Software – Page 7 – Daniel Estévez

Decoding Crew Dragon Demo-2

The launch last Saturday of Crew Dragon Demo-2 undoubtedly was an important event in the history of American space exploration and human spaceflight. This was the first crewed launch from the United States in 9 years and the first crewed launch ever by a commercial provider. Amateur radio operators always follow this kind of events with their hobby, and in the hours and days following the launch, several Amateur operators have posted reception reports of the Crew Dragon C206 “Endeavour” signals.

It seems that the signal received by most people has been the one at 2216 MHz. Among these reports, I can mention the tweets by Scott Tilley VE7TIL (and this one), USA Satcom, Paul Marsh M0EYT. Paul also managed to receive a signal on 2272.5 MHz, which is not in the FCC filing, so this may or may not be from the Crew Dragon.

Scott has also shared with me an IQ recording of one of the passes, and as I showed on Twitter yesterday, I have been able to demodulate the data. This post is my analysis of the signal.

LES-5 telemetry Grafana dashboard

Scott Tilley VE7TIL is making a serious effort and a great job of recording and processing LES-5 telemetry. He is recording all the passes over his home in western Canada (which last several days, due to the sub-synchronous orbit), and sharing the data on a Github repository, together with Jupyter notebooks that analyse the data and plot some of the telemetry variables, such as the values recorded by the RFI experiment.

I am storing this data in InfluxDB 2.0 and using Grafana to plot it and explore it. The Grafana server has been running for quite some time now, but I never announced it publicly, so very few people have used it. I guess that now is a good time to share it with a wider audience. The server is at eala.destevez.net:3000 and the LES-5 dashboards can be accessed by using user “les5” and password “les5”.

gr-satellites v3.0.0-rc1

In GRCon last year I presented the roadmap for a large refactor of gr-satellites that would eventually be released as gr-satellites v3.0.0. The refactor started near the end of September, and after nearly 8 months I have now arrived at a point where I feel that all the work I’ve done should be packed and released. Not all the ideas I had in my head when I started have made it to the release (some of them require a large amount of work), but I think that the new gr-satellites is still much better than the old one and I would like to start seeing people switching over. Therefore, I have released today v3.0.0-rc1.

Rather than summarising here all the changes that v3.0.0 brings, I invite you to head over to the new gr-satellites documentation and discover by yourselves.

As anything bringing large change, I think that gr-satellites v3.0.0 will probably break some old habits and workflows. However, I hope that it breaks them for good, and that you will find a better workflow with v3.0.0. If not, please head over to the Github issues and let me know what you’re missing in the new release.

A few more notes about project management: starting with this release, I have decided to concentrate all the support and discussion about gr-satellites in the Github issues. This is an idea I’ve stolen from Kate Temkin. In the past I’ve done a lot of discussion with gr-satellites users over email, and while I don’t have any objections to the use of email, Kate makes an extremely good point about the usefulness of having this discussion in public forums. Just the possibility of past issues appearing in Google searches when a user is looking for help makes it worth the effort.

To try to have better coordination with satellite teams planning to use gr-satellites for their missions (a few such as OPS-SAT and Quetzal-1 have already done so), I have written a note for them.

The plan is for v3.0.0-rc1 to become the final v3.0.0 at the beginning of June if no major issues show up. So please go ahead and check out all the new features that v3.0.0-rc1 brings, and let me know in the issues any problems you might find.

Simulating delta-range observations in GMAT

During the DSLWP-B (Longjiang-2) mission, we made a number of VLBI observations of the spacecraft’s UHF signal by performing GPS-synchronized recordings at Dwingeloo (The Netherlands), Shahe and Harbin (China), and Wakayama (Japan). The basic measurement for these observations is the time difference of arrival (TDOA), which measures the differences between the time that it takes the spacecraft’s signal to arrive to each of the groundstations. This can be interpreted in terms of the difference of distances between the spacecraft and each groundstation, so this measurement is also called delta-range.

One very interesting practical application of the VLBI observations is to perform orbit determination. The delta-range measurements can be used to constrain and determine the state vector of the spacecraft. This would give us an autonomous means of tracking Amateur deep-space satellites, without relying on ranging by a professional deep-space network. Even though the measurements we made showed good agreement with the ephemerides computed by the Chinese deep-space network, during the mission we never ran orbit determination with the VLBI observations, mainly due to the lack of appropriate software.

While GMAT has good support for orbit determination, it doesn’t support delta-range measurements. Its basic orbit determination data type is two-way round-trip time between a groundstation (or two) and the satellite, as shown in the orbit determination tutorial.

