China launches a 'Reusable Experimental Spacecraft' - a Space Plane? [UPDATED MULTIPLE TIMES]

Early September 2020, the space tracking community was in nervous anticipation of a rather mysterious Chinese launch. Amidst tight security measures, a Changzeng-2F (CZ-2F) rocket was readied at SLS-1 of Jiuquan's Launch Area 4. Chinese tracking ships were taking up positions near South America and in the Arabian Sea. Two NOTAM's appeared suggesting a launch between 5:20 and 6:00 UT on September 4. Something was afoot! Speculation was, that this was the long anticipated inaugural launch of a robottic Space Plane, a version of the Shenlong, China's answer to the American Air Force's X-37B robottic Space Plane.

Then, on September 4th, the Chinese news agency Xinhua published a very brief news item announcing that a CZ-2F from Jiuquan had launched a 'Reusable Experimental Spacecraft' earlier that day. 

The bulletin was scarce in information but stated that "after a period of in-orbit operation, the spacecraft will return to the scheduled landing site in China. It will test reusable technologies during its flight, providing technological support for the peaceful use of space".

No further details were given on launch time, orbit or character of the spacecraft. The description of the spacecraft is a bit ambiguous. Instead of a space plane, a 'reusable spacecraft' could in theory also be some sort of capsule (e.g. like the SpaceX Dragon): but most analysts think this indeed refers to the long rumoured space plane, China's answer to the US X-37B.

Pre-launch, and based on the positions of the hazard zones from the two NOTAM's, I calculated a launch into an orbital inclination of ~45 degrees, incidentally similar to the orbital inclination of the X-37B OTV 6 mission currently on-orbit. What's more, the launch window given (the NOTAM windows were from 5:23 to 6:05 UT) indicated the possibility of a launch into the orbital plane of OTV 6! The orbital plane of OTV 6 passed over Jiuquan at 6:00 UT - near the end of the launch window.

I published the following expected track for a launch into a 45 degree inclined orbit (which we now know is wrong):

Initial pre-launch trajectory guess. Click map to enlarge

When later that day the first orbital elements by the US military tracking network appeared on the CSpOC portal, it turned out that the orbital inclination was not ~45 degrees, but 50.2 degrees, 5 degrees higher than I anticipated. The reason for the mismatch, is that the rocket apparently did a dog-leg manoeuvre during ascend. This is very clear when we plot the orbital ground track in relation to the launch site and hazard zones from the two NOTAM's: it passes obliquely between them rather than lining up.

Actual orbital track. Click map to enlarge

 A 'dog-leg' manoeuvre is usually done for safety reasons, to avoid overflying a particular area downrange (e.g. a city or a foreign nation), but can also be done to insert the spacecraft into an orbital inclination that otherwise cannot be reached from the launch site. The latter is however not the case here - [editted] the orbital inclination is higher than the launch site latitude (you cannot reach an orbital inclination that is lower than your launch site latitude without a dog-leg, but higher you can.). So the reason must be range safety.

It is clear that the launch occurred well outside the NOTAM time window (why, is not clear). My analysis, based on a proximity analysis using the orbits of the spacecraft, the upper stage of the CZ-2F rocket, and that of four engine covers ejected upon spacecraft separation, indicate spacecraft separation and insertion into orbit around 7:41 UT on September 4th, over the Chinese coast with the orbital plane lining up with Jiuquan (see image below which depicts the orbital position at orbit insertion). The launch itself then should have occured some 8-10 minutes earlier i.e. around 7:30 UT, give or take a few minutes.

