# Which Voyager spacecraft “mutinied”, and what really happened?

The August 2017 BBC News Science in Action podcast The Algae that Changed the Earth includes other topics, including the following:

In August and September 1977, Nasa's probes Voyager 2 and Voyager 1 were launched. Since then the two spacecraft have been exploring our Solar System and interstellar space. Exceeding all expectations, the probes have taught us so much about our planets and beyond. The Voyager mission's chief scientist, Professor Ed Stone, looks back over Voyager's highlights.

After about 10:00 in the podcast he says (rough, amateur transcription):

...and we did have sort-of a mutiny at the time when the spacecraft went off and did what its programs told it to do but not what we thought it should be doing.

And it took us several days to get things sorted out to realize that what had happened; the spacecraft is that it had been subjected to the effects of the launch vehicle which had not been taken into account in the initial software that the spacecraft had been given.

But that all worked out and we were on our way to be ready for Jupiter which was less than two years away.

## 1 Answer

It was Voyager 2 (launched before Voyager 1).

Technical details on Voyagers are surprisingly hard to find. The most detailed account I found was in Voyage to Jupiter, the official NASA history of the project.

During the first minutes of flight, there seemed to be two difficulties with the AACS.The first was a problem with one of the three stabilizing gyroscopes, but fortunately, the gyroscope began operating normally without intervention from the ground. The other problem appeared to be with one of the AACS computers; the spacecraft switched to a backup computer during the Titan burn, and initial data transmissions were incomplete. Early analysis seemed to indicate that an event during the launch itself, rather than a faulty spacecraft computer system, was the cause of the data loss. At first, on August 23, officials suspected that perhaps the spacecraft had been bumped by the rocket motor one hour after liftoff and again about seventeen hours later, when telemetry signals indicated that the spacecraft had been jolted. However, by the next day, flight engineers determined that electronic gyrations in the AACS seemed to have caused the difficulty.

After describing other problems in the cruise phase, the book goes on to say

In general, these reactions were the result of programming too much sensitivity into the spacecraft systems, resulting in panic over-reaction by the onboard computers to minor fluctuations in the environment. Ultimately,part of the programming had to be rewritten on Earth and then transmitted to the Voyagers, to calm them down so that they would ignore minor perturbations, yet still be ready to perform automatic sequences required to protect the spacecraft from major threats.

AACS = Attitude and Articulation Control System