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.

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

[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:

Numbers: the SpaceX Starlink constellation in perspective with what is currently orbiting earth

click to enlarge

The image above was taken by me in the evening of May 28 with a Canon EOS 60D and Samyang 1.4/85 mm lens. It shows a part of the now already dispersing "train" of SpaceX Starlink objects. They briefly flared, one by one, while passing north of Corona Borealis.

In this post, I want to put in perspective what adding 12000 Starlink objects to the current population of satellites orbiting Earth means.

Quite some numbers are floating about in articles and on internet, concerning current numbers of objects orbiting Earth. I made a tally this morning, including both classified and unclassified objects. Datasources were the database of classified objects maintained by Mike McCants; CSpOC's satellite catalogue for all unclassified objects; and the UCS Satellite database for the number of operational satellites. Numbers given in the diagrams in this post are rounded numbers.

A number of  "44000" is floating around the internet regarding the number of objects orbiting earth currently. This figure is wrong: CSpOC is tracking some 23000 objects of which some 18000 are well-tracked and can be indentified as to origin. This excludes, of course, objects that are not well-tracked, or are not tracked at all (e.g. because they are very small), the exact number of which is unknown. In the remainder of this post, we will restrict us to the ones that are known. These are generally objects larger than 10 cm.

In addition, our amateur network tracks some 300 additional "classified" objects.

The "44000" figure comes from the fact that the catalogue numbers (the unique identifiers given to each object) have now added up to 44306 entries: however, this concerns all objects catalogued since 1957, including many objects that have since re-entered into the atmosphere.

So the correct number to go with for objects currently in orbit around Earth and well-tracked, is slightly over 18300 objects.

Of these 18300, about 5500 are payloads, both operational and defunct. The UCS database currently lists some 2000 operational payloads, leaving 3500 defunct payloads.

In addition to operational and defunct payloads, there are some 2000 spent rocket boosters orbiting our planet. The remainder, almost 11000 objects, concerns other space debris (including sometimes very small objects, only detectable by radar).

Here I have visualized these basic data in the form of a pie-diagram:

click to enlarge

So, in perspective to these numbers for the current population of Earth-orbiting objects, what will be the result of the addition of  the 12000 planned objects in the Starlink constellation? How does their number compare to the other objects?

In the pie diagram below, you can see that adding 12000 Starlink objects would mean they would represent about one third of all objects orbiting Earth:

click to enlarge

In the diagram, I have lumped payloads and rocket stages as these generally represent larger objects, and put the rest into "other debris". The latter category includes very small objects, fragments from exploded rocket stages and disintegrated satellites. The diagram includes objects in geostationary orbit.

Starlink will operate in Low Earth Orbit. Musk's plan is to launch 1600 satellites to an operational altitude of 550 km; another 2800 to an operational altitude of 1150 km; and a whopping 7500 to an operational altitude of 340 km.

click to enlarge

When we only count objects with a perigee below 1150 km, the topmost orbital altitude shell of the proposed Starlink constellation, there are currently some 13800 objects orbiting up to these altitudes. Adding 12000 Starlink objects would almost double the population total.

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When we only count objects with a perigee below 550 km, which includes the lower and middle of the three orbital altitude shells of the proposed constellation, some 2900 objects are currently orbiting up to these altitudes. Adding almost 9100 Starlink objects (the sum of the lower and middle shell objects), would mean that about three quarter of the resulting population would be Starlink satellites (!).

click to enlarge

In other words: the amount of objects added by Starlink, compared to the current population of objects, is certainly significant, especially where it concerns the lower parts of Low Earth Orbit.

Below 550 km, the population would increase to four times as much as currently - and this includes all very small debris pieces that can only be observed by radar in the tally. If we restrict the comparison to the larger objects, it means an at least five times increase in object number. That is truely significant.

With these massive additions by just one company, the question arises whether some kind of regulation is in order, e.g. through the UN. If not, we allow one company to, basically, take over and massively dominate Low Earth Orbit. There are all kinds of ramifications: like, will current Space Tracking Networks be able to deal with the increased detection load on their networks? (if not, space will become less safe).  What will this do to our night sky? Etcetera.

(with regard as to what might be the effect to our night sky, I refer to this twitter tread by Cees Bassa, who has cracked some numbers as to visibility)

It seems to me that the World, the international community as a whole instead of one US corporation,  should have some say into this. I am otherwise a fan of Elon Musk, who undoubtedly has given space exploration and space technology a new impetus and good shake-up: but concerning Starlink, this all seems not well thought out to me.

The Starlink "train" on 28 May 2019. Click to enlarge

WOWOWOW!!!! A SPECTACULAR view of the SpaceX Starlink satellite train!

On 24 May 2019 at 2:30 UT, SpaceX launched STARLINK, a series of 60 satellites that is the first launch of many that will create a large constellation of satellites meant to provide global internet access.

Just short of a day after the launch, near 22:55 UT on May 24, this resulted in a spectacular view over NW Europe, when a "train" of bright satellites, all moving close together in a line, moved across the sky. It rained UFO reports as a result, and the press picked it up as well.

There were no orbital elements for the objects available yet on Space-Track, but based on the orbital information (53 degree inclination, initially 440 km orbital altitude) I had calculated a search orbit and stood ready with my camera.

My search orbit turned out to be not too bad: very close in sky track, and with the objects passing some 3 minutes early on the predictions. And what a SPECTACULAR view it was!

It started with two faint, flashing objects moving into the field of view. Then, a few tens of seconds later, my jaw dropped as the "train" entered the field of view. I could not help shouting "OAAAAAH!!!!" (followed by a few expletives...).

Here is the video I shot, be prepared to be mind-blown!



The video was shot, in a partly clouded sky, with a WATEC 902H low-light-level surveillance camera, equipped with a Canon FD 1.8/50 mm lens. I could count at least 56 objects in the original video.

Over the coming days the "train" of objects will be making 2-3 passes each night. As they are actively manoeuvering with their ion thrusters, they will be more spread out with each pass, so the "train" will probably quickly dissipate.

The objects were launched into a ~440 km altitude, 53 degree inclined orbit. Using their ion thrusters, they will raise their orbits to ~550 km the coming days/weeks.

Orbital Reflector has joined the Dark Side

image: Nevada Museum of Art

Orbital Reflector will not shine brightly in our night sky. The extraordinary Art project by Trevor Paglen and the Nevada Museum of Art (see my earlier post here) has run on the cliffs of American politics, and was sadly lost as a result.

In a May 1 press announcement by the Nevada Museum of Art, it was indicated that contact with the satellite has been lost, so the command to inflate the balloon can no longer be sent.

That command should have been sent weeks ago, but was postponed because of, basically, the childish state of US politics. The satellite operators needed to have FCC approval to inflate the balloon: approval that should have been given after enough space had been created between the various payloads of the SSO-A launch.

But then, as the Nevada Museum of Art press release puts it:

"two unanticipated events occurred: 1) Due to the unprecedented number of satellites on the rocket, the U.S. Air Force was unable to distinguish between them and could not assign tracking numbers to many of the them. Without a tracking number to verify location and position, the FCC could not give approval for inflation; and 2) The FCC was unavailable to move forward quickly due to the U.S. government shutdown."

The US Government shutdown referred to was the US Federal shutdown imposed by President Trump, when US Congress did not agree to his proposed spending bill for 2019 (notably, the demand for $5.7 billion in funding for his proposed Border Wall). The shutdown lasted until the end of January 2019 (the longest Federal shutdown ever) and affected the functioning of several Federal agencies including the FCC.

As Trevor himself put it recently:

"We needed to coordinate with the FCC to deploy the reflector, but there was no one to take our calls: there was no government".

In the weeks immediately after the SSO-A launch, the Orbital Reflector operators were in radio contact with the satellite. But over time, the radio pings became weaker and by the time the Federal shutdown was finally over and the FCC had resumed functioning again, the radio of Orbital Reflector had fallen silent.

I am very sad about this outcome. I had looked forward to observing and tracking Orbital Reflector, both to admire it as an unusual global piece of art, and to see how its orbital evolution over time would (or would not) match my earlier modelling. I am also sad because I know how much time, energy and thought Trevor, who is a personal friend, has put into this art project, one of his most challenging so far. It is a pitty it worked out this way, even more so because it happened just because of petty US politics, not flaws in the concept.

But even though the original plan was ruined due to a President that was trying to blackmail Congress into submission, Orbital Reflector still serves a goal. One of the goals of Orbital Reflector, besides being seen, was to trigger debate about who owns space, what does and does not belong there, and who gets to decide about that. That debate certainly happened around Orbital Reflector (see a previous post). In that sense, Orbital reflector was a success.

I also like how Orbital Reflector, which was meant to be the very opposite of the dark shady, anonymous and unseen use of space by the military, now has joined the Dark Side itself: unseen, but there, orbiting in anonymity, and in this state as a result of geopolitical power play the effects of which reach all the way into space.

In a way, Orbital Reflector now has become a symbol of how geopolitical powerplay corrupts everything, even Space, which in a  way was the very thing it was intended to make people think about. That's art for you, even if this developed in a way that was not quite foreseen.

Why India's ASAT test was reckless (updated)

Today, I published a large article in The Diplomat:

"Why India’s ASAT Test Was Reckless. Publicly available data contradicts official Indian assertions about its first anti-satellite test"

The paper is online here: https://thediplomat.com/2019/05/why-indias-asat-test-was-reckless/

Summary - In this paper, I present an OSINT analysis of data available from Indian and US sources. From missile telemetry data visible in a DRDO released video (!) I reconstruct the last 2.7 seconds of the missile's trajectory relative to the trajectory of Microsat-R, showing that the missile hit the satellite under a clear upwards angle. I also discuss what can be gleaned from the orbital elements of the 84 debris pieces tracked so far.

The main conclusion is that the ASAT test was conducted in a less responsible way than originally claimed by the Indian government. First, the missile hit the target satellite on a clear upwards angle, rather than “head-on” as claimed by DRDO. Second and third, the test generated debris with much longer orbital lifetimes (up to 10 times longer), which ended up at much higher altitudes than the Indian government is willing to admit.

As much as 79 percent of the larger debris fragments tracked have apogee altitudes at or above the orbit of the International Space Station. Most of the tracked debris generated by the test orbits between 300 km and 900 km altitude, well into the range of typical orbital altitudes for satellites in Low Earth Orbit. As these debris fragments are in polar orbits, they are a potential threat to satellites in all orbital inclinations at these altitudes.This threat will persist for up to half a year (rather than the 45 days claimed by the Indian government), with a few fragments lingering on (much) longer, up to almost two years.


UPDATE, 2 May 2019:

On Twitter, I was asked to elucidate a bit more on how I did the analysis.

The delta V calculations have been done using equations from chapter 6 of "Space Mission Analysis and Design", third edition (Wetz and Larson (eds.), 1999).

The missile trajectory relative to the satellite trajectory was calculated with quite simple goniometry from the telemetry values (azimuth, range and elevation from the camera site) extracted from the DRDO video. Azimuth and range allow to calculate delta X, delta Y relative to the camera site on the flat reference plane. Elevation and range allow to calculate altitudes above the reference plane. AS the calculations are done with respect to a flat reference plane tangent to the earth surface at the camera location, this approach is sufficient. Earth curvature and true altitudes above the earth surface are irrelevant, a we are only interested in relative postions with regard to the satellite vector of movement.

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

click to enlarge

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:

click diagram to enlarge

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":

click diagram to enlarge

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:

click diagram to enlarge

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:

click diagram to enlarge

Why even low altitude ASAT intercepts are a threat to operational satellites in higher orbits

Click diagram to enlarge. Orbital data from CSpOC

So how big a threat is this Indian Anti-Satellite (ASAT) test of 27 March to operational satellites at higher altitudes, given that it was performed at relatively low altitude (283 km, see an earlier post)?

In an earlier post, I noted that the US ASAT demo on USA 193 ("Operation Burnt Frost") in February 2008 was a good analogue (read here why). Like the March 27 Indian ASAT test on Microsat-r, the USA 193 ASAT demonstration happened at relatively low altitude, even lower than the Indian test: 247 km. So where did debris from that test end up, altitude-wise?

The diagram above is a so-called "Gabbard Diagram" which plots apogee and perigee altitudes of individual debris fragments from the 2008 USA 193 intercept against their orbital period. (apogee is the highest point in its elliptical orbit, perigee the lowest point). The diagram can be of help to show insight into how high fragments are ejected in an ASAT test. Please do note that it concerns a subset of well-tracked larger fragments: most of the smaller fraction of debris, difficult or impossible to track, is absent from this sample.

As is visible in the diagram, many fragments ended up being ejected into highly eccentric ("elliptical") orbits with apogee, the highest point in their orbit, well above the intercept altitude. Many ended up with apogee altitudes well into the range of operational satellites (typically 400+ km).

I have indicated the International Space Station (ISS) orbital altitude (its current perigee altitude at ~407 km, not that of 2008) as a reference. Some 64% of the larger fragments in the pictured sample ended up with perigees apogees (well) above that of the ISS. Quite a number of them even breached 1000 km altitude.

This makes clear that even low altitude ASAT tests generate quite some debris fragments that can endanger satellites at higher altitudes. True, most of it reenters within hours to a few days of the test, but still plenty remain that do not. In my earlier post I showed the orbital lifetime of these same fragments from the USA 193 ASAT demonstration. Many survived on orbit for several weeks to months, occasionally even up to almost two years after the test:

click diagram to enlarge

So it is clear that a "harmless" low altitude ASAT test on an orbital object does not exist (note that I say orbital and not sub-orbital). Every test generates a threat to satellites at operational altitudes. Hence NASA administrator Bridenstine was quite right in his recent condemnation of the test. It is indeed very likely that debris fragments ended up in orbits with apogee at or above the orbital altitude of the ISS and other operational satellites in Low Earth Orbit.

An earlier, failed (?) ASAT test by India on 12 February 2019

image: DRDO

In my previous two posts (here and here), I analysed the much discussed Anti-Satellite (ASAT) test by India taking out Microsat-r on 27 March 2019.  Now the story gets a new twist.

Yesterday, Ankit Panda had a scoop in The Diplomat: it turns out that India attempted an ASAT intercept earlier, on February 12, 2019, which ostensibly failed according to US government sources.

Ankit is well sourced within the US Government, and his sources told him that a missile launch was observed on February 12th, which reportedly failed 30 seconds after lift-off.

A NOTAM and Area Warning had been given out for that day by the Indian government, for the "launch of an experimental flight vehicle" (the latter detail mentioned in the NOTAM but not the Maritime Area Warning). The Indian Government later published a bulletin omitting any reference to a missile failure, instead suggesting the succesful test of an "interceptor missile", launched from Abdul Kalam island, against an "electronic target".


 HYDROPAC 448/2019 (63,71)
(Cancelled by HYDROPAC 485/2019)

BAY OF BENGAL.
NORTHERN INDIAN OCEAN.
INDIA.
DNC 03.
1. HAZARDOUS OPERATIONS 0515Z TO 0645Z DAILY
   12 AND 14 FEB IN AREA BOUND BY
   20-48.07N 087-02.23E, 18-07.27N 086-25.02E,
   01-46.62N 087-30.51E, 02-57.91N 093-50.49E,
   18-33.79N 088-46.21E, 20-48.95N 087-06.99E.
2. CANCEL THIS MSG 140745Z FEB 19.

( 080903Z FEB 2019 )


The hazard area from the Area Warning for Feb 12 is very similar to that of the March 27th ASAT test. Compare these two maps, for February 12 and March 27 (the track shown is the groundtrack of Microsat-r, the target of the March 27 ASAT test. The blue and red areas indicated, are the hazard areas from the Area Warnings):

February 12 Area warning and Microsat-r track

March 27 Area Warning and Microsat-r track.

The hazard areas are virtually indistinguishable, and so is the location of the Microsat-r ground track. Microsat-r clearly was the target ("electronic" or not) of the February 12 attempt as well. Even the pass times are close for both dates: compared to March 27, the Microsat-r pass over Abdul Kalam happend about 1 minute earlier on Feb 12. With the benefit of hindsight, it is all very clear.

Indeed, press reports based on the mentioned Indian Government bulletin give 11:10 am Indian Standard Time (05:40 UT) as the time for the Feb 12 attempt. From the listed time, we can deduce that the virtual intercept would have happend at 271 km altitude, some 12 km lower than the 283 km altitude of the succesful March 27 intercept.

Microsat-r was in a slightly different orbit on February 12th: a slightly more eccentric, but stable 240 x 300 km orbit. During the succesful ASAT test of March 27, Microsat-r was in a slightly more circular 260 x 285 km orbit.

click diagram to enlarge

An open question is whether the February 12 attempt was a rehearsal and not a real attempt to hit and kill the satellite; or if it was a real attempt but failed. If Ankit Panda's US government sources are correct that the missile failed 30 seconds after lift-off, it would seem a failure, unless the cut-off after 30 seconds was intentional. Another open question is whether the US government was aware on February 12 that it was an ASAT test (see also this Twitter thread by Brian Weeden).

With the February 12th attempt so soon after launch of Microsat-r (January 24th), it would appear that Microsat-r was specifically launched to function as an ASAT target.

Debris from India's ASAT test: how long until it is gone?

click diagram to enlarge

After India's ASAT test on 27 March 2019, on which I wrote in detail in my previous post, many people asked the obvious question related to the debris threat from this test: how long would debris pieces stay on-orbit?

At the moment of writing (late 31 March 2019), no orbits for debris pieces have been published yet, although CSpOC has said they are tracking some 250 pieces of debris currently.

Some insight into the possible lifetimes of debris fragments can however be gleaned from the debris generated by "Operation Burnt Frost", the destruction with an SM-3 missile of the malfunctioned USA 193 satellite by the United States of America on 21 February 2008.

The USA 193 ASAT demonstration in 2008 provides a reasonably good analogue for the Indian ASAT test on Microsat-r on March 27. The orbital altitudes are somewhat comparable: USA 193 moved in a ~245 x 255 km orbit and was intercepted at ~247 km altitude. Microsat-r moved in a ~260 x 285 km orbit and was intercepted at 283 km altitude, i.e. a difference of ~36 km in altitude compared to USA 193. Both intercepts happened in years with low solar activity, i.e. similar upper atmospheric conditions. There are some differences too: USA 193 was intercepted near perigee of its orbit, Microsat-r near apogee. There is a difference in orbital inclination as well: 58.5 degrees for USA 193, and a 96.6 degree inclined polar orbit for Microsat-r. Nevertheless, the USA 193 intercept is a good analogue: much more so than the Chinese Fengyun-1C ASAT in 2007, which was at a much higher altitude and yielded much longer lived debris fragments as a result.

CSpOC has orbital data available for 174 debris fragments from USA 193. I mapped the decay dates of these fragments and constructed this diagram. The x-axis of the diagram shows you the number of weeks after the destruction of USA 193, and the bars show you how many fragments reentered that week:

click diagram to enlarge

The distribution of reentry dates shows that most fragments reentered within two months, with a peak about 3 weeks after the destruction of USA 193. Almost all of it was gone within half a year. Yet, a few fragments ejected into higher orbits had much longer orbital lifetimes, up to almost two years. This shows that even low altitude ASAT tests on objects in Earth orbit do create at least a few fragments with longer orbital lifetimes.

The 174 debris fragments in question constitute a subset of larger, well-tracked particles within the USA 193 debris population. There were thousands more fragments, most very small, that were not (well) detected. Most of these likely reentered within hours to a few days after the destruction of  USA 193, given that small fragments have a large area-to-mass ratio (meaning their orbits decay faster, as they are more sensitive to drag).

Given the similarities, we can expect a similar pattern as the diagram above for debris fragments from the Indian ASAT test. As the Indian intercept occured slightly (about 35 km) higher, fragments might perhaps last a little bit - but probably not that much - longer.


UPDATE (2 April 2019):
A follow-on post with an analysis or orbital altitudes of generated debris can be read here.

India's surprise ASAT test of 27 March 2019 (updated)

Click to enlarge. Reconstruction made with STK.

The Indian Prime Minister Narendra Modi made a surprise announcement in the morning of 27 March 2019, claiming that India conducted an anti-satellite (ASAT) test that night under the codename "Mission Shakti".

In the hours after the announcement, some sparse details appeared in Government statements and the Indian press: these included that the launch of the interceptor took place from Abdul Kalam island on the Indian East Coast, and the target was intercepted at an altitude of ~300 km. The missile used was a three-staged missile with two solid fuel boosters. The target satellite was not identified, other than that it was an Indian satellite.

T.S. Kelso, @Dutchspace on twitter and myself were however able to identify the target as being likely Microsat-r (2019-006A), a 740 kg Indian military satellite launched two months earlier, on 24 January 2019, on PLSV-C44 from Satish Dhawan Space Centre. We were also able to determine that the test must have happened near 5:40 UT (27 March 2019).

There are only two Indian satellites that fit an orbital altitude of ~300 km: Microsat-r (2019-006A) and Microsat-TD (2018-004T). Of these, Microsat-r was in a very low orbit (roughly 260 x 285 km). It would also pass right over Abdul Kalam island around 5:42 UT on 27 March 2019.

A Maritime Area Warning for "Hazardous operations" was given out before the test, which in hindsight is likely related to the test:


HYDROPAC 955/19

 NORTHERN INDIAN OCEAN.
 BAY OF BENGAL.
 INDIA.
 DNC 03.
 1. HAZARDOUS OPERATIONS 0430Z TO 0830Z DAILY
 27 AND 30 MAR IN AREA BOUND BY
 20-48.06N 087-02.24E, 18-07.27N 086-25.03E,
 01-46.62N 087-30.52E, 02-57.91N 093-50.49E,
 18-33.79N 088-46.21E, 20-48.95N 087-06.99E.
 2. CANCEL THIS MSG 300930Z MAR 19.//

 Authority: NAVAREA VIII 248/19 221002Z MAR 19.

 Date: 222130Z MAR 19
 Cancel: 30093000 Mar 19


Plotted on a map, it defines an elongated conical hazard area with the tip at Abdul Kalam island. The hazard area fits an object in a polar orbit. Moreover, it exactly fits the track of Microsat-r:

click map to enlarge

click map to enlarge

The fit shows that the intercept might have occured near 5:40 UT, give or take a few minutes, at 283 km altitude while Microsat-r was northbound moving towards Abdul Kalam island. The fit to the hazard area is excellent.

Microsat-r was launched by PLSV-C44 on 24 January 2019, ostensibly as a military earth observation satellite. The satellite was initially in a 240 x 300 km orbit but manoeuvered into a more circular, less eccentric ~260 x 285 km late February.

PLSV-C44 (including Microsat-r) launch. Photo: ISRO

click illustration to enlarge

click diagram to enlarge

click diagram to enlarge

With this ASAT test, India joins a very small number of countries who have shown to have ASAT capabilities: the USA, Russia, and China. The test will certainly cause uneasiness with several countries and provoke diplomatic reactions and condemnation. This is technology many countries do not like to see proliferate, and testing ASAT weapons in space is widely seen as irresponsible, because of the large number of debris particles it generates on orbit, debris that can be a threat to other satellites. Our modern society is highly reliant on satellite technologies, so any threat to satellites (either from ASAT test debris, or by deliberate ASAT targetting) is a serious threat.

In this case, because of the low altitude of the target satellite, the debris threat will be limited (but not zero). Few satellites orbit at this altitude (the ISS for example orbits over 100 km higher). The vast majority of debris generated will quickly reenter into the earth atmosphere, most of it within only a few weeks. But previous ASAT tests like the Chinese Fengyun 1C intercept in 2007 and the USA's response to that, "Operation Burnt Frost" destroying the malfunctioned spy satellite USA 193 in 2008, have shown that a few debris pieces will be ejected into higher orbits, so even at this low altitude the danger of such a test is not zero. Nevertheless, the Indian government seems to have learned from the outcry following China's 2007 test, and they specifically point out the lower altitude of their intercept target, and the lower risk stemming from that.

As to the "why" of the test, there are several answers, some of which can be read in this excellent twitter thread by Brian Weeden. One reason is military posturing towards China. Another one, as Brian points out, is the current emerging call to restrict ASAT tests: India perhaps wanted to have a test in before these calls result in international treaties prohibiting them. Last but not least, the test could perhaps also be a first step towards an anti-ballistic missile system. [edit 30 Mar 2019: ] India already tested an anti-ballistic missile system before, and this can be seen as a next step in building such a  missile defense system.


UPDATE 30 March 2019:

In the press, on twitter and in a message on the Space-Track portal, CSpOC has indicated it is now tracking more than 250 debris pieces from the ASAT test. So far, no orbital elements for debris pieces have been released however.

#JFSCC, via #18SPCS, is actively tracking more than 250 pieces of debris associated with Indian ASAT launch that occurred at 0539 UTC Mar 27, and issuing conjunction notifications to satellite operators as needed to support
spaceflight safety.

— 18 SPCS (@18SPCS) March 29, 2019

They also confirm the time of the test as 5:39 UT. In this article, it is indicated that the launch and intercept was detected by US Early Warning satellites, i.e. the SBIRS system of infrared satellites that has been discussed several times previously on this blog.

clickimage to enlarge

click to enlarge

05:39 UT corresponds to the time the satellite first appears over the horizon as seen from the interceptor launch site at Abdul Kalam island: theoretical appearance over the horizon as seen from that site was at 05:38:38 UT.

So I assume the 05:39 UT time corresponds to the moment the interceptor was launched after first detection of the target (assuming a detecting radar located on the launch site), at a range of 8700 km. Indian sources say the intercept, from launch to impact, took 3 minutes. This would place the actual intercept at ~05:42 UT, near 17.68 N, 87.65 E, at an altitude of ~283.5 km and a range of ~450 km from the launch site.

Click to enlarge. Reconstruction made with STK.

The interceptor was a three-staged missile with a kinetic kill vehicle, i.e. a kill vehicle that smashes into the satellite, destroying it by the force of impact. The Indian Dept. of Defense released this image of the launch of the interceptor:

click image to enlarge

Note (31 March 2019): a follow up post discussing likely orbital lifetimes of fragments created, can be read here.

Note 2 (2 April 2019): a second follow up post discussing an earlier failed attempt on February 12, can be read here.