Moment of orbital insertion. click to enlarge

 

The spacecraft was inserted into a 50.2 degree inclined, initially 332 x 348 km orbit. During the hours after launch, the spacecraft made small orbital manoeuvres (see diagram below). At the time of writing (5 September 20:45 UT) it is in a 331 x 347 km orbit.

click diagram to enlarge

The later than initially expected launch time and, through a dog-leg manoeuvre, insertion into a 50.2 degree inclined orbit moved the orbital plane away from that of the X-37B OTV 6, although the two orbital planes are still near. Igor Lissov has pointed out some resemblance to the orbital plane of another US classified payload, USA 276, which has a similar orbital inclination to the Chinese spacecraft (but 50 km higher orbital altitude). The RAAN difference is 8 degrees:

click to enlarge

Based on the current orbits of all three spacecraft, there will be no close approaches of the Chinese spacecraft to either of these classified US payloads over the coming two weeks.

OTV 6 is currently in a 383 x 391, 45.0 degree inclined orbit. The difference in RAAN with respect to the Chinese spacecraft is 13.4 degrees, with a 5.2 degree difference in inclination and about 40-50 km difference in orbital altitude.

USA 276, the mysterious spacecraft that made a close approach to the ISS in May 2017 (see my July 2017 article in The Space Review), is currently in a 397 x 395, 50.0 degree inclined orbit. The difference in RAAN with respect to the Chinese spacecraft is 7.9 degrees, with a 0.2 degree difference in inclination and about 50-60 km difference in orbital altitude.

The Chinese 'reusable' spacecraft was launched from SLS-1, one of two launch platforms at Launch Area 4 of the Jiuquan Space Launch Center. Below is a Copernicus Sentinel 2B image of the launch complex, taken on September 2nd, two days before the launch. The two launch platforms are indicated: the southernmost one is the platform used for this launch.

click image to enlarge

It will be interesting to see where the 'reusable spacecraft' will eventually land. One likely candidate is a military airfield, the Dingxin Test and Training Base, that is located some 75 km southwest of the launch site. I have indicated both the launch site (A) and the potential landing site (B) in the Copernicus Sentinel 2B image below. The second image gives a more detailed look on the airbase.

Click image to enlarge

 

Click image to enlarge

We have no clue how long the spacecraft will stay in orbit. It will be interesting to see when and where it lands.

The 'reusable spacecraft' has the CSpOC catalogue entry #46389 (COSPAR ID 2020-063A). The CZ-2F upper stage is object #46390 (2020-063B). The four ejected engine covers (with apogees in the 458 to 566 km range), have numbers 46391-46394 (2020-063A to 202-063F).

UPDATE 6 Sept 2020 8:45 UT:

Xinhua reports on Sept 6 that the spacecraft has landed after 2 days on-orbit. Depending on the landing site, landing should have been (based on orbital overpass) either around 1:55 UT at Lop Nor (an alternative landing site suggested), or 6:45 UT at Dingxin Airbase.

UPDATE 2, 9:30 UT:
As the Chinese version of the Xinhua bulletin dates to an hour after the first option (1:55 UT), it seems that the landing was near 1:55 UT near Lop Nur in the Taklamakan desert (HT to Jonathan McDowell).

UPDATE 3, 10:30 UT:
This is the potential landing site, a triangular arrangement of 5 km long landing strips in the Taklamakan Desert. The orbital track of the spacecraft passed some 42.5 km northwest of it around 1:54 UT, more or less parallel to what appears to be the main landing strip:

Click image to enlarge

Click image to enlarge

UPDATE  4, 14:00 UT:
This is an updated diagram of the orbital evolution over the test flight. It seems no large manoeuvers were tried during this flight.

Click diagram to enlarge

UPDATE 5, 16:00 UT:

Jonathan McDowell noted that a new object related to the launch has been catalogued, object 2020-063G, #46395. My analysis suggests it was ejected from the experimental spacecraft near 22:25 UT on the 5th, two revolutions before landing. It likely is a cubesat of some sort. It is in a  332 x 348 km, 50.2 degree inclined orbit. (Update 8 Sept: on Twitter, Bob Christy has suggested that it might be a small inspector satellite, used to inspect the outside of the experimental spacecraft prior to deorbit)

Imaging the X-37B Space Plane OTV 5 post-manoeuvre

click image to enlarge

The image above shows the secretive X-37B Space Plane OTV 5, a robottic mini space shuttle flown by the US Air Force, over my house in Leiden, cruising through Leo (the bright star above the chimney is Regulus). It was a bright, easy naked eye object with a brightness of magnitude +1.

