Imaging North Korea's new Kwangmyŏngsŏng-4 satellite, and the flash period of its UNHA-3 rb

Kwangmyŏngsŏng-4 on 28 Feb 2016
(click image to enlarge)

North Korea's recently launched new satellite (see a  previous post), Kwangmyŏngsŏng-4 (KMS-4: 2016-009A), is finally starting to make visible evening passes here at Leiden.

Yesterday evening, 28 Feb 2016 near 19:45 UT (20:45 local time), I shot the image above, one of two images showing the satellite passing near the Celestial pole. It is a short exposure of 2 seconds with the 2.8/180 mm Zeiss Sonnar lens on my Canon EOS 60D.

Below is the same image, but in black-and-white negative, showing the trail a bit better:

Kwangmyŏngsŏng-4 on 28 Feb 2016
(click image to enlarge)

The object is very faint (probably near mag +7). It needs a rather big lens (the Zeiss 2.8/180 mm has a lens diameter of 6.4 cm), which unfortunately also means a small FOV. Over the two images, a total imaging arc of ~6 seconds, it however appeared to be stable in brightness with no sign of a periodicity due to tumble. So either it is not tumbling, or if it is tumbling at all it must be a very slow tumble.

Some 16 minutes earlier, near 19:28 UT, I also imaged the upper stage of the Kwangmyŏngsŏng/UNHA-3 rocket (2016-009B) that was used to launch the satellite. This object is brighter and shows a nice tumble resulting in periodic flashes. Below are crops from three images spanning 19:28:32 - 19:28:44 UT. The brightness variation is well visible (the bright star it passes in the first image is beta Umi):

brightness variation of UNHA-3 r/b 2016-009B on 28 Feb 2016
(click image to enlarge)

A fit to the measured brightness variation over these three images shows several specular peaks at regular intervals, with a slightly asymetric profile:

click diagram to enlarge

The fit shown in red is the result of two combined sinusoids: a major period of 2.39 seconds with a minor period of 1.195 seconds superimposed (resulting in the slight asymmetry). Pixel brightness over the trails was measured with IRIS. The data were fitted using PAST.


UPDATE 1 March 2016:

I imaged both the UNHA-3 r/b and Kwangmyŏngsŏng-4 again in the evening of 29 Feb 2016. The sky conditions wer less good, and the pass was much lower in the sky. I used the 1.4/85 mm SamYang lens this time, to get a larger FOV in order to try to capture a larger arc.

KMS-4 was captured on four images (2 second exposures) between 19:19:17 - 19:19:34 UT. It was barely visible on the images, but again the brightness appeared to be stable over this 17 second time span.

The UNHA-3 r/b was also captured, and 3 images (5 second exposures) between 18:58:42 - 18:59:07 UT again showed a very nice flash pattern, fitting (like the observations of Feb 28) a flash period of 2.39 seconds:

click diagram to enlarge

The image below is a stack of these three images. The rocket stage moves from upper right to lower left in the image.

CBERS 2B flash pattern

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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

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: a brief note on how I construct these brightness curves

Some people have asked me how I get the brightness curves from my images. So here is a brief explanation.

On each image, the satellite has made a trail. Start and end times of the exposure are well known, and the start and end of the trail corresponds to these times.

Next it is as simple as using software (e.g. MaximDL, or IRIS) that can read pixel values along a line: let the software read a line that corresponds to the satellite trail on the image! With MaximDL or IRIS, this is as simple as drawing a line over the screen with your mouse, exactly over the satellite trail. The software then reads the pixel values along this line. The resulting data can be exported as a data table.

These data are then read into a spreadsheet I created, that for each data point interpolates the corresponding time (remember that the time of the first and last datapoint in the dataset is known: start and end of the exposure).

Now, this assumes the movement of the satellite on the image is linear. Strictly speaking, the apparent speed of the satellite is not linear. However, with short exposures (10s) that will not be a really big source of error.

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.

