Indian Moon landing followed by radio telescope

This year 2019 is a busy year for lunar exploration. On January 3, China successfully landed a probe and rover on the backside of the Moon, and on April 11, Israel attempted to land Beresheet, a small lander. Unfortunately that landing failed, as we observed with the Dwingeloo radio telescope.

On September 6, India was the third country to attempt a lunar landing this year. The Chandrayaan-2 mission included the Vikram lander, which was aimed to land near the lunar South Pole. Fortunately, the Moon was above the horizon, and the Dwingeloo radio telescope was ready to track the landing attempt. Simon Bijlsma, Michel Arts, Tammo Jan Dijkema and Cees Bassa used the 13 cm horn antenna to listen to radio transmissions from the Vikram lander at 2284 MHz.

The Dwingeloo signal chain was tested around 18:20 UTC (20:20 CEST), just before the Vikram lander disappeared behind the Moon for its final orbit. At 19:18 UTC, as predicted, the lander reappeared from behind the Moon and quickly got in contact with the Madrid Deep Space Network station; the radio signals received by the Dwingeloo telescope showed that Vikram locked to Madrid and began downlinking telemetry.

The landing burn started at 20:08 UTC when Vikram was at 30 kilometers altitude. The effect of the burn was immediately visible as a sharp kink in the Doppler curve, shortly followed by the announcements from the Indian livestream, which had a delay of about half a minute. The landing burn consisted of two phases: a ten minutes long rough braking phase to reduce the velocity as quickly as possible, followed by a two minutes fine braking phase to reduce errors in the trajectory. With the start of this fine braking phase at 20:18 UTC, when Vikram was at 7 kilometers altitude, the Doppler curve as received by the Dwingeloo telescope started to show unexpected small oscillations, which grew during the next two minutes, with the signal disappearing at 20:20UTC, three minutes before Vikram was planned to land on the Moon.

The oscillations in the Doppler curve, and the loss of signal three minutes before the expected landing time, suggests that Vikram had a problem during the final phases of the descent, and probably crashed onto the lunar surface. It is not clear how hard Vikram crashed and if the lander survived. About a day later the Indian Space Research Organization (ISRO) managed to image the lander on the lunar surface using the orbiter of the Chandrayaan-2 mission. So far ISRO has not managed to communicate with the lander.

Israeli Moon landing tracked with the radio telescope

The Dwingeloo radio telescope had a prime seat during the lunar landing attempt of the Israeli Moonlander “Beresheet”. Cees Bassa and Paul Boven used the new 13 cm horn antenna to listen to the carrier signal of Beresheet at 2280 MHz.

The Beresheet lander was launched on Februari 22, 2019, and made several orbits around Earth before maneuvering into an orbit around the Moon on April 4. The landing in Mare Serenitatis was planned for Thursday April 11, 21:25 CEST (Central European Summer Time).

From the radio telescope the lander signal appeared from behind the Moon on that Thursday, as expected, at 20:55 CEST. The Israeli webstream reported that the lander turned around to prepare itself for landing. Exactly as planned, the radio signal showed a kink due to the Doppler effect, indicating that the rocket enginges had started. The next eight minutes all went according to plan; the Israeli webstream showed decreasing speed and height of the lander, while the radio signal decreased in frequency. The full landing would last for 20 minutes.

Unfortunately, after those eight minutes, something went wrong. First, the radio signal disappeared temporarily; the webstream reported that one of the orientation sensors was reset. When the radio transmitter on Beresheet became active again, it was clear from the radio signal that the rocket engine was not working, because the Doppler curve showed an acceleration.

During the next three minutes there was still contact with the lander, but the engine could not be restarted. This is clearly visible in the recording from the Dwingeloo radio telescope: the Doppler curve does not change. At 21:23:01 CEST, the signal suddenly disappeared: the moment Beresheet crashed into the Lunar surface.

Despite the failed landing, Israel has showed a great achievement. Hopefully future missions from Israel and other countries have more luck, and hopefully the Dwingeloo radio telescope can tune in again.

Doppler curve of the Beresheet signal, as measured with the Dwingeloo Radio Telescope. Times are in UTC (two hours earlier than Central European Summer Time).

