Nanosail-D: a pattern in the Chaos

Earlier I reported on my August 14 observations of the experimental Solar sail Nanosail-D (2010-062L), including a brightness variation diagram derived from one of the images.

Initially, I could not see any clear pattern in it, so I called it "irregular". Next, Alain Figer from France pointed out it was not so irregular after all. His own images from August 16th (URL's here) show a very neat pattern of one major flash, then two secondary flashes, then a major flash again. On his images, the major flashes are 0.73 seconds apart.

Going back to my observations, it turns out it is indeed possible to find a similar periodicity of 0.73 +/- 0.03 seconds. The secondary flashes appear to be 0.73/3 = ~0.24 from these main peaks: in other words, main and secondary peaks fit a ~0.24s pattern.

Below diagram shows it. the lowest line gives the observed peaks, with the red triangles representing the main 0.73s cycle. The yellow tringles point out several secondary maxima at ~0.24s after the main cycle peak; the grey/white triangles point at a hint of a similar pattern ~0.24s before he main cycle peaks.
The upper line shows the modelled behaviour: a main peak (black triangle) each 0.73s, with secondary and tertiary peaks at ~0.24s intervals.

click diagram to enlarge

Nanosail-D flashing rapidly and brightly

As in late May and early June, Nanosail-D (2010-062L), the experimental NASA Solar Sail is making favourable passes again and under favourable conditions becomes bright and is flashing rapidly.

Yesterday evening around 22:50 local time (20:50 UTC) I observed it when it made a near-zenith pass, from SW to NE. While ascending and going through the zenith it was quite bright and an easy naked-eye object, reaching mag. +1.5. It was rapidly and very irregularly, rather nervously flashing.

I shot four images, two of which are shown below: in the first image, the brightness variation is photographically less apparent than it was visually, because the trail is near saturation. It shows the Solar sail passing just below Lyra (Vega in top left) along with a stray, the French Optical Remote Sensing satellite Spot 4 (98-017A, the fainter of the two trails).

The second image, shot while Nanosail-D was getting fainter, shows the sharp flashes more readily.

click images to enlarge

From the latter image, I could derive this brightness variation diagram:

click diagram to enlarge

A large number of sharp brightness peaks can be seen: I count some 26 peaks in a 10.05 seconds time span, the one more prominent than the other. No regularity in the pattern is apparent.

NanoSail-D: evolution of the flash pattern during a pass

Yesterday evening at 23:00 CEST I observed a twilight pass of the experimental NASA solar sail NanoSail-D again (see earlier and later observations here).

This pass allowed me to capture a series of brightness curves, which document the evolution of the flash pattern during a single pass, as the looking angle is changing (looking "edge on" aroudn culmination, and then more and more "on the tail"as it is descending) . The change in flash pattern is profound: this is clearly a very complex matter where the flash pattern highly depends on the relative position of the object to the observer.

click images to enlarge

It starts (image and diagram 1) with a lot of irregular flashes, spaced 0.3 - 0.9s apart (average 0.49s but with large standard deviation).

Next (image and diagram 2), a nice semi-regular sinusoid pattern develops, flashes spaced 1.24 - 1.45 s (average 1.33s)

Then (image and diagrams 3 and 4), the period increases, the pattern transforming to a slower sinusoid with peaks first 5.61s apart, then somewhat decreasing again to 4.11s apart (edit: or maybe not: the firts "peak"might be a sub-peak. The valleys seem at similar distance to the previous diagram). Superimposed on this, a shorter cycle of minor subvariation can be suspected, with various periods.

This slower variation in the last two diagrams is why Bram, me and some other observers got the impression, on this and some past passes, of the period almost "disappearing" when NanoSail-D was descending on altitudes of ~35 degrees.

Two of the trail images in a bit more detail: note the difference in flash pattern:

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NanoSail-D Galore

Yesterday evening, I observed a twilight pass (sun at -7 degrees altitude and a still bright blue sky) of NanoSail-D, the NASA experimental solar sail (see earlier posts here). It passed at 44 degrees in the east, and after culmination became very bright again, flashing to mag. 0.

Because of the bright twilight sky I had to tone down the ISO to 400 and diaphragm to F4.0. The images show the flashing behaviour very neatly, and I obtained two spectacular sinusoid brigthness curves (the second one is from the image shown):

click images to enlarge

The flash period is definitely slightly variable, varying between 1.2 and 1.5 seconds with an average of 1.35 +/- 0.12 seconds.

With the current orbit, decay is projected for mid-August.

note added: click the 'Nanosail-D' label below to see later posts on NanoSail.

More flashing NanoSail-D, and flaring KH-12 USA 224

A week after my May 24 observations, I observed NanoSail-D (2010-062L) again, the experimental NASA solar sail.

NanoSail-D (image: NASA/MSFC)

As a week ago, it became very bright after culmination, while descending in the south, and was rapidly flashing again. It was easily seen by the naked eye, reaching mag. +1 or possibly +0.5.

In fact it is so bright, that the pixel brightness of the trail reached saturation on two of the three images. The first image (below) did yield brightness information: the resulting curve is shown beneath it. The flash period is irregular, but periods of 0.5s and 1.0s pop up frequently in the diagram (for actual determined flash times, see here. Astrometry on the satellite itself can be found here).

click images to enlarge

As can be seen on the images, the satellite was in a race with an untimely field of clouds (the orangish streaks in the images), staying just ahead of it. Visually, the brightness fluctuation was much more apparent than it is on these images (due to the saturation of the latter): it was very clearly flashing.

Nanosail-D was not the only object flashing. USA 224 (11-002A), the new KH-12 Keyhole launched on January 20 this year, flared too, while passing through the zenith, with flares at 23:48:27.3 and 23:48:31.8 UTC (May 31). The "saddle" and elevated brightness between the two flares is interesting (the trail is notably fainter before the first flash, and subsequent images show it is fainter again after the second flash):

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This was the second time I imaged USA 224 (The first time was May 24). In addition to USA 224 and NanoSail, I also imaged another KH-12 Keyhole, USA 161 (01-044A), and a Lacrosse SAR, Lacrosse 3 (97-064A).

Nanosail-D: a spectacular show of bright flashes!

Last night I finally was able to capture Nanosail-D (10-062L), the NASA experimental solar sail. It put on a spectacular show, flashing rapidly, becoming an easy naked-eye object after culmination when it reached magnitude +1.

As it gradually brightened from invisibility to naked-eye brightness while passing at 61 degrees altitude due east, it initially flared rapidly, in an irregular pattern, at a rate of 1 to 3 flashes per second. below is the first image, and two other where the trail runs out of the image frame (in haste, I aimed badly when repositioning the camera):

click images to enlarge

When it descended towards the South-Southeast, it became brighter, reaching mag. +1. The flashing pattern became somewhat more regular and slowed down to about one flash per 1.6 seconds. On the image, the trail is quite saturated and hence the brightness variability on the image below is less apparent than it was visually. Visually, the objet was clearly "winking", very cool to see:

click images to enlarge