Where did Starship fragments end up after its in-flight destruction? [UPDATED]

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The second SpaceX Starship Integrated Test Flight initially launched successfully on November 18. The spacecraft separated succesfully from the first stage (which however violently disintegrated almost immediately after this). However, at 148 km altitude just before engine shutdown and coasting phase commencement, something went wrong and the spacecraft's auto-destruction mechanism destroyed the spacecraft.

I estimate the point of destruction to be in the middle of the Gulf or Mexico, near 25.0 N 88.9 W, although it could perhaps be slightly more downrange than that, closer to Cuba and Florida.

The question then popped up: how far downrange from the destruction point would any remaining debris end up? The answer to that question strongly depends on amongst others the speed upon destruction, and the sizes and masses of any debris. 

The map in top of this post gives an indication based on a somewhat simplistic modelling attempt, further discussed below.

After some initial educated guesses, I decided to investigate the issue further using a simple model in GMAT (the General Mission Analysis Tool). Live-feed data shown in the webcast from just before telemetry contact was lost indicated a speed of about 6.7 km/s, at 148 km altitude.

Using these base values and my estimated location for the point of destruction, I modelled the resulting vector in GMAT, using the MSISE90 model atmosphere that is part of GMAT. I modelled results for a number of masses, ranging from 0.1 kg to 50 kg, and with a fixed drag surface of 1 m² for each fragment irrespective of mass. This is not very realistic by the way, but sufficient for a general idea nevertheless.

Another deviation from reality is that there was no further mass loss (e.g. because of ablation upon reentry) of the debris pieces in the model. So, this is a bit a case of a proverbial "spherical cow reentering" (but not in a vacuum: the MSISE90 model atmosphere was used to model atmospheric drag).

Nevertheless, this academic exercise does give a rough idea of where surviving debris might have ended up: likely some 1500 km downrange from the point of destruction, near the southeastern Bahamas, and north of Cuba and the Dominican Republic. see the map in top of this post, depicting the model results.

(I thank Ian Benecken, Scott Manley and Jonathan McDowell for initial discussions and suggestions on twitter. Any mistakes are solely mine)

UPDATES:

This NOAA weather radar image below by Kenneth Howard (source this tweet by Jonathan McDowell) shows a radar debris trail near Puerto Rico. There is also video footage from Puerto Rico of what looks to be a large Starship remnant reentering and breaking up, see this tweet. This is some 800 km further downrange than the model results, and probably caused by a sizable part of Starship (i.e. considerably larger and heavier than the debris pieces I modelled) disintegrating upon atmospheric reentry.

I modelled an intact Starship upper stage (120 tons dry mass, 63.6 m²drag surface) for two initial speeds at the "disintegration" point: 6.7 km./s and 7.0 km/s. 

The latter value brings it close to where the weather radar depicts the debris trail. This could implicate it was largely intact untill it broke up in the upper atmosphere north of Puerto Rico:

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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 1408, 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 test 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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One year after India's ASAT test

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Today it is one year ago that India performed an ASAT test codenamed 'Mission Shakti'. The test consisted of the on-orbit destruction of the Microsat-R satellite (2019-006A), launched specifically to function as target for this test. The intercept occurred at 285 km altitude, but created debris pieces with apogee altitudes much higher than that. I have earlier published an extensive OSINT analysis of the test in The Diplomat of 30 April 2019.

The test generated large amounts of debris. A total of 125 larger debris pieces have been tracked and catalogued by the US tracking network. Note that these only concern larger pieces: most of the generated debris probably was too small to be tracked.

Over the past year I have periodically posted an update on the status of these larger debris pieces on this blog. Whereas the Indian DRDO claimed at the time that all debris would have been gone 45 days after the test, the reality has been quite different: 45 days after the test, 29% (less than a third) of the larger debris pieces had reentered. It took 121 days for half of the pieces to reenter, and some 200 days before 75% of the tracked debris pieces had reentered.

One year after the test, some 114 of the tracked debris pieces have reentered according to CSpOC tracking data. And two more objects for which no decay message was published by CSpOC, 2019-006AR and EA, have reentered according to my own analysis with SatEvo, bringing the total tally of reentered larger tracked pieces to 116.

