Saturday, 19 October 2019

The structure of space: orbital families

click diagram to enlarge

Asteroid observers are well acquainted with the kind of diagram above: a plot of the semi-major axis of the orbit against orbital inclination. Doing this for asteroids allows to discern resonances, and clusters visible in such a diagram point to related objects with a shared origin (asteroid 'families').

The diagram above is however not showing asteroids in heliocentric orbits, but is a similar diagram showing orbits for all 18439 well-tracked artificial objects (satellites, rocket stages and debris) in orbit around our Earth. A number of clusters can be seen: the distribution of the objects in a-i space (*) is not random but structured.

The structure corresponds to satellites with a specific purpose (and the related rocket stages and debris), or from a specific family. Some functions of satellites demand a specific type of orbit distinguishable in a-i space.

Well recognizable clusters for example in the plot above, are Geosynchronous satellites; and satellites in HEO ('Molniya') orbit. These are often communication or SIGINT satellites. NAVSTAR navigation satellites (GPS) form a recognizable cluster too.

Two loose clusters of objects can be seen that correspond to Geostationary Transfer Orbits (GTO). These are the rocket stages left from launches into Geostationary orbit. They move in eccentric orbits with low inclination. Two groups can be discerned: those launched from Kourou in French Guyana by ESA, and those launched from Cape Canaveral by NASA and NRO. The fact that these two groups group and distinguish in inclination, is because the inclination of GTO launches correlates to the latitude of the launch site.

Some clusters are debris clusters which are the result of the breakup of objects (usually exploding rocket stages) in space: two of these are indicated in the plot above.

Interesting is also the cluster that represents Earth Observation satellites in sun-synchronous Polar orbit. Let us look at this part of the plot in more detail:

click diagram to enlarge

Sun-synchronous objects are objects in orbits designed to have a rate of RAAN (node) precession that matches the precession of the sun in Right Ascension. This is beneficial to optical remote sensing observations of the earth, as it means the orbital plane moves along with the shift in Right Ascension of the sun, thus ensuring that images are made around the same solar time each day, which aids shadow analysis.

The objects in this cluster display a clear obliquely slanted trend in a-i space. This is because the sunsynchronous character of an orbit is a function of semi-major axis, eccentricity and orbital inclination. Hence, a specific orbital inclination is necessary for each orbital altitude, causing the slant in the distribution in the plot above.

[EDIT 19 oct 2019, 21:55 UT]

In the diagram below, the black line is the theoretical trend in a-i space for a circular sun-synchronous orbit. For more elliptical orbits, the slant of the line is slightly different:

click diagram to enlarge

I am not entirely sure what is behind the noticable gap visible in the distribution around inclination 101 degrees. The upper sub-cluster around 102 degrees inclination contains a number of meteorological satellites, plus debris from associated, broken up rocket stages, so it might be a sub-cluster representing a specific family of satellites

A couple of other object 'families' can be seen in this detail diagram as well, as distinct clusters. There is another breakup event visible (Kosmos 1275, a Soviet navigation satellite that disintegrated in orbit some 50 days after launch), as well as two payload families, including the Iridium satellites. The Westford Needles are tiny metal rods that are the result of a weird,  ill-conceived and eventually abandoned communication experiment during 1961 and 1963 (read more here).

* note: a-i means: semi major axis (a) versus orbital inclination (i)

Friday, 27 September 2019

Six months after India's ASAT test

Six months ago today, on 27 March 2019 at 5:42:15 UT, India conducted its first successful Anti Satellite (ASAT) Test, under the code name Mission Shakti. I wrote an in-depth OSINT analysis of that test published in The Diplomat in April 2019.

Part of that analysis was an assessment - also discussed in various previous posts on this blog - on how long debris from this ASAT test would stay on-orbit. Half-a-year after the test, it is time to make a tally of what is left and what is gone - and make a new estimate when the last piece will be gone.

