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Astronomy and space

Astronomy and space

Tracking China’s rapid rise in lunar exploration

01 Sep 2021
Taken from the 2021 issue of the Physics World China Briefing, where it appeared under the headline "Exploring other worlds". You can enjoy the full issue via the Physics World app.

Ling Xin talks to Su Yan from the National Astronomical Observatories of China, Chinese Academy of Sciences, about the technology involved in monitoring China’s Moon missions

Su Yan
Lunar vision Su Yan has been involved with China’s Moon and Mars missions. (Courtesy: Su Yan)

As chief designer of the data acquisition systems for China’s lunar and Mars missions, what are you currently working on?

I oversee developing and running ground-based antennas and receivers for China’s lunar and Mars missions. We have built three 40–50 m-level steerable radio tele­scopes in Beijing and Kunming to obtain data from the lunar missions and last year we completed a 70 m telescope in Tianjin for the Mars mission. I am also overseeing data processing related to various ­microwave-band scientific payloads. This includes the lunar penetrating radar on the Chang’e-3 mission and the low-frequency radio spectrometer on Chang’e-4. That will also apply for the upcoming lunar regolith penetrating radar on Chang’e-5. In addition, I oversee radar data from the orbiter and rover of the current Mars mission Tianwen-1.

Planetary science is thriving in China and the number of planetary scientists has increased exponentially over the past decade

Su Yan

How does that work differ for the lunar and Mars missions?

Mars is much more distant than the Moon so the technologies involved are quite different. For instance, we can use a 50 m telescope to receive data from the Moon, but it won’t work for Mars since the signals are extremely weak. That is why we built the new telescope in Tianjin and integrated the four telescopes so they now function as a 103 m-aperture telescope. This way, we can meet the massive data needs from a total of 13 scientific instruments onboard the orbiter and rover of Tianwen-1.

How did you get involved in lunar exploration?

I was very lucky. My background is in electrical engineering and as a graduate student I joined the pre-research team of the Five-hundred-meter Aperture Spherical radio Telescope (FAST) under the supervision of Nan Rendong. I spent a lot of time at the Miyun ground station in suburban Beijing developing receivers for pulsar signals. I also had the opportunity to spend a year at the Jodrell Bank Observatory in the UK, where I developed feeds and the “orthomode” transducer for a radio telescope array called MERLIN.

How important were those early days on FAST?

FAST was then in the design phase and the budget to construct it seemed astronomical. However, Nan never stopped advocating for the project even when he was diagnosed with cancer. I admire his devotion to FAST. He used to say “No matter what we accomplish, it’s going to be trivial compared to the vast universe out there. What’s important is to enjoy the process of life.” I will always remember that.

Speaking of enjoyment, you must have had some unforgettable moments in the lunar control room

I still remember how nervous we were when the Chang’e-1 orbiter was supposed to start transferring data and there was no signal on the screen. I was nervous, but a few minutes later the data came pouring in. Another intense moment was when we learned that the Chang’e-3 lander had just touched down safely on the Moon’s surface. We were thrilled! Our team was the first to confirm the success and the landing images we received were so much better than what we had expected.

Which findings from the Chang’e missions excite you the most?

I was thrilled about the world’s first high-resolution radar image of the Moon’s far side, taken by the ground penetrating radar on the Chang’e-4 rover. For the first time, the image showed three distinct ­geological ­layers less than 40 m below the lunar surface (Science Advances 6 eaay6898). The rover has travelled nearly 700 m so far on the far side and we hope that it will continue to head west to “see” a different geo­logical landscape that is mainly made up of basalts.

What is the most challenging part of your job?

I always enjoy field work, but sometimes it is difficult. For example, to test the ground-penetrating radar on the Mars rover, we went to the Laohugou glaciers in western China because the dielectric constant of the glaciers is like the Martian regolith. The site was more than 4400 m above sea level and I suffered from severe altitude sickness. I felt weak, but we had to get the work done. During one outing, the snow was so heavy that we had to carry all the instruments up the glaciers ourselves. It was very challenging physically and mentally for the whole team.

I sincerely hope more young people who are passionate about space exploration will join us

Su Yan

What are you working on next?

We need to complete the data processing for the Chang’e-4 radar and the instruments on Tianwen-1 to see if there are interesting findings. I am also involved in the development of radar devices on future missions such as China’s asteroid probe.

Planetary science is thriving in China and the number of planetary scientists has increased exponentially over the past decade. I sincerely hope more young people who are passionate about space exploration will join us.

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