Nine, or some 7%, of the original 125 larger tracked debris pieces are still on orbit.

It concerns objects 2019-006V, AJ, AX, BD, DC, DD, DE, DM and DU (red orbits in the image below: the white orbit is that of the ISS, as a comparison).  They have apogee altitudes varying from 600 to 1500 km, and perigees generally near 260 to 280 km. Six of these are expected to reenter over the next half year 9 months. And the last debris pieces may not reenter before 2022-2023.

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Nine months after the Indian ASAT test: what is left?

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Yesterday it was 9 months ago that India conducted its first succesful Anti-Satellite (ASAT) test, destroying it's MICROSAT-R satellite on-orbit with a PDV Mark II missile fired from Abdul Kalam Island. I earlier wrote several blogposts about it, as well as an in-depth OSINT analysis in The Diplomat (in which I showed that the Indian narrative on how this test was conducted, can be questioned).

Over the past year, I have periodically written an update on the debris from this test remaining on orbit. In this post I again revisit the situation, nine months after the test.

At the time of the test, the Indian DRDO claimed that all debris would have reentered within 45 days after the test. As I pointed out shortly after the test in my blogpost here and in my article in The Diplomat, that was a very unrealistic estimate. This was underlined in the following months.

A total of 125 larger debris fragments have been catalogued as well-tracked. Over 70 percent of these larger tracked debris pieces from the test were still on-orbit 45 days after the test (the moment they all should have been gone according to the Indian DRDO!).

Now, nine months after the test, 18 of these debris fragments, or 14 percent, are still on orbit. Their orbits are shown in red in the image in top of this post (the white orbit is that of the ISS, shown as reference).

In the diagram below, the number of objects per week reentering  since the ASAT test is shown in blue. In grey, is a future prediction for the reentry of the remaining 14% of debris. The last pieces might linger untill mid-2023:

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All but four of the remaining pieces currently have apogee altitudes well above the orbital altitude of the ISS, in the altitude range of many operational satellites. Nine of them have apogee altitudes above 1000 km, one of them up to 1760 km. Their perigees are all below ~280 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.

[UPDATED & CORRECTED] Observing the SpaceX Dragon CRS-3, the ISS and two pieces of Dragon launch debris

CORRECTION (21/04/2014 12:55 UT): in the initial post, the two debris pieces were misidentified. "2014-022C" turned out to be 2014-022H, and "2014-022H" turned out to be 2014-022G.

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Last Friday at 19:25 UT, SpaceX launched the Dragon CRS-3 commercial supply ship to the International Space Station ISS. It passed over Europe 20 minutes later but unfortunately I was clouded out in Leiden. In the middle and eastern parts of the Netherlands as well as elsewhere in Europe, observers were treated to a spectacular view of the Dragon, the Falcon upper stage, and two faint pieces of debris passing by as a thight group of objects.

SpaceX Dragon CRS-3
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I was more lucky yesterday when the sky was clear and the Dragon and ISS made a late twilight pass culminating at approximately 26 degrees altitude in the SW near 20:06 UT (22:06 local time, sun at -12 deg.). The image above shows the Dragon CRS-3 due south already somewhat past culmination. It was easy to see with the naked eye, attaining magn. +1.5. Its brightness is more similar to a Progress or ATV then to the much fainter commercial Orbital Sciences Cygnus.

The Dragon was about 1m 12s behind the ISS, a visual distance of somewhat over 40 degrees. Pre-observation predictions based on elements a few hours old had put it in front of the ISS, so at first I was wondering whether I missed it. Then, as the ISS was descending towards the SE, I saw it approaching in the SW, chasing the ISS. A very fine sight!

The ISS passing the same sky area as the

earlier image, 1 min earlier

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While I was photographing at the nearby city moat, I had also set up the video in my girlfriend's appartment, and this capture both objects as well: first the ISS, then a minute later the Dragon:




(the display says "GPS BAD" because my GPS time inserter failed to lock on a GPS satellite. I hope it is not broken...)

