Monday, 4 September 2017

OT: imaging the close flyby of Amor asteroid (3122) Florence

On 1 September 2017 near 12:06 UT the Amor class Near Earth Asteroid (3122) Florence made a relatively close approach to Earth. The nominal pass distance, 0.047 AU or about 18 Lunar distances, was a safe distance. It does not often come this close: the asteroid had last been about similarly close in 1930, and will not be really close again until 2057.

(3122) Florence is one of the more rare larger NEA's. It is about 5 km in diameter and currently has a theoretical MOID (Minimum Orbit Intersection Distance) of 0.044 AU, only slightly less than the pass this year.

While this is a safe distance for now, orbital disturbances in the (distant) future could bring it closer, and the size of the object is such that it would be of future impact concern. It is therefore on the PHA list, where PHA stand for "Potentially Hazardous Asteroid" (for some reason, I always make "Potentially Hostile Asteroid" of this in my mind, probably because of the similar "Potentially Hostile Aircraft").

(3122) Florence became quite bright during this close pass, and was visible in binoculars at a maximum brightness of about magnitude +8.7 just before the moment of closest approach.

About 1.5 days after the moment of closest approach, near local midnight of September 2-3, I imaged the fast moving asteroid from Leiden with my Celestron C6 telescope. It was about mag +9.1 at that time. The movie above, and the stacked image below, was made from 87 images (each an exposure of 10 seconds with a 5 second interval) taken over a 17-minute period between 22:31:32 - 22:48:47 UT (Sep 2).

The asteroid was at a distance of 0.048 AU at that time and moving fast through Delphinus, at an angular speed of about 22".5 per minute.

The equipment used was a Celestron C6 (15 cm) Schmidt Cassegrain telescope with F6.3 focal reducer, and a Canon EOS 60D DSLR at ISO 3200 in the prime focus of the telescope.

(the satellite that can also be seen zipping past in the movie, is a Russian GLONASS, Kosmos 2425)

stack of 87 images taken over a 17-minute time interval
(click image to enlarge)

Friday, 1 September 2017

The other subliminal message in Kim Jong Un's missile test map

image: KCNA
The image above (from North Korea's KCNA) shows the North Korean leader Kim Jong Un and a map. It was likely taken on the day of the 29 August missile test that shot a Hwasong-12 MRBM over Japan, into the Pacific Ocean. I analyzed this map and what it shows in detail in my previous post, showing that the trajectory which seems to be sketched on the map deviates from the real missile flight path.

But there is more to this map, it turns out after further analysis. There are not one, but two subliminal messages contained in this map.

The first subliminal message, already discussed at the end of my previous post, is that it depicts a 3300 km trajectory (the real flight trajectory appears to have been shorter, 2700 km). This is the approximate distance to Guam.

But there is a second subliminal message. The map also contains a veiled threath to Hawaii.

click to enlarge

As can be seen in the annotated georeferenced version of the map image above (see also my previous post), the trajectory skeched on the map (white) is very close in direction to what a trajectory towards Hawaii would be.

In the map above, there are two lines representing such a trajectory targetting Hawaii:

- The green dashed line shows what a real, 7400 km range trajectory towards Pearl Harbour would be (this takes earth curvature and earth rotation into account);

- The yellow dashed line shows what the trajectory is if launched into the same azimuth as for  targetting Pearl Harbour, but with a shorter 3300 km range, as on the map in front of Kim Jong Un.

The latter yellow line obviously is very close to what is sketched on Kim Jong Un's map. In fact, I think that within the error margins of my georeferencing effort, they might well be the same.

The white line, my best effort to represent the trajectory sketched on the map, would be a missile launched into azimuth ~77.25 degrees. The dashed yellow and green lines, are both for missiles fired into azimuth ~76.9 degrees. 76.9 and 77.25 degrees are very close, a difference of only ~0.35 degrees.

To clarify further what the map depicts: the reason that, even though the launch azimuth is the same, the green and yellow lines do not overlap is because of earth rotation and earth curvature. Firing a missile into the same azimuth (~76.9 degrees) from Pyongyang Sunan, yields a slightly more southern trajectory if the range of the missile is ~3300 km (as on Kim Jong Un's map) instead of ~7400 km (the distance to Pearl Harbour). This is because a flight to Pearl Harbour takes longer in time, and the earth surface is meanwhile rotating under the flight path.

So the trajectory sketched on the map contains two subliminal messages: the length (~3300 km) is roughly the distance to Guam. The launch direction is the launch direction towards Pearl Harbour. Two veiled threaths in one. No wonder Kim Jong Un smiles so exuberantly: "Riddle this, you Imperialist agressor Puppets!".

I firmly believe that the North Korean propaganda machine deliberately includes these images into what it makes public. When they show a map or monitor with a trajectory, however oblique and vague, it is not unintentional but (I firmly believe) intentional.

(this post is a follow-on to my earlier analysis here)

Thursday, 31 August 2017

North Korea's 29 August Hwasong-12 test with Japan fly-over: did it go as planned?

image: KCNA
It are hectic times for those (like this author) interested in the North Korean rocketry program. The past months have seen a steady series of increasingly bold missile tests (along with a threath of test-firing missiles towards Guam), that have been the subject of three earlier posts on this blog the past months.

And now a new one has occurred, and it is perhaps the boldest of these test flights so far. Last Thursday, 29 August 2017, at 20:57 UT, North Korea launched a Hwasong-12 MRBM on a trajectory over Japan: a politically bold move that caused air-raid sirens to go off in Northern Japan.

images: KCNA

Western military sources say that the missile was fired from Pyongyang Sunan airfield. It reportedly travelled 2700 km, crossing over Hokkaido, coming down in the Pacific Ocean about 1180 km from Cape Erimo in southeast Hokkaido, Japan. Apogee of the trajectory is quoted as 550 km.

This allows us to produce the trajectory reconstruction below (with some leeway as the quoted ranges are probably balpark figures). It shows that the missile crossed Japan over the southern tip of Hokkaido, a trajectory that seems designed to minimize Japanese landmass overflown, mitigating risk levels. The two red circles on the second map are depicting a 2700 km range around Pyongyang Sunan and 1180 km range around Cape Erimo. Where they are closest, is the resulting impact point (near 41.92 N, 157.56 E). Using STK I get a flight-time of ~14 minutes.

click to enlarge

click to enlarge
That odd-looking second of the two maps above is based on an interesting photograph published by the North Korean State News Agency KCNA. It shows an exuberant Kim Jong Un sitting on a desk with a map in front of him:
image: KCNA

We have recently seen more of this kind of shots from KCNA published after previous tests, and they often yield interesting information. In this case, the interesting detail is that a trajectory appears to be depicted on the map, as a thin line (the arc above it ending at the same point likely is a 3D representation):

If the sketched line indeed is the intended trajectory, then the interesting point of it is that it does not match the observed trajectory according to Western military sources.

I used my GIS skills to georeference the map on the image (with QGIS). Like in the case of the 'Guam map', the low resolution of the image and very oblique angle of te map on it make this a challenge, and the georeferencing obviously is not perfect - but good enough for some conclusions. This is the result (look for the vague line that possibly represents a trajectory on the image):

click to enlarge
Here is the same map but with annotations added, and with the trajectory sketched on the map (white line) and the actual observed trajectory (black dashed line):

click to enlarge

It is immediately obvious that the two trajectories do not match well. The trajectory (if it is one) sketched on the Kim Jong Un map is located more to the south, and indicates a larger range, about 3300 km (interestingly, it does conform to a real ballistic trajectory with earth rotation and curvature taken into account, unlike the straight line drawn on the infamous "Guam map").