In a previous post I detailed how (and why), following the launch in September 2017, we had a hard time tracking down the whereabouts of this fifth OTV mission. Untill Cees Bassa located it on April 11th, in a 54.4 degree inclined orbit. It is the first OTV mission bringing it to the latitudes of the Netherlands.

Clouded weather in the Dutch coastal region after Cees' recovery prevented me from seeing it untill yesterday. During the past week, OTV 5 moved from morning passes to evening passes. Weather improved too medio last week, but still OTV 5 initially escaped me. Because it manoeuvered!

On April 18th, a week after it was first located in orbit, OTV 5 made a manoeuvre. It was a no-show for several observers, including me, on the 19th, but two observers, Tristan Cools in Belgium and Marian Sabo in Slovakia, reported an "unidentified" object some 8 minutes earlier (which means it passed while I was setting up my camera on the 19th). Based on Tristan's photograph of that object, a post-manoeuvre orbit was guessed by Mike McCants as well as by me. Yesterday evening on the 20th, we were ready to look for it, and we did recover OTV 5, a few minutes in front of the estimated new orbit.

The new orbit is still preliminary, but it seems as if the orbit has been lowered from a ~355 km circular orbit to a 307 x  320 km orbit. In a few days, when we have more observations, we'll know more about the new orbit, and when the manoeuvre exactly happened.

The video below which I shot yesterday evening shows OTV 5 cruising through the Coma Berenice cluster:



This was my very first observation of an X-37B! Very cool to see this enigmatic object pass in my own sky. Given that previous OTV missions frequently manoeuvered, it will be an interesting object to follow.

All kinds of nefarious motives and purported specific targets have been ascribed to the X-37B program by the aluminium hat brigade, but the reality probably is that the X-37B is an experimental test-bed for new space technologies, testing these under real space conditions and at various thermospheric regimes, over a prolonged time period, before retrieving them.

I do find it interesting though that this new OTV mission is in a 54.4 degree inclined orbit, rather than the previous 38-43 degree inclined orbits (see comparison in my previous post). Over the past year we have now seen three experimental missions going (or planned to go) into 50-55 degree inclined orbits: USA 276; the failed Zuma; and OTV 5. All three are clearly experimental missions. For Zuma, I suspect it was meant as an experimental radar satellite, and maybe OTV 5 tests radar as well. Or maybe not.

At any rate, I welcome this new attention to ~50-55 degrees inclination, as objects in such orbits are well observable from my 52-degree latitude in the Netherlands.

A new launch attempt for ZUMA [updated twice]

Probable launch trajectory of ZUMA
(click map to enlarge)

 UPDATE 1 4 Jan 2018 22:00 UT: The launch has again been postponed by one day, to January 7th (January 6 local time)

 UPDATE 2 5 Jan 2018 14:00 UT: The launch has yet again been postponed by one day, to January 8th (January 7 local time) and I have partly rewritten this post to reflect this.

UPDATE 3 11 Jan 20:00 UT: a follow-up post reflecting my changed thinking on what Zuma could be now we know it targetted a ~900-1000 km orbit, is here. 

****

[text updated/rewritten twice to reflect launch postponements]

If it isn't delayed even further, SpaceX will finally launch the secretive classified ZUMA satellite for the US Government on January 8th (January 7th local time in the USA) from Cape Canaveral pad 40 in Florida. The launch already has slipped three days from the initial January 5 aim.

The satellite was originally to be launched last November (see an earlier post) from Kennedy Space Center pad 39A but was postponed because of  issues with the payload fairing.