Apart from the Dragon and the ISS, I observed and photographically imaged a third debris object related to the launch. It is the object catalogued by JSpOC as 2014-022C/#39682. 2014-022H, #39687. It is either the jettisoned Dragon nose cone cover, or one of the solar panel covers   or possibly one of the Nanosat dispensers: I think it is too bright to be one of the several released nanosats itself. It was faint and slowly tumbling, alternating between invisibility and a max magnitude of about +3.5:

tumbling Dragon debris 2014-022H

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[UPDATE:] Later I discovered a second piece of Dragon CRS-3 launch debris on my imagery. It is faint, irregular in brightness and present on two images, the best of which is this one from 20:04:07 UTC:

tumbling Dragon debris 2014-022G
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This turns out to be the object designated 2014-022H, #39687  2014-022G, #39686. This is the other solar panel cover.

Aftermath of a space collision

Over 200 fragments of the Feb 10th collision between Kosmos 2251 and Iridium 33 have now been catalogued. Together, they form two impressive orbital planes filled with debris. The amount of Kosmos 2251 debris catalogued so far is about twice as large as that for Iridium 33 - it seems the Kosmos took the most serious blow.

Most of this debris will stay up for tens of years. About 6% of the Kosmos and 3% of the Iridium debris will decay in the next 2.7 years.

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Feb 15 Texas-Nebraska daylight fireball was NOT satellite debris

Sightings of a bright daylight fireball seen from Texas to Nebraska on February 15th, have been widely reported in the press.

Contrary to what the FAA appears to be stating, this was definitely NOT debris from the collision between the Iridium 33 and Kosmos 2251 satellites on February 10th.

Video footage of the fireball (see below) shows that it moved clearly too fast for that, and was of too short duration, to be decaying satellite debris. In stead it is in line with a meteoritic fireball (asteroidal debris).

There is a clear difference in speed between the two categories: asteroidal/cometary debris moves at at least 11 km/s (and usually much faster) and typically lasts only a few seconds (as this fireball did). Satellite debris decaying moves at 7.5 to 8 km/s, so clearly slower, and typically has a much longer duration (due to the slower speed, but also because it enters at shallow angles). The video footage is incompatible with the appearance of decaying satellite debris. It is completely compatible with a meteoric fireball (asteroidal debris).

Oberg on the USA 193 shootdown

The renowned veteran space journalist and former mission control engineer James Oberg has published another article about the reasons for the USA 193 shootdown in february (see my detailed coverage of the USA 193 saga here).

Like in an earlier article, Oberg is strongly opposing suggestions that there is more to this all than the official reason given for the shootdown - the danger of the tank with Hydrazine reaching earth intact. He argues that that reason given was the true and sole reason.

As much as I respect Oberg, I am still not convinced (but then, I am merely only what Oberg calls an "amateur specialist". I observe satellites and determine their orbits. I do not launch them).

First, about disintegration of the satellite. Oberg makes an argument from a comparison with meteorite falls. That argument, at least in the way he presents it, is flawed.

Oberg argues - and he is correct in this!- that it is a widespread misunderstanding that meteorites arrive on earth surface 'red hot'. He points out that in fact they are cool when reaching earth surface, and then tries to argue that they do not heat up during their fall:

Though a thin outer layer is briefly exposed to very hot air, for most of the descent that air is thinner than the purest vacuum inside thermal-shielding thermos bottles.

Now he is correct in this: small meteorites indeed arrive cold on earth surface, and of the object which does reach earth surface, only a thin outer layer has been heated.

But this is only part of the story, and as such the meteorite analogy is a very poor one.

There are two reasons why meteorites arrive cold on Earth. One is that from 25 km altitude, after being slowed down by the atmosphere to subsonic speeds, they stop ablating and enter a free fall that takes minutes to complete. During this phase they cool, much like the air the ventilator in your pc blows over your computer CPU cools your CPU.

A more important factor however is that heat generated during the incandescent phase of a meteorite fall, the result of atmospheric friction when the object still has cosmic speeds, is carried away immediately with the ablating material. It is for this reason that heat generated does not transfer much into the meteorite. This is basically what Oberg points out, but he neglects to tell something which is quite relevant:

that in this process of meteorite ablation, at least 70% (and usually more) of the meteorite ablates and hence vanishes. What reaches earth surface is at best 20-30% of the original mass.

