Monday, 4 January 2010

GOCE flares compared (second UPDATE)

With four timed brightness profiles now available for GOCE flares, I created a comparison chart.

In this diagram, each profile has been shifted in Y value to keep them clearly separated. The delta values refer to the offset of the observed flare path tilt and the theoretical panel tilt (either 67.5 or 22.5 degree, depending on which panel caused the flare). This is a measure of distance to the theoretical central flare path.

As can be seen, there appears to be no clear correlation between delta/distance and the quality of the flare peak.

The profile for November 26th 2009 is less reliable as it suffered from thin cloud interference.

click diagram to enlarge

The flares are (perhaps - see below) caused by the solar-panel covered sun-facing side of the space probe:

With regard to the identification of the panels: below is a schematic cross-section of the GOCE probe. Two solar panels on the solar-facing side of the eight-plane shaped probe are responsible for the flares: one inclined at 22.5 degree and one at 67.5 degree.

click image to enlarge

This creates the geometric situation below (with the green trails being the theoretical central flare paths for the two panels indicated):

click image to enlarge

There is a baffling aspect to these flares and this model though. Flares from flat panels should be highly specular ("narrow") in both directions: angle and tilt. In essence: with regard to the probe's major axis (angle) and minor axis (tilt).

But they are not!

They are highly specular in angle ( = with regard to the probe's long axis) as evidenced by the short duration of the flares (FWHM ~0.5s). But not in tilt.

This is not what you expect from a satellite with an angular surface such as GOCE: it is what you expect from a tubular object (which GOCE isn't). This is a bit baffling. It could mean it aren't actually the solar panels which are causing the flaring behaviour, but some other part of the GOCE body. Problem is, there is no clear candidate for it...

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