In my previous post I spoke about the recording of the telemetry signal from the Psyche spacecraft that I made just a few hours after launch with the Allen Telescope Array. In that post I analysed the physical aspects of the signal and the modulation and coding, but left the analysis of the telemetry frames for another post. That is the topic of this post. It will be a rather long and in-depth look at the telemetry, since I have managed to make sense of much of the structure of the data and there are several protocol layers to cover.
As a reminder from the previous post, the recording was around four hours long. During most of the first three hours, the spacecraft was slowly rotating around one of its axes, so the signal was only visible when the low-gain antenna pointed towards Earth. It was transmitting a low-rate 2 kbps signal. At some point it stopped rotating and switched to a higher rate 61.1 kbps signal. We will see important changes in the telemetry when this switch happens. Even though the high-rate signal represents only one quarter of the recording by duration, due to its 30x higher data rate, it represents most of the received telemetry by size.
On Friday, the Psyche mission launched on a Falcon Heavy from Cape Canaveral. This mission will study the metal-rich asteroid of the same name, 16 Psyche. For more details about this mission you can refer to the talk that Lindy Elkins-Tanton, the mission principal investigator, gave a month ago at GRCon23.
The launch trajectory was such that the spacecraft could be observed from the Allen Telescope Array shortly after launch. The launch was at 14:19 UTC. Spacecraft separation was at 15:21 UTC. The spacecraft then rose above the ATA 16.8 degree elevation mask in the western sky at 15:53 UTC. However, the signal was so strong that it could be received even when the spacecraft was a couple degrees below the elevation mask, so I confirmed the presence of the signal and started recording a couple minutes earlier. At this moment, the spacecraft was at a distance of 18450 km. The spacecraft continued to rise in the sky, achieving a maximum elevation of 32.9 degrees at 16:53 UTC, and setting below the elevation mask on the west at 19:22 UTC. At this moment the spacecraft was 103800 km away. The signal could still be received for a few minutes afterwards, but eventually became very weak and I stopped recording.
Since the recording started only 30 minutes after spacecraft separation, we get to see some of the events that happen very early on in the mission. Most of the observations of deep space launches that I have done with the ATA have started several hours after launch. This Twitter thread by Lindy Elkins-Tanton gives some insight about the first steps following spacecraft separation, and I will be referring to it to explain what we see in the recording.
I intend to publish the recordings in Zenodo as usual, but the platform has been upgraded recently and is showing the following message “Oct 14 12:03 UTC: We are working to resolve issues reported by users.” So far I have been unable to upload large files, but I will keep retrying and update this post when I manage.
Update 2023-10-19: Zenodo have now solved their problems and I have been able to upload the recordings. They are published in the following datasets: