China rebounded from a failed March 2024 space mission by successfully saving two off-orbit satellites over the course of 123 days, thanks to a novel navigation technique.
Ironically, the satellites were intended to create a constellation of beacons to improve the precision of space navigation. After a failed rocket launch damaged the satellites and threw them off course, Chinese scientists scrambled to salvage the mission
China’s Distant Retrograde Orbit Satellites
The distant retrograde orbit (DRO) navigation satellites are another element of China’s growing space program and will provide reference points for autonomous spacecraft and play a role in future lunar missions. The two new satellites, DRO-A and DRO-B, form a constellation with the earlier DRO-L, providing 100 million kilometers of navigation coverage between Earth and the moon.
“They will act as lighthouses in space,” Central Southern University researcher Mao Xinyuan explained. “(With these satellites in position), we can locate a spacecraft in just three hours, unlike the two days or more with traditional, land-based positioning.”
China’s space program envisions its DRO constellation enabling autonomous spacecraft or autopilot functionality for crewed missions.
“We just give it a target position, and the spacecraft will automatically find its way to the destination,” said Wang Wenbin, a CSU researcher who participated in the mission.” It’s a natural space harbor.”
A Failed Launch
This month, China announced its success in retrieving the satellites. Following the 123-day rescue mission, the satellites are now fully functional and in their planned orbits. Staff at the Technology and Engineering Center for Space Utilization (CSU) were caught off guard by the March 2024 mishap that caused their mission to go off track.
“That was the first launch mission I watched, and I didn’t think about launching glitch at first,” said Zhang Hao, whose team found the final rescue route.
Zhang says that ascertaining the condition of the satellites was the team’s foremost priority immediately following the accident.
“If the satellites were destroyed, that would have been a waste of the years of effort that we put in and the money invested in the mission. It would also be a mental blow to the team,” Zhang explained.
“Luckily, that’s not the case,” Zhang added.
Gravity Slingshot Rescue Mission
After locating the wandering satellites, the team was surprised to discover that DRO-A and DRO-B were spinning wildly and much closer to Earth than initially projected. Zhang’s team struggled to calculate a new trajectory for the wayward satellites, leading them to work nonstop for two consecutive nights. Eventually, the pressure pushed the team to develop multiple potential routes for mission control to choose from.
“If you don’t want to consume much energy, you must replace it with something else. We chose to consume more time in order to save energy,” Mao said.
While being off-course was a major challenge, rectifying the issue was complicated further by damage sustained during the launch malfunction. The damage hindered the satellites’ ability to collect solar energy, leaving them without the power generation needed for significant course corrections. To work around these suboptimal conditions, the team had to rely on the natural gravitational forces of the Earth, Sun, and Moon to slingshot the satellites toward their intended orbits. While the overall rescue mission lasted 123 days, the first—and most difficult—maneuver took only 20 minutes.
“I got more and more stressed as the clock ticked,” said Zhang. “I just kept staring at the screen until it said ‘normal.'”
“For the following maneuvers, I kind of got used to them and no longer got so stressed,” Zhang added.
“It’s like raising a child. The baby phase is the hardest.”
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.