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Lunar Satellite Rescue: China’s Mission to Salvage Stranded Spacecraft
HELSINKI – A pioneering endeavor to rescue two lunar satellites left adrift following a launch malfunction has revealed the intricate challenges overcome by the mission team. Launched from Xichang spaceport on March 13, 2024, China’s DRO-A and DRO-B spacecraft, with a combined mass of 581 kilograms, were intended for placement in a distant retrograde orbit (DRO) around the Moon. This mission aimed to connect the pair with the pre-existing DRO-L satellite in low Earth orbit to evaluate intersatellite communication and demonstrate the advantages of distant retrograde orbits for future deep space exploration missions.
Initial Launch Anomaly
The mission encountered an unexpected anomaly with the Yuanzheng-1S upper stage rocket, resulting in the satellites being placed into a highly elliptical Earth orbit. This unintended orbit had a significantly lower apogee, the farthest point from Earth, than originally planned. Compounding the issue, the conjoined satellites were rapidly spinning at a rate of once every 1.8 seconds. This rapid rotation threatened the structural integrity of the spacecraft as well as their operational and communication capabilities. Details of the complex rescue operation were published in a report by China Youth Daily on April 16.
Rapid Response: Correcting Spin and Addressing Solar Array Concerns
The immediate priority was to counteract the detrimental spin. Utilizing the attitude control thrusters of the DRO-B satellite, the team successfully stabilized the rotation within 20 minutes. However, subsequent telemetry data uncovered complications with the solar arrays on both satellites, requiring further intervention.
Formulating the Recovery Strategy
A specialized team, comprised of researchers from the Innovation Academy for Microsatellites (IAMCAS) and the Technology and Engineering Center for Space Utilization (CSU), both affiliated with the Chinese Academy of Sciences (CAS), worked urgently to devise a recovery strategy within a critical 40-hour window. The rescue plan had to account for the complexities of orbital mechanics, gravitational forces from Earth, the Moon, and the Sun, and the critically limited fuel supply onboard the satellites. Time was of the essence, as the team faced a tight deadline of mere days to execute the initial crucial maneuver to maintain any possibility of reaching the intended DRO.
Achieving Lunar Orbit: A Series of Orbital Adjustments
The first pivotal engine ignition, initiated on March 18, spanned 1,200 seconds. This crucial burn elevated the apogee from 134,000 to 240,000 kilometers. Subsequent reports detail how the DRO-A and DRO-B spacecraft conducted an additional four orbital maneuvers, incorporating gravity assists and further trajectory adjustments over the following four months. This series of precise operations successfully guided the spacecraft toward their designated lunar orbit.
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Mission Success: Satellite Deployment and Inter-satellite Communication
By July 15, 2024, these extensive efforts culminated in the satellites achieving stable placement within their predetermined lunar orbits, having traversed approximately 8.5 million kilometers. The satellites journeyed over one million kilometers from Earth, enabling a low-energy capture and insertion into lunar orbit. Following successful separation on August 28, the pair exchanged images, revealing substantial damage: the solar panels of DRO-A were bent at nearly a 90-degree angle, while DRO-B’s arrays were described as “broken wings.”
Demonstrating Advanced Communication Capabilities
The two satellites then successfully established K-band microwave intersatellite communication links with the DRO-L satellite, confirming the functionality of a three-satellite network spanning the Earth-Moon distance.
Ground Station Transformed: Satellite-Based Tracking
Wang Wenbin, a CSU researcher, explained to China Central Television (CCTV), “For the first time globally, we have demonstrated the capability to employ satellites for tracking other satellites, removing the reliance on ground stations.”
“Essentially, the ground station has been transformed into a satellite positioned in low orbit. This innovation paves the way for new technological advancements in future Earth-moon space and deep space exploration,” Wang added.
Scientific Research and Future Applications
DRO-A also features an all-sky detector designed for monitoring gamma-ray bursts, similar to the instrumentation utilized in China’s GECAM mission launched in 2020. Wang further stated that China plans to leverage DRO and its inherent long-term stability for conducting fundamental scientific investigations in areas such as quantum mechanics, atomic physics, and related scientific disciplines.