(the second map shows exactly the same map area, but with a DEM and country shapefile as background. It shows you how the topography matches that on the georectified map from the photograph)

The difference between the two trajectories amounts to a range difference of 600 km and a 45 km difference in apogee. It represents a difference in launch azimuth of 6 degrees and of 3.7 degrees in launch elevation. It points to an underperformance of around 0.4 km/s in the missile's burnout speed.

click to enlarge
It is interesting to note that while North Korea for some previous tests (and their proposed Guam shot) published very accurate figures for range, flight time and apogee, they did not do that this time. It is also interesting to note that some Western military sources report that the missile "broke into three pieces".

So there are multiple indications that the test did perhaps not go entirely as planned, with an underperformance of the rocket engine and an error in launch direction, and perhaps structural failure. This would imply that the targetting of the Hwasong-12 is not quite fail-safe yet, which has implications for Kim Jong Un's proposed Guam enveloping missile demonstration.

This was the first test of the Hwasong-12 on a "normal" trajectory and it shows why it is important for North Korea to test its missiles on such a normal operational, rather than a 'lofted' trajectory: it is a different regime of stress on the missile and has the engines perform under more realistic conditions than on a 'lofted' trajectory. Errors in targetting and missile performance become more apparent.

For North Korea to do such tests on a "normal" trajectory for its MRBM's and ICBM's, they have to fly it over Japan. We are going to see more of this kind of tests the coming months is my prediction.

Update 31 Aug 2017:

(1) The 38 North blog has an interesting post suggesting the possible failure of a post-boost vehicle.
(2) South Korean and US military analysts appear to come to the same analytical conclusions as I did, according to this Korean news bulletin
(3) As Ankit Panda rightfully remarked, the situation drawn on Kim Jong Un's map need not comply to reality. It could be merely meant as a propaganda message (3300 km is roughly the distance from the launch site to Guam).

Update 1 Sep 2017:

A further follow-on post is here, discussing how the map contains two veiled threaths, to Guam and to Pearl Harbour.

Sunday, 13 August 2017

[UPDATED] My take on North Korea's hypothetical threath to Guam

click to enlarge

The sabre rattling between North Korea and the United States is continuing, with increasingly colourful and volatile language and threaths from both sides.

In response to Trumps statements on August 8 that North Korea better stop its threaths or else "they will be met with fire and fury like the world has never seen", the North Korean General Kim Rak Gyom, commander of the Strategic Force of the Korean People's Army, released a  statement through KCNA on August 10 that included a surprisingly detailed threath about firing four Hwasong-12 missiles towards the US island (and important Pacific Naval and Air Base) of Guam.

Two relevant parts of the statement read (emphasis added):

As already clarified, the Strategic Force of the KPA is seriously examining the plan for an enveloping strike at Guam through simultaneous fire of four Hwasong-12 intermediate-range strategic ballistic rockets in order to interdict the enemy forces on major military bases on Guam and to signal a crucial warning to the U.S.
The Hwasong-12 rockets to be launched by the KPA will cross the sky above Shimane, Hiroshima and Kochi Prefectures of Japan. They will fly 3 356.7 km for 1 065 seconds and hit the waters 30 to 40 km away from Guam.

The details listed, allow to reconstruct the intended launch site for this scenario. It points to launch of the missiles in the vicinity of Sinpo, an important North Korean Naval Base that is home to its experimental SLBM force and according to satellite imagery analysts has recently seen "high levels of activity" (although that is not necessarily related to the issue under discussion).

The distance from the Sinpo submarine SSBA dockyard to Anderson AFB on Guam is ~3357.5 km, in agreement with the distance mentioned in the KCNA statement. Taking into account Earth rotation, the flight trajectories of the missiles when launched from Sinpo would indeed cross over the three Japanese prefectures mentioned, as can be well seen in the diagram in the top of this post. Together with the listed flight time, it would point to a flight apogee at ~865 km altitude and a launch elevation of ~31.4 degrees, i.e. a "normal" flight trajectory for an IRBM (as opposed to the "lofted", reduced range trajectories of previous tests).

click to enlarge

The map in the top of this post displays the flight trajectories based on this scenario, with the four missiles straddling Guam at ~40 km distance of its shores, uprange, downrange and lateral to both sides of the main flight direction needed to reach Guam.

While the language of the KCNA release is threathening, it is important to realize it is not threathening an actual "attack" on Guam. They talk about a strike that will "envelope" the island with the missiles, each of them impacting at a distance of 30-40 km of the Guam shore.

With the listed 30-40 km offshore impact distances, the missiles would land outside of Guam's territorial waters: but in its Exclusive Economical Zone (EEZ). While sensitive, this is something else than actually hitting Guam or the territorial waters directly surrounding it. The latter would be a real attack on US territory.

Targetting the EEZ has earlier precedents, as recent North Korean missile tests have landed in the Japanese EEZ. What makes it different this time is that it is the EEZ of the US itself, not of an ally, and involves a fly-over of Japan.

Rather than an attack, the scenario painted by the KCNA announcement would be best described as a missile test and demonstration. A test, because it would be the first flight of the Hwasong-12 on a "normal" battle trajectory rather than a "lofted" trajectory. A test, as it would for the first time have the Reentry Vehicle (RV) face the atmospheric reentry conditions it would face if used in an actual conflict. A demonstration, as it would demonstrate that the Hwasong-12 can indeed reach targets at the distance of Guam. A demonstration, as straddling Guam with missile impacts obviously sends a very clear message to the US and its allies.

It would also potentially test the Hwasong-12's performance against US missile defense measures. And it would be a (risky) political test to see how the US and its allies would react to such a demonstration of military power.

How likely is it that it will happen? On the face of it, not that likely. It most likely is hollow rethoric. Firing missiles towards a US military base and US territory is very risky as it could provoke a disastrous counter-attack. A full scale US counter strike would mean the end of the North Korean regime.

However, the oddly detailed August 10 KCNA announcement (which as some analysts on Twitter mentioned almost reads like a NOTAM) could also be seen as a way to mitigate this risk. It clearly signals the intention to not hit Guam itself, just fire near it in a demonstration of power. It is in essence a (tough worded) notice of an upcoming missile demonstration, not an actual war threath.

We should also realize that a US counter-attack would be disastrous for both North Korea and the US and its allies. If the US counter-attacks, North Korea will respond by shelling Seoul into oblivion and, if it can, firing missiles towards targets in South Korea, and possibly towards Japan and US bases in the Pacific. The carnage will be incredible. Hence, a military strike on North Korea as a gut-reaction to North Korean missiles landing near Guam is not as likely as it might at first glance seem. A sane US response would be to restrain from such a counter-attack unless there are strong reasons to do so, like missiles actually hitting targets on Guam. North Korea might have made a similar assessment. But it is a risky one (also taking potential missile malfunctions into account).

