The flashing behaviour of USA 81 (1992-023A)

The video footage above was shot by me on 25 July 2017 and shows the classified satellite USA 81 (1992-023A). It is flashing rapidly, at ~5 flashes per second.

USA 81 is one of two satellites (the other is USA 32; the attempted launch of a third one failed) on which little is known, but that were probably ELINT gathering satellites, probably in the Singleton/SBWASS program. It was launched from Vandenberg AFB on 25 April 1992 with a Titan 23G.

With its earlier sistership USA 32, USA 81 is renowned for the light shows it puts on. It has a very rapid and at times very conspicuous flash cycle of sharp specular flashes, like a disco-ball: the video above shows an impressive example of this. How pronounced the flashing is depends on the viewing angle: the video above catches a brief period, halfway the footage, where it becomes very pronounced.

The flashing is very regular and specular, with a main period of 0.2 seconds and a secondary period half of that, 0.1 seconds.

The diagrams below show this periodicity well. They are the result of an analysis of (part of) the video above with LiMovie and PAST - the analyzed part of the video was the second part, after the camera repositioned, when flashing was most pronounced.

The first diagram shows the observed very specular flashes (blue) and a fitted double sinusoid of 0.2 and 0.2 seconds (red, dashed). They fit very well:

click diagram to enlarge

The two periods are also well discernable in the Lomb periodogram and the fast Fourier analysis below:

click diagram to enlarge

click diagram to enlarge

The earlier sister ship of USA 81, USA 32 (1988-078A), shows the same brightness behaviour (but with a main periodocity of 1.2 seconds) with the same periodicity. This points out that the flashing is intentional.

There are two options to explain the flashing behaviour. One is that the satellite is spin-stabilized. The other is that the satellite could have a large and shiny rotating element, for example a large rotating antenna.

The tumble period of the UNHA-3 upper stage from the recent North Korean launch is slowly changing

click image to enlarge

The image above, taken in the evening of 5 March 2016,  is a 10-second exposure showing several flashes of the tumbling UNHA-3/Kwangmyŏngsŏng rb 2016-009B, the upper stage from North Korea's recent Kwangmyŏngsŏng-4 launch. It was taken during a very favourable 67-degree elevation pass, using my Canon EOS 60D and a SamYang 1.4/85mm lens (set at F2.0). The sky had cleared just in time for this pass (a last wisp of clouds is still visible in the image).

The flashes had a brightness of about mag. +3.5 and were visible by the naked eye. The resulting brightness variation curve is this one:

click diagram to enlarge

I have briefly mentioned the tumbling behaviour of this rocket stage in an earlier post. Over the past week I have been following this rocket when weather allowed, obtaining observations in the evenings of Feb 28, Feb 29, March  3 and March 5. This now allows a first look at how the tumble rate is (very) slowly changing.

The theory behind tumbling rocket stages and why their tumble rate changes over time, is briefly discussed here on the satobs.org site. After the payload and the upper stage separate, usually by means of exploding bolts, the upper stage gets a momentum from this separation.

Over time, the resulting tumble is influenced by interaction of the rocket stage body with the earth's magnetic field. Spent upper stages are basically hollow metal tubes, and the Earth's magnetic field causes induction in it, leading to the tube getting an electric charge. Basically, the rocket stage becomes a dynamo. The Earth's magnetic field then further interacts with this electrically charged rocket stage, by means of the Lorentz force exerting a magnetic torque on the rocket stage's spinning motion. It is the latter effect which by "tugging" on the tumbling stage, changes its momentum, with a changing tumble period as a result. The resulting change is one towards a slower tumble rate, and eventually the stage might stop tumbling altogether.

I earlier established a peak-to-peak period of 2.39 seconds for 2009-009B from observations on Feb 28 and 29. Analysis of the new data obtained on March 3 and 5 show that the period is changing: I get 2.43 seconds for March 3 and 2.45 seconds for March 5.

