More on the USA 193 shootdown

The online Bulletin of the Atomic Scientists has published an essay by Harvard astrophysicist Yousaf Butt with a very critical view of the official reasons given for the USA 193 shootdown.

Butt filled a request through the Freedom of Information Act and obtained the report featuring the re-entry model and analysis that was used. And found it to be flawed and on closer look not quite supportive of the alledged 'danger' of the re-entry of USA 193's hydrazine fuel tank.

The report is very cautious and it's authors already note that some of the model assumptions are not realistic. Importantly, it shows that even with these assumptions maintained, much of the tank's titanium outer layer will ablate according to the model (remember how Oberg denied this in his essay?!), leaving only a very thin outer shell 1/5th or less of the original thickness. This assumes uniform ablation (which is not realistic).

Butt argues that when more realistic assumptions are made, this suggests the tank would likely have been destroyed upon reentry.

You can read the essay here, and it includes a link to the report pdf.

The essay highlights:

• A NASA study on the survivability of USA-193's hydrazine fuel tank used an oversimplified model, leading to an overly optimistic assessment of the tank's survival.
• But even this study showed how the tank would have burned up when reentering the atmosphere.
• Therefore, Washington's contention that the tank would have hit the ground intact, posing a health hazard, seems questionable.

Another thing to note is that the tank was not completely filled with fuel, but 76% filled. This turns out to be of importance in assessing the fate of the tank.


(with thanks to John Locker for te 'heads up')

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

NOTAM warns aircraft of decaying USA 193 debris (updated again 02/03)

John Locker brought a new chapter to the attention in the ongoing USA 193 soap story, by pointing to a NOTAM released by the US FAA here on the Satobs list. The text of this NOTAM:

8/5536 - SPECIAL NOTICE .. THIS NOTAM REPLACES FDC 8/5501 DUE TO ADDITION OF CONTACT NUMBER. EFFECTIVE IMMEDIATELY UNTIL 0803092300 UTC. AIRCRAFT ARE ADVISED THAT A POTENTIAL HAZARD MAY OCCUR DUE TO REENTRY OF SATELLITE USA-193 DEBRIS INTO THE EARTHS ATMOSPHERE. FURTHER NOTAMS WILL BE ISSUED IF MORE INFORMATION BECOMES AVAILABLE. IN THE INTEREST OF FLIGHT SAFETY, IT IS CRITICAL THAT ALL PILOTS/FLIGHT CREW MEMBERS REPORT ANY OBSERVED FALLING SPACE DEBRIS TO THE APPROPRIATE ATC FACILITY TO INCLUDE POSITION, ALTITUDE, TIME, AND DIRECTION OF DEBRIS OBSERVED. FAA HEADQUARTERS, AIR TRAFFIC SYSTEMS OPERATIONS SECURITY, 202-493-5107, IS THE FAA COORDINATION FACILITY. WIE UNTIL UFN

This is weird. I cannot think of any real danger to aircraft by the decay of small fragments of USA 193 debris. Most will burn up well above the flight altitude of aircraft. Those that don't, will be rare and not a real concern in my humble opinion. Moreover, hadn't "they" told us the danger was gone after they successfully shot it to bits?

The Public Relations behind this whole operation is bizarre, from start to end. I am at a loss to understand what is going on behind the scenes here. It is becoming a soap story.

Reading the NOTAM carefully, it seems actually to be more about trying to get information about where something might have come down, then that it really concerns the "danger" to aircraft. The latter merely appears to be the "vehicle", just as the hydrazine "danger" was in the argument to shoot USA 193. Perhaps some component wasn't that destroyed after all and they are after it. And no, that will not be the hydrazine tank.

UPDATE: Strike that last remark. One of the commenters to the topic on the Bad Astronomy blog here has managed to dig up the actual date of issue of this NOTAM. That appears to be Feb 20th, so before the ASAT strike. Which means it is clearly not the result of a debris-analysis made after the ASAT strike.