The implications for the USA 193 tank, if we properly use the meteorite analogy, is therefore this. Either one of these two things will happen:

1) over 70% of the tank mass ablates and at best 20-30% and probably less of the original tank mass will reach earth surface;

Oberg however argues specifically against the notion of the tank being destroyed by ablation. The alternative option which remains then is:

2) the tank, due to it's special construction, does not ablate. In that case however, the heat dissipation mechanism Oberg brings up in his meteorite fall comparison will be absent too. In other words: the tank will heat up in its interior, unlike a meteorite.

In this case, Oberg's analogy is flawed.

Now, if I understand Oberg's article correctly, modelling (and who am I to question this) of the USA 193 tank entry would have nevertheless suggested the frozen hydrazine to remain intact.

In that case, you can actually question what the real danger is of a solid chunk of hydrazine ice contained in a metal casing reaching earth surface. It will only be dangerous when someone directly handles it (but even then).

Here, we should realize that tanks with -unfrozen!- hydrazine fly through our airspace daily. Most fighter jets contain a tank with hydrazine as an emergency fuel backup. The effects of this falling down on you will not much differ from those of the USA 193 tank falling down on you. Such crashes are not rare. For example, our relatively modest Dutch airforce lost 32 of its F16 fighters, which carry a hydrazine tank, through flight crashes. Some of these aircraft came down in populated areas (one actually hit a house).

All commercial aircraft carry tanks with fuel too - not hydrazine, but still not pleasant stuff. Chances that one of these tanks will descend on your head - and this happens from time to time- are much larger than that the tank of USA 193 would have. And we don't quite bother about that. So why bother about the USA 193 tank then?

USA 193 was not the first failed fuel-carrying satellite to fall back to earth in an uncontrolled way. Nor will it be the last. In fact, launch failures where final rocket stages fail to fire are common. It will be interesting to see whether future cases will get a similar treatment.

In my opinion, the USA 193 shootdown was done for multiple reasons, and the "danger" of the hydrazine tank is only one of these. It is a convenient one to defend the exercise to outsiders, but not the only reason.

I am quite convinced that other reasons were of equal or even paramount importance in making the decision:
- that USA 193 presented a very convenient target for a practical test of ASAT capabilities (thus also making the money spent on the satellite at least partly pay off);
- that it would prevent new experimental technology falling (literally) into wrong hands;
- and that it was a timely moment to remind China, the US Senate and Congress and the US public that the USA has ASAT capabilities too and that the technology in a wider sense (missile defense) was worth further funding. Note that in April 2008, barely two montsh after the USA 193 intercept, the US Congress re-examined the status of missile defense of which the used Aegis system is part.


Note: considering the USA 193 shootdown, John Locker's summary and the links he provide are worthwhile reading

Early Ammonia Servicer (EAS)

This evening the sky was very dynamic: very clear, but also with lots of small rapid moving cloud fields traversing the sky.

I observed the Early Ammonia Servicer (EAS), 98-067BA, making a near zenith pass. Untill a year ago, EAS was part of the International Space Station ISS. On July 23rd 2007, during an EVA (Space Walk) by the ISS astronauts, it was detached from the station and ejected in space. Since then, the object, about the size of a large US refridgerator, has steadily spiralled down and currently is down to a 273 x 283 km orbit (ISS is at a 338 x 351 km orbit). If the current rate of decay continues, it will burn up in the atmosphere late 2008 or early 2009.

I observed it a year ago shortly after its release from ISS, and it was faint then, about magnitude +4 to +4.5. I observed it again this evening, and due to its much lower orbital altitude compared to last year it now reached mag. +2.5, perhaps even +2.0, in Cygnus while just past the zenith descending to the east. It moved fast.

I also managed to capture it on photograph, using the Canon EOS 450D and the EF 50/2.5 Macro lens stopped to +2.8. The image is below.

(Click image to enlarge)