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):

click images to enlarge

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

Manoeuvring KeyHoles and the flashing Iridium 33 wreckage

July 2010 so far yielded a nice series of clear evenings, due to very warm, sunny weather (in most cases allowing observations in shorts and shirt). I observed on July 3, 4, 6, 12, 15, 16, 17 18, 19 and 22.

Two manoeuvring KeyHoles

Prime targets this month were the KH-12 KeyHoles USA 186 (05-042A) and USA 161 (01-044A). These both manoeuvred on the 14th of July, giving us observers a nice task of recovery and renewed tracking.

The manoeuvre of USA 186 (05-042A) was first noted by Pierre Neirinck in France. After some other observers missed it, he observed it being very late, but initially lost his reference points. Ted Molczan next created a number of search orbits, based on different presumed manoeuvre times. Next Alberto Rango and me again recovered the satellite (Alberto first while I still had daytime, then me on the next orbit, in deep twilight), in an orbit very close to one of Ted's search orbits.

Using pre-manoeuvre and post-manoevre orbits calculated by Ted Molczan from our observations, the manoeuvre occurred on July 14th at the ascending equator crossing at about 15:00 UTC, over Indonesia.

Next it turned out that another KH-12 Keyhole, USA 161 (01-044A) had also manoeuvred early on the 14th. Again, Pierre noted it first, observing it 12 minutes late on July 17th. Next Ted and a number of other observers joined the recovery (including me at some point). Using pre- and post-manoeuvre orbits calculated by Ted and Mike from our observations, the manoeuvre ocurred at the ascending equator crossing near 00:20 UTC, July 14th, near Hawaii.


The flashing behaviour of the Iridium 33 wreckage

On 10 February 2009, the American Iridium 33 (97-051C) telephone communication satellite and a defunct Russian satellite, Kosmos 2251, collided in space. A large number of debris pieces were spread over Low Earth Orbit (see here), and the main wreckages of the two objects kept orbiting, now wildly out of control.

The Iridium 33 wreckage (97-051C) made some fine passes last month, displaying the same kind of flashing behaviour due to tumbling that I also observed shortly after the collision in 2009 (see here, here and here). Some of these flashes are easy naked eye flashes, reaching mag. +0. The object interchanges bright flashes like these with (more numerous) fainter flashes in the +4 range.

I targetted the satellite wreckage several times this month to determine the flashing behaviour. In March 2009, it showed a period of 4.7 seconds. Analayses of the imagery of the past few nights, shows this has changed to about 3.1 seconds. Below is one of several images, taken on July 16th, showing a series of fainter and brighter flares:

click image to enlarge

Below are graphic representations of the flare positions (yellow dots) observed on consecutive nights (resp 16-17, 17-18, 18-19 and 22-23 July 2010). Please note: only flares happening during photographic exposures are shown here. There were more flares, but these happened while the camera wasn't open:

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(maps made using Heavensat)

An unusual flare was captured on July 17-18, consisting of a triple flare with flares within 0.5 seconds:

click image to enlarge

Other objects besides the KH-12 Keyholes USA 161 and USA 186, and the Iridium 33 wreckage observed last 3 weeks include:

- the geostationary objects Milstar 5, Mentor 2 and Mentor 4 (USA 202);
- the HEO objects USA 184, the USA 40 rk;
- the LEO objects Progress-M 04M, MSX, Lacrosse 5, the Lacrosse 5r, IGS 1B, the IGS 5r, USA 32, the NOSS 3-3 duo and the USA 144 decoy,;
- plus a large number of GEO and LEO strays.

I have yet to analyse the USA 144 decoy (99-028C) data from July 20 for a new tumble period determination.

March 21 Iridium 33 flashes

Like yesterday and 4 days ago, I captured the Iridium 33 wreckage (97-051C) flashing again in a very regular pattern. Like the days before, the flash period was 4.66 seconds:

photo 1:

19:39:02.51
19:39:07.17
19:39:11.85

Photo 2:

19:39:44.46
19:39:49.13

Images with the flashes indicated by arrows below:

(click images to enlarge)