

But with regard to the far more important rendezvous solutions, they were verifiably used, and proved useful -- even if only as a "proof of concept": a programmable calculator could be a useful tool in spaceflight.