Starlink "train" photographed from the International Space Station

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The image above (image ISS062-E-148365, original at high resolution here) was shot from the International Space Station (ISS) on 13 April 2020, 21:25:02 UT. It shows the Aurora Australis (southern lights) and a train of SpaceX Starlink satellites.

The presence of the Starlink train in this image was first noted by Twitter user Riccardo Rossi (@RikyUnreal) and brought to my attention by Huub Eggen (@phi48). It is present in two earlier images as well, taken the preceeding minute (images ISS062-E-148363 and ISS062-E-148364).

ISS was at 48.25 S, 81.03 E and 440 km altitude at the time the photo above was taken. With this information, I came to the following probable satellite ID's (annotations in image below) for the objects in the imaged "train": these are all objects from the 17 February 2020 launch ("Starlink 4").

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Dragon CRS-20, 23 minutes after launch, with thruster firings

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SpaceX launched the Dragon CRS-20 cargoship to the ISS this morning at 4:50:31 UT. Some 23 minutes after launch from SLC-40 at Cape Canaveral in Florida, it was visible from the Netherlands around 6:13 local time (5:13 UT) in morning twilight. There were some fields of clouds in the sky, but I nevertheless got a clear view of the four objects associated to the launch, all still closely together.

The image above is a 2-second exposure at 800 ISO which I took during the pass, using a Canon EOS 80D DSLR and a SamYang 1.4/85 mm lens. The image shows the trails of  four objects, two of which are tumbling. In the annotated image below, I identify what is what:

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The Dragon cargoship, the Falcon 9 upper stage and the two solar panel covers were easy naked eye objects. The Dragon and Falcon 9 upper stage were very bright and steady, while the two solar panel covers slowly flashed alongside them. These solar panel covers varied in brightness between invisible (with the naked eye) and magnitude +1.5. The Falcon 9 upper stage and Dragon were about +1.5 to +2: with the naked eye, being very close together they seemed one object, while on the photographs they are clearly two.

The image below, taken a few seconds after the previous image, shows one of the tumbling, slowly flaring solar panel covers at its brightest, rivalling the Dragon and Falcon 9 upper stage in brightness:

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The slow regular flashing behaviour was nice to see: the two tumbling solar panel covers were alternating, when one of the two was bright, the other was faint (clearly visible in the image above and the video below). Due to the alternatingly flashing panel covers above and below the Dragon, it looked a bit like an aircaft.

I also captured a small part of the pass on video, using the WATEC 902H with a 1.8/50 mm lens on a fixed tripod in autonomous mode (I was outside myself witha sceond tripod and the photo camera). In this video segment (below), a thruster firing is visible as a cloudy upwards moving "puff"starting at 5:13:00 UT:



Dragon CRS-20 will berth to the ISS on Monday 9 March near 11:00 UT.

This was the last flight of a Dragon 1, and the concluding flight of a contract awarded in 2008. All future Dragon supply flights will be done by an updated model, the Dragon 2 as well as the crew-rated Crew Dragon variant of the latter.

The stars did not align well for Starliner, it seems

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Yesterday's Boeing CST-100 Starliner Orbital Flight Test was a true nailbiter. This blogpost briefly reitterates what happened, and what could have happened had they not been able to eventually raise the orbit.

Launched atop an Atlas V rocket, this uncrewed inaugural test flight of the new Boeing Starliner crew transport vehicle should have gone on its way to a docking at the ISS today, followed by undocking and landing at the White Sands Missile Range a week from now. The map above which I prepared pre-launch from information in the Starliner Press Kit and Starliner Notebook, shows what should have been the launch track and some keypoints on that track. As we now know, it went wrong at one of these keypoints.

Launch was at 11:36:43 UT. The Atlas V and Centaur upper stage performed fine, the Centaur inserting the Starliner in a 76 x 191 km suborbital trajectory some 12 minutes after launch. Three minutes later, the Starliner separated from the Centaur.

Next, 31 minutes after launch near 12:08 UT, it should have fired its own thrusters, in order to raise perigee and in this way circularize the orbit, becoming truely orbital.

And that went wrong.

Due to a misfunctioning Mission Elapsed Time clock, the Starliner's orbit insertion burn did not go as planned. Initially, an "attitude problem" was reported as well. The next half hour or so was nailbiting, as Boeing and NASA were not quite coming forward with information, apart from the ambiguous comment that the Starliner had "stabilized" its orbit (which is extremely ambiguous wording).

Those of us who know about orbits, realised that if no orbit insertion burn took place, the Starliner would continue on a suborbital trajectory, and reenter with or shortly after the Centaur upper stage (see also the end of this post, where I modelled this). The Centaur reentry was expected to occur south of Australia at about 12:30-12:35 UT (see the map in top of this post), and as the clock approached that time, it became really nailbiting: was the Starliner crew module still on orbit, or breaking up and burning up over the Indian Ocean?

