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Eight years ago, on September 27, 2008, the Shenzhou-7 carying three taikonauts deployed the microsatellite Banxing-1 for testing maneuvers and external imaging. A few hours later at 15:07 UTC the pair passed the ISS with only about 45 kilometers between Shenzhou-7 and the ISS. Banxing-1 is described in detail here.

Read more at the WSJ commentary China's Close Call (also archived):

On September 27 at 3:07 p.m. Greenwich Mean Time, the Shenzhou-7 ship passed within 45 kilometers of the International Space Station, according to the U.S. Strategic Command...

No one has offered a full explanation for why Beijing would do this. But China's track record of using all of its Shenzhou missions since 1999 for dual military-civil missions justifies speculation that it might have been part of a test of a new antisatellite missile technology. About four hours before Shenzhou's point of closest approach to the space station, Shenzhou-7 started one of its main missions: the launching of a 40-kilogram maneuvering microsatellite called BanXing-1 or BX-1...

It seems that after it was deployed, Banxing-1 was out of control during this close pass. The intended purpose was to remain and maneuver close to Shenzhou-7 and photograph it. Luckily it was drifting on the opposite side from the ISS.

Chinese state television reported on October 2 that "after the satellite was released by the Shenzhou-7 last weekend, it quickly started drifting away from its intended trajectory." NASA has not responded to questions about the BX-1 ventured closer to the space station than the Shenzhou incident. Neither has Washington.

Is that unusually close to the ISS to deploy and test a new satellite's propulsion and maneuvering without warning? The relative velocity seems to be about 3 kilometers per second!

Below are plots made from the TLEs. I've rotated the data into the frame of the ISS (black dot at the origin) with the thin black line pointing Earthwards (Nadir). Distances in kilometers. Blue/solid = Shenzhou-7, red/dashed = Banxing-1.

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  • $\begingroup$ Those darn "pranksats"! $\endgroup$ – uhoh Nov 9 '16 at 7:01
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    $\begingroup$ The ISS seems a strange target to test antisatellite technology on. If anything went wrong, it'd generate the biggest possible international incident. China has lots of its own satellites it could maneuver towards. $\endgroup$ – Hobbes Nov 9 '16 at 8:11
  • $\begingroup$ @Hobbes That part seems to be speculation by the WSJ article. I'm going to remove that line from the quote because I'm afraid it will be distracting to the purpose of the question. I'm really just curious - is this unusually close for this kind of maneuver without warning? $\endgroup$ – uhoh Nov 9 '16 at 8:51
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    $\begingroup$ @Chris the 600 km cubes show the moment of closest approach (3km/sec means a total of five minutes), the 6,000 km cubes show 6 hours of motion. All are in shuttle-fixed coordinates. Both have top-down and side views. Let me think about how to add the information about the ISS orbital plane. If I can find a way I will. But I don't want ot make these professional looking otherwise people will start using them elsewhere, and I can't guarantee they are 100% technically accurate. $\endgroup$ – uhoh Nov 10 '16 at 3:13
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    $\begingroup$ @uhoh it's probably fine as-is, really. I just needed to stare a little more. $\endgroup$ – Chris Nov 10 '16 at 3:18
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I know nothing of this specific incident, but the generic ISS COLA (COLlision Avoidance) "box" is sized such that a body passing at 45 km could be inside the COLA box, but wouldn't trigger the "notification" rule.

enter image description here (source)

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  • $\begingroup$ That link doesn't work for me. Is this the same paper: iaassconference2013.space-safety.org/wp-content/uploads/sites/… $\endgroup$ – uhoh Nov 9 '16 at 23:01
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    $\begingroup$ Yes, thanks for pointing that out. Fixed the link. And I realized that I need to fix my answer too. Wow. $\endgroup$ – Organic Marble Nov 9 '16 at 23:29
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    $\begingroup$ This is interesting stuff! I can try a simple "nodal analysis" for fun. There's no guarantee the historical TLEs for the recently launched SZ-7 are accurate so it will be an exercise for fun only. Thanks! $\endgroup$ – uhoh Nov 9 '16 at 23:51

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