North Korea however has taken bold calculated risks before. They recently fired missiles into the EEZ of Japan, a key US ally. They took a risk in sinking the Cheonan in 2010, and shelling Yeonpyeong island that same year.

It is important to note the recent impact of North Korean missiles into the EEZ of Japan, given that the August 10 KCNA announcement points to targetting the EEZ of Guam. This firing into the EEZ of Japan did not lead to military retaliation by the US and allies (and in a sense perhaps might be seen as "testing the waters"). This might embolden North Korea to fire into the EEZ of Guam, expecting (rightfully or not) a similar non-response.

What could the US realistically do in response? As mentioned, a counter-attack in response to the missile firings would lead to dramatic results for the US and its allies. Seoul and Tokyo and who knows Honolulu burning seems a steep price to pay for "acting tough" when the missiles provoking the response harmlessly landed in the Pacific Ocean outside of Guam territorial waters. I fail to see how the US can justify such a result to its citizens and allies when the target of the missiles is in the Guam EEZ and not Guam itself.

Alternatively, the US or allies could perhaps attempt to intercept the missiles. That sounds like a good middle ground but isn't, as it has its own risks. Intercepting missiles on a trajectory that would not reach Guam territorial waters would provide political fuel to North Korea, who can claim their missile test was attacked. Moreover, there is a serious risk that an intercept attempt partly or wholy fails. That would seriously damage the credibility of the US and its capacity to defend itself and its allies, and with that seriously undermine the faith of US allies in the region (apart from the general loss of face). An attempted missile intercept would therefore be unwise in my opinion, as it would be a win-win situation for North Korea no matter the outcome.

So to me, it seems that North Korea is playing a high level (if dangerous) game of chess here, and has managed to checkmate the US. There seems very little the US realistically can do about it, apart from denouncing it. And the tougher the talk from Washington, the more face they will lose if it happens. "Hold my beer", you can hear Kim say in response, knowing he got them cornered.

In case North Korea does go forward with the announced missile demonstration, I expect Trump to do what he has done before: back-peddle on his earlier tough talk and grand-standing. And obscure this by making some unrelated outrageous policy decision or statement in order to deflect attention away from this political defeat, just as he has done with earlier political defeats.

Maybe the North Korean announcement is just a hollow threath. Maybe it is not. More likely than not it will not happen. But I would not exclude it entirely from happening, if North Korea made a similar assessment as outlined above. We will see.

UPDATE  15 aug 13:25:

The North Korean KCNA published a  bulletin on August 15, also carries by Rodong Sinmun. Apart from some interesting statements that might suggest North Korea has put a test fire towards Guam on hold for a while, the Rodong Sinmun newspaper contains some interesting photo's (pdf here via KNCA Watch):

images: KCNA/Rodong Sinmun

Two items on these photographs are of interest: the image on the wall at right, which depicts Anderson AFB on Guam. The other one is the map in front of Kim Jong Un (I put it upside-down here to have north up in the map):

image: KCNA/Rodong Sinmun
This map clearly depicts a missile trajectory towards Guam, that is very close to the trajectory I presented earlier in this blog post. The point of origin of the trajectory indeed seems to be Sinpo on the southeast coast.

UPDATE 2 & 3, 16 Aug 2017 00:30 & 2:45 UT:

Some claims appeared on Twitter that according to South Korean analysis, the map points to launch from Musudan-ri rather than Sinpo:

I do not agree. I used my GIS skills to georeference and reproject the map in front of Kim Jong Un. Below is the preliminary final result:

click to enlarge

What can be seen is that the drawn trajectory points clearly and unequivocally to Sinpo, not Musudan-ri.

What also can be seen is that the line drawn on Kim Jong Un's map is a simple straight drawn line rather than a real missile trajectory. The blue line I have drawn in the map is a true trajectory, including earth curvature and earth rotation and taking the map projection into account. The dashed red line I have drawn is merely a straight line (ignoring map projection).

The country outlines have been added in by me to show how the georeferenced image matches a true map.

Saturday, 29 July 2017

North Korea's July 28 ICBM test

On 28 July 2017 around 14:45 UT, North Korea tested another ICBM. Early reports from US Military sources indicate a night-time launch from a new location (Mupyong-ni), an approximately 45 minute flight time, and launch into a highly lofted trajectory with an apogee as high as 3700 km and a range of about 1000 km, with the launch direction towards Hokaido.

These ballpark figures allow us to estimate a ballpark maximum range for this ICBM. Because this was (again) a lofted test with an almost vertical launch, the true range of the missile is much more than the ~1000 km of the test when it would have been launched on a more normal trajectory.

The results I get are shown in the figure above: using the same delta V impulse as the lofted test but putting the apogee at 1200 km (a typical ICBM apogee) and roughly same launch direction, I get a range of ~8700 km.

That is probably a conservative figure. The true range depends on various factors (including the weight of the warhead, but also whether this test was at maximum missile performance. Reasons why it was perhaps not, is that North Korea might have shown some restraint and  taken precautions in order not to land their missile in or too much near Japan. This is also why they launch in a lofted trajectory).

In the figure above, I have drawn what this cautious reconstruction of the real range entails. It surpasses the distance to Hawaii. It brings San Francisco on the US West Coast in range. Today's test therefore implies that North Korea can strike the US mainland.

Towards the other direction, it brings Moscow in range, and if the true maximum performance of the missile is slightly larger, also Western Europe (*).

By the way, just as with the previous July 4th test, the Russians have come with maverick data for this test again, quoting a much smaller range and lower apogee (732 km and 681 km) based on their own Early Warning Radar observations. There are suspicions that their data only pertain to observations of the ICBM's first stage, explaining the discrepancy.

The analysis in this post is based on the first released ballpark figures for this test. If better data are released, the outcome might slightly change.

UPDATE: North Korea has now published the following figures for their test: apogee  3724.9 km, range 998 km, flight time 47m12s. They say it was a Hwasong-14 tested to simulate maximum range. Photographs published indeed show a missile similar to the one launched on July 4.

photo: Rodong Sinmun

photo: Rodong Sinmun

* the maximum range is (unlike depicted above) not a neat 8700 km circle. The maximum range depends on which direction is launched into, due to Earth rotation effects. Due to this, when launched towards the east the missile will have a somewhat larger range than when launched towards the west. Launched towards the east it gets an extra "push" from the rotating Earth.

Saturday, 1 July 2017

OT: Broek in Waterland, the sixth Dutch meteorite (observed fall, 11 January 2017)

Last Monday was a special and extremely busy day. At Naturalis, the Dutch National Museum of Natural History, we presented a new meteorite: Broek in Waterland (provisional name). It is an L6 chondrite and only the 6th authenticated meteorite of the Netherlands in 177 years time, after Uden (LL7, fall, 1840), Utrecht (L6, fall, 1843), Diepenveen (CM-an, fall, 1873), Ellemeet (DIO, fall, 1925) and Glanerbrug (L-LL4-5, fall, 1990).

(left to right) The author and Leo Kriegsman (Naturalis) and Niek de Kort (Royal Dutch Association for Astronomy) with the new Broek in Waterland meteorite at the presentation in Naturalis Biodiversity Center, 26 June 2017

On 11 January 2017 at 16:08:40 UT (17:08:40 local time), just after sunset, a bright fireball appeared over the Netherlands. The sun was only 3 degrees below the horizon and the sky still bright blue and star-less at that moment, so unfortunately the Dutch-Belgian photographic all-sky network and the CAMS BeNeLux videonetwork where not yet operational. Dozens of people from the Netherlands and Belgium however visually spotted the fireball and reported it.

A driver on a highway near Weerde in Belgium, 165 km from the fall locality, captured the fireball with a dashcam and uploaded the video to a Belgian UFO investigation website. No other video records besides this one have surfaced, unfortunately. From a comparison of the road marking patterns on the video with Google Earth imagery, I determined that the fireball (going almost straight down in the video) appeared near geodetic azimuth 11-15 degrees. Broek in Waterland, where the meteorite was subsequently found, is in azimuth 11.5 degrees as seen from this locality, i.e. a very good match.

The next day, the owners of a garden shed near Broek in Waterland, a rural village just a few km north of Amsterdam, noted roofing tile shards on the ground next to the shed. Upon investigation, they discovered something had smashed through the roof and lodged on the supporting latticework. It was a 530 grams black stone, about 9 cm in diameter, the size of a small fist.

The Broek in Waterland L6 chondrite (click images to enlarge. Photographs by the author, 3 Feb 2017)

Puzzled by the curious incident, one of the finders started to search the internet for explanations. Two and a half weeks after the fall, she phoned Niek de Kort, who runs the Meteorite Documentation Center of the Royal Dutch Association for Astronomy and Meteorology. Niek was abroad at that moment, but the description and subsequent e-mail with pictures sounded very promising. He allerted Leo Kriegsman and the author (Naturalis Biodiversity Center, the Dutch National Museum of Natural History). We made an appointment with the finders and visited them at the fall locality on February 3, where we formally established that the stone was indeed a meteorite. From the look of it, I provisionally determined it as likely an L6 Ordinary Chondrite (a common type of stony meteorite). Subsequent laboratory testing has confirmed that initial assessment.

We arranged a temporary loan of the stone with the owners and got permission to cut off 20 grams for research. Subsequent laboratory research at Naturalis and Utrecht University with thin sections, XRF and microprobe confirmed that the petrology, mineralogy and chemistry was consistent with an L6 Ordinary Chondrite. Measurement of shortlived isotopes at the VU University Amsterdam found isotopes that confirm this is a recent fall.

The meteorite's pre-sampling weigth was 530 grams. It is fist size, and almost completely fusion crust covered, bar a few chips and scratches from the impact on the roof. One side of the stone is rounded, the other side shows flat facets, the larger ones of which are covered in "thumb prints" (regmaglypths). This evidences breakup of the stone during the ablative phase of entry into the atmosphere.

search activities in the fall area, February 2017 (photograph by author)

In the weeks after the stone came to light, I teamed up with Felix Bettonvil of Leiden Observatory to organise a search for more fragments in the surrounding area. Some fifteen volunteers, many of them veterans from earlier meteorite search attempts, from the Dutch Meteor Society, the KNVWS meteor section, Naturalis and Leiden Observatory, spend several weekends  meticulously searching a large area around the fall site, but no other fragments were found. The area in question has a lot of open water and is very swampy: part of the area is a nature reserve and a peat bog where, if you jump up and down, the ground surface starts to form waves, and it makes squishy sounds when you walk there. We used long metal rods to probe suspicious holes in the ground. Searches were halted when late March the bird breeding season started, and the area became temporarily prohibited for that reason.

Broek in Waterland is only the 6th authenticated meteorite of the Netherlands. The previous meteorite fall, Glanerbrug on 7 April 1990, was 27 years ago. It impacted on the roof of a house. We suspect, based on the total land surface of our small country, that on average about each three years a 0.5 kg meteorite lands somewhere in the country. Yet, we have on average recovered one only each 30 years. Evidently, a lot of them, 9 out of 10, fall straight into oblivion. The large amount of open water and generally swampy nature of much of the Netherlands, with very soft peaty and clayey substrates, might play a role here.

The location of Broek in Waterland, and the other Dutch meteorite fall localities (map by author)

All six Dutch meteorites are witnessed falls. The pre WW-II falls (Uden, Utrecht, Diepenveen and Ellemeet) all were recovered because the meteorite landed close to someone working the fields. With the mechanisation of agriculture post WW-II this no longer happened. The two post WW-II meteorites, Glanerbrug and the new Broek in Waterland, were recovered because they hit a building and caused damage.

We are actively trying to find meteorites and have been organizing dedicated searches a number of times, based on fireballs captured multistation by our photographic all-sky fireball camera network. Examples are a fireball from 2013 near Hoenderloo and another one from 2015 in Gaasterland. None of these searches was succesful.

The press attention on June 26, when the existence of the Broek in Waterland meteorite was made public by Naturalis, was enormous. We have been busy from 7 am in the morning to 1:30 am the next night, with Leo, Niek and I giving dozens of newspaper, radio and TV interviews. In the late evening of June 26 I was a table guest in a well-watched talkshow on Dutch television, RTL Late Night, live broadcast from Hotel Schiller in Amsterdam, showing the meteorite and talking about it with host Humberto Tan, with science journalist Govert Schilling as my side kick (or me as his, depending on your point of view).

the author (middle) as well as science journalist Govert Schilling (left) with the meteorite in RTL Late Night, 26 June 2017
RTL Late Night show host Humberto Tan with the meteorite

Tuesday, 6 June 2017

[UPDATED] Close Encounters of the Classified Kind: a post-event analysis of the close approach of USA 276 to the ISS on June 3

3 July 2017: A paper which is a further evolved version of this blog post has appeared in The Space Review. I advise you to read that paper

(UPDATED 7 Jun 2017 15:50 UT with two new figures showing circular motion of USA 276 around the ISS)

Something odd happened a few days ago, high above our heads. In an earlier blogpost, I discussed in detail how the odd spy satellite USA 276 (2017-022A) was set to make a peculiarly close approach to the International Space Station ISS on 3 June 2017. The spy satellite was recently launched for the NRO as NROL-76 by SpaceX, on 1 May 2017.

With the close approach moment now in history and post-approach observations of USA 276 available (as well as an orbit for ISS based on tracking data, rather than an orbital prognosis), I present my final analysis of the situation in the current post.

With the new data included, we can establish the moment of closest approach as 3 June 2017, 14:01:52 UT. It happened over the southern Atlantic north of the Falklands, near 43o.75 S, 45o.45 W, with a miss distance of only 6.4 ± 2 km (the  ± 2 km stems from the fact that TLE predicted positions have a typical positional accuracy of no more than 1 km at epoch).

The latter is significantly closer than the approach distances calculated before the approach (which were in the order of 17-20 km, see my earlier post). Ted Molczan also analyzed the situation and he finds an even closer nominal distance of 4.5 km (but within uncertainty intervals our results overlap).

For the ISS, I used elset  17154.48611204. For USA 276, I used the elset below which I calculated based on amateur observations including my own:

USA 276
1 42689U 17022A   17155.88026473 0.00004763  00000-0  65979-4 0    01
2 42689  50.0047 103.5284 0014136 110.9138 249.3345 15.56256291    00

rms     0.020                             arc May 31.92 - Jun 4.90 UT

For detailed purposes like this, the orbit determination is a bit sensitive to what observer data are included. I restricted myself to observers with known high accuracy in the orbital solution above.

click image to enlarge

click image to enlarge

Below is an updated animation of the situation:

A table of all close approach moments with distances smaller than 500 km:

DATE       UT         km 
3 JUN 2017 02:28:52   478.5 
3 JUN 2017 03:13:37   464.4 
3 JUN 2017 04:01:17   413.2 
3 JUN 2017 04:46:14   398.9 
3 JUN 2017 05:33:41   347.8 
3 JUN 2017 06:18:50   333.3 
3 JUN 2017 07:06:04   282.4 
3 JUN 2017 07:51:26   267.7 
3 JUN 2017 08:38:28   217.1 
3 JUN 2017 09:24:03   202.2 
3 JUN 2017 10:10:52   151.9 
3 JUN 2017 10:56:39   136.6 
3 JUN 2017 11:43:15    87.1 
3 JUN 2017 12:29:16    71.0
3 JUN 2017 13:15:38    26.3 
3 JUN 2017 14:01:52     6.4  **
3 JUN 2017 14:48:01    48.8 
3 JUN 2017 15:34:28    60.5 
3 JUN 2017 16:20:24   112.5 
3 JUN 2017 17:07:05   126.1 
3 JUN 2017 17:52:46   177.5 
3 JUN 2017 18:39:41   191.7 
3 JUN 2017 19:25:09   242.9 
3 JUN 2017 20:12:18   257.4 
3 JUN 2017 20:57:31   308.3 
3 JUN 2017 21:44:54   323.1 
3 JUN 2017 22:29:53   373.7 
3 JUN 2017 23:17:30   388.8 
4 JUN 2017 00:02:15   439.2 
4 JUN 2017 00:50:07   454.5

Note: as positions from TLE's have an intrinsic uncertainty (about 1 km at epoch time), the values in the table above have an uncertainty of about 2 kilometer.

The distance variation around close approach in diagram form:
click diagram to enlarge

click diagram to enlarge

The variation in orbital altitude of both objects around the time of close approach (actual geoid heights):

click diagram to enlarge
As can be seen, USA 276 was a few km (nominally 3.65 km) above the ISS at closest approach. It was nominally also a little bit over 5 km behind the ISS.

In the following diagram, nominal distances in km in X, Y and Z of USA 276 are measured with respect to the ISS. The X is in the direction of movement of the ISS, Y is perpendicular (lateral) to it, Z is the zenith-nadir direction:

click diagram to enlarge

[UPDATE 7 Jun 2017, 15:45 UT, revised 21:14 UT] The variation in position of USA 276 with respect to the ISS was such that it effectively circled the ISS at close approaches, both laterally (cross-track) as wel as along-track, as can be seen in these diagrams below. Please note that, to get a more clear diagram, the axes of the first diagram (crosstrack circling) are not to scale. The second diagram is the same figure, but with axes to scale. The third diagram (along track circling) is also to scale:

click diagram to enlarge
click diagram to enlarge
click diagram to enlarge

A collision avoidance manoeuvre is usually evaluated if an object comes within a box of 4 x 4 x 10 km of the ISS.

If upon further evaluation the chance of collision is larger than 1:10000, an avoidance manoeuvre is done, if circumstances allow this.

USA 276 remained just outside the 4 x 4 x 10 km box at closest approach, as can be seen in the illustration below (red box, the situation shown is for the moment of closest approach). The box represents a collision risk in the order of 1 in 100 000.

USA 276 relative to the ISS proximity safety box . Click image to enlarge  (image made with STK)

I remain agnostic on the question whether this close approach was intentional or not (see discussion in my previous post regarding some possible goals would the approach  have been intentional).

Ted Molczan published a discussion of pro and contra arguments on the question whether the approach was on purpose or not on the Seesat-L list on June 3. While Ted argues that the April 16 and April 30 postponements of the launch indicate a non-planar preference of the orbit (which argues against intention), this also means that this close approach could have been avoided by picking another launch moment.

While USA 276 remained just outside the safety concern box, it is weird to have your just launched classified payload pass so close (6.4 ± 2 km) to a high profile, crewed object like the ISS.

I can and do not believe for a moment that the NRO was not aware that the launch on May 1 would lead to the close ISS approach a month later. It would be extremely sloppy of them, from a Space Situational Awareness viewpoint, if they were not aware, especially given how close the orbital parameters are to that of the ISS.

So I am struggling to understand why the NRO allowed this close approach to happen, if it was not intentional. This event was bound to attract attention and that harms the classified character of the mission. USA 276 is relatively brigh and the approach was bound to be noted by independent observers. Indeed, some space enthusiasts in Europe unaware of the issue who were out to spot DRAGON CRS-11 and Cygnus OA-7 close to the ISS on June 4, did accidentally spot USA 276 passing some 3 minutes in front of it.

It is also an extremely sloppy thing to do because this close an approach to a high profile object like ISS is politically risky. As the ISS is an international cooperation which includes two parties (the United States and the Russian Federation) that are currently geopolitically on an uneasy footing, sending your military payload so close to the ISS as one party is eyebrow raising.

This, and the timing (the close coincidence with the Dragon CRS-11 arrival at the ISS [edit: this refers to the originally planned date of arrival at June 4, later postponed by one day]) was bound to generate questions and suspicions (as it did). What the NRO did with USA 276 in the last few days was therefore really weird.

But then, the current administration of the USA is doing very weird things, and perhaps someone in the new administration signed off on this without fully understanding the depths of it. The Trump administration after all is not quite the posterchild for competence.

(the video below shows a USA 276 pass I filmed in evening twilight of June 4, at low elevation)

Monday, 5 June 2017

Cygnus OA-7 and Dragon CRS-11 chasing the ISS in a twilight sky

ISS and Cygnus OA-7. Click to enlarge

June 3, the launch date of SpaceX's Dragon CRS-11 cargo spacecraft to the International Space Station (ISS), was clouded out in Leiden, much to my frustration.

But yesterday evening was (sort of) clear, albeit with cirrus in the sky and a moon that was quite a nuisance. It allowed me to observe the ISS, the Dragon CRS-11, and Orbital ATK's Cygnus OA-7, which had de-coupled from the ISS a few hours earlier, making a low elevation pass (less than 35 degrees elevation) in the southern sky.

The image above shows the ISS (the bright object near the tree) and, as a faint trail, the Cygnus OA-7 (upper right corner, in the cirrus), descending towards the SE horizon.

Below is a better picture of Cygnus OA-7, shot 25 seconds later (ISS is already behind the tree here):

Cygnus OA-7. Click image to enlarge

Cygnus OA-7 passed ~25 seconds after the ISS. One minute later, ~1m 25s behind the ISS and on a slightly lower elevation track came another object: Dragon CRS-11:

Dragon CRS-11. Click image to enlarge

I did not expect the Dragon to be behind the ISS: I expected it somewhat in front of it. So initially I was miffed that I missed it (see below, this evening did not go quite well): to be surprised by it appearing behind the ISS!

This evening did initially not go well, but in a weird way eventually turned out fine.

A number of objects would pass in a short timespan of a few minutes: USA 276, the Dragon solar panel covers, Dragon, ISS, and somewhere nearby the ISS also Cygnus OA-7.

