Decoding ArgoMoon

ArgoMoon is one of the ten cubesats that were launched in the Artemis I mission. It was built by the Italian private company Argotec, and its main mission was to image the ICPS after the separation of Orion, and while the other cubesats were deployed.

In 2022-11-16, about seven hours after launch, I used two antennas from the Allen Telescope Array to record telemetry from the Orion vehicle and some of the cubesats. Since then, I have been posting regularly as I analyze these recordings and publish the data to Zenodo. In this post I will look at two recordings of the X-band telemetry signal of ArgoMoon at 8475 MHz. In the two recordings, different modulation and data rate is used.

The recordings are available in the dataset Recording of Artemis I ArgoMoon with the Allen Telescope Array on 2022-11-16 in Zenodo.

Decoding EQUULEUS

Here is a new post in my Artemis I series. EQUULEUS (called EQUL by the DSN) is one of the ten cubesats launched in the Artemis I mission. It is a 6U spacecraft developed by JAXA and University of Tokio. Its mission is to study the Earth’s plasmasphere and to demonstrate low-thrust trajectories in the Earth-Moon region using its water thrusters. The spacecraft communications are supported mainly by the Japanese Usuada Deep Space Center, but JPL’s Deep Space Network also collaborates.

I did an observation of the Orion vehicle and some of the cubesats with two antennas from the Allen Telescope Array some seven hours after launch. As part of this observation, I made a 10 minute recording of the X-band telemetry signal of EQUULEUS as it was in communications with the DSN station at Goldstone. I have published the recording in the Zenodo dataset Recording of Artemis I EQUULEUS with the Allen Telescope Array on 2022-11-16. In this post, I analyze the recording.

Decoding LunaH-Map

This post is a continuation of my Artemis I series. LunaH-Map, also called Lunar Polar Hydrogen Mapper (and called HMAP by the DSN) is one of the ten cubesats that were launched with Artemis I. It is operated by Arizona State University, and its main mission was to use a scintillation neutron detector to investigate the presence of hydrogen-rich compounds such as water around the lunar south pole. Unfortunately, it was unable to perform its required lunar orbit insertion burn. Nevertheless, the spacecraft seems to be functioning well and some technology demonstrations and tests are being done with its subsystems. With some luck, there might be opportunities for this satellite to move to lunar orbit in the future.

In my observation with the Allen Telescope Array done about seven hours after the Artemis I launch I did some recordings of the LunaH-Map X-band telemetry signal when it was in communications with the DSN grounstation at Goldstone. First I did a 10 minute recording at 15:00 UTC. Then I noticed that the spacecraft had changed its modulation, so I did a second recording at 15:16 UTC, which lasted ~7 minutes. Unfortunately, I didn’t record the moment in which the telemetry change happened.

I have published these two recordings in the dataset Recordings of Artemis I LunaH-Map with the Allen Telescope Array on 2022-11-16 in Zenodo. This post is an analysis of the signals in these recordings.

Artemis I Orion recordings published

In my previous post, I described the observations I had made with the Allen Telescope Array of the Orion vehicle and some of the cubesats of the Artemis I mission following the launch. I showed how to decode the 2 Mbaud OQPSK S-band telemetry signal from Orion using GNU Radio and aff3ct for LDPC decoding. In the post I indicated that I wanted to publish all these recordings in Zenodo, but since I had recorded a large amount of IQ data, I first needed to review the recordings and see what to publish and how to reduce the data.

I have now reviewed the recordings of the Orion 2216.5 MHz signal, and published them in the following datasets:

Additionally, I have published the decoded AOS Space Data Link telemetry frames in the dataset Decoded Artemis I Orion S-band telemetry frames recieved with the Allen Telescope Array on 2022-11-16.

Decoding the Artemis I Orion vehicle

On Wednesday 16th, the Artemis I mission was launched from Kennedy Space Center. This mission is the first (uncrewed) flight of the Orion Multi-Purpuse Crew Vehicle that will be used to return humans to the Moon in the next few years. Together with Orion, ten cubesats with missions to the Moon and beyond were also launched.

Seven hours after launch, I used two spare antennas from the Allen Telescope Array to record RF signals from Orion and some of the cubesats. By that time, the spacecraft were at a distance of 72000 km, increasing to 100000 km during the 3 hours that the observations lasted.

I have collected a lot of data on those observations, around 1.7 TB of IQ recordings. I am going to classify and reduce this data, with the goal of publishing it on Zenodo. Given the large amount of data, this will take some time. I will keep posting in this blog updates on this progress, as well as my results of the analysis of these signals.

Today’s post is about Orion’s S-band main telemetry signal, which is transmitted at 2216.5 MHz. This signal has attracted great interest in the spacecraft tracking community because back in August NASA published an RFI giving the opportunity to ground stations belonging to private companies, research institutions, amateur associations and private individuals to track the S-band signal and provide Doppler data to NASA. Some of the usual contributors of the amateur space tracking community, including Dwingeloo’s CAMRAS (see their results webpage), Scott Chapman K4KDR and Scott Tilley VE7TIL (see his Github repository) are participating in this project.

Shortly after Artemis I launched, Amateur observers in Europe, such as Paul Marsh M0EYT, the Dwingeloo 25m radiotelescope, Ferruccio Andrea IW1DTU, Roland Proesch DF3LZ, were the first to receive the signals. They were then followed by those in America.

Radiometry for DELFI-PQ, EASAT-2 and HADES

On January 13, the SpaceX Transporter-3 mission launched many small satellites into a 540 km sun-synchronous orbit. Among these satellites were DELFI-PQ, a 3U PocketQube from TU Delft (Netherlands), which will serve for education and research, and EASAT-2 and HADES, two 1.5U PocketQubes from AMSAT-EA (Spain), which have FM repeaters for amateur radio. The three satellites were deployed close together with an Albapod deployer from Alba orbital.

While DELFI-PQ worked well, neither AMSAT-EA nor other amateur operators were able to receive signals from EASAT-2 or HADES during the first days after launch. Because of this, I decided to help AMSAT-EA and use some antennas from the Allen Telescope Array over the weekend to observe these satellites and try to find more information about their health status. I conducted an observation on Saturday 15 and another on Sunday 16, both during daytime passes. Fortunately, I was able to detect EASAT-2 and HADES in both observations. AMSAT-EA could decode some telemetry from EASAT-2 using the recordings of these observations, although the signals from HADES were too weak to be decoded. After my ATA observations, some amateur operators having sensitive stations have reported receiving weak signals from EASAT-2.

AMSAT-EA suspects that the antennas of their satellites haven’t been able to deploy, and this is what causes the signals to be much weaker than expected. However, it is not trivial to see what is exactly the status of the antennas and whether this is the only failure that has happened to the RF transmitter.

Readers are probably familiar with the concept of telemetry, which involves sensing several parameters on board the spacecraft and sending this data with a digital RF signal. A related concept is radiometry, where the physical properties of the RF signal, such as its power, frequency (including Doppler) and polarization, are directly used to measure parameters of the spacecraft. Here I will perform a radiometric analysis of the recordings I did with the ATA.

Decoding James Webb Space Telescope

The James Webb Space Telescope probably needs no introduction, since it is perhaps the most important and well-known mission of the last years. It was launched on Christmas day from Kourou, French Guiana, into a direct transfer orbit to the Sun-Earth L2 Lagrange point. JWST uses S-band at 2270.5 MHz to transmit telemetry. The science data will be transmitted in K-band at 25.9 GHz, with a rate of up to 28 Mbps.

After launch, the first groundstation to pick the S-band signal from JWST was the 10 m antenna from the Italian Space Agency in Malindi, Kenya. This groundstation commanded the telemetry rate to increase from 1 kbps to 4 kbps. After this, the spacecraft’s footprint continued moving to the east, and it was tracked for a few hours by the DSN in Canberra. One of the things that Canberra did was to increase the telemetry rate to 40 kbps, which apparently is the maximum to be used in the mission.