A few more debris pieces have been catalogued by CSpOC since my last tally. As of 27 September 2019, orbits for 125 debris pieces from the ASAT test have been catalogued. Of these 125 objects, 87 (or 70%) had reentered or had likely reentered by 27 September, leaving 38 (or 30%) still on orbit.

click diagram to enlarge
click diagram to enlarge

Remember that the Indian DRDO had made the claim that all debris would have reentered 45 days after the test. This is clearly not correct: of the well-tracked debris for which we have orbits (presumably there is a lot more for which we have no orbits), only 29%, i.e. barely one-third, reentered within 45 days. Over 70% did not. At 120 days after the test, only half of the catalogued population of larger debris had reentered.

click diagram to enlarge
click diagram to enlarge

I used SatEvo to produce reentry estimates for the 38 objects still on orbit on 27 September 2019. By the end of the year, some 15 to 16 of these larger debris fragments should still remain on-orbit.

One year after the test, at the end of March 2020, about 90% of all tracked debris should have reentered. The last or the tracked debris fragments for which we have orbits, might not reenter untill mid 2024.

The current apogee altitudes of the objects on-orbit spread between 270 and 1945 km. They have now well-dispersed in RAAN too, no longer sharing the same orbital plane:

click to enlarge
click to enlarge

Some 90% of the debris fragments still on-orbit have an apogee altitude above that of the ISS, meaning that they almost all have orbits that reach well into the orbital altitudes of operational satellites.

Sunday, 1 September 2019

Image from Trump tweet identified as imagery by USA 224, a classified KH-11 ENHANCED CRYSTAL satellite

click to enlarge. image: US Government

The incredibly detailed image above was leaked declassified and revealed to the world by US President Donald Trump, very characteristically in a tweet, on 30 August 2019.

It shows the aftermath of the failed Iranian Safir launch of August 28/29, with considerable damage to the platform and vehicles. Obviously, there was an explosion or crash of some sort, likely an explosion of an engine or rocket stage or failed lift-off.

The image is a photograph of a printed photograph: you can see the reflection of the camera flash on the photographic print near the center of the image and the silhouet of the person photographing it. There is also some image distortion, likely because the print was curling somewhat at the edges. But the level of detail is amazing (and the original might have been even more detailed).

That level of detail quickly led to speculation: what platform took this image? A drone? A high altitude reconnaissance aircraft? A satellite?

Some initially argued that the level of detail was too high for a satellite. But as we will see in this post, it was made by a satellite, and we can even say which satellite.

The level of detail in the image is incredible and points to one of the NRO's classified KH-11 EVOLVED ENHANCED CRYSTAL electro-optical reconnaissance satellites (they are also known as ADVANCED CRYSTAL, KENNEN, and colloquially as 'KeyHole').

These are high resolution optical satellites that resemble the Hubble Space Telescope, but look down to Earth instead of to the heavens. It is known that the optics of these satellites are 2.4-meter diameter mirrors. Theoretically, from the perigee of their orbits this would yield a resolution of just under 10 cm.

Christiaan Triebert analysed the shadow directions on the image and placed the time of the image between 9 and 10 UT (August 29), or 13:30-14:30 local Iranian time. Michael Thompson pointed out on Twitter that one of the KH-11 satellites, USA 224 (2011-002A), made a pass over the launch site in that time window.

This satellite is a classified satellite, but we do know its orbit because amateur trackers track this object regularly. This is USA 224 passing over my hometown Leiden in June 2014 for example:

USA 224 passing over Leiden, 21 June 2014

This blogpost consolidates two analysis which I initially published through Twitter. I will show in this analysis that there is very little doubt that USA 224 took this image.

Matching view angles 

The map below shows how USA 224 passed almost right over the launch site at 9:43:47 UT on August 29, with a maximum elevation of 87.7 degrees. The photograph tweeted by President Trump was taken post culmination, from the location indicated by the white cross in the map above. That position is based on the analysis that now follows.

click map to enlarge

The depicted trajectory for USA 224 is based on amateur tracking data. I used elset 19239.00965638 which was ~2.5 days old at the time of the overflight. In the absence of a manoeuvre, it should be accurate to a few seconds in time along-track and very little error cross-track.

USA 224
1 37348U 11002A   19239.00965638 0.00010600  00000-0  95384-4 0    03
2 37348  97.9000 349.1166 0536016 134.6567 225.3431 14.78336728    04

The imaged launch site itself is located at 35.2346 N, 53.9210 E, altitude 936 m, and indicated by the blue dot in the map. The launch platform is part of Iran's Imam Khomeini Space Port, near Semnan.

click to enlarge. Image: US Government

Trump's image shows the platform viewed under an oblique angle, looking in a northern direction (i.e. with the satellite to the south of the site). As the launch platform is circular, we can use the ellipticity of the platform on the image to estimate the angle under which the platform was imaged. For this, we have to measure the semi-minor and semi-major axis of the ellipse (denoted Y and R in the diagram below): their ratio corresponds to the sinus of the viewing angle.

