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Alerted by a tweet from Hong Kong-based @cosmic_penguin, Bob Christy of zarya.info spread the word that one of three Chinese satellites launched together on July 19 made a sudden maneuver yesterday.

The satellite, Shiyan 7 (SY-7, Experiment 7), already had completed a series of orbital changes that put it close to one of the companion satellites with which it was launched — Chuangxin 3 (CX-3).    Suddenly, however, it made a surprise rendezvous with a completely different satellite, Shijian 7 (SJ-7, Practice 7), launched in 2005.

Jonathan McDowell of Jonathan’s Space Report characterizes SJ-7′s own mission as “mysterious.”  Over the past eight years, it has changed its orbit several times followed by long periods of “quiescent decay.”  Its most recent orbit change was in January 2013 according to McDowell.

As for SY-7, it was launched last month along with CX-3 and Shijian-15 (SJ-15).   China’s Xinhua news service said at the time that all three satellites would be used to conduct “scientific experiments on space maintenance technologies.”

Christy reported soon after launch that “[i]t is known” that one of the three satellites carries “a prototype manipulator arm to capture other satellites” that might be “a predecessor of an arm destined to be aboard China’s large space station set for launch in 2020 or soon thereafter.”

He could not confirm which of the three satellites carries that arm.   McDowell said that SY-7 “is testing a robotic arm,” while SJ-15 was thought to be observing space debris and CX-3 might be carrying “technology experiments and/or serve as a target for the robotic arm tests.”

After a series of minor orbital adjustments, the first unexpected orbit change for SY-7 occurred on August 16 according to Christy, who said that it suddenly lowered its orbit by 150 kilometers.  Christy’s analysis at the time suggested that it was preparing to rendezvous with CX-3.  Then, yesterday (August 18) it rendezvoused with SJ-7 instead.

Christy reports that as of this morning SY-7 and SJ-7 remain about 2 kilometers apart in a 565 x 610 kilometer orbit.   Christy remarks that “[t]here are several possibilities for what looked like a space station rendezvous and docking simulation….satellite inspector, satellite servicing experiment, ASAT..?”

ASAT stands for antisatellite, a capability to render a satellite non-operational.  China conducted an ASAT test in 2007 when it launched a satellite interceptor against one of its own satellites.

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