STS 134 and ISS observed post final separation burn

From: Ted Molczan (
Date: Mon May 30 2011 - 10:15:29 UTC

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    On 2011 May 30, at 08:39 UTC, shuttle Endeavour, on mission STS 134, made its final manoeuvre to separate from ISS. The
    STORRM rendezvous test had just brought STS 134 back to ISS, to within about 300 m. During the period from 08:48 -
    08:50:30 UTC, I observed both objects on a pass that culminated at 89 deg. 
    I spotted them easily, despite light fog and moderately bright twilight. The initial sighting was with my unaided eye,
    shortly after they exited eclipse, at elevation 13 deg, azimuth 237 deg. At that point, I could not resolve them with
    the unaided eye. I immediately switch to mounted 25 x 100 binoculars, with which I easily separated them. Endeavour
    followed directly behind ISS. During the roughly one minute that I observed them with the 25 x 100s, their range
    decreased from about 1000 km to less than 600 km. I did not have reference stars to enable accurately estimating their
    angular separation, but at one point, I estimated them to be about 0.05 deg apart. As a guess, they were probably about
    600 km away at that point, so 0.05 deg represented about 500 m, but since I observed them on a considerable slant, their
    true separation would have been quite a bit greater.
    Beginning about 08:49:30 UTC I switched to observing with either my unaided eye or handheld 7 x 50 binoculars. At that
    point, they were near 37 deg elevation, and about 550 km away, and still unresolvable as separate objects with the
    unaided eye, but just barely with the 7 x 50s. By about 08:50 UTC, as they approached culmination, their angular
    separation increased to the point that I could now very easily separate them with my unaided eye, as a guess a couple of
    tenths of one degree apart. My observations ended just as they reached culmination, near 08:50:30 UTC. At that point,
    0.1 deg represented 603 m.
    If reliable TLEs corresponding to the time of my observation become available, they will provide the means to check the
    accuracy of my angular separation estimates, which tends to be poor in the absence of reference stars.
    My one surprise, which I want to verify with further observations, was that in the 25 x 100s, I could easily resolve the
    shape of ISS, which appeared to be rectangular, apparently the result of seeing its main solar arrays at a favourable
    orientation. I suspect that the fog and twilight were helpful in suppressing a lot of the glare of ISS. Although I
    observe ISS many times in a typical year, I believe this was the first time I used my 25 x 100s. Unfortunately, this
    type of hi-res viewing does not enable recording the raw frames.
    ISS and Endeavour were a lovely sight, and with only one shuttle mission remaining, quite possibly the last such
    observation I will make.
    Site 2701: 43.68764 N, 79.39243 W, 230 m
    Ted Molczan
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