I re-analyzed the Feb 28 and 29 data as well, this time using a fit to a running 5-point average on the raw data, which leads to somewhat better refined peaks. I also found that the initial autofit made by PAST is actually not the best fit, based on the r-square values of the fit. re-analysis leads to a 0.01 second revision to 2.38 seconds of the Feb 28 period, while the Feb 29 period stays at 2.39 seconds as initially established.

So the sequence is:

peak-to-peak periods
-----------------------------------
Date        TLE date    Period(sec)
-----------------------------------
Feb 28.81   16059.81    2.38 ± 0.01
Feb 29.79   16060.79    2.39 ± 0.01
Mar 03.79   16063.79    2.43 ± 0.01
Mar 05.82   16065.82    2.45 ± 0.01
-----------------------------------

(NB: the listed uncertainty is an estimate)

Even though the differences are very small, there appears to be an increasing trend to the periodicity, at the rate of about 0.01 second per day. As the difference is systematic, it is probably real and not just scatter due to measuring uncertainty (time will tell if this indeed holds).

[edit 7 March 2016 19:55]
One caveat: the synodic effect. As the viewing angle changes over the pass, this has some influence on the determined period. For fast tumblers this effect is small, but as we are talking about differences in the order of a few 0.01 seconds, the synodic effect comes into play.
The observations of Feb 28, 29 and March 3 were all made some 30 degrees beyond culmination, so the synodic effect should be about the same. The March 5 observation was done at culmination (I actually have a second image post-culmination as well but have not analysed it yet)
[end of edit]

Below are the brightness curves on which these values are based (click diagrams to enlarge):

click diagrams to enlarge

Appendix: on the construction of these brightness curves

I got a number of questions on how, and with what software, I produce these brightness curves. I will briefly explain below.

(a) calibrate exposure duration
What is first necessary, is that the real duration of the exposure is carefully calibrated. A "10-second" exposure set on your camera is not exactly 10.000 seconds: with my Canon EOS 60D for example, it is 10.05 seconds in reality (this deviation seems to increase exponentially with exposure time: a "15-second" exposure for example is in reality closer to 16 seconds!).

(b) measure pixel values with IRIS
The pixel brightness over the trail on the photograph is measured using the free astrophoto software IRIS.  Load the image, and chose "slice" from the menu option "view". Put the cursor at the start of the trail, and draw a line over the trail to the end of the trail. A window pops up with a diagram. You can save the data behind this diagram as a .txt table.
NB: be aware that Iris always measures from left to right (no matter how you draw the line), so if the satellite moved from right to left, you will later have to invert the obtained data series.

(c) Excel manipulation
The resulting .txt data file is read into excel. There, if necessary I first invert the series (see remark above). The result is a table with a column with pixel brightness values,  to which I ad an increasing pixel count. I then ad another column, representing the time for each pixel measurement. The value of the first cell is the start time of the image in seconds (I usually take the number of seconds after a whole minute, e.g. if the image started at 19:43:32.25 UT the value in this cell is "32.25". If I have a total number of pixels of say 430 (with 430 corresponding pixel brightness values), and an exposure time of 10.05 seconds, then I type this in the cell below it: "=[cell above it]+(exposure/number of pixels - 1)". In our example: "[cell above it] +(10.05/429)".
Then drag this down to the end of the column: the last value now should correspond to the end time of the exposure (in our example, it should be "42.30", i.e. 32.25 + 10.05).

If the raw data graph shows a lot of scatter, it can be useful to apply a running average to the data.

(Note: this approach assumes that the angular motion of the tumbling satellite or rocket stage was fixed over the exposure time in question. In reality, this is not the case. But for short time spans of a few seconds, this can usually be ignored, certainly if the image was taken near culmination of the object. It does introduce some deviation in the result though. Compensating for this makes the exercise a hell of a lot more complicated).