I have started to modify GMAT in the gmat-dswlp Github repository to implement the support for this kind of VLBI observations. As a first step, I am now able to create and simulate delta-range observations.

Idle data in BepiColombo X-band signal

Yesterday I posted about decoding the data in an X-band recording of BepiColombo. I only made a very shallow analysis of the data, which consisted of CCSDS TM Space Data Link frames. However, I showed that most of the data was transmitted on virtual channel 7. A few hours later, Oleg_meteo in Twitter noted that this data in virtual channel 7 was just a 511 bit PN sequence. After some analysis I’ve confirmed what Oleg_meteo said and shown another interesting and unexpected property of this data.

All the Space Data Link frames in virtual channel 7 have a first header pointer field of 2046, which means “idle data only”. When the payload in these frames is concatenated (there are 8792 payload bits per frame) we obtain an infinite sequence that fits the following description.

Decoding BepiColombo

BepiColombo is a joint mission between ESA and JAXA to send two scientific spacecraft to Mercury. The two spacecraft, the Mercury Planetary Orbiter, built by ESA, and the Mercury Magnetospheric Orbiter, built by JAXA, travel together, joined by the Mercury Transfer Module, which provides propulsion and support during cruise, and will separate upon arrival to Mercury. The mission was launched on October 2018 and will arrive to an orbit around Mercury on December 2025. The long cruise consists of one Earth flyby, two Venus flybys, and six Mercury flybys.

The Earth flyby will happen in a few days, on 2020-04-10, so currently BepiColombo is quickly approaching Earth at a speed of 4km/s. Yesterday, on 2020-04-04, the spacecraft was 2 million km away from Earth, which is close enough so that Amateur DSN stations can receive the data modulation sidebands. Paul Marsh M0EYT, Jean-Luc Milette and others have been posting their reception reports on Twitter.

Paul sent me a short recording he made on 2020-04-04 at 15:16 UTC at a frequency of 8420.535MHz, so that I could see if it was possible to decode the signal. I’ve successfully decoded the frames, with very few errors. This post is a summary of my decoding.

Decoding LES-9

After decoding a recording of the LES-5 236.7MHz telemetry beacon made by Scott Tilley VE7TIL, I have decoded an older recording made by Scott of the S-band beacon of LES-9. This satellite was launched in 1976 and it has a 100 baud BPSK beacon at 2250MHz. Scott twitted about it in April 2019, and in January 2020 he reported that the modulation had stopped and the beacon was now a CW carrier.

I have used this recording made by Scott in 2020-01-13. The GNU Radio demodulator, which is very similar to the one for LES-5, is here and the Jupyter notebook with the results is here. Below, I make a brief summary of the results.

Decoding LES-5

LES-5 is a satellite launched in 1967. It was built by the MIT Lincoln Laboratory and its main payload was an experimental transponder for the military 230MHz band. It was placed in a subsynchrounous orbit with an altitude of around 33400km (GEO altitude is 35786km). Its operations ceased in 1971.

A couple days ago, Scott Tilley VE7TIL discovered that LES-5 was still transmitting, and was able to receive its beacon at 236.749MHz. Scott reports that LES-5 is the oldest GEO-belt object that he knows to be still transmitting.

The beacon is modulated, rather than being a CW carrier, so Scott sent me a short recording for analysis. This post is a summary of my study.

Decoding images from AMICal Sat

AMICal Sat is a 2U cubesat developed by the Space Centre of the Grenoble University, France, and the Skobeltsyn Institute of Nuclear Physics in the Lomonosov Moscow State University. Its scientific mission consists in taking images of auroras from low Earth orbit. The satellite bus was built by SatRevolution. Currently, the satellite is in Grenoble waiting to be launched on a future date (which is uncertain due to the COVID-19 situation).

A few weeks ago I was working with Julien Nicolas F4HVX to try to decode some of the images transmitted by AMICal Sat. Julien is an Amateur radio operator and he is helping the satellite team at Grenoble with the communications of the satellite.

This post is an account of our progress so far.

Fifth alpha for gr-satellites 3

Today I have released gr-satellites v3-alpha4, the fifth alpha in the series that will lead to the refactor of gr-satellites in which I’ve been working since September. This alpha release has been focused on improving the performance of the BPSK and FSK demodulators. Here I summarise the improvements and new features that this alpha brings, and look at the roadmap leading to the release of gr-satellites 3.0.0.