Tuesday, 4 September 2018

Capturing a flaring NOSS duo (NOSS 3-6)

click to enlarge

On 30 August 2018 near 20:59 UT I was imaging the NOSS 3-6 duo (2012-048A & 2012-048P) during a near-zenith pass, when they briefly flared. They were at a sky elevation of 77.5 degrees at that time.

The image above is a stack of the video frames showing the flaring spacecraft: the flare of the leading P component was captured just before it peaked (I was adjusting the camera FOV during the seconds before it), the flare of the A component was captured in its entirety. Below is the video itself from which these frames were extracted (video shot with a WATEC 902H + Canon FD 1.8/50 mm lens):

I next used LiMovie to analyse the video and extract brightness curves from the video frames, with the following results. The data points shown are 3-point averages of the raw data. small discontinuities visible in the curves are where the satellite passed a star:

click diagram to enlarge

click diagram to enlarge

The leading P component seems to exibit only one flare peak. The traling A component shows an interesting  double or tripple peak. The centroids of the peaks of the P and A component were some 6.5 seconds apart.

In the diagram below, I have transposed both curves on each other by shifting the curve for the A component along both axes untill it matches that of the P component:

click diagram to enlarge

What can be seen is that the curve for the A component pre- and post-peak follows the pattern of that of the P component, but unlike the P component it shows a pronounced valley at the peak, with a small secondary peak in the valley bottom. The shape of the valley is the inverse of the peak shape of the P component. Intriguing!

The rather sudden change in steepness some seconds before and after the peaks as shown by both components is interesting too. The main peak shape is slightly asymmetric.

One option for the difference in the shape of the curve for the A component (i.e. for the "valley"at the top) might be the presence of a rotating component interfering with the flare pattern caused by the satellite body, perhaps.

NOSS (Naval Ocean Surveillance System) satellites are SIGINT satellites operated by the US Navy to locate shipping, based on geolocation of the ship's radio emissions. They are also known by the code name INTRUDER. They always operate in close pairs, such as can be seen on the video.

The P component peaked at 20:59:11.85 UT (Aug 30, 2018), at position RA 313.222 DEC +45.628. The A component has a first major peak at 20:59:17.33 UT at RA  313.331 DEC +45.077; the small secondary peak at 20:59:18.37 UT at RA 313.765 DEC +45.307; and a third major peak at 20:59:19.33 UT at RA 314.170  DEC +45.518. The two major peaks are 2.0 seconds apart.

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