(d) read into PAST and analyse
I then copy the columns with the times and pixel brightness values, and paste them into PAST v.3 (very neat and free statistical software developed by paleontologists. I like it because it is versatile and able to create publication quality vector-format diagrams - the latter ability is something often lacking in such packages).
Press "shift" and select the two columns. Next, under "model" chose "sum-of-sinusoids". Next, a pop-up screen with a diagram appears.
Select "points" under "graph style". I leave "Phase" on "free". You then check the checkbox "fit periods" and click the "compute" button. It will fit a period.
However, I have noted that for some odd reason, the fitted period is not always the best fitting period! Check this by unchecking the "fit period" box, and in the box with the period result, varying the value from the initial fit slightly, after which you press the button "compute" again (leave the "fit period" box unchecked). Look at the R^2 values, and by trial and error find the best R^2 value. This is your actual period.
If your graph shows clearly skewed rather than sinusoidal peaks, than there is a second period interacting with the main period (for example, complex spin motion over two axis, or weaker secondary peaks present). You can try to model this by chosing "2" under "partials".

If you want a nice publishable diagram, press "graph settings" after you are done and adjust the diagram to your liking. Save it as .svg if you want to edit it further in for example Illustrator (as I do), otherwise use one of the other image formats available.

The tumble periodicity of the Chang'e 3 upper stage (2013-070B) revisited

click image to enlarge

Brightness variation due to tumbling of the Chang'e 3 upper stage (2013-070B)
stack of 15 images taken with the 0.51-m telescope of MPC Q65 Warrumbungle
11 September 2015

I have written before on this blog about tracking very distant space debris: the CZ-3C upper stages of the Chinese Lunar missions Chang'e 2 and Chang'e 3, which move in chaotic trans-Lunar orbits. I have embarked on a long-term project to follow these objects.

Apart from positions to keep their orbits up to date, these observations also provide information about the tumbling behaviour of these objects. Both objects have a periodic variation in brightness: a very rapid one for 2010-050B, the Chang'e 2 upper stage, and a slow one for 2013-070B, the Chang'e 3 upper stage.

Earlier, in July 2015, I had established a tumbling periodicity of  ~7 minutes for 2013-070B. I have now been able to refine that value much better, to only a few hundreds of a second.

With the help of Peter Starr from Warrumbungle Observatory (MPC Q65) in Australia and Krisztián Sárneczky from Szeged University's Piszkéstető Observatory (MPC 461) in Hungary, I could obtain two nice series of data the past week. The data were gathered on September 11 (Warrumbungle 0.51-m telescope) and September 14 (Piszkéstető 0.60-m Schmidt telescope).

The first set, taken by Peter from Warrumbungle, is a set of 15 exposures of 30 seconds each, taken in ~1 minute intervals. The image at the top of this post is a stack of these images. The brightness maxima can be clearly seen.

The second set, obtained in twilight by Krisztián from Piszkéstető at the end of a run of the Szeged Asteroid Survey, is a set of 18 exposures of 3 seconds (!) each, in ~20 second intervals, with a brief pause halfway the series.

Single sinusoid fit to data from Sep 11 (lef) and Sep 14 (right)
click diagram to enlarge

The data allow to fit a sinusoid to both sets simultaniously, and from that get a very accurate periodicity. The double diagram above shows this sinus-fit to the data. It allows to establish a peak-to-peak periodicity of 423.01 ± 0.03 seconds for the tumbling of 2013-070B.

Rapid tumbling of the Chang'e 2 r/b (2010-050B) and Rollercoaster orbital evolution

(click image to enlarge)

Recently, I have posted several times about my tracking of two extremely remote pieces of space junk: 2010-050B and 2013-070B, the CZ-3C upper stages of the Chinese Chang'e 2 and 3 Lunar missions. These orbit in orbits with (currently) perigee just within, and apogee beyond one Lunar distance, i.e. a trans-Lunar orbit.

In a recent post I discussed the tumbling behaviour of 2013-070B, the Chang'e 3 booster. At that time, I stated that by contrast the Chang'e 2 booster, 2010-050B, appears steady.

