Flare of USA 129 Keyhole satellite

Yesterday evening I captured this image of the American Keyhole imaging satellite USA 129 (96-072A, #24680) starting to flare brightly near the zenith. A few seconds after the end of this exposure it reached magnitude -1.5. A second exposure starting 30 seconds later only shows a faint trail, estimated about magnitude +3.0.

This picture and the second one provided three positions