There were no post-ISS-release elements for the Cygnus yet, so its position would be a guess, although I reckoned it probably still was close to the ISS. Cygnus are usually faint (this time too) and only naked eye objects under favourable circumstances (usually, as this time, close to shadow ingress).

For Dragon, only a day old elements were available. These placed Dragon a few minutes in front of the ISS. As it no doubt would have manoeuvered during that day, I expected it to be closer to the ISS in reality, but that it was behind the ISS, that was a bit unanticipated.

The passes occurred in twilight (sun about 10 deg below the horizon). As obtaining new astrometric data on USA 276 (see story here for as to why) was important, I had set up the WATEC video camera to capture it, from the loft window (the only spot in my house where I can view that low south). That took  me longer than expected, as I initially had some trouble finding the target area in the video view (it was still deep twilight).

When I finally had found the target starfield through which USA 276 should pass, I discovered to my dismay that the pass was already imminent within minutes. As I could not visually observe through the same loft window, nor photograph, I had to be outside for that, at the city moat near my house which offers a view low south. So I grabbed my photo gear and ran outside. Arrived at the observing spot, I found that I already missed the opportunity to visually see and photograph USA 276 (luckily, the video camera in the loft window did film it). I also feared I had missed Dragon CRS-11, as I already could see the ISS approaching in the southwest. So I said a few strong words...

As ISS had passed the moon (which was a bloody nuisance, smack in the middle of the trajectory line) and was descending into the trees low in the south-southeast, I spotted a second, not too bright object chasing it (see first two images above). As I was photographing it and it descended into the trees, I re-aimed my camera hoping to catch it in a gap on the other (left) side of the tree.

Then I saw yet another object descend into the right side of the tree, and realised this was either Dragon or Cygnus. I initially thought, to my dismay, that it would be just outside my camera FOV. Luckily, back home later it turned out it still was in the FOV (I used a 35 mm lens).

The first, faint object on the same trajectory as the ISS some 25 seconds behind it I for this moment identify as Cygnus OA-7. The second, brighter one, on a trajectory just south of that of the ISS some 1m 25s behind it, I for the moment identify as the Dragon CRS-11.

Thursday, 1 June 2017

The Plot Thickens (Ball Aerospace, USA 276, RAVEN and the ISS)

(I acknowledge that what I write below is, again, matter of a highly speculative nature, and should be treated as such)

In a previous post, which is currently gaining media traction (e.g. here for a serious article on CNet, and here for a raunchy UK tabloid version, which is also NSFW by the way), I wrote in detail about the curious situation with the recently launched US spy satellite USA 276 (launched as NROL-76 on May 1). It appears to be moving towards a series of surreptitious very close approaches with the International Space Station (ISS). For more details see my post here.

While browsing the website of Ball Aerospace, the company that built USA 276, I found that they also have built RAVEN, an instrument delivered to and installed on the outside of the ISS in February this year.

RAVEN. Image: NASA’s Goddard Space Flight Center/Chris Gunn

As Ball Aerospace writes about RAVEN on their website:

"RAVEN is a technology demonstration mission that aims to advance the state-of-the art in rendezvous, proximity operations and docking. Raven includes visible cameras, an infrared camera and a flash LIDAR, called the Vision Navigation Sensor (VNS). In building and designing the VNS, Ball has provided Raven with its “eyes,” which will watch vehicles approach and depart the ISS."

So, let that sink in: Ball Aerospace, the company that built USA 276, a spacecraft that appears to be secretly moving towards a  series of clandestine very close approaches to the ISS, also built RAVEN, an experiment installed on the ISS to monitor close approaching spacecraft. 

NROL-76 is said to have been part of a "delivery to orbit" contract: e.g. the spacecraft and its launch is the responsibility of the builder (Ball Aerospace, who hired SpaceX for the launch), who hands over the spacecraft to the customer (the NRO) once in operational orbit. The question now is, is USA 276 at this stage still operated by Ball Aerospace, or has it been handed over to the NRO already?

(even if it isn't, I cannot believe that the NRO would have been kept in the dark about these ISS approaches. It would, however, create 'plausible deniability').

RAVEN was built by Ball Aerospace for NASA’s Goddard Space Flight Center. It is a possibility that it was jointly funded by NASA and the NRO (but that is pure speculation). Still, to use the ISS in this way is quite brazen, to say the least.

Note that while NASA participates in the ISS, the ISS is not owned by NASA: it is an international partnership that besides NASA includes ESA (Europe), JAXA (Japan), Roscosmos (Russia) and Canada, who would probably reject the idea of the ISS being made part of a classified US military experiment (certainly the Russians would).

Of course, this is all, and I emphasize this, pure speculation. But it is curious, to say the least, how Ball Aerospace and close approach monitoring come together here, from multiple angles (pun not intended). The plot thickens....

UPDATE, 3 June 13:15 UT:

A good summary of the pro's and con's on whether the ISS-USA 276 conjunction is coincidence or not, and whether there is a connection to RAVEN , by Ted Molczan is on the SeeSat-L list.

Tuesday, 30 May 2017

[UPDATED] USA 276 (the NROL-76 payload) and the ISS near DRAGON CRS-11 berthing.

click image to enlarge

>> UPDATES to this story with new observational data, updated calculations and new visualizations ARE AT THE END OF THE POST, below the main story <<

(NOTE: this post contains matter of a *very* speculative nature. I am the first to admitt this...and you are forwarned) 

Five days ago I wrote about the odd NROL-76 payload, USA 276, which was launched as NROL-76 for the NRO by SpaceX on 1 May 2017. In that post  I pointed out that its orbit was peculiarly close to that of the International Space Station ISS.

I have prepared two animations to show the extend of this, and what will happen in the first week of June if USA 276 does not change its orbit before that date (this is an important caveat!).

This is what will happen on June 3, when USA 276 would make a couple of very close approaches to the ISS, perhaps to distances as close as 20 km (!) near 14:48 UT (3 June 2017):

Note how the satellite is effectively circling around the ISS, at close range.

If the DRAGON CRS-10 history is to go by, and CRS-11 is launched on-time, the latter will be close to the ISS as well (although perhaps not as close as in the animation). [UPDATE June 2: the launch of CRS-11 was postponed to June 3 due to the weather]

The next day, June 4 near 15:30 UT, the DRAGON CRS-11 supply ship will berth to the ISS if launch goes as planned. This is the situation around the time of berthing [UPDATE June 2: the launch of CRS-11 was postponed to June 3 due to the weather] :

Again, and I can't say this enough: this will be the approximate situation if USA 276 stays in the orbit we currently have for this satellite, and does not manoeuvre.

In terms of the closest approaches, these happen the day before the CRS-11 berthing.