I can now say that is not true: 2010-050B is tumbling too. And very rapidly, which is why I didn't notice it earlier.

My earlier imaging sessions were done while 2010-050B was at well over one Lunar distance (beyond 400 000 km), towards its apogee. On July 18th I imaged it from MPC Q65 Warrumbungle while it was only a few hours from its perigee, at a distance of 280 000 km (about three quarter of a Lunar Distance), moving at 47" per minute. The result is a much longer trail on the image than in earlier imaging sessions.

Rather than being a trail, suddenly the trail is resolved in a series of dots: typically three (and in one image two) per 30 second exposure. See the image in the top of this post. The reason this was not visible during earlier imaging sessions, was that the trail was so short (a  few arcsecs) when imaging the object at larger distance, that the dots merge into one trail.

The 3 dots per image, and once two dots, indicate a flash period of ~15 seconds, testifying to a rapid tumble. This is close to the period determined by Peter Birthwhistle (MPC J95 Great Shefford) in 2010 shortly after the launch.

I also imaged 2013-070B that night, at a distance of about 479 000 km (1.25 Lunar Distances). This object is tumbling much slower than 2010-050B: the brightness variation in the animated GIF below fits nicely with the 7m 05s flash period determined from June 26 and July 5.

The orbits of 2010-050B and 2013-070B are changing extremely fast, in a chaotic way, notably as a result of Lunar perturbations. As you can see in the table that is part of my SeeSat-List post here, the apogee of the 2010-050B orbit for example changed from about 550 000 km to about 446 000 km between May 7 and July 18. The perigee changed from about 350 000 km to about 280 000 km, i.e. from about 1 Lunar Distance to about 0.73 Lunar Distance, during that same period. The orbital period was shortened by almost 10 days.

While the apogee and perigee distances are currently decreasing for this object, a new Lunar perturbation might make them increase again in the future. The orbital inclination also widely varies over time. Such changes are very sudden, especially in connection to close Lunar encounters. These objects are on a true Rollercoaster ride through the Earth-Moon system.

As it turns out, this kind of chaotic orbit is very difficult to model, even over relatively short time scales. Attempts using GMAT show that very small variations in the determined orbit yield very different outcomes within only a few years. Variations in the order of a few hundred meters (!) in apogee and perigee will already do it, i.e. variations well within the uncertainties in the determined orbital parameters.

GMAT-simulated chaotic orbital evolution of 2010-050B over a 1.5 year period. Grey is the Moon orbit, red is 2010-050B orbit, blue grid is earth equatorial plane. In reality, the orbital evolution might be different as small variations in initial conditions (see text) yield large differences after 1.5 years.

So we have to observe these objects to see how their orbits evolve in the future. And this is what I will do: keep following them, over the coming years.

Basically, three eventual future fates are possible for these objects: one is eventual ejection into a Heliocentric orbit (so it will leave the Earth-Moon system); two is an eventual Earth impact (i.e. a decay in the Earth atmosphere); and three is an impact on the moon.

The flashing behaviour of North Korea's tumbling Kwangmyongsong 3-2 satellite

North Korea's first satellite Kwangmyongsong 3-2 (KMS 3-2) cannot be seen from the northern hemisphere at the moment (and hence cannot be observed by me currently). On the southern hemisphere, Greg Roberts (CoSatTrak) in South Africa is however successfully tracking the satellite.

He had a particular good pass on December 20th and obtained a very nice video record, tracking on the satellite with a motorized mount (note: movie has a period of black screen between opening title and start of the video record):

Greg Robert's video from S-Africa

(posted with permission)

The satellite is the object near the center of the screen, flashing about each 8.5 seconds with periods of invisibility inbetween. The moving streaks are stars (the mount is tracking the satellite as it moved along the sky): the other stationary dots in the image are hot pixels on the sensor of the video camera.

