Some first analytical results on the debris from the Russian ASAT test of 15 November 2021

 

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In my previous post I discussed the November 15 Anti-Satellite (ASAT) test on the defunct Kosmos 1408 satellite by Russia. On December 1, CSpOC released the first sets of orbital elements for debris fragments created by the test. As of yesterday 2 December, when I made the preliminary analysis presented below, orbits for 207 fragments were published (many more will probably be added in the coming days and weeks). 

They allowed to construct the Gabbard-diagram below, which for each debris fragment plots the apogee altitude (blue) and the perigee altitude (red) against orbital period. They also allowed a preliminary analysis on the delta V's (ejection velocities) imparted on the debris fragments by the intercept.

 

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Let's first discuss the Gabbard diagram. Gabbard diagrams show you at a glance what the altitude distribution of the created debris fragments is. As can be seen, most of the debris has a perigee (lowest point in the elliptical orbit) near the original orbital altitude of the Kosmos 1408 satellite (490 x 465 km: the intercept happened at an altitude of ~480 km): but a part of the generated debris evidently has been expelled into orbits with perigees (well) below that altitude too. The apogee altitudes (highest point in the elliptical orbit) are mostly scattered to (much) higher altitudes. In all, debris moves in orbits that can bring some debris as low as 185 km and as high as 1290 km. As can be seen, the debris stream extends downwards into the orbital altitudes of the ISS and the Chinese Space Station. About 35% (one third) of the currently catalogued debris has a perigee altitude at or below the orbit of the ISS: about 18% at or below the orbit of the Chinese Space Station. Upwards, the distribution extends well into the altitudes were many satellites in the lower part of Low Earth Orbit are operating, with the bulk of the debris reaching apogee altitudes of 500 to 700 km.

The plots below show the altitude distributions for apogee and perigee of fragments as a bar diagram:

Distribution of perigee altitudes. Click diagram to enlarge

Distribution of apogee altitudes. Click diagram to enlarge

From the change in apogee and perigee altitudes and change in orbital inclination of the debris fragments in comparison to the original orbit of Kosmos 1508, we can calculate the ejection velocities (delta V) involved. It is interesting to do this and compare it to similar data from two other ASAT tests: the Indian ASAT test of 27 March 2019 and the destruction by an SM-3 missile of the malfunctioned US spy satellite USA 193 on 20 February 2008.

In the plot below, I have plotted the density of debris against ejection velocity (in meter/second) for the Nov 15 Russian ASAT tests as a bar diagram (with bins of 5 m/s: the blue line is the kernel density):

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In the diagram below, where I have removed the bars and only plotted the kernel density curves, a comparison is made between ejection velocities from the Russian ASAT test and the Indian and US ASAT tests of 2019 and 2008:

 

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The two diagrams below do the same, in combined bar-graph form, for both the earlier ASAT tests. The first diagram compares the delta V distribution from the Russian ASAT test (blue) to that of the 2008 USA 193 destruction (red); the second diagram does the same but compared to the 2019 Indian ASAT test:

delta V of Russian ASAT fragments vs USA 193. Click diagram to enlarge

delta V of Russian ASAT fragments vs Indian ASAT. Click diagram to enlarge

The diagrams clearly show two things: the distribution of ejection velocities from the Russian ASAT test peaks at lower delta V's than that of the debris from the USA and Indian ASAT tests. In addition, the distribution is more restricted, lacking the tail of higher ejection velocities above 200 meter/s present in the distribution from the other two ASAT tests (we should note here however that this is all still based on early data, and addition of new data over the coming weeks might alter this picture somewhat).

This tallies with what we know about the Russian ASAT test: rather than a head-on encounter with the interceptor moving opposite to the movement of the target, such as in the 2008 American and 2019 Indian ASAT tests, the Russian ASAT intercept was performed by launching the interceptor in the same direction of movement as the target (as shown by NOTAM's related to the launch of the interceptor, see map below), letting the target "rear-end" the interceptor. This results in lower kinetic energies involved, explaining the more compact fragment ejection velocity distribution emphasizing lower ejection velocities. In addition, the possible use of an explosive warhead on the interceptor rather than a kinetic kill vehicle might have some influence.

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So the Russian test seems to have been designed to limit the extend of ejection velocities and from that limit the extend of the orbital altitude range of the resulting fragments. That is in itself commendable, but it doesn't make this test less reckless or irresponsible. 

The Gabbard diagram near the top of this post, and the bar graphs below it, show that debris was nevertheless ejected into a wide range of orbital altitudes, from as low as 200 km to as high as 1200 km, with a peak concentration between 400 and 700 km altitude. The orbital altitude range of the debris includes the orbital altitudes of crewed space stations (ISS and the Chinese Space Station), thereby potentially endangering the crews of these Space Stations, as well as the busiest operational part of Low Earth Orbit. The diagram below gives the perigee altitude distribution of objects (including "space debris") in Low Earth Orbit, for comparison (note, as an aside, the prominent peak caused by the Starlink constellation at 550 km).

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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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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:

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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.

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

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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:

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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.