HELSINKI \u2014 A team behind the rescue of a pair of lunar satellites left stranded by a launch anomaly have revealed the challenges they faced in salvaging the mission.<\/p>\n
China launched the DRO-A and DRO-B spacecraft<\/a> from Xichang spaceport March 13, 2024, intending to send the pair, totalling 581 kilograms, into distant retrograde orbit (DRO) around the moon. The pair were designed to link up with the earlier-launched DRO-L satellite, operating in low Earth orbit, to test intersatellite links and demonstrate the utility of distant retrograde orbits\u2014high lunar orbits in which spacecraft travel opposite to the moon\u2019s orbital direction around Earth.<\/p>\n However, an anomaly experienced by the mission\u2019s Yuanzheng-1S upper stage left the satellites in a highly elliptical Earth orbit, with a much lower apogee, or farthest point from Earth, than planned. Simultaneously, the joined satellites were spinning once every 1.8 seconds, threatening the structural integrity of the spacecraft and their ability to operate and communicate. The rescue operations are detailed by an April 16 report<\/a> from China Youth Daily.<\/p>\n The team first eliminated the spin, using the DRO-B satellite attitude control engines to correct the rotation over the course of 20 minutes. Telemetry, however, then revealed issues with both satellites\u2019 solar arrays which needed addressing.<\/p>\n Next, a team, including researchers from the Innovation Academy for Microsatellites (IAMCAS) and Technology and Engineering Center for Space Utilization (CSU), both under the Chinese Academy of Sciences (CAS), formulated a rescue plan over the following 40 hours. This needed to take into consideration the complexity of orbital dynamics and gravitational perturbations from the Earth, moon and Sun, and very limited fuel. The team also faced a deadline of mere days, needing to quickly execute a first maneuver or lose the opportunity of reaching DRO.<\/p>\n