As JWST moved away from Earth, its footprint started moving west. After Canberra, the spacecraft was tracked by Madrid. Edgar Kaiser DF2MZ, Iban Cardona EB3FRN and other amateur observers in Europe received the S-band telemetry signal. When Iban started receiving the signal, it was again using 4 kbps, but some time after, Madrid switched it to 40 kbps.

At 00:50 UTC on December 26, the spacecraft made its first correction burn, which lasted an impressive 65 minutes. Edgar caught this manoeuvre in the Doppler track.

Later on, between 7:30 and 11:30 UTC, I have been receiving the signal with one of the 6.1 metre dishes at Allen Telescope Array. The telemetry rate was 40 kbps and the spacecraft was presumably in lock with Goldstone, though it didn’t appear in DSN now. I will publish the recording in Zenodo as usual, but since the files are rather large I will probably reduce the sample rate, so publishing the files will take some time.

In the rest of this post I give a description of the telemetry of JWST and do a first look at the telemetry data.

Imaging Cygnus A at 8.45 GHz with ATA

Earlier this year, I published a post showing our results of the interferometric imaging of Cassiopeia A and Cygnus A at 4.9 GHz with the Allen Telescope Array. Near the end of July, I decided to perform more interferometric observations of Cygnus A at a higher frequency, in order to obtain better resolution. I chose a frequency of 8.45 GHz because it is usually a band clean of interference (since it is allocated to deep space communications), it is used by other radio observatories, so flux densities can be compared directly with previous results, and because going higher up in frequency the sensitivity of the old feeds at ATA starts to decrease.

This post is a summary of the observations and results. The code and data is included at the end of the post.

GPS spectrometry at Allen Telescope Array

Over the last few weeks I have been helping the Allen Telescope Array by calibrating the pointing of some of the recently upgraded antennas using the GNU Radio backend, which consists of two USRP N32x devices that are connected to the IF output of the RFCB downconverter. For this calibration, GPS satellites are used, since they are very bright, cover most of the sky, and have precise ephemerides.

The calibration procedure is described in this memo. Essentially, it involves pointing at a few points that describe a cross in elevation and cross-elevation coordinates and which is centred at the position of the GPS satellite. Power measurements are taken at each of these points and a Gaussian is fitted to compute the pointing error.

The script I am using is based on this script for the CASPER SNAP boards, with a few modifications to use my GNU Radio polarimetric correlator, which uses the USRPs and a software FX correlator that computes the crosscorrelations and autocorrelations of the two polarizations of two antennas. For the pointing calibration, only the autocorrelations are used to measure Stokes I, but all the correlations are saved to disk, which allows later analysis.

In this post I analyse the single-dish polarimetric spectra of the GPS satellites we have observed during some of these calibrations.

Interferometric imaging with Allen Telescope Array

In the weekend experiments that we are doing with the GNU Radio community at Allen Telescope Array we usually have access to some three antennas from the array, since the rest are usually busy doing science (perhaps hunting FRBs). This is more than enough for most of the experiments we do. In fact, we only have two N32x USRPs, so typically we can only use two antennas simultaneously.

However, for doing interferometry, and specially for imaging, the more antennas the better, since the number of baselines scales with the square of the number of antennas. To allow us to do some interferometric imaging experiments that are not possible with the few antennas we normally use, we arranged with the telescope staff to have a day where we could access a larger number of antennas.

After preparing the observations and our software so that everything would run as smoothly as possible, on 2021-02-21 we had a 18 hour slot where we had access to 12 antennas. The sources we observed where Cassiopeia A and Cygnus A, as well as several compact calibrators. After some calibration and imaging work in CASA, we have produced good images of these two sources.

Many thanks to all the telescope staff, specially to Wael Farah, for their help in planning together with us this experiment and getting everything ready. Also thanks to the GNU Radio team at ATA, specially Paul Boven, with whom I’ve worked side by side for this project.

This post is a long report of the experiment set up, the software stack, and the results. All the data and software is linked below.