The video allows for an analysis of the flashing behaviour of the satellite. I used LiMovie to measure the satellites' brightness on the frames, resulting in the following lightcurve:

click diagram to enlarge

Visible is a clear ~8.45s periodicity with flashes of a specular character (suggesting a flat reflective surface). I have marked this with red triangles 8.45 seconds apart. In between the main flashes, a pattern of smaller secondary flashes can be discerned in a semi 8.45 second peridicity too (green triangles). They are not exactly positioned halfway between major flashes.

Assuming that each major flash is a flash caused by one of the sides of the KMS 3-2 cube-shaped body, then it completes a tumble once every ~33.8 seconds. Assuming that the less clear secondary flashes are due to a side of the cube as well, the tumbling periodicity would be half of that, i.e. 16.9 seconds.

Greg recorded the UNHA-3 r/b from the launch too. That one too is tumbling:

Greg Robert's video from S-Africa

(posted with permission)

Again, I used LiMovie to extract brightness information from each video frame. That was less successful with this video, because Greg's mount had difficulty keeping up with the fast-moving r/b for much of the record. A considerable part of the video could not be used for analysis, and I had to chop up the analysis in little non-continuous chunks:

click diagram to enlarge

What can be seen, is a flashing behaviour that starts slow and gentle and is increasing in rapidity near the end of the analysis, this being an effect of changing viewing angle.

Contrary to what some alarmist (sometimes almost hysterical) media reports have suggested, the tumbling of KMS 3-2 is by no means dangerous. David Wright over at All Things Nuclear has a very good debunking story about this all, pointing out the many misconceptions rampant in the reporting.

CBERS 2B flash pattern

click image to enlarge

Last night I set up the camera with a Tamron 2.8/17-50mm lens set at f3.2/17mm to run automatically (using an Aputure timer), in order to catch some Perseids.

AS part of the image series, I captured a satellite showing a regular flash pattern. The top image above is a stack of 7 images of 20s each, showing the repeated flashing (including a brighter flare).

It turned out to be CBERS 2B (07-042A) which was launched from China on 19 September 2007 as the third Chinese-Brazilian Earth Resources Satellite. It ceased operations in June 2010.

By measuring the positions of the flashes and relating these to a recent TLE, I was able to determine the flash pattern. It is a combination of two series: one with flashes each 23.7s (series a), and another one (which includes the bright flare) with flashes each 47.4s (series b). The latter is the double of the series a period. The sequence of flashes is a-a-b-a-a-b-a-a-b but the b-flashes are not nicely in the middle of the a-series flashes.

click diagram to enlarge

The two series probably relate to different reflective surfaces. The flashes from series a are conspicuously orange, while those from series b are bluish-white.

click image to enlarge

As can be seen on the CBERS website, the satellite body itself is wrapped in orange insulation foil, suggesting the orange flashes could be reflections from the satellite body. The bluish-white flashes could be from the solar panels. The satellite would then rotate once each 94.8 seconds during which 2 solar panel flares and 4 body flares (4 sides of the cubus) can be seen.

CBERS 2B was not the only satellite captured flaring this night: I'll report on the other later. Amongst others, Envisat was seen flaring again.

Perseids

I indeed captured some meteors as well: 7 Perseids and one sporadic meteor. Here is a nice Perseid:

click image to enlarge

A flashing GPS satellite (Navstar 39, USA 128)

This blog's readers will be familiar with the Global Positioning System (GPS). These US navigational satellites provide us with navigational aid, whether you are on a boat, aircraft, in a vehicle, hiking, or just using your cellphone. Our modern world would be nowhere without them.

But have you ever seen a GPS satellite?

click image to enlarge

In the evening of June 25 I by chance captured one of the 41 operational a GPS satellite that was decommisioned last year on photograph: Navstar 39 (USA 128, GPS 2A-27, 1996-056A). It showed up as a very bright small trail  and was flashing at a rate of  2-3 flashes per 10 seconds. Above is a compilation of the photographs taken (Canon EOS 60D with Samyang 1.4/85mm lens).