Dwingeloo observes the BEESAT-3

Almost five years after the launch, Jan van Muijlwijk observed the BEESAT-3 picosatellite during the CAMRAS Club Day on Sunday January 7, 2018. This “Berlin Experimental and Educational SATellite” is low-Earth orbiting since its launch in 2013. Unfortunately, the scientists of the Technical University of Berlin have not yet been able to observe the satellite after the launch. Based on extensive analysis, they think the most likely cause is that the antenna is not unfolded. BEESAT-2 from the same launch is still working perfectly. And the older BEESAT-1 has been responding well for more than 8 years. In addition, the BEESAT-4 launched in 2016, and the twenty-kilo-heavy nanosatellite TechnoSat launched in 2017 work perfectly.

Because they had heard of the exceptionally good receiving possibilities of the Dwingeloo Telescope, project leader Merlin Barschke asked CAMRAS to give it a try. By default, the BEESAT-2 and -3 are on ‘off’, so they had to send a command to both satellites to turn them ‘on’. In Dwingeloo, we heard BEESAT-2 as expected with very strong signals. Moreover, to everyone’s excitement half an hour later BEESAT-3 came above the horizon and was just as strong to receive!

180108_B3_frameThereafter, with the data collected by Jan van Muijlwijk, the BEESAT-3 team could contact their satellite themselves and retrieve data by using the ground station of the Technical University of Berlin. The attached image shows the first data frame ever received from BEESAT-3 in Berlin – the satellite is in excellent condition!

Photo’s: CAMRAS (Michel Groenewegen) and BEESAT-3 team

Two satellites reactivated

Saturday, June 10, we tried to ‘save’ three satellites using the Dwingeloo Radio Telescope. They are all part of the QB50 mission, fifty small satellites that have all been launched very recently. Universities or colleges build most. They explore the lower thermosphere, an air layer of the atmosphere between about 200 and 380 kilometer altitude.

Two Australian satellites and one South African satellite showed absolutely nothing. That is why CAMRAS was asked by the University of New South Wales (UNSW) in Sydney if we could make a rescue attempt. By e-mail we discussed the details and the technique to send commands that could make the satellites possibly ‘talk’ again. These were commands of a few ‘computer beeps’ on 435 MHz (70 centimeter) of less than a second, which ordered the satellite to expand the antenna.

We heard nothing from two satellites and there was no response to our commands. We received a very weak signal from one satellite (the i-INSPIRE-2) which remained so after our commands. Afterwards we went home with the feeling that we did not succeed with any of the satellites despite our best efforts.

However, great was the surprise when it turned out that the INSPIRE-2 had come to life through our signals! It only took a while before the sent command ‘unfold antennas’ had been fully implemented. By then the satellite had already disappeared behind the horizon.

Next day, when the satellite flew across Europe, I received very strong signals at home! The satellite has been heard in Australia also. In addition, UNSW received reports from all over the world that the satellite was heard loudly! Moreover, all data were as expected. The satellite is just one hundred percent OK! With our outstanding dish antenna in Dwingeloo we could give the satellite a stronger signal to expand the antenna than the scientists in Australia.

Meanwhile on Saturday June 17, we also succeeded with the other Australian satellite (the UNSW-EC0). The South African satellite (the ZA-AEROSAT) is of a different type that does not receive 70 cm. The German radio amateur Reinhard Kuehn (DK5LA) succeeded in waking up this satellite at 145 MHz (2 meter) last Sunday, July 2.

Of course these successes led to the necessary media attention, among others (all three in Dutch), RTVDrenthe Satellite saved by Drenthe radio telescope and Drenthe radio telescope rescues satellite and the Dagblad van het Noorden Amateurs Dwingeloo rescue satellite and many thanks from the i-INSIRE-2 and UNSW-EC0 teams.

See also the article i-INSPIRE-2 activated by Jan van Gils (PEØSAT) and the article  UNSW in thrilling rescue of ‘lost’ Aussie satellites of the Australian scientists published in the UNSW Newsroom.

Photo’s CAMRAS (Harry Keizer)