Orbital ATK's Cygnus AO-9 cargoship chasing the ISS

click to enlarge

click to enlarge

The two images above show Orbital ATK's Cygnus AO-9 cargoshi  chasing the International Space Station (ISS), a few hours prior to berthing. The Cygnus OA-9 cargoship, launched on May 21 from Wallops Island, brings supplies (food, equipment etc.) to the Space Station.

I could observe three passes of the two objects during the night of May 23-24: in all three cases the two objects could be seenr at the same time in the sky, with the Cygnus (the fainter trail in the images above) somewhat behind ISS.

The images above are from the first pass (21:48 UT, 23:48 local time), a high pass,  and the third pass (01:00 UT, 03:00m local time), low over the southwest horizon. The Cygnus spacecraft was about 22 seconds behind the ISS on the third pass. The sky over Leiden was somewhat hazy.

The very short third trail near the ISS on the first image is Kosmos 2392.

As usual, the Cygnus spacecraft was quite faint (mag +4.5), so not an easy naked eye target. The brightness of these Cygnus spacecraft is strongly phase-angle dependent. The Dragon spacecraft of their competitor SpaceX are much brighter and easier to see.

The video footage below is from the third pass:

[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)

[UPDATED & CORRECTED] Observing the SpaceX Dragon CRS-3, the ISS and two pieces of Dragon launch debris

CORRECTION (21/04/2014 12:55 UT): in the initial post, the two debris pieces were misidentified. "2014-022C" turned out to be 2014-022H, and "2014-022H" turned out to be 2014-022G.

click image to enlarge

Last Friday at 19:25 UT, SpaceX launched the Dragon CRS-3 commercial supply ship to the International Space Station ISS. It passed over Europe 20 minutes later but unfortunately I was clouded out in Leiden. In the middle and eastern parts of the Netherlands as well as elsewhere in Europe, observers were treated to a spectacular view of the Dragon, the Falcon upper stage, and two faint pieces of debris passing by as a thight group of objects.

SpaceX Dragon CRS-3
click image to enlarge

I was more lucky yesterday when the sky was clear and the Dragon and ISS made a late twilight pass culminating at approximately 26 degrees altitude in the SW near 20:06 UT (22:06 local time, sun at -12 deg.). The image above shows the Dragon CRS-3 due south already somewhat past culmination. It was easy to see with the naked eye, attaining magn. +1.5. Its brightness is more similar to a Progress or ATV then to the much fainter commercial Orbital Sciences Cygnus.

The Dragon was about 1m 12s behind the ISS, a visual distance of somewhat over 40 degrees. Pre-observation predictions based on elements a few hours old had put it in front of the ISS, so at first I was wondering whether I missed it. Then, as the ISS was descending towards the SE, I saw it approaching in the SW, chasing the ISS. A very fine sight!

The ISS passing the same sky area as the

earlier image, 1 min earlier

(click image to enlarge)

While I was photographing at the nearby city moat, I had also set up the video in my girlfriend's appartment, and this capture both objects as well: first the ISS, then a minute later the Dragon:




(the display says "GPS BAD" because my GPS time inserter failed to lock on a GPS satellite. I hope it is not broken...)

Apart from the Dragon and the ISS, I observed and photographically imaged a third debris object related to the launch. It is the object catalogued by JSpOC as 2014-022C/#39682. 2014-022H, #39687. It is either the jettisoned Dragon nose cone cover, or one of the solar panel covers   or possibly one of the Nanosat dispensers: I think it is too bright to be one of the several released nanosats itself. It was faint and slowly tumbling, alternating between invisibility and a max magnitude of about +3.5:

tumbling Dragon debris 2014-022H

(click image to enlarge)

[UPDATE:] Later I discovered a second piece of Dragon CRS-3 launch debris on my imagery. It is faint, irregular in brightness and present on two images, the best of which is this one from 20:04:07 UTC:

tumbling Dragon debris 2014-022G
(click image to enlarge)

This turns out to be the object designated 2014-022H, #39687  2014-022G, #39686. This is the other solar panel cover.

A farewell view of Space Shuttle Discovery

This evening in twilight (sun at -8 degrees altitude) we had a last pass of the "dynamic duo" Space Shuttle Discovery STS-133 and the International Space Station (ISS).

After it's landing tomorrow late afternoon, Discovery will be retired.

The two were well visible in a still bright blue sky, with Orion just visible. They sailed under Orion through Lepus, the Shuttle leading 37.4 seconds (about 19 degrees at culmination) in front of the ISS.

Below is one of the images I shot, using the EF 2.8/24mm lens at 4 second exposure, 200 ISO. The Shuttle is the trail on the left, ISS on the right:

click image to enlarge

Several other European observers reported a water-dump, visible as a "comet tail" behind the Shuttle. I didn't see it from Leiden though, likely because the sky was still too bright.

A magnificent view of the Space Shuttle Endeavour STS-130 and the ISS in tandem!

click image to enlarge

The weather predictions for this morning suggested a possibility of clear sky - and hence a possibility to see a morning twilight pass of the duo Space Shuttle Endeavour STS-130 and the International Space Station, which decoupled a few hours earlier.

I observed from the appartment of my girlfriend this time, who lives at the 2nd floor of the same building as me. This allowed a wide vista over the rooftops towards the west and southwest. The pass happened around 6:49 am local time (5:49 UTC on the 20th), the sun was at an altitude of -10 degrees, and hence twilight coloured the sky already. I could see Saturn, Spica and a couple of other stars, low in the southwest. The pass would reach a maximum altitude of 20 degrees.

The pair was easy to see as they majestically sailed over the rooftops in the twilight sky, rising over the rooftops below Saturn and then passing Spica. They were very close, 1.7 degrees apart around 5:49:30 UTC (measured from the photograph above), passing the same point about 3.7 seconds apart. The Shuttle, at around magnitude 0 to +1 the fainter of the two, was slightly ahead of, and a tiny bit lower in declination than, the ISS, which attained about magnitude -1 to -2. A magnificent view!

Above is one of three pictures I took. They suffered a bit from vibrations, as I had only limited space to put up the tripod in the window-sill of my GF's bedroom, and the window-sill apparently did transfer some vibrations to the tripod & camera. The picture shown above shows the duo close to Spica (alpha Virgo) and is the image with the least "wobbly" trails. Movement of both objects is from right to left in the picture.

ISS yesterday

Yesterday in twilight, I shot this image of a fine pass of the International Space Station:

(click image to enlarge)

A close call for the ISS

Shortly after the collision of Iridium 33 and Kosmos 2251, the news agencies are buzzing with a close call of the International Space Station and a piece of space debris. Astro/Kosmonauts in the station shortly evacuated to their Soyuz re-entry capsule for safety reasons.

The piece of space debris in question was 93-032D (25090), a piece of a PAM-D rocket engine, part of the launch of the Navstar 32 GPS satellite on 13 May 1993. It is small, but even small can be lethal to the ISS. The nominal orbits for the ISS and the space debris piece have it pass as close as within 2.4 km of each other at 12 March, 16:39:41 UTC. The close encounter occurred over the southern Atlantic, near the southernwest coast of Africa.

(click images to enlarge)