KH-12 type Keyhole optical imaging reconnaisance sat USA 186
(05-042A, #28888) brightly flared to mag. -2 in the northwest at 21:13:06 ± 3s UTC. When I first saw it, looking up from triggering the 10 second camera selftimer, it was very bright, and it faded gradually as the camera opened (see image below). It was a very slow flare lasting tens of seconds, unlike the very brief glints I had observed so far from this satellite (e.g. report and photograph here
(click image for larger picture)
It was as much as 9 seconds early and 0.10 deg off in cross-track with respect to 4 day old elset 06249.87384698, and 2.5s early with respect to Russel's observations 25 hours earlier: is it manoeuvring?
About an hour earlier I also captured another keyhole, USA 129
(96-072A, #24680). The trail was faint, the two obtained positions are about 1s early.