The result of this measurement is a nominal view angle of 46.03 degrees. For USA 224, this elevation with respect to the imaged site was reached at 09:44:20.7 UT (nominally), post-culmination when the satellite was to the south of the site. From the satellite ephemeris, the satellite was at an azimuth of 194.85 degrees as seen from the imaged site at that moment. The satellite's geographical position was near 33.005 N,  53.220 E at an altitude of  283 km. The range to the imaged site was 385 km.

I used these values as input in STK and simulated the view of the damaged launch platform as seen from USA 224 for 29 August 09:44:20.7 UT. The images below compare the original image from President Trump's tweet (top) and the simulated view from USA 224 (bottom):

click to enlarge

Ignoring the shadow directions, the simulated view is very similar to the actual image, pointing out that indeed the image very likely was taken by the USA 224 satellite.

(the simulated view uses an overhead commercial satellite image taken at another time, rendered to mimic an oblique view, hence the different shadow directions).

Cees Bassa, in an independent analysis, has calculated very similar figures for the viewing angle and from that azimuth and elevation.

Matching times

In a second analysis, I tried to improve on the time of the image derived from the shadow directions.

When projecting a line through the shadow of one of the masts at the edge of the platform, this line passes almost through the middle of the access road at top right in the image:

click to enlarge

I used this observation to measure the direction of the shadow in Google Earth. It corresponds to an approximate azimuth of 40.45 degrees, which would place the sun at an azimuth of about 220.45 degrees (+- 1 degree error or so):

click to enlarge

Looking this direction up in the solar ephemerids for the imaged site (calculated with MICA), this solar azimuth corresponds to 09:46:25 UT (Aug 29). This is only 2 minutes later than the time for which the image best matches the USA 224 view of the site, as reconstructed earlier in this post.

This again confirms that this image could very well have been taken by USA 224. Both the time matches, and the view matches.

With the uncertainties in the shadow direction measurement taken into account (including uncertainties introduced by possible image deformations), within error margins the two times match. The difference between the measured (~220.45) solar azimuth and the solar azimuth calculated for 09:44:21 UT is 0.85 degrees, i.e. under a degree and hence small.

The 09:44:21 UT  derived from matching the satellite view to the image, probably is more accurate than the time derived from the shadow analysis. This time is probably accurate to a few seconds, given that the satellite TLE used was 2.5 days old.


And then the baffling question: why did President Trump tweet an image that otherwise would be considered highly classified?

The KH-11 satellites are classified, and so is imagery from these satellites. If an adversary gets her hands on KH-11 imagery, it reveals information about the optical capacities of these space assets.

In 1984, a Navy intelligence analyst was sent to prison for leaking three KH-11 images to the press.

Reconnaissance satellite imagery made public by the US Government itself over the past decades were either from commercial DigitalGlobe satellites, or purposely degraded in quality such as not to reveal the optical capacities of the KH-11. But now we see a US President tweet, on what appears to be a whim for the purpose of gloating, a very detailed image that as was shown in this post definitely was taken by a KH-11 satellite.

The occassion at which this happened, is eyebrow raising. A failed space launch hardly is a matter of great geopolitical concern. It is something trivial compared to e.g. imagery showing preparations for an invasion, the production of WMD, or atrocities against humanity. The latter could perhaps be argued to be a valid reason to publish imagery that also divulges the capacities of your best space-based imaging platforms: this occasion was not.

Which makes this a rather momentous occasion.

(note: there is a black block in the upper left of the image that seems to be placed there to redact some information that might have been printed there. I think it is likely this information was the time of image, space platform ID and the location of the latter. It points out that some deliberate thought was given to the release of this image, before it was tweeted).

