Shijian-31 launched on a Long March 3B from Xichang spaceport on June 16. Navigation warnings and the launch vehicle type suggested an insertion into geostationary transfer orbit, and the satellite was later tracked in a specialized Molniya orbit. In doing so it joined China’s two Shiyan-10 satellites and TJS-13 and TJS-21, though outside analyses say China has applied the Molniya concept in a way not previously observed.
Molniya orbits use an inclination of 63.4 degrees to prevent drifting of a satellite’s argument of perigee, caused by Earth’s asymmetric mass distribution. Traditionally the orbit maintains apogee over the northern hemisphere, useful for high latitude communications and missile early warning. Shijian-31 instead reaches apogee over the equator, allowing it to sweep GEO, situated at around 35,786 km above the equator. Integrity ISR first flagged the satellite’s orbit in a June 26 post using orbital data from SpaceTrack.
While Molniya satellites usually orbit every 12 hours, Shijian-31 orbits once every 12.5 hours, so it does not pass the same longitude each orbit. Each swing shifts it approximately 15.7 degrees in longitude, meaning it can sweep the entire GEO belt roughly once every 23 days. Its apogee of approximately 39,900 km carries it a few thousand kilometers beyond the belt. ComSpOC noted the satellite’s activities in a July 21 post, describing it as a satellite with an orbit it had never seen before and including a video illustrating the trajectory.
Shijian-31 is nominally part of a broad series of often classified experimental satellites. The China Aerospace Science and Technology Corporation provided no images and described it tersely as mainly used for space environment exploration. Integrity ISR said observing the satellite closely may be extremely challenging. Its perigee of just under 2,000 km is well above most low Earth orbit remote sensing satellites, and it passes thousands of kilometers from spacecraft such as the U.S. GSSAP series in GEO. Integrity ISR noted that a relatively small retrograde burn at perigee, a velocity change of 50 meters per second, would lower apogee to roughly 36,671 km, resulting in the satellite passing directly through the GEO neighborhood.
Integrity ISR stated that with Shijian-31, Chinese space operators have displayed orbital mechanics mastery and more than a little creativity. Victoria Samson of the Secure World Foundation called the mission pretty unusual and hard to characterize with limited information, noting that more details may be revealed through the satellite’s behavior over time. Samson said the mission could be part of a larger trend toward inspector satellites and increased interest in strong situational awareness of activities and hardware in GEO. The U.S. operates the GSSAP inspector series, while Russia has the Luch 2 satellite in GEO following the demise of the original Luch satellite in January.
Samson noted that Shijian-31 has only been in orbit for about a month. Analysts expect the satellite’s future behavior and any maneuvers, including a possible perigee burn to intersect the GEO belt, to reveal more about its purpose and capabilities.