GPS satellites do not usually get this bright: the satellite was evidently flaring due to a favourable sun-satellite-observer line-up. As this is a decommisioned satellite, the flashing could be due (I am not sure) to the satellite having lost attitude control and being spinning.

ISS, Prowler, and a flashing Vortex 1 rocket

Apart from a  glimpse through clouds of the ISS on January 2nd (video posted here earlier), I managed to do my first observations of 2012 this weekend, in the evening of January 7 from Leiden and (using a remote telescope in the USA) on January 9.

Conditions were not ideal on January 7th: a lot of moonlight and intermittent clouds. I observed the HEO object USA 200 (08-010A), but due to the moonlight interference the trails were weak (but good enough to get a few positions) and the pictures not pretty.

For the night of January 8-9, I scheduled a few observations on a "remote" telescope, the 61-cm F10 Cassegrain of SSON in California. Target was Prowler (90-097E), an enigmatic object discussed here earlier.

click image to enlarge

The image series on Prowler (I always take a series of at least three images at minute intervals, in case the object is a bit off from predictions) contained a flashing stray.

This turned out to be a classified object as well: Vortex 1r, the r/b from the Vortex 1 launch (78-058B). This rocket stage is clearly tumbling or spinning, as attested by a quite regular flash pattern:

click image and diagram to enlarge

The main flashes are 2.96 seconds apart, and flanked on each side by slow secondary flashes about 0.47s before and after the sharp main flashes, giving the trail on the image a dash-dotted appearance.

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:

click images to enlarge

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.

Yet more bright NanoSail-D, and an unidentified object from the same launch

Yesterday evening (Wednesday evening) was very clear and saw another fine pass of NanoSail-D (10-062L), the experiental NASA solar sail. As on previous occasions, it became very bright after culmination, while descending to the southern horizon: reaching an easy naked eye magnitude of +0.5. It is still flashing, but trail saturation on the images meant I could not get a reliable brightness variation curve this time. Below are two images: one that shows it just north of the Coma Berenices star cluster, the other shows it passing south of Bootes into Virgo somewhat later (bright star in the top is Arcturus):

click images to enlarge

Tonight (Tuesday evening) I had another pass, a low west pass at 35 degrees altitude this time. And....it was invisible, to the naked eye at least.

On April 27th, Russell Eberst observed an unidentified object that moves in the same orbital plane as NanoSail-D and appears to be "something" from the same launch (see also here). It was subsequently observed by a number of other observers (and perhaps earlier, on March 3, by Greg Roberts), and yesterday I photographed it:

click image to enlarge

Another object observed this evening was Lacrosse 5 (05-016A).

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

The flash period of USA 81 on June 2nd (UPDATED with February 24 results)

In my previous post I reported on a bright stroboscopic flash display by the SIGINT satellite USA 81 (92-023A) on June 2. I now had some time to analyse the images. Below are diagrams showing the brightness behaviour in the two images that captured the event.

click diagrams to enlarge

In the first image, the median period between succesive peaks is a very neat 0.20 seconds (average: 0.18s; modus: 0.19s). The same period also is present in the series from the second image, but with more "noise" in terms of either extra "peaks" or missing peaks. Below images shows it as diagrams of the delta time between peaks, and the deviation of these to the 0.20s period established by the first image:

click diagrams to enlarge

The results compare with similar results I obtained in February this year, which for some reason I never published on this blog. These are diagrams from my February 24, 2010 observations (two images), when it showed a series of sharp glints in the zenith, similar to those of June 2nd, with a period of ~0.41s (multiple of the 0.20s of June 2nd). Lower in the sky, it changed to a slower cycle of less sharp peaks with a period of 1.26s.

click diagrams to enlarge

The brightness behaviour hence is quite similar to that for it's older sister ship USA 32 (see here).