USA 224 passing through Corona Borealis, 17 June 2014

Edit (2 Sep 2019):

In the comments, Russ Calvert makes a very valid point: the phone camera used to photograph the photographic print might also introduce some slant. But I suspect the error introduced this way is small as normally you would try as best as you can to hold the camera perpendicular to the paper you are photographing. A clear slant angle of the camera also would introduce a sharpness gradient that does not seem to be there. The good match between the image and the simulated view from the satellite also bears out that error introduced in this way is likely small.

Edit II (2 Sep 2019): 

Added two archive images of USA 224 passing through the night sky over my hometown Leiden.

Edit III (24 Sep 2019)

Between the infamous 1984 leak by Samuel Moring Lorrison and Trumps 2019 tweet, there was one other occasion that (parts of a) full resolution KH-11 imagery became public. That was an image from the Snowden files published in September 2016 as part of an article in The Intercept,
which according to the annotations on it was taken on 28 January 2009 at 5:16 UT,

I had forgotten about it untill this article by Dwayne Day brought it to my attention again, and then I remembered that I had already identified this image as being taken by USA 129 (1996-072A), a now deorbitted KH-11 reconnaissance satellite.

image source: The Intercept 6 Sept 2016

In 2018 Bill Robinson geolocated the image as showing a part of Zaranj, a southern Afghanistan village on the border with Iran. I in turn was able to show that USA 129 was near this location (see Bill's blog post), in an appropriate position to make the image. As een from the position of USA 129 at 5:16 UT, Zaranj was located at a range of 368 km. Seen from Zaranj, the satellite was in azimuth 216 degrees, elevation 66 degrees at that time.
click map to enlarge

Saturday, 17 August 2019

The Chinese ICBM test of August 7 [UPDATED]

Just after local midnight of August 7-8, 2019, the South Korean amateur astronomer Mr Lee Won-Gyu was taking images of the night sky at Mount Jiri in Korea when he observed and photographed a cloud-like illuminating phenomena in Corona Borealis that to the expert eye is clearly the exhaust cloud from a rocket engine burn.

Mr Lee Won-Gyu's images of the cloud are featured in this article in the Korea Times, where they were presented as a 'UFO'. The images were taken between 00:14 and 00:24 Korean time (corresponding to August 7, 15:14-15:24 UT). Mount Jiri, the location of the sighting, is at approx. 35.34 N, 127.73 E. In this blogpost, I will identify this 'UFO' as a Chinese ICBM test.

Initial speculation on the internet was that this was perhaps related to the AEHF 5 geosynchronous satellite launch from Florida on August 8, 10:13 UT. The observation was however done 19 hours before this launch (there was some initial confusion due to the date difference in local time and UT), and the cloud was seen in a wrong part of the sky for a launch to geosynchronous altitude. So I suggested it could be a Russian or Chinese ICBM test launch.

As it turns out, additional evidence suggests this indeed was an ICBM test, by China. As the result of a private request by me, Twitter user @Cosmic_Penguin managed to dig up NOTAM's for the date and time of the event posted on a Chinese forum by a forum member nicknamed 'kktt'. These NOTAM's with temporary airspace closures from "ground to unlimited" in two parts of China corroborate an ICBM test launch:

A4092/19 NOTAMN
Q) ZBPE/QRTCA/IV/BO/W/000/999/3909N10940E019
A) ZBPE B) 1908071449 C) 1908071511

A4094/19 NOTAMN
Q) ZWUQ/QRTCA/IV/BO/W/000/999/3712N08311E108
A) ZWUQ B) 1908071451 C) 1908071548

The NOTAM's have a time window between 14:49 UT and 15:48 UT on 7 August 2019, which fits the phenomena observed from Korea (7 August 15:14-15:24 UT). They also fit the direction of the sky phenomena as seen from Korea: the exhaust cloud was seen at 30 degrees elevation in the sky at azimuth 290-291 degrees (west-northwest). This sightline points directly to the area designated in NOTAM A4092/19.

The map below plots the two areas designated in the NOTAM's. The smaller rectangular area from NOTAM A4092/19 represents the launch area near Hongjian Nur in Shaanxi province. The larger circular area from NOTAM A4094/19 at the southern edge of the Taklamakan desert represents the RV target area. The two areas are some 2300-2400 km distant from each other:

click map to enlarge

I have depicted the sightline from Mr Lee Won-Gyu's photographs from Mt. Jiri in Korea on the map as well (white): it points towards the launch area and it lines up with the direction of that rectangular area. Both time and direction therefore fit the Korean sighting. So does the character of the photographed cloud, which is similar to missile exhaust clouds observed during other ICBM launches.