I calculate these close approach moments, from a USA 276 orbit that is a week old by the time these events happen (the ISS orbit used is the planned orbit for that date available here). The table provides the times for approaches closer than 500 km to the ISS [edit June 2: SEE UPDATES of table in the updates at the bottom of  this post):

3 JUN 2017 03:13:34   476.5 
3 JUN 2017 04:01:30   443.3 
3 JUN 2017 04:46:11   411.8 
3 JUN 2017 05:33:53   378.8 
3 JUN 2017 06:18:48   347.1 
3 JUN 2017 07:06:16   314.3 
3 JUN 2017 07:51:25   282.5 
3 JUN 2017 08:38:39   249.9 
3 JUN 2017 09:24:02   217.8 
3 JUN 2017 10:11:02   185.6 
3 JUN 2017 10:56:39   153.1 
3 JUN 2017 11:43:25   121.5 
3 JUN 2017 12:29:16   88.5 
3 JUN 2017 13:15:47   58.5 
3 JUN 2017 14:01:53   24.1 
3 JUN 2017 14:48:10   20.3 
3 JUN 2017 15:34:31   41.3 
3 JUN 2017 16:20:32   75.7 
3 JUN 2017 17:07:08   105.8 
3 JUN 2017 17:52:55   139.2 
3 JUN 2017 18:39:45   170.4 
3 JUN 2017 19:25:17   203.4 
3 JUN 2017 20:12:22   235.1 
3 JUN 2017 20:57:39   267.7 
3 JUN 2017 21:44:59   299.7 
3 JUN 2017 22:30:01   332.0
3 JUN 2017 23:17:36   364.3 
4 JUN 2017 00:02:23   396.4 
4 JUN 2017 00:50:14   428.9 
4 JUN 2017 01:34:45   460.8 
4 JUN 2017 02:22:51   493.5

Note that the calculated distances in the table have quite some uncertainty, perhaps by a factor of 2 or more. Likewise, the times listed have uncertainties of at least several seconds. And then there is the possibility that USA 276 manoeuvres into another orbit between now and June 3....

The planned moment of CRS-11 berthing to the ISS, around 4 June 15:30 UT, coincides with another close approach of USA 276, although not as close as the previous day: about 1040 km:

4 JUN 2017 15:25:53   1039.5

I am still not sure what to think of this all. Is this coincidence? You would almost start to think that USA 276 is a demonstrator for technology to closely monitor third party space berthings....

While I admittedly go out on a limb here, this idea does not come out of the blue. China and Russia have been busy practising such berthings and (very) close approaches in space with dedicated satellites disguised as space debris the past 10 years, which has the US military worried. Is the technology demonstrated by USA 276 perhaps meant to test whether such events can be observed (either optically, with radar, lidar, or whatever technology) from close by, to determine in detail what is going on?

It would be incredible (and politically sensitive) to use the International Space Station as a test subject in this way, which is why I and others are hesitant to accept this idea.

On the other hand, the ISS is there and you get frequent dockings and berthings of DRAGON's, PROGRESS, SOYUZ and HTV to watch for free, objects you don't have to launch yourself (saving development and launch costs and time. Launching a bunch of satellites for this purpose also atttracts attention, as the story with the Russian satellites shows).

I still don't know what to think of this all. Are these figments of my imagination or is there really something going on here? I am at a loss. Opinions are welcome.

Postscript, 30 May 2017, 21:15 UT :
I used the following TLE for USA 276, based on amateur tracking of the satellite between May 24 and May 27:

USA 276
1 42689U 17022A   17147.01934012 0.00004742  00000-0  65889-4 0    01
2 42689  50.0000 149.4666 0015489  97.4973 262.7756 15.56150729    04

The positions of DRAGON CRS-11 in the animations are based on elsets of DRAGON CRS-10 relative to those of ISS at the time, and (for the 3 June animation) are less certain than the ISS and USA 276 orbital positions.

UPDATES  (newest at the bottom):

UPDATE 1:  31 May 2017, 8:55 UT

The issue of launch windows and orbital plane shifts was rightfully raised on e.g. the NASA Spaceflight forum. It is true that the launch time needed to target the ISS orbital plane shifts by ~20 minutes each day. The crubbed launch on April 30 targetted 11:15 UT, the same time as the eventual launch a day later. Curiously enough, the Area Warning given out before the launch does open 20 minutes earlier, at 10:55 UT. Very confusing (and I initially goofed with that in a comment on the NASA Spaceflight forum).

It should be noted that USA 276 of course isn't in the exact plane of ISS (there is a 1.6 degree inclination difference anyway). A small difference in RAAN does not matter that much in this situation, it transpires.

I have looked into the effect would NROL-76 have actually been launched at 11:15 UT on April 30, when the launch was scrubbed.

The effects of a fixed launch time at 11:15 UT rather than a daily launch time shift to match the plane crossing time are actually not that large, it turns out. To investigate the effect, I adjusted the RAAN of the current orbit accordingly to match launch on 30 April, 11:15 UT..

USA 276 actually then would have made even somewhat closer passes to the ISS (to minimum distances less than 15 km on June 3 near 18:44 UT), but with the approach times  some 4 hours shifted compared to those for the actual launch date.

 During CRS-11 berthing on June 4, it would actually have been somewhat closer too, although with all other parameters of the orbit kept equal the time of approach would not match so neatly with berthing. These are not things that cannot be solved by a small manoeuvre however.

UPDATE 2: 1 June 2017, 10:30 UT

After updating the orbit of USA 276 with observations from last night, the time of closest approach has shifted a bit to an earlier approach instance (14:01:53 UT, June 3) and to a slightly smaller nominal distance (~18 km). The overall scenario remains the same, its details that change.

USA 276
1 82689U 17022A   17151.89933357 0.00004751  00000-0  65887-4 0    01
2 82689  50.0016 124.1750 0015094 116.7818 243.4697 15.56210183    01

Distance of USA 276 with regard to ISS in diagram form, from June 2.0 to June 5.0 (x-axis is in decimal days, e.g. 3.50 = 3 June 12:00):

click diagram to enlarge
click diagram to enlarge

This is the new updated list of close approach times:

3 JUN 2017 01:40:58   503.4 
3 JUN 2017 02:28:57   468.5 
3 JUN 2017 03:13:35   438.3 
3 JUN 2017 04:01:20   403.6 
3 JUN 2017 04:46:12   373.3 
3 JUN 2017 05:33:43   338.7 
3 JUN 2017 06:18:49   308.2 
3 JUN 2017 07:06:06   273.9 
3 JUN 2017 07:51:25   243.1 
3 JUN 2017 08:38:29   209.1 
3 JUN 2017 09:24:02   178.1 
3 JUN 2017 10:10:52   144.6 
3 JUN 2017 10:56:39   113.1 
3 JUN 2017 11:43:15   80.6 
3 JUN 2017 12:29:16   48.2 
3 JUN 2017 13:15:38   22.6 
3 JUN 2017 14:01:53   17.7   * closest
3 JUN 2017 14:48:00   54.4 
3 JUN 2017 15:34:30   82.3 
3 JUN 2017 16:20:23   117.6 
3 JUN 2017 17:07:07   147.3 
3 JUN 2017 17:52:45   182.0
3 JUN 2017 18:39:44   212.3 
3 JUN 2017 19:25:07   246.6 
3 JUN 2017 20:12:21   277.3 
3 JUN 2017 20:57:29   311.3 
3 JUN 2017 21:44:58   342.2 
3 JUN 2017 22:29:51   376.1 
3 JUN 2017 23:17:35   407.2 
4 JUN 2017 00:02:13   440.8 
4 JUN 2017 00:50:12   472.2 
4 JUN 2017 01:34:34   505.6 
4 JUN 2017 02:22:49   537.1 
4 JUN 2017 03:06:56   570.3 
4 JUN 2017 03:55:26   602.1 
4 JUN 2017 04:39:17   635.0
4 JUN 2017 05:28:04   667.0
4 JUN 2017 06:11:38   699.7 
4 JUN 2017 07:00:41   731.9 
4 JUN 2017 07:43:59   764.4 
4 JUN 2017 08:33:18   796.7 
4 JUN 2017 09:16:20   829.1 
4 JUN 2017 10:05:55   861.6 
4 JUN 2017 10:48:41   893.7 
4 JUN 2017 11:38:32   926.4 
4 JUN 2017 12:21:01   958.3 
4 JUN 2017 13:11:09   991.2 
4 JUN 2017 13:53:21   1022.9 
4 JUN 2017 14:43:46   1055.9 
4 JUN 2017 15:25:41   1087.4  * CRS-11 berthing
4 JUN 2017 16:16:23   1120.6

