02:04 2016年02月23日(更新 02:08 2016年02月23日)
俄联邦国防部空天部队航天设备侦察中心长官 - 安德烈·卡柳塔上校星期一（22日）表示，朝鲜确实将其地球遥控探测侦察卫星送入了轨道。
荷兰业余卫星观测者Marco Langbroek报告，2月28日从地面观测到了“光明星4号”卫星以及发射所用的火箭第三级。Imaging North Korea's new Kwangmyongsong-4 satellite, and the flash period of its UNHA-3 rbKwangmyongsong-4 on 28 Feb 2016
North Korea's recently launched new satellite (see a previous post
(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:
Kwangmyongsong-4 on 28 Feb 2016
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 Kwangmyongsong/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
A fit to the measured brightness variation over these three images shows
several specular peaks at regular intervals, with a slightly asymetric
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
.posted by SatTrackCam Leiden at 2/29/2016 11:48:00 AM
UPDATE 1 March 2016
I imaged both the UNHA-3 r/b and Kwangmy?ngs?ng-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
The image below is a stack of these three images. The rocket stage moves from upper right to lower left in the image.
===Kwangmyongsong 4 - Not So Dead?
It is possible to look at the compensated/corrected plot and draw some tentative conclusions as to what the distribution of readings is telling us. This is one view and there will be others with equal validity. However, the overall conclusion stays the same - there was change in the way Kwangmyongsong 4 was oriented in space and it probably managed to get rid of any significant spinning or tumbling.
Initally the satellite was probably rotating slowly (a number of seconds per revolution) rather than tumbling rapidly, or even spinning as some would have seen it. There is a lot of scatter in the Ndot2 values but the trend is to stay roughly constant, just below 0.00008. it implies that Kwangmyongsong's average cross sectional area stayed constant. Around February 13 there is a relatively fast transition to 0.00010 where it stays constant for a while.
The implication of the change is that air drag increased. Air drag is determined by the cross sectional area presented towards the direction of travel. Kwangmyongsong is a cuboid about 1.3 times as long as it is wide. It will experience a little more drag if one of the larger surfaces is facing the forward direction than it will if one of the square-shaped ends is leading. With a tumble, drag will appear to be constant based on an average of the large and small faces of the shape as they are presented alternately to the oncoming air.
KMS-4 solar panelsThe February 13 change could be related to deployment of the solar panel. At launch, Kwangmyonsong 4 had solar panels covering three of the longer sides. Two of them were hinged so that they could swing out either side of the third to form a single flat surface covered in solar cells. Opening the panel itself would have reduced the satellite's rotation speed through conservation of angular momentum. The average cross sectional area would have increased, leading to higher drag, hence the exhibited rise in value of Ndot2.
Kwangmyongsong 4's design is similar to Kwangmyongsong 3. There is a discussion of the solar panel deployment mechanism in Zarya.info's pages covering the earlier launch. The picture here depicts the fully-opened panel on Kwangmyongsong 4.
The change around February 17 is distinct and suggests that the stabilisation mechanism kicked in. The two possibilities are that it extended a gravity-gradient stabilisation boom or that gyros were spun-up. Whichever, it seems to have settled into a relatively stable regime with a fluctuation that has a period of 7-8 days. The fluctuation seems to be damped as the second peak is significantly less than the first. It may eventiually settle down to a constant value when all rotation is damped out.
It may explain the Russian comment on February 22. Russia has its own tracking network that produces observations similar to those that feed the Twoline Orbital Elements. Its analysts will have seen this pattern and could justifiably have concluded that Kwangmyongsong 4 had been "activated".