Eventually, it became clear that, many minutes after the original burn time, Boeing did manage to do a burn that raised perigee from 76 to 180 km.

As an interesting sidenote: during the post-launch press conference, Boeing's Jim Chilton seemed to suggest (at 7:25 in below video) that following the timer anomaly, they tried to uplink new commands, but were faced with delays caused by the relay satellite(s) used (TDRS). It also transpired that on a crewed flight, the crew itself would have intervened in this stage:





Orbital data released by CSpOC provided the first unambiguous information to the world about the whereabouts of Starliner. A pre-burn orbit appeared first, showing a 76 x 191 suborbital orbit. As this was pre-burn, this still did not say much about Starliner's state. But shortly after that, a 186 x 221 km orbit was published, somewhat later followed by a new 180 x 221 km orbit. These showed that Starliner had reached a safe orbit around the earth.

The diagram below shows the altitudes of apogee and perigee of the orbit published so far (21 december 12 UT): currently it is in a 241 x 265 km orbit.

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The amount of fuel spent in the emergency manoeuvres after the planned burn did not occur, was thus that it was no longer feasible to reach and dock to the ISS. Over the night, a new burn or series of burns therefore raised the orbit to 241 x 265 km, 58.4 degree inclined, lining it up for a landing at White Sands Missile Range on Sunday 22 December.

The current orbit (epoch 19355.3601887) results in a landing opportunity at White Sands between 12:45-12:55 UT on Sunday 22 December, approaching the range from over the eastern Pacific, as can be seen in the map I prepared below:

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This is based on the current (epoch 19355.3601887) orbit. If new orbit adjustments happen, the projected time of landing might change slightly (e.g. a lowering of the orbit would make the Starliner speed ahead a bit, resulting in a slightly earlier landing time).

[UPDATE 21 Dec 22:15 UT: NASA has announced that the landing will be around 12:57 UT]

What if the orbit raise had failed completely?

Starting from the first, pre-boost orbit released, 76 x 191 km, I used GMAT to model what would have happened. I find that the Starliner, had it continued in that orbit, would have reentered over Polynesia around 12:50 UT,  about 1h 15m after launch, with its first revolution still uncompleted:

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The Mating Call of the CUCU [updated]

The ISS is seeing busy times. On July 20, Soyuz MS-13 was launched from Baikonur bringing a new crew to the ISS. Then, on July 25, SpaceX launched the Dragon CRS-18 cargoship to the ISS from Cape Canaveral, docking today (July 27). And it will get even busier: in a few days, currently slated for July 31,  a Progress cargoship will be launched from Baikonur towards the ISS as well.

Soyuz MS-13

As is usual these days, the Soyuz MS-13 launch from Baikonur on 20 July 2019 was a fast-track mission, launching at 16:28:21 UT (20 July) and docking at 22:48 UT, a mere 6 hours 20 minutes later.

One orbit before docking, near 21:05 UT, the Soyus-ISS pair was visible chasing each other in a still bright twilight sky over Leiden, the Netherlands, the two objects being some 20 degrees apart. In the image below, the leading bright streak is the ISS, the fainter trailing streak near the clouds is the Soyuz (enlarge the image to see it). Visually, the Soyuz was about magnitude +1 and easy to see:

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During the next pass, near 22:40 UT , they already were too close to visually separate, but I could hear the kosmonauts onboard the Soyuz talk (in Russian) at 121.75 MHz FM during this pass, only minutes before docking to the ISS at 22:48 UT. Here is a recording of the best part received:

 

The Mating Call of the CUCU

Only 5 days after Soyuz MS-13, on 25 July 2019, the SpaceX Dragon CRS-18 launched from SLC-40 at Cape Canaveral. The timing of the launch, 22:01:56 UT, was unfavourable for initial sightings from the European mainland (Ireland and western UK did have sighting opportunities) as it already was in earth shadow while passing over mainland Europe 20 minutes after launch.

The next night did see visible passes, that unfortunately for me in Leiden were clouded out. I did however detect related telemetry signals at 400.5 MHz during two passes (19:22 UT, in daylight; and again during the clouded out 20:59 UT pass).

The three peaks in the frequency diagram and broad yellow bands in the spectrogram below (from the 19:22 UT pass) are the CUCU signal. CUCU stands for the "COTS UHF Communication Unit":

CUCU signal on 400.5 MHz

CUCU is a duplex telemetry broadcast that allows the ISS to communicate with the Dragon and vice versa, homing it in for berthing. It is what you could call the 'mating call' of the pair. CUCU was not active right after launch during the first Dragon revolution (I listened), but was notably active the next day, as Dragon CRS-18 was slowly approaching and climbing towards the ISS.