Here is a photograph of last night's pass of USA 276 over my house:

click image to enlarge

I also captured part of the pass on video:

UPDATE 3:  2 June 2017, 12:45 UT

Updated orbital elements based on observations from June 1:

USA 276                                                  389 x 408 km
1 42689U 17022A   17152.86247082 0.00004757  00000-0  65966-4 0    06
2 42689  50.0043 119.1561 0014209 109.6377 250.6127 15.56228316    08

USA 276 appears to have been making small manoeuvers over the past days. The current schedule for close approaches to the ISS, based on the elements above, is:

DATE           UT    DISTANCE (KM) 
3 JUNE 2017 01:41:01   503.2 
3 JUNE 2017 02:28:55   460.1 
3 JUNE 2017 03:13:38   437.9 
3 JUNE 2017 04:01:19   395.0
3 JUNE 2017 04:46:14   372.6 
3 JUNE 2017 05:33:42   329.9 
3 JUNE 2017 06:18:51   307.3 
3 JUNE 2017 07:06:05   264.8
3 JUNE 2017 07:51:28   242.1 
3 JUNE 2017 08:38:29   199.8 
3 JUNE 2017 09:24:05   176.8 
3 JUNE 2017 10:10:52   135.1 
3 JUNE 2017 10:56:41   111.5 
3 JUNE 2017 11:43:15   71.0
3 JUNE 2017 12:29:18   46.3 
3 JUNE 2017 13:15:37   18.1 **
3 JUNE 2017 14:01:55   19.6 **
3 JUNE 2017 14:48:00   64.1 
3 JUNE 2017 15:34:32   84.6 
3 JUNE 2017 16:20:22   128.0
3 JUNE 2017 17:07:08   149.8 
3 JUNE 2017 17:52:45   192.7 
3 JUNE 2017 18:39:45   215.0
3 JUNE 2017 19:25:07   257.6 
3 JUNE 2017 20:12:22   280.3 
3 JUNE 2017 20:57:28   322.6 
3 JUNE 2017 21:44:59   345.5 
3 JUNE 2017 22:29:50   387.6 
3 JUNE 2017 23:17:35   410.7 
4 JUNE 2017 00:02:12   452.6 
4 JUNE 2017 00:50:12   475.9 
4 JUNE 2017 01:34:33   517.5 
4 JUNE 2017 02:22:49   541.1 
4 JUNE 2017 03:06:54   582.5 
4 JUNE 2017 03:55:26   606.3 
4 JUNE 2017 04:39:15   647.5 
4 JUNE 2017 05:28:03   671.5 
4 JUNE 2017 06:11:36   712.4 
4 JUNE 2017 07:00:39   736.6 
4 JUNE 2017 07:43:56   777.3 
4 JUNE 2017 08:33:16   801.7 
4 JUNE 2017 09:16:17   842.2 
4 JUNE 2017 10:05:53   866.8 
4 JUNE 2017 10:48:37   907.1 
4 JUNE 2017 11:38:30   931.8 
4 JUNE 2017 12:20:57   971.9 
4 JUNE 2017 13:11:07   996.8 
4 JUNE 2017 13:53:16   1036.7 
4 JUNE 2017 14:43:43   1061.8 
4 JUNE 2017 15:25:35   1101.5 
4 JUNE 2017 16:16:20   1126.8 
4 JUNE 2017 16:57:54   1166.2 
4 JUNE 2017 17:48:57   1191.7 
4 JUNE 2017 18:30:13   1230.9 
4 JUNE 2017 19:21:34   1256.6 
4 JUNE 2017 20:02:32   1295.6 
4 JUNE 2017 20:54:10   1321.5 
4 JUNE 2017 21:34:50   1360.2 
4 JUNE 2017 22:26:47   1386.3 
4 JUNE 2017 23:07:07   1424.8 
4 JUNE 2017 23:59:24   1451.1

Distance variation over time in diagram form:
click diagram to enlarge
click diagram to enlarge
It will be interesting to see whether the schedule will change with new orbit updates, now the launch of DRAGON CRS-11 has been postponed to June 3.

Update 4, 3 June 13:15 UT:

In a post on SeeSat-L, Ted Molczan has summed up the pro's and con's of the  conjunction between ISS and USA 276 being coincidental or not. Like me, he does not really know what to think of it.

Update 5, 3 June  14:00 UT:

Updated elements based on adding observations from June 2:

USA 276                                                  388 x 408 km
1 42689U 17022A   17153.82560337 0.00004761  00000-0  65966-4 0    09
2 42689  50.0075 114.1658 0015063 110.3625 249.8963 15.56237668    07

Updated list with times and distances of close approaches to the ISS:

DATE          UT       DISTANCE (km)
3 JUN 2017 01:40:57   505.7 
3 JUN 2017 02:28:57   460.2 
3 JUN 2017 03:13:35   440.4 
3 JUN 2017 04:01:20   395.1 
3 JUN 2017 04:46:12   375.1 
3 JUN 2017 05:33:43   330.0
3 JUN 2017 06:18:49   309.8 
3 JUN 2017 07:06:06   265.0
3 JUN 2017 07:51:26   244.5 
3 JUN 2017 08:38:29   200.0
3 JUN 2017 09:24:03   179.3 
3 JUN 2017 10:10:52   135.3 
3 JUN 2017 10:56:40   114.0
3 JUN 2017 11:43:14    71.2 
3 JUN 2017 12:29:17    48.8 
3 JUN 2017 13:15:37    18.7 **
3 JUN 2017 14:01:54    17.4 **
3 JUN 2017 14:47:59    64.1 
3 JUN 2017 15:34:31    82.1 
3 JUN 2017 16:20:21   127.9 
3 JUN 2017 17:07:08   147.3 
3 JUN 2017 17:52:43   192.5 
3 JUN 2017 18:39:46   212.5 
3 JUN 2017 19:25:04   257.4 
3 JUN 2017 20:12:23   277.8 
3 JUN 2017 20:57:26   322.3 
3 JUN 2017 21:45:00   343.0
3 JUN 2017 22:29:47   387.3 
3 JUN 2017 23:17:37   408.2 
4 JUN 2017 00:02:08   452.3 
4 JUN 2017 00:50:14   473.4 
4 JUN 2017 01:34:29   517.3

Distance to the ISS with time in diagram form:
click diagram to enlarge

UPDATE 6, 6 June 15:25 UT:

A new blog post with a detailed post-event analysis of the close approach can be read here