By Wang Hairong
On aerospace engineer Wen Bo’s cellphone are four identical photos of herself against the same backdrop taken at four different junctures marking milestones in her career and China’s lunar probe program.
The first photo was taken in 2007, the year she started working at the China Academy of Space Technology (CAST) upon graduating from university, which also happened to be the year China launched Chang’e-1, its first lunar probe. The second, third and fourth photos were taken right after the launches of the country’s second lunar probe in 2010, third in 2013, and the most recent one in December 2018, respectively.
“More than 10 years have breezed by in the blink of an eye,” she remarked while flipping through the photos taken at the front gate of CAST.
China’s Chang’e-4 lunar probe made the first ever soft-landing by a spacecraft on the far side of the moon on January 3, and the China National Space Administration dubbed the lunar probe mission a success on January 11.
While watching the lander touch down on the moon from the Beijing Aerospace Control Center, Zhang He, executive director of the Chang’e-4 probe project, could not hold back tears.
Speaking of the emotional moment, Zhang declared in an interview on January 25, “I was very excited. For the past three to four years, our team has worked together diligently. The success was hard earned.”
Meeting the Challenge
“I am proud to have been a part of this mission,” Zhang said. “We have done things that have never been done before and overcome many difficulties.”
One of the main challenges in probing the far side of the moon is communications because it is not directly accessible to signals from Earth, so a communications relay satellite is necessary to complete the operation.
The problem was solved when China launched a satellite named Queqiao on May 21, 2018 to relay data transmission.
Because the far side has been more frequently bombarded by shooting stars and meteorites, the rugged terrain presented another challenge. This makes landing riskier with increased possibility of the lander capsizing or crashing.
To overcome this difficulty, a relatively safe landing site was determined. Zhang and other team members consulted many relevant reference materials, talked to numerous aerospace scientists and analyzed lunar soil and landscape characteristics to find the best one. Eventually, Li Fei, a key designer of the lander, picked a target landing site in the Von Karman crater which is relatively flat. Li, born in the 1980s, is nicknamed “walking encyclopedia” for his broad-range of knowledge.
The lander was also made smarter with artificial intelligence technology, Zhang explained. Sensors measuring velocity and distance that can process 3D-images were installed on the lander so that it could analyze surface declivity, identify rocks and dodge obstacles. Zhang added that the technology is cutting-edge internationally.
Since the moon’s far side is also more pockmarked than the near side, rover Yutu-2 faces bigger challenges than its predecessor Yutu which landed in 2013. Wen, a key designer of Yutu-2, said the rover was improved significantly to prevent mechanical failure.
Wen was tasked with controlling the rover remotely after it landed on the lunar surface. She explained that because the terrain is very complex, after every step the rover must stop and photograph the surface and send data back to Earth via the relay satellite. Scientists on Earth then process the data and chart a route. The rover’s antennas need to be adjusted to point toward the relay satellite, and the solar panels need to face the sun to maximize power generation.
Overcoming these challenges creates many promising opportunities, Zhang said, noting that the far side is older than the near side, so studying its soil could shed more light on the origin and evolution of the moon.
Moreover, the far side is an ideal place for low-frequency radio astronomical observations because the moon blocks radio interference from Earth. Zhang illustrated that the Earth has an ionosphere which makes it difficult to receive low-frequency radio signals. Experiments need to be carried out in space to capture weak signals emitted from remote celestial bodies to study the origin and evolution of stars, galaxies and the universe. Conducting such experiments in near-Earth orbits makes findings vulnerable to corruption from electromagnetic disturbance from Earth, but there is no interference from Earth on the far side of the moon.
It usually takes three to four years to develop a lunar probe and involves tens of thousands of people, Zhang said. For Chang’e-4, models were designed first and then parts developed, manufactured, assembled and tested. The lander consists of more than 200 devices and the rover of nearly 100, which were tested and revised repeatedly.
Because the aerospace industry is so significant to national development and human civilization, aerospace engineers are usually passionate about their work and totally devoted to it, she said.
“The most prominent aspect of a spacecraft is that once launched, it is virtually irreparable, unlike a car that can be recalled if found defective or a plane that can be periodically maintained,” she explained. Any negligence can throw years of hard work down the drain, so aerospace engineers are obsessed with quality. “We must identify all potential risks and do everything we can to control them,” she added.
“The space industry is high-risk and needs long-term investment, so everyone is under a great deal of pressure,” Li illustrated. On the wall of an aerospace control room, opposite gigantic screens are several boards that read, “Zero defects, zero failure… high standards,” reminding staff to work meticulously.
While being cautious and detail-oriented, Zhang’s colleagues often raced against time to beat deadlines. Developers of Chang’e-4 lunar probe often worked overtime, and at times even moved into a hotel next door to CAST to avoid commuting.
Moreover, not all work was done in comfortable air-conditioned offices. Some tests were carried out in northeastern China where winter is very cold and some in desolate areas of the Gobi Desert in the northwest. However, Zhang’s colleagues never complained about the poor living environments.
More than two decades have passed since Zhang started working at CAST after graduating from Beihang University, previously known as Beijing University of Aeronautics and Astronautics—the first higher education institution of aeronautics and astronautics established after the founding of the People’s Republic of China in 1949. During this period she has grown from a recruit analyzing dynamics to executive director of the country’s second lunarlanding project.
She is also now mother of a teenage son. As a career mother, she does not consider professional and family roles contradictory. “A working mother is a role model for her child,” she said, noting that her son also loves science.
Admittedly, some of Zhang’s colleagues have missed some important moments in their children’s lives because of work assignments. When aerospace engineer Cheng Ming went to the Xichang Satellite Launch Center to make last minute preparations for the launch of Chang’e-4 last December, his son was undergoing an operation. Five years earlier, Cheng missed his son’s birth because he was busy preparing for the launch of Chang’e-3.
Cheng’s guilt was somewhat assuaged when he proudly explained to his son that his father helped send a probe to the moon. This sense of pride has been the driving force in Cheng’s career in space science.