Analysis of Jay Respler's OneWeb Magnitudes

From: Anthony Mallama via Seesat-l <seesat-l_at_satobs.org>
Date: Tue, 15 Dec 2020 10:42:01 -0500
Jay Respler posted his observed magnitudes for the OneWeb satellite
constellation here: satobs.org/seesat/Dec-2020/0058.html. The mean
magnitude adjusted to the standard satellite distance of 1000 km is 7.4 +/-
0.2. The dispersion of the 34 individual data points is 0.9 magnitude.

The mean magnitude and dispersion are consistent with OneWeb values
recorded by the MMT automated observatory in Russia. I posted the results
of that study here: https://arxiv.org/abs/2012.05100.

The large dispersion of OneWeb magnitudes is probably due to their complex
shape. The satellite bus has a boxy form with dish-like antennas mounted on
short arms and a pair of large solar panels attached to longer arms.
Satellite attitude (orientation) contributes strongly to the observed
brightness of such complicated bodies.

One difference between the two data sets is that Respler's magnitudes show
a stronger dependency on the illumination phase angle than do those of MMT.
The R-squared values of the correlations are 0.26 and 0.04, respectively.

The reason for the stronger correlation is not known with certainty,
however it might be related to altitude. Only 4 of the satellites observed
by Respler had reached their nominal 1200 km orbit. The others were still
in the ascent phase at an average height of 689 km. If attitude is being
held constant during ascent that could explain the correlation.

Tony Mallama
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Received on Tue Dec 15 2020 - 09:43:11 UTC

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