This was an interesting ICBM launch in that it appears to have been highly lofted, with an apogee at approximately 3000 km altitude. This is based on both the estimated flightime (about 37 minutes) deduced from the NOTAM time window durations; and from an assessment of the exhaust cloud sightings from Korea, the direction and elevation of which point to a burn at 3000 km, close to apogee of the orbit, when combined with a ballistic trajectory between the two areas of the two NOTAM's. The launch happened near 15:00 UT (August 7), the missile engine burn seen from Korea happened some 15 minutes later close to mid-course and was probably meant to change the direction of the missile.

The situation is spatially depicted in the diagram below. The sightline from Korea crosses a 3000 km apogee trajectory twice, at about 2300 km altitude when the missile is ascending, and near apogee at 3000 km altitude. The latter altitude is the most likely location of the engine burn. At these altitudes, exhaust clouds are well above the earth shadow and hence brightly sun-illuminated.

click image to enlarge

When launched on a less lofted trajectory, this missile would have had a ground range of at least 6300 km. The reason to launch it into a lofted trajectory, rather than a more typical trajectory with apogee at 1200 km, is that in this way the test could be done completely within the borders of China. We have seen such lofted trajectories earlier with some early North Korean ICBM tests.

The ICBM appears to have done a dog-leg manoeuvre near apogee, changing the course just before mid-course. One piece of evidence for this is that the orientation of the launch hazard area from NOTAM A4092/19 does not match with a simple ballistic trajectory towards the target area. Neither does the sightline direction from Korea. They would result in a target area more to the north than the area from NOTAM A4094/19.

This can be well seen in the map, where I depicted both a direct ballistic trajectory (solid black line) between the two areas from the NOTAM's, as well as a 'dog-legged' trajectory (dashed black line), with the dogleg at the near-apogee burn imaged from Korea and initial launch direction according to the orientation of the NOTAM A4092/19 area:

click map to enlarge
The direct trajectory clearly does not fit the launch area direction and Korean sighting well, whereas a launch into the direction of the NOTAM A4092/19 area and a dogleg near apogee does, with the latter also clearly fitting the Korean sighting.

A reason for such a dog-leg manoeuvre might be to confuse and evade mid-course anti-Ballistic missile intercepts. So I am wondering if this perhaps was an anti-ballistic missile test as well.

This missile test must in theory (and ignoring cloud cover) have been widely visible over Eastern Asia. The Korean Times article presents one other observation, also from Korea, but I have not seen other observations so far.

UPDATE: Twitter user @LaunchStuff sent me this link to a Weibo page, which includes several photographs of the event from various parts of China and a very cool video shot from Inner Mongolia, showing the spiralling behaviour seen during other ICBM tests as well.

Acknowledgement: I thank Ravi Jagtiani for bringing the Korea Times article to my attention; @Cosmic_Penguin for digging up the NOTAM's; and Jim Oberg and Jonathan McDowell for discussions.

Saturday, 27 July 2019

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:

click to enlarge

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:

click to enlarge
click diagram to enlarge

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):

click to enlarge

Thursday, 25 July 2019

X-37B fact and fiction

X-37B. Photo: USAF

If there is one classified space object that speaks to the public's imagination, then it is the US Air Force's  X-37B robottic space plane, also known as Orbital Test Vehicle (OTV).  These 9 meter long uncrewed spacecraft have wings, with a wingspan of 4.5 meter, and look like a mini Space Shuttle. They are launched on a rocket like a normal satellite, but return to earth by landing like an airplane (or indeed like the Space Shuttles did). They have a payload bay of 2.1 by 1.2 meter in which they carry experiments and from which they could perhaps also release and retrieve small satellites. They are launched in very low orbits, between 250 and 450 km orbital altitude (i.e. generally below the orbit of the ISS).

The US Air Force has two X-37B's and is currently flying it's 5th OTV mission with one of them, with 685 days on orbit on the day of writing.

The winged design and the coloquial 'space plane' lead many people to think the X-37B flies and banks like an airplane or a Star Wars X-wing fighter while in space - its infamous purported "manoeuverability", a notion recently fuelled again by remarks of former SecAF Heather Wilson (see below).

