ENVISAT and other satellites flaring over the Italian Dolomites

During the second half of July, I travelled through northern Italy, including an 8-day mountain hike from mountain hut to mountain hut through the high Alpine parts (up to 2770 m) of the Rosengarten Dolomites. The latter mountains are truely marvelous, and perhaps the most beautiful mountains I have ever seen.

During two clear evenings I did some limited astrophotography: limited, as because of weight considerations I had only two lenses with me  (a Canon EF 100mm Macro and a Tamron 17-50mm zoom) . After all, we already had to carry 16 kg on our backs every day while scaling the mountain.

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The image above was shot at 2238m altitude from Rifugio Vajolet on July 23rd. It shows ENVISAT (02-009A) flaring. Since contact with this legendary Europe remote sensing satellite was lost on 8 April 2012, it appears to have started to tumble. Two brightness maxima (one brighter and one fainter preceding it) are visible on the original of the above 30 second exposure, and other (faint) maxima are visible on an earlier and on subsequent images.

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A 45 image series (30s exposure each) from the same location was used to create the above image of startrails circling the celestial pole. The mountain at right is the 3004m high Kesselkügel.

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A few days earlier (16 July), while at lower altitude (1188m) in Aldein (Aldino) where we visited the nearby Bletterbachschlucht, I shot this image of a double Iridium flare. The brighter of the two is Iridium 63, the other one is Iridium 14. The classified Japanese satellite IGS 7A (11-075A) can be seen as well as a fainter steady trail near the center of the image (the original image has 3 more very faint satellite trails as well). The bright star top right is Arcturus.

All images were made with a Canon EOS 60D at 2000 ISO (and part of image series driven by a programmable timer) using a Tamron 2.8/17-50mm set at 17mm.

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.

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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.

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

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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...