The CUCU signal sounds like a humming noise and a regular sharp "Beep! Beep! Beep!". Below is an audio recording of the CUCU signal, from the 19:22 UT pass, roughly corresponding to the spectrum shown above:






Initially I thought this was the CUCU of DRAGON CRS-18 itself, but looking at the Doppler curve of the signal, it was actually the CUCU signal of the ISS calling out to the fledgling Dragon (HT to Cees Bassa for noting it corresponded to the ISS rather than DRAGON).

The spectrogram below shows the signal as received during the second pass, near 20:59 UT, with the characteristic Doppler S-curve. The diagram below it shows how this Doppler curve matches with the Doppler curve for the ISS at that time:

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This was the first time I have heard the CUCU mating call, and I was surprised by how strong the signal was. The reception was made with a homebrew 120-deg V-dipole antenna with ground plane reflector, optimized for 400 MHz, and an SDR dongle.


UPDATE 28 July 2019

Dragon CRS-18 docked to the ISS earlier today, near 14:00 UT. During the 18:33 UT and 20:09 UT passes (I did not monitor the third pass at 21:46 UT), there was again radio activity around 400.5 MHz connected to the ISS/Dragon. It was different in character than when the Dragon was still free-flying. Compare the spectrogram below, from the 20:09 UT pass, with thatfrom the previous day  above (note: the fuzzy band in this case is interference - the ISS/Dragon signals are the s-shaped lines):

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First debris pieces from the Indian ASAT test of 27 March catalogued

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Today the first 57 orbital element sets for Microsat-r debris, debris from the Indian ASAT test on March 27, appeared on CSpOC's data-portal Space-Track (I have posted on aspects of this Indian ASAT test earlier: here, here and here). They have catalogue numbers 44117 - 44173. The analysis below is based on these orbital element sets.The elements confirm what we already knew: that Microsat-r (2019-006A) was the target of the ASAT test.

The image above plots the orbit of the 57 debris fragments, in red. The white orbit is the orbit of the International Space Station ISS, as a reference. Below is a Gabbard diagram of the debris pieces, plotting their perigee and apogee values against their obital period. The grey dashed line gives the orbital altitude of the ISS, as a reference:

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Again, it is well visible that a large number of the 57 fragments (80% actually) have apogee altitudes above the orbit of the ISS, well into the altitude range of operational satellites. This again shows (see an earlier post) that even low-altitude ASAT tests on orbiting objects, creates debris that reaches (much) higher altitudes. The highest apogee amongst the 57 debris pieces is that of 2019-006AR at 2248 km.

Below is the apogee altitude distribution as a bargraph (including a kernel density curve), again showing how pieces do reach the altitudes of operational satellites:

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Most of the created debris in the current sample of tracked larger debris has apogee altitudes between 400 and 700 km. It is interesting to compare this to a similar diagram for debris from the 2008 US ASAT demonstration on USA 193, "Operation Burnt Frost":

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The Operation Burnt Frost debris distribution peaked at a somewhat lower apogee altitude, ~250 km (the same orbital altitude as the target, USA 193) while the peak of the Indian ASAT debris apogee distribution is higher, ~400-500 km (there could however be detector bias involved here).

It is interesting to note that both distributions appear to be double-peaked, both having a secondary peak near 700-800 km. I remain cautious however, as that could be due to detector bias.

Overall, the two distributions are similar, as I already expected.

The question now is, how long this debris will survive. To gain some insight into the expected lifetimes, I used Alan Pickup's SatEvo software to make a reentry forecast for the debris fragments. It suggests that most of the debris will stay on orbit for several weeks to months: by half a year from now, most of it should be gone however, except for a few lingering pieces. Note that this forecast should be taken with some caution: it assumes a constant solar activity at the current level, and takes the NDOT values of the element sets face value.

The following bar diagram charts the forecast number of debris objects reentering per week (the x-axis being the number of weeks after the ASAT test) resulting from the SatEvo analysis:

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Again, the result is quite similar to the actual lifetimes displayed by the USA 193 debris fragments after Operation Burnt Frost in 2008 (see an earlier post, with the same diagram), as expected:

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More images of Kounotori (HTV) 7

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The image above is a stack (combination) of six images, taken at 10-second intervals with a 5-second exposure (Canon EOS 60D + EF 2.0/35 mm, 800 ISO). It shows Kounotori HTV 7 (2018-073A), a Japanese cargoship on its way to the ISS launched on September 22. This image was taken some 17 hours before it berthed to the ISS.

The cargoship was about 1m 38s behind the ISS at the time of observation. As no recent orbital elements were available, I did not know where to expect it relative to the ISS, so I started watching well before the ISS pass, and next noted it ascending over the roof just after the ISS had disappeared in Earth shadow.

The HTV 7 spacecraft was very bright during this pass: near magnitude +1, and a very easy naked eye object. Just like the day before (see an earlier post), it flared brightly, to at least mag -1/-2 at 19:50:18 UT (26 Sep 2018). The flare can be seen on the composite image above, and on the single image from this series below:

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Also note the distinct orange colour of the trail, which is due to the fact that HTV 7 is wrapped in gold-coloured insulation foil.

The flare happened while HTV 7 was passing through the field of view of my video setup:

The image below is a composite of the images taken while the ISS passed, and the images of HTV 7 passing 1m 38s later (i.e., they didn't move this close in the sky in reality!). The orange colour of HTV 7 stands out. Also well visible is that HTV 7 was somewhat faster than the ISS, due to a difference in orbital altitude (and hence orbital period):

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Imaging a pass of Kounotori (HTV) 7 on it's way to the ISS

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On 22 September 2018 (and after several launch delays, amongst others due to a typhoon), at 17:52:27 UT, Japan's Space Agency JAXA launched Kounotori (HTV) 7, a cargoship destined for the ISS. It will dock to the ISS tomorrow on September 27th.

The 9.8 x 4.4 meter HTV (HTV stands for "H-II Transfer Vehicle". The name Kounotori stands for "white stork") are easily visible, bright objects with a distinct orange colour due to the use of gold-coloured insulation foils.  See the image below of HTV 7 being assembled at the Test and Assembly Building at Tanegashima Space Center before launch:

image: JAXA

After days with bad weather, the sky cleared yesterday. I had a low pass in the southwest near 19:18 UT (Sep 25) and went to the nearby city moat with my camera, as I have a better view lower at the horizon there. Some whisps of thin clouds still lingered in the sky.

First, at 19:04 UT, I watched HTV 7's destination, the International Space Station (ISS), sail past as a very bright object. The image below is a stitch of two image stacks (!): one stack of two images, and a stack of 4 images with the camera FOV shifted horizontally. Camera: Canon EOS 60D with an EF 2.0/35 mm lens. I used exposures of 4 seconds at ISO 800.

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Then  I waited for HTV 7. As the latest orbital elements at that point were almost a day old, I was not sure about the exact time it would show up.

Some 14 minutes after the ISS it emerged, clearing the trees and houses low at the southwest horizon, and to my surprise and joy featured a bright flare to at least magnitude -1. My first image just captured the end of this brief flare (first of the two images below):

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The object was easily visible with the naked eye and had an orange hue. The image stack below was made of 5 images taken at 10-second intervals, with each image a 4-second exposure (camera details the same as for the ISS image). It shows HTV 7 from the bright flare to the moment it disappeared in the Earth's shadow:

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Capturing a pass of the X-37B OTV-5, and imaging an ISS transit over the Sun

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Yesterday evening was very clear, and the moon low in the south no real hindrance. I observed a very fine pass of the X-37B secret space plane OTV-5. It was an easy naked eye object. The photograph above (10-second exposure with an EF 2.0/35 mm lens) shows it ascending in the southwest, through Bootes (Arcturus is just above the open window).

The next morning (26 June) at 10:17:21 local time (8:17:21 UT), the International Space Station ISS was predicted to make a transit over the solar disc as seen from my house in Leiden.

I set up the Celestron C6 telescope in the courtyard, put a Baader Solar Foil filter in front of it, and hooked up the Canon EOS 60D to the prime focus. Instead of photographing at rapid burst, the technique I used for imaging with previous transits, I this time put the camera in HD movie mode. While this yields a lower resolution image than photography, the upside is that it yields more images showing the ISS silhouetted in front of the sun. And the ISS is big enough that the reduced resolution is not a real problem, the solar panels of the ISS are still well visible.

The image below is a composite of 21 frames from the resulting movie:

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Here is the movie itself, showing you how rapid such an ISS transit over the sun is (the total duration was only 0.8 seconds - it is over in a blink of the eye). The ISS had an apparent size of 45.8" during the transit, with the sun at 41 degrees elevation in the east:

The movie was made in the prime focus of a Celestron C6 (15-cm, F1500 mm Schmidt-Cassegrain, equiped with a Baader Foil solar filter) with a Canon EOS 60D DSLR in HD movie mode at 25 frames/second, with each frame having an exposure time of 1/4000th of  a second to avoid blurring the ISS. The track and time of the transit had been checked before the observation by loading the latest orbital elements for the ISS into Guide.

The biggest challenge with this kind of imagery is always to focus properly, certainly when the sun is spotless as it was this day. I always find focussing on the sun cumbersome. The focus this time turned out to be reasonably good though.

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

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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:

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

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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

[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)