This is mostly a misunderstanding and part of the mythos that surrounds the X-37B: in space, the wings of the X-37B are useless and it behaves and orbits the earth like any other satellite. The X-37B does not change its orbital plane at a whim - or at least not generally. That is quite clear from amateur monitoring of the five OTV missions so far.

In this post I will show that the only significant manoeuvers the OTV's make are frequent alterations of their orbital altitude: they do not significantly change orbital plane during a mission. Periodically changing orbital altitude is something other satellites do too, so the X-37B is not special in this either, except that during recent OTV missions the X-37B's have done this more often than ordinary satellites typically do. And let me add, so you understand me well: you don't need (or indeed use) wings for that. These orbital altitude changes are done with an engine burn, just like 'normal' satellites do.

The X-37B OTV 5 filmed by the author on 26 June 2019

The wings of the X-37B are not for manoeuvering in space, but primarily for use in the lower atmosphere upon its return to earth, when it lands like an aircraft (as the Space Shuttle did). Yet every now and then, the myth of the supposed wing-supported "manoeuverability" pops up again, and connected to it is a whole ecosystem of suspicions and theories about the potential "function" of the X-37B - most notoriously the (almost certainly incorrect) notion that it is some kind of "Space Bomber" ready to be flown to any target on earth within 90 minutes to drop a destructive weapon. The Space Treaty, to which the USA is a signatory, prohibits to deploy weapons from space, and it is really unlikely that the X-37B is such a 'space bomber'.

The X37-B instead likely is a testbed for new space hardware, testing new technologies under real space conditions and then returning them to earth for inspection. We know for example that during the OTV 4 mission, a XR-5a Hall-effect thruster was tested. The frequent changes in orbital altitude are part of this: testing space hardware under various drag regimes.

So what about that "manoeuverability" then? New fuel was fanned on the idea of extraordinarily "manoeuverability" recently by intriguing statements made by former SecAF Heather Wilson. She claimed that the X-37B:

"Can do an orbit that looks like an egg and, when it's close to the Earth, it's close enough to the atmosphere to turn where it is. [...] Which means our adversaries don't know -- and that happens on the far side of the Earth from our adversaries -- where it's going to come up next. And we know that that drives them nuts."

Two things are apparently being claimed here:

(1)  The X-37B can manoeuvre by briefly dipping into the upper atmosphere;

(2)  This makes the X-37B difficult to track.

The wording of the statement is wonderfully opaque, but Wilson seems to suggest that the X-37B can seriously change its orbital inclination by briefly dipping into the upper atmosphere and using its wings to manoeuvre.

I have two problems with this. One is that bringing the X-37B down into the upper atmosphere by an engine burn (there is no other way), have it change orbital plane by using the wings, and then do a burn to get back to orbital altitude again, probably costs as much fuel as a more regular on-orbit engine burn to change orbital plane. So where is the gain in using this dip-and-wing-manoeuvre?

The other problem I have, is that I do not see the claimed behaviour in our tracking data. Contrary to the impression that Wilson is trying to give us, i.e. that the X-37B's are difficult to track due to the tricks they perform, the X-37B OTV missions have been regularly tracked by our amateur network. And we do not see significant changes in the orbital plane during a given OTV mission.

The X-37B OTV 5 imaged by the author in April 2018 (click to enlarge)

Looking at the tracking data we have for these X-37B missions, they show only very minor changes in orbital inclination during a given mission. There is no evidence for sudden, significant changes in the orbital plane, as is illustrated by these diagrams that for each OTV mission plots the orbital inclination against time (the data are from observations by the satobs amateur network):

The only exception appears to be mission OTV 4, which does show a temporary change in orbital inclination and then back again in the last quarter of 2016. The orbital plane change is of little significance however (only 0.6 degrees) and could have been done by a normal engine burn. So if the X-37B indeed can use a drop into the upper atmosphere to make use of it wings to significantly change orbital plane, they so far do not seem to have clearly demonstrated this capability.

(the changes in orbital inclination at the end of the OTV 2 and OTV 3 missions, probably are in preparation for landing).

