Sunday, 31 March 2019

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.

Wednesday, 27 March 2019

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.




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.

Wednesday, 20 March 2019

No, the failed Venus lander from Kosmos 482 is not about to come down yet


Venera landing craft (photo: NASA)


Late February 2019, a number of news outlets (e.g. here and here) copied a story that originally appeared on Space.com, titled: "Failed 1970s Venus Probe Could Crash to Earth This Year".

It concerned an unusual object launched 47 years ago, called the Kosmos 482 Descent Craft (1972-023E, CSpOC nr 6073). Word was that it was about to reenter into the atmosphere, maybe even this year.  But will it?  Short answer: almost certainly not.

The source of the prediction is attributed to Thomas Dorman in the Space.com article, but how the prediction was done is not clear from the news coverage. On the request of David Dickinson, who was preparing an article on the topic for Universe Today, I made my own assessment of the issue. I looked at the orbital decay of 1972-023E since 1973 and did some GMAT modelling to gain insight into how the orbital decay will develop in the future.

As I will show in this post, my modelling suggests the Kosmos 482 Descent Craft is not to come down yet for several years.


Kosmos 482, a failed Venera mission


During the 1960-ies and '70-ies, the Soviet Union launched a number of Venera space probes destined for the planet Venus. Some of these probes did reach Venus and even briefly took pictures before succumbing to the very hostile atmospheric environment on this planet. But not all of the probes reached Venus. Several attempts went awry.

Kosmos 482, a probe similar to and launched only a few days after the Venera 8 probe, was launched from Baikonur on 31 March 1972. Reaching a highly elliptic parking orbit around Earth, its apogee kick motor failed to put it into an heliocentric orbit. The space probe broke up into at least four pieces that remained in Low Earth Orbit. Two of these, parts of the rocket engine, reentered within weeks of the failure. Another piece, presumably the main space probe bus, reentered in 1981.

A fourth piece, 1972-023E, is left on orbit, and it is interesting, as it most likely concerns the Descent Craft, the lander module in its protective cover that was to land on Venus, similar to the Venera lander module imaged in the photograph in the top of this post. That makes this a highly interesting object, as it will likely survive reentry into the atmosphere (it was designed to survive reentry into Venus' atmosphere after all).


Orbital decay 1973-2019


Initially stuck in a highly elliptic ~9600 x 220 km, 52.25 degree inclined orbit 47 years ago, its orbit has since decayed considerably. Currently (March 2019) it is in a ~2400 x 202 km, 52.05 degree inclined orbit:

click to enlarge

The diagram below shows how the apogee and perigee changed between January 1973 and March 2019. The orbit has become markedly less eccentric. Orbital decay strongly acted on the apogee altitude. The apogee altitude (blue line in the diagram) has come down steadily and by a large amount, from ~9600 km to 2397 km.This lowering of the apogee is to continue over the coming years. By contrast, the perigee altitude (red line) has changed only minimally, from 210 to 202 km over the past 46 years.


click diagram to enlarge

The apogee altitude will continue to come down. Once it is below ~1000 km, in combination with the low perigee at ~200 km. decay will go progressively fast.


Modelling future orbital decay


To gain insight into the validity of the claim that object 1972-023E might reenter this year, I modelled the future decay of the orbit using General Mission Analysis Tool (GMAT) software. Modelling was done for a 495 kg semi-spherical lander module 1 meter in size, using the MSISE90 model atmosphere.

The result suggests that the Kosmos 482 Descent Craft still has at least 5 to 7 years left on orbit. My model has it nominally reenter late 2025. Taking into account the uncertainties, a reentry between late 2024 and late 2026 seems most likely. That is still several years away.

click diagram to enlarge
click diagram to enlarge

The model result fits well with the trend in the actual tracking data, which gives confidence in the results (the thick lines in the diagrams above are actual tracking data, the thinner lines the GMAT modelled future orbital decay. The latter extend the previous trend in the tracking data well, there are no clear pattern breaks).

It should be well noted that modelling the decay of highly elliptic orbits with high apogee and low perigee is notoriously difficult. Yet, both the past and current orbital parameters and my modelling forecast do lead me to think a reentry is not imminent.

I am not the only one casting some doubt on a reentry of 1972-023E this year. Both NBCnews and Newsweek quote earlier results by Pavel Shubin that predict reentry around 2025-2026, quite similar to my results. They also quote well-known and respected space analyst Jonathan McDowell who is similarly opting for a reentry several years into the future, rather than the coming year.


Conclusions 


From my look at the current orbital decay rate and my modelling of future orbital decay, supported by assessments from other sources, it appears that the newsreports suggesting that the reentry of the Kosmos 482 descent craft is imminent and might even occur this year, are in error.

As to the why of the discrepancy: in the Space.com article, Dorman is quoted claiming "Our guess is maybe as much as 40 to 50 percent of the upper spacecraft bus may still be there". It is not clear at all what this "guess" is based on. My own modelling shows that the mass and size of the landing module only (i.e. without other parts still attached), fits the current orbital decay rather well. It is not clear how Thomas reached his conclusion, but modelling with a wrong mass and/or size might explain the discrepancy between my result and that claimed in the Space.com article.

I am hesitant with regard to accepting the high resolution imaging attempts by Ralph Vandebergh featuring in the Space.com article as evidence for object 1972-023E being more than the lander module only, as the weak and rather irregular protrusions visible might be image artefacts from atmospheric unrest and camera shake rather than real structure. Even when telescopically imaged at minimal range in perigee, we are talking about apparent object sizes at the arcsecond level and single pixel level here, conditions under which it is very challenging to image detail. Under such challenging conditions, spurious image artefacts are easily introduced.

Acknowledgement: I thank David Dickinson for encouraging me to probe this issue.