[UPDATED] Cosmic Ballet: approach of MEV-2 and Intelsat 10-02 imaged

image from 2 April 2021. Click image to enlarge

At geosynchronous altitudes, a cosmic ballet is happening between Intelsat 10-02 (2004-022A) and MEV-2 (2020-056B). I imaged the pair last night, spurred to do so by Bob Christy. The pair was almost due south at 30 degrees elevation for me. 

 

click image to enlarge

click image to enlarge

 

A small complication was imposed by the current Corona-curfew, as it means I cannot go out to the spot where I normally photograph geosynchronous objects: so I had to target the camera through the loft window (which has a limited FOV).

MEV-2 ("Mission Extension Vehicle 2") is the second of Northrop-Grumman's satellite servicing missions. It's mission is to dock to Intelsat 10-02, a communication satellite launched in 2004, and extend the lifetime duration of this satellite by 5 years, providing it with fresh fuel and a new engine.

MEV-2 has made a number of close approaches to Intelsat 10-02 over the past weeks (see Bob Christy's detailed account of their movements on his website), in preparation for docking..

The MEV-2 predecessor MEV-1 successfully docked to Intelsat 901 in February of 2020 and then brought it from a graveyard orbit into an operational geosynchronous orbit. It also had to make several close approach attempts before effecting the docking at the time.

In the image above, I have labelled the brightest object as Intelsat 10-02 and the fainter one as MEV-2. Space-track has it the other way around, but according to observers who are following the duo for a while, they have mixed up the ID's. This often happens with objects close to each other in GEO, as it is acknowledgedly difficult to keep track of which is which. In this case, the brightness difference of the objects provide a  way to discern them. One expects Intelsat to be brighter than MEV-2.

The image is a 10-second exposure with a Canon EOS 80D and a Samyang 2.0/135 mm lens at ISO 1000.

UPDATE 1  30 March 2021 22:00 UT

I imaged MEV-2 and Intelsat 10-02 again this evening. They are still in the same relative position to each other as yesterday. The image below is a stack of 10 images (10s exposure each): the stack brings out the fainter MEV-2 a bit better than in yesterday's single image sabove.

click image to enlarge

Space-Track has, in their latest orbital updates, switched the identities back to what they should be, now designating the fainter object as MEV-2. You'd almost say they read my tweets... ;-)

UPDATE 2, 2 April 2021 13:00 UT:

Lats night was clear, so I imaged the duo again, after they came out of earth shadow. Due to the good phase angle, they were quite bright. Several other geosats visible in the vicinity as well. The image below was shot at 00:52:57 - 00:53:07 UT on April 2 (1600 ISO, 10 seconds, Canon EOS 80D + Samyang 2.0/135 mm):

click image to enlarge

Imaging a pass of the Crew Dragon Demo-2, and a close fly-by of the Crew Dragon by USA 245! [UPDATED]

click photograph to enlarge

Yesterday May 30 at 19:22 UT finally saw the launch of the SpaceX Crew Dragon Demo-2 with astronauts Hurley and Behnken on board, returning a human spaceflight capability to the USA after nine years of having to hitch rides on a Russian Soyuz.

When the Crew Dragon first passed over the Netherlands some 23 minutes after launch (see map with the launch trajectory in  a previous post), the sun was still just above the horizon for my Leiden location. I nevertheless tried with binoculars, using the moon as a guide, but saw nothing.

But two hours after launch on the second revolution, near 21:18 UT, we did have a visible pass, albeit in late twilight and very low above the horizon: at a maximum elevation of only 9 degrees over the horizon and a range of almost 1200 km!

To observe this pass I went by bicycle to Cronesteyn Polder at the edge of Leiden, where I have an uninterupted view to the horizon, and set up my photo camera. First, at 23:14 local time (21:14 UT), I saw the ISS pass with the naked eye low on the southwest horizon. I then took to binoculars and waited for the Crew Dragon, which should pass somewhat lower in the sky some 4 minutes after the ISS.

I picked the Crew Dragon up in my 10 x 50 binoculars starting around 21:17:30 UT, while it was passing through Crater and Corvus. I watched it untill it entered Earth shadow at about 21:19:00 UT. It was not particularly bright, due to the low elevation and still bright sky background. By comparison to stars in Corvus I estimate it to have been magnitude +3 to +3.5, too faint at this elevation and with this sky brightness to be seen naked eye. It was at a range of almost 1200 km at that time, over Northern Spain!

Click photograph to enlarge

The image above shows the Crew Dragon during this pass. It is a stack of 45 exposures of 0.5 seconds each, with a Canon EOS 80D and SamYang 1.4/85 mm lens at F2.0, 500 ISO, 21:17:40 - 21:18:09 UT (May 30). Stars in the image belong to the constellations Crater and Corvus. The small breaks in the trail are the brief moments between the successive photographs that make up the stack.