What the X-37B missions in contrast do have demonstrated, especially during the last two missions, are repeated changes in orbital altitude and orbital eccentricity (in Wilsons words: it "can do an orbit like an egg"). This is illustrated by these plots of the apogee and perigee altitudes against time for the five OTV missions so far:

As I already mentioned this is something other satellites do too, so the X-37B is not particularly special in this either, except that during recent OTV missions the X-37B's do this more often than ordinary satellites typically do. The changes in orbital altitude probably are related to testing equipment under different drag, gravity and irradiation regimes.

So the X-37B missions so far set themselves apart from regular satellite missions by their low orbital altitudes and frequent changes in orbital altitude (in which the wings play no role at all). They can do so because their missions are relatively short compared to a typical satellite mission. Unlike a regular satellite, at one point they will land and be refuelled, and then relaunched after a while.

But as intriguing as the suggestions are, the orbital history of the five X-37B OTV missions so far do not evidence the alledged manoeuverability in orbital plane.

Nor of course, are the X-37B that difficult to track as is claimed. Our amateur network regularly observed and observes the OTV missions. We might lose the OTV for a (usually brief) moment when it has made a manoeuvre to a higher or lower orbit, but a plane scan is enough to relocate it (and as the diagrams above show, they do not manoeuvre daily or even weekly).

So Wilson's remarks appear to be just part of the myth-making around the X-37B.

Tuesday, 18 June 2019

Two-and-a-half months after the Indian ASAT test: What's Up?

On 27 March 2019, India conducted it's first succesful Anti-Satellite (ASAT) test, destroying Microsat-R on orbit. I have blogged on this before here, here, here and here; and published a detailed OSINT analysis of this test in The Diplomat, in which I have shown that the Indian version of events concerning this ASAT test is not entirely correct.

So what is the current situation? The Indian government claimed right after the test that 45 days after the test, the space debris generated by the ASAT test would be gone. We are now a month after that deadline. Is everything gone indeed? Far from it.

Some 92 larger debris pieces resulting from the test have been catalogued by CSpOC. Of these, 56,  i.e. some 60% were still on orbit 45 days after the ASAT test. And 46 (that is 50%) were still in orbit on June 15, one full month after all should have been gone according to the Indian Defence Research and Development Organisation (DRDO). These numbers are in line with my earlier forecast here.

The diagrams below visualize these data, including (grey lines) a new forecast for the remainder of the debris still orbiting. The top diagram is the cumulative percentage of reentered debris from the test, the lower diagram gives the number of objects reentering per week.

click diagram to enlarge
click diagram to enlarge

Many of these objects still on-orbit have apogees still well into the range of operational satellites, i.e. they remain a threat to other objects in space. In my current forecast for these remaining objects, at least 5 objects will stay in orbit for at least a year to come, and the last one might not reenter until mid-2021. So clearly, Indian DRDO estimates were much too optimistic.

click diagram to enlarge

Saturday, 1 June 2019

[UPDATED] Erratic orbital evolution of four Starlink objects

Edit 5 June 2019: updated at end of post with new data

During a talk at MIT on May 29, SpaceX President Gwynne Shotwell reportedly mentioned that four of the 60 Starlink objects launched on May 24 are having issues (but she reportedly also said that these four are in contact with SpaceX  ground control: i.e. it is too early to consider these four objects a failure).

These four objects are probably object J, AA, AG and AQ. Their orbital evolution so far stands out from the rest of the objects: while 56 objects have gone up, these four either stayed near the altitude of orbit insertion, or are in fact going down.

This can be cleearly seen in these two diagrams I made today, showing the total amount of altitude gained for each object. Objects J, AA, AG and AQ (red) clearly stand out form the rest (black).

click to enlarge

click to enlarge

The other four objects (blue) that did not raise their orbit, are the 'FALCON 9 DEB' objects (with DEB standing for 'debris'. These are four support bars that held the satellite stack together untill deployment. Our observations show that these four are tumbling, as they can be seen flashing in a regular pattern.

Two of these support bars can be seen as fainter flashing objects at about 25 seconds into my video from May 24th (the other two were filmed as well, moving somewhat in front of the "train", but are not in the video I posted):

UPDATE 5 June 2019:

 One of the four objects, object AA, has come to life and is raising orbit now. Objects AG, AQ and J have not changed: