Post a Comment On: SatTrackCam Leiden (b)log

 [Image]click image to enlarge
 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. [Image]click diagram to enlarge
 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:

[Image]Distribution of perigee altitudes. Click diagram to enlarge

[Image]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):

[Image]click diagram to enlarge
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: [Image]click diagram to enlarge

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:
[Image]delta V of Russian ASAT fragments vs USA 193. Click diagram to enlarge


[Image]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.

[Image]click map to enlarge

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).
[Image]click diagram to enlarge