The image below is another stack, this time of 52 photographs with the same camera setup, made between 21:18:25 - 21:18:59 UT. You see the Crew Dragon disappear in Earth shadow at the left end of the image. The image is slightly wobbly - my tripod was on a soft grassy surface. I like this image best though:

Click photograph to enlarge

It was pretty cool seeing the Crew Dragon, while knowing it was carrying two astronauts!

But it becomes even more interesting: in two images around 21:18:19 UT, I have another brighter satellite moving under a slant upwards in the opposite direction. You can see it in the upper right corner of this image (several lay observers saw this brighter satellite too and mistook it for the Crew Dragon):

Click photograph to enlarge

This object is the classified US KH-11 spy satellite USA 245 (2013-043A).

And as it turns out, it was really close to the Crew Dragon, and my image truely captures, within a few seconds, the actual moment of closest approach! This was serendipity, as I had not planned this and the presence of USA 245 took me by surprise.

Nominally, the minimum distance between USA 245 and the Crew Dragon during this fly-by was only 125 km with closest approach happening at 21:18:17 UT. USA 245 was flying this distance 'above' the Crew Dragon. Both objects were over northern Spain around the time of the flyby, with the point of closest approach over 43.40 N, 2.50 W, on the Basque coast.

There is some uncertainty in the actual fly-by distance (see below), but not much.

This is the output from a COLA analysis for this fly-by:

DATE      UT          SSC   NAME    TARGET      KM  
5/30/2020 21:18:16.99 39232 USA 245 CREW DRAGON 125.3

My analysis is based on CSpOC elset epoch 20151.85044152 for the Crew Dragon, and amateur elset 20146.86101776 for USA 245. There is some leeway in the exact time and distance of the flyby, for two reasons:

1)  from my observations, the Crew Dragon was some 3 seconds late on the used elset;

2)  the USA 245 elset epoch, based on amateur observations that include my own, was 5 days old. However, the sky position of USA 245 in the image is very close to the ephemeris, so the 5-day-old orbit nevertheless seems a good fit to reality.

Taking these points into account, I estimate that the uncertainty in the minimum distance between both objects is no more than 30 km, and only a few seconds in time.

In the map below, I have plotted the trajectories of both objects (I have accounted for the fact that the Crew Dragon was ~3 seconds behind on the elset in this map). USA 245 was moving nortwest-wards, the Crew Dragon southeast-wards.

Note that the USA 245 trajectory was situated some 125 km above that of the Crew Dragon. So to be clear, there was no danger of a collision. This is a safe distance.

click map to enlarge

 This is an animation of the close fly-by:




In fact, it could very well be that this close flyby was intentional, and that USA 245 was actually imaging the Crew Dragon at that moment.

USA 245 is a KH-11 electro-optical reconnaissance satellite: a satellite that resembles the Hubble Space Telescope and makes high resolution images of the earth surface (similar to this infamous one) with resolutions of 10 cm or better.

There have long been rumors, reported by amongst others NBC News, that KH-11 satellites were used to inspect the outside of Space Shuttles post-launch (e.g. that of the inaugural STS-1 flight) for tile damage. We also suspect that KH-11 satellites inspect X-37B's after launch, based on the odd jumps in launch times of the latter (see this analysis by Bob Christy).

So there is a real possibility that this close flyby of the Crew Dragon by USA 245 was intentional, and used to image the spacecraft to see if it was not damaged and everything deployed as it should.

UPDATE 1 June 2020 13:50 UT:

I am retracting the notion of intentionality of this encounter. Both Michael Thompson and I have done an extended analysis of potential KH-11 encounters with the Crew Dragon, where we looked at potential encounters had the Crew Dragon launched on the original launch date of 27 May.

There appear to have been no particularly close encounters would the Crew Dragon have launched on May 27, which calls into question the intentionality of the encounter on May 30.

That said: it is still possible that imaging of the Crew Dragon took place, as of course this would have been a perfect opportunity. I guess we'll never know. Unless, as someone put it to me in private, tongue in cheeck: "if they put it in a briefing, maybe Trump will tweet about it!". 

The analysis also found a second close encounter for May 30, with the KH-11 satellite USA 224 (2011-002A), on 30 May 20:07:50 UT, some 45 minutes (half a revolution) after launch, with a nominal miss distance of 105 km. This however was a pass where the Crew Dragon was in Earth shadow, so not illuminated (which does not preclude infra-red imaging however). COLA output for this encounter:

DATE      UT          SSC   NAME    TARGET      KM 
5/30/2020 20:07:50.30 37348 USA 224 Crew Dragon 105.4

[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)

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