HP-65 and NASA/JPL Missions

[Matt Agajanian]

Hi all.

What types of calculations were the 65 used for in the missions the HP-65 was brought onboard?

[RMollov]

what happens if I hit enter twice?

[Steve Simpkin]

(09-08-2022 09:49 PM)Matt Agajanian Wrote:  Hi all.
What types of calculations were the 65 used for in the missions the HP-65 was brought onboard?

I believe it was only used on the 1975 Apollo-Soyuz (ASTP) flight.
The following post by Gene Dorr has more information on how it was used.
https://www.hpmuseum.org/forum/thread-17...#pid149149

[Matt Agajanian]

(09-09-2022 06:54 AM)Steve Simpkin Wrote:  

(09-08-2022 09:49 PM)Matt Agajanian Wrote:  Hi all.
What types of calculations were the 65 used for in the missions the HP-65 was brought onboard?

I believe it was only used on the 1975 Apollo-Soyuz (ASTP) flight.
The following post by Gene Dorr has more information on how it was used.
https://www.hpmuseum.org/forum/thread-17...#pid149149

Thanks for the article with further details. Much appreciated.

[Maximilian Hohmann]

Hello,

one nitpicking addition maybe: The thread title states NASA/JPL. JPL was only involved in unmanned missions (https://www.jpl.nasa.gov/who-we-are/history). But I am convinced that JPL scientists and engineers were among the first to receive HP-65 calculators when these were released! But they probably never reached a higher altitude than the shirt pocket of a upright standing scientist.

Regards
Max

[Matt Agajanian]

Quite an informative nitpick. Thanks!

(09-10-2022 10:02 AM)Maximilian Hohmann Wrote:  Hello,

one nitpicking addition maybe: The thread title states NASA/JPL. JPL was only involved in unmanned missions (https://www.jpl.nasa.gov/who-we-are/history). But I am convinced that JPL scientists and engineers were among the first to receive HP-65 calculators when these were released! But they probably never reached a higher altitude than the shirt pocket of a upright standing scientist.

Regards
Max

[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.

[Maximilian Hohmann]

Hello!

(09-10-2022 09:12 PM)Gene Dorr Wrote:  ...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. ...

Don't forget that there was always a backup (or main, depending on the point of view) source of solutions during the Apollo missions: Ground control. The orbital rendezvous manoeuvers of the Mercury program and were flown with ground control guidance alone, Gemini had a rather simple onboard computer to assist.

And all the real critical rendezvous manoeuvers of the Apollo program, especially some of those in the lunar orbit, were flown with the Apollo Guidance Computers alone and no backup at all. So as much as we calculator afficionados would like it, the pocket calculator was never an essential piece of kit during these flights.

Regards
Max

[Gene Dorr]

Max,

Yes, you are absolutely correct, and I myself oversimplified the situation. The solutions generated by the RTCC (Real-Time Computer Complex at Houston) were in fact the main source of solutions for rendezvous.

Two nits: (1) there was no rendezvous during the Mercury program; (2) there were always backups, even if that backup was a paper chart.

I certainly never intended to portray the HP-65 as a critical component; I just wanted to refute a commonly repeated misconception that it was carried and never used. Its role was certainly nothing more than a cameo, but it was at least that.