The launch hazard zones and the Falcon 9 upper stage de-orbit zone as gleaned from the Maritime Broadcast Warnings are virtually the same as in November, as was to be expected (there is a very small lateral shift in the launch hazard zone, which is probably related to the change in launch pad, but the direction of the area is the same). They are depicted on the map above.

From the launch azimuth (as gleaned from the launch hazard zones) and the location, extent and time window of the Falcon 9 upper stage de-orbit area, ZUMA will be launched into an approximately 50 degree inclined Low Earth Orbit. In the map above, a trajectory has been plotted for launch into a 50 degree inclined, approximately 400 km orbital altitude orbit. The orbital altitude is a bit uncertain and the eventual real orbit might be higher. [update: it probably is twice as high, from post-launch info discussed in a new post here]

The launch window runs from 1:00 UT to 3:30 UT (January 8th). The de-orbit of the Falcon 9 Upper stage happens some 2 hours after launch over the southern Indian Ocean north of Kerguelen, halfway during the 2nd orbital revolution.

As remarked in my earlier post from November, the launch hazard area and the apparent orbit aimed for as decuced from these hazard zones seem to be very similar to that of USA 276, the classified SpaceX launch for the US government from May 2017 which went into a 50 degree inclined, 400 km altitude orbit (see my article in The Space Review of July 2017). Compare the launch hazard zones of these two launches, they are very similar:

Launch hazard area of ZUMA (red) compared to that of USA 276 (blue)
(click map to enlarge)

Back in November there was some speculation that ZUMA might target the ISS orbital plane, just like the odd classified satellite USA 276 appears to have done last year (see my article in The Space Review of July 2017).


[the now following paragraphs have been heavily editted to reflect the situation change brougth on by the repeated launch delays. I retained some of the original text in striken-out grey for reference]

Another option is that it targets the plane of USA 276. For the initial launch date and window in November 2017, the orbital plane of  USA 276  would have passed over the launch site during the launch window, allowing a launch into the same orbital plane. After several days delay of the launch, the launch was postponed to January after the USA 276 orbital plane moved out of the launch window.

The new launch window for January 8th is the same as it was in November: 1:00 UT to 3:30 UT.

This excludes a launch (exactly) into either the ISS or USA 276 orbital planes, as the latter only pass over the Florida launch site after the launch window has ended.

This means launch into the orbital plane of USA 276 has become viable, as the latter's orbital plane passes over the launch site near 3:38 UT on January the 8th, only minutes after the end of the launch window. Note that for the original January 5 launch date, this was not possible.


This would seem to suggest that the coincidence in time of the launch window and orbital plane passages in November was indeed coincidence (but there is a "but": see below...).

[Edit 4 jan 22:00 UT: or maybe not. There are new delays, launch has now shifted to January 7 UT (January 6 local time) and passage through the USA 276 orbital plane is now very close to the end of the launch window. And it will shift into the launch window if more delays occur.]

On January 6th, the orbital plane of USA 276 passes over the launch site around 4:27 UT, an hour after the end of the launch window. The orbital plane of the ISS passes over the launch site around 7:04 UT, some 3.5 hours after the end of the launch window.

The image below shows the spatial separation of the orbital planes for launch on January 8th (January 7 local time).  For ZUMA, two planes are given (in red), one for launch at 1:00 UT and one for launch at 3:30 UT, representing the start and end of the launch window. The orbital planes for a 3:30 UT launch (end of launch window) and USA 276 (blue) almost coincide:

Relative orbital plane positions for ZUMA (red), USA 276 (blue) and the ISS (white)
Image has been updated twice
(click image to enlarge)

The launch already has slipped three days, and a few days more delay would slip the passage of the USA 276 orbital plane increasingly forward into the launch window, as the moment of orbital plane passage shifts about 24 minutes earlier in time each day. And a further delay eventually would do the same for the ISS orbital plane passage after several more days.

The official reason given for the delays of the past few days is "extreme" weather (strong high altitude winds). This might well be true, but there is always a possibility that the delays are a ruse to obfuscate (if that is the case) that the orbital plane of USA 276 is the actual target (there are historic precedents for such a ruse). That however remains speculation (emphasis), and it could well be that the actual launch time, when it happens, will be off from the moment the orbital plane of USA 276 is passed. We will see.

There is therefore very little to say with certainty about the possible function of ZUMA. But ZUMA is likely a technology demonstrator, i.e. an experimental satellite to show that a particular technology is feasible, as we also pressume USA 276 to be. I could (again) speculate that perhaps ZUMA and USA 276 are part of the same experimental program. As these two spacecraft were built by two different companies (Northrop-Grumman and Ball Aerospace), perhaps they are technology demonstrators in competition for a follow-up contract. But this is pure speculation. Many options are open.

Exactly how (if at all) the two satellites are related to each other remains murky. Maybe future orbital behaviour will shed some light on what ZUMA is doing.

For a further discussion of the ZUMA mission, see my earlier post from November 2017. Some TLE estimates for the orbit are here. They are based on the 50 degree orbital inclination gleaned from the launch azimuth, and an assumed ~400 km orbital altitude. [update: post-launch information leads me to think it went into a higher orbit, 900-1000 km, see the link to the new post below]

UPDATE 9 January 2018: a follow up is here, with spectacular images of a fuel vent by the Falcon 9 Upper Stage.

UPDATE  11 Jan: a second follow-up post reflecting my changed thinking on what Zuma could be now we know it targetted a ~900-1000 km orbit, is here.

[UPDATED] Tomorrow's SpaceX Zuma launch

click map to enlarge

If nothing interferes (the launch has been postponed twice already), SpaceX will launch the classified Zuma satellite from Cape Canaveral Pad 39A in the early hours (UT) of  November 18.

Zuma  was originally scheduled for November 16, but was delayed a day to November 17, and then yet another day to November 18.

The published Maritime Area Warnings give a window from 00:55 to 03:37 UT for the launch. From the Area Warnings, the de-orbit of the Falcon 9 Upper stage happens some 2 hours after launch over the southern Indian Ocean, during the 2nd orbital revolution.

The launch and Upper stage de-orbit hazard zones (I plotted them in red on the map above) strongly suggest a launch into a 50-degree inclined, ~400 km orbital altitude Low Earth Orbit.

The map above plots the trajectory for the first ~1.5 revolutions in such an orbit. As can be seen in the map, such an orbit lines up well with the direction of the launch hazard zones, and with the Falcon 9 upper stage de-orbit hazard zone in the Indian Ocean. The fact that the first stage will return to the Cape for a landing argues for a launch into Low Earth Orbit too.

If a ~50-degree inclined, ~400 km altitude orbit sounds familiar to you: that is because this orbit would be very similar to that of the enigmatic classified satellite USA 276 which was launched - also by SpaceX - in May 2017. This is the one that made all those peculiar close approaches to the ISS in June (see some previous posts from June and my Space Review article here). Perhaps, but this is pure speculation based on suspected potential orbital similarities only, Zuma is up for a similar mission.

It is very interesting that Zuma seems to have been contracted via a similar procedure as USA 276, and that like for USA 276, it has not been made public which Agency will operate the Zuma satellite. So there appear to be similarities from that aspect as well.

It will therefore be interesting to see how the orbit of Zuma, once launched, compares to that of USA 276 and the ISS. The orbital plane of the ISS will be overhead for Cape Canaveral near 2:38 UT on the 18th, so a launch exactly into the ISS orbital plane is possible - and will stay possible for several days to come in case the launch is postponed again (the moment of the ISS orbital plane passing over the Zuma launch site happens ~24 minutes earlier each day).

On the 18th, the orbital plane of USA 276 will be overhead for Cape Canaveral some 10 minutes before the launch window opens. With the newest delay, a launch exactly into the orbital plane of USA 276 is therefore no longer feasible.

But by launching directly at the opening of the launch window on the 18th, the orbits of Zuma and USA 276 would nevertheless still be quite close (launch at 1:00 UT would result in a difference in RAAN of 3 degrees), and differential rates of precession of the RAAN might still slowly drift the two orbits towards each other over the next weeks and months, depending on what the actual orbital altitude and inclination Zuma ends up in would be.

Therefore a launch exactly into the orbital plane of either USA 276 or the ISS, strictly speaking is not necessary to engineer close approaches (indeed, USA 276 itself was not launched exactly into the ISS orbital plane in May).

So it might be worth monitoring Zuma and its behaviour in relation to both USA 276 and the ISS in the weeks after launch. Still, it is also very well possible that Zuma has nothing to do with both spacecraft whatsoever.

UPDATE 1  17 Nov 2017, 13:00 UT:

The  maps below show a comparison of the hazard zones (from Maritime Area Warnings) for the launch of USA 276 in May 2017, and for Zuma.

click maps to enlarge

The USA 276 de-orbit area is shifted more West-wards, because the Falcon 9 upper stage de-orbit from that launch was de-orbitted one orbital revolution later than apparently planned for Zuma. The small difference in size might point to slightly different orbital altitudes for the upper stage (e.g.due to  a somewhat different collision avoidance manoeuvre after payload separation)


UPDATE 2  17 Nov 2017, 13:00 UT:

SpaceX has released a statement that, while not taking a launch tonight off the table, might indicate a further prolonged delay.


Appendix:

These are the Area Warnings published for the launch. They are graphically depicted in the map in the top of this post and the two maps above.

NAVAREA IV 1067/17

WESTERN NORTH ATLANTIC. FLORIDA. 
1. HAZARDOUS OPERATIONS, ROCKET LAUNCHING
160055Z TO 160337Z NOV, ALTERNATE 
170055Z TO 170337Z NOV IN AREAS BOUND BY: 
A. 28-38N 080-43W, 29-12N 080-06W, 
30-04N 079-00W, 29-56N 078-52W, 
28-41N 080-10W, 28-26N 080-21W, 
28-22N 080-38W. 
B. 30-04N 079-00W, 30-52N 
078-17W, 31-32N 077-25W, 
31-54N 076-49W, 31-49N 076-45W, 
31-36N 076-57W, 30-44N 077-53W, 
29-56N 078-52W. 
2. CANCEL THIS MSG 170437Z NOV 17.// 

Authority: EASTERN RANGE 072156Z NOV 17. 

Date: 110428Z NOV 17 
Cancel: 17043700 Nov 17 


HYDROPAC 3895/17 

SOUTHERN INDIAN OCEAN. 
DNC 03, DNC 04. 
1. HAZARDOUS OPERATIONS SPACE DEBRIS 
160300Z TO 160637Z NOV, ALTERNATE 
170300Z TO 170637Z NOV IN AREA BOUND BY 
30-27S 064-51E, 30-44S 067-03E, 
38-10S 082-43E, 47-22S 108-39E, 
50-30S 124-39E, 51-55S 126-03E, 
53-32S 125-05E, 54-24S 116-01E, 
53-34S 101-27E, 47-46S 082-05E, 
39-58S 069-31E, 31-56S 063-23E. 
2. CANCEL THIS MSG 170737Z NOV 17.// 

Authority: EASTERN RANGE 072155Z NOV 17. 
Date: 110407Z NOV 17 
Cancel: 17073700 Nov 17

Close Encounters of the Classified Kind

The Space Review has just published my paper on the close ISS flyby of US spy satelllite USA 279.

[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 43^o.75 S, 45^o.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)

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.

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.

[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):


DATE       TIME (UT)  DISTANCE (km)
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:


DATE       TIME (UT)  DISTANCE (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:

DATE       TIME (UT)  DISTANCE (km)
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