Still the issueing of this NOTAM remains weird. It does indicate that for some reason, they want to keep track of where debris comes down. Something among it has their interest.

Oh dear: that "they" sounds awfully conspiratory, isn't it? I apologize....and assure you I don't wear tinfoil hats... ;-)

Debris of shot spysat USA 193 endangers and delays new spysat launch

An interesting article has appeared on space.com. NROL-28, the launch of a new spy satellite by the NRO, has been delayed because the NRO doesn't want to risk it being hit by debris fragments of the destroyed spy satellite USA 193.

Meanwhile, 12 more orbits have been released for additional fragments of USA 193 besides those released earlier.

In my post here on the latter issue, I mentioned I could not provide graphics of the orbits. Since then, such graphics have appeared on a number of other websites, so I feel I do no harm in doing so too as it already has become public domain. The following pictures show the orbit distribution of the created ring of USA 193 debris around the Earth in 3D, plus a ground map for this afternoon which shows how the fragments have spread along the full orbital extend by now.

(click images to enlarge)

Fragments of destroyed spysat USA 193 still in orbit

In a surprise move, Space-Track, the on-line orbital database of USSTRATCOM (formerly the NORAD database), has released orbital elements for 17 fragments of USA 193 still in orbit.

This is surprising, as normally they don't publish anything connected to a classified satellite launch: for example, they do not publish elements for things like spent rocket booster stages or fairings connected to classified launches. I guess they want to show the world that USA 193 is now indeed reduced to fragments, and that they keep track of them.

On February 24, Norwegian observer Christian Kjaernet observed one of these fragments visually through his telescope. His observation remained uncorroborated for some time (notably because of bad weather experienced by several active amateur trackers), but it is clear now that it was indeed a USA 193 debris fragment.

The 17 fragments for which orbital elements have now been released, have spread over almost the full former orbit of USA 193 in the days between the ASAT intercept and the moment of writing this post. Unfortunately, Space-Track restrictive rules of data dissemination do not allow me to provide a map of the spread of fragments.

Most of the 17 fragments now catalogued will decay over the coming month.

USA 193: life and death of a spy sat (twice updated 29 Feb)

UPDATE 29/02/08 (II): New NOTAM warns aircraft for decaying USA 193 debris between now and March 9th. See my post here.
UPDATE 29/02/08 (I): NROL-28 launch delayed because of USA 193 debris risk. See my post here
UPDATE 27/02/08: Fragments of USA 193 still in orbit and observable: see my post here

21/02/08: THEY DID IT! more below.

UPDATE 20/02/08: Sources say rough seas in the Pacific might prevent taking a shot at USA 193 on Wednesday/Thursday night.
UPDATE 19/02/08: John Locker has drawn attention to a second NOTAM for the same area, one day later. This is probably for a possible second attempt if the first one fails.
UPDATE 18/02/08: Ted Molczan has drawn attention to a NOTAM issued by the US Government that might point to a possible ASAT attempt on USA 193 on Feb 21, 3:30 UTC as USA 193 passes near Hawaii. See below for more.
UPDATE 17/02/08: Russia has now accused the USA that it is all a cover-up for an ASAT test..
UPDATE 14/02/08: News reports today suggest the US military has serious plans to shoot the satellite from orbit before the time of the expected decay, and are now confirmed by the US military. See the note at the end of this post.


Latest (21/02): USA 193 destroyed with a missile! News comes in that the American Navy last night (20/21 Feb) made a successful attack on USA 193, destroying it into multiple pieces with a SM-3 missile shot at 3:26 am GMT from the USS Lake Erie.

Link: Missile Intercept. Video released by the Pentagon

Amateur observers on the Canadian west coast report observing a spectacular shower of fragments re-entering in the atmosphere over Canada within 10 minutes after the successful attack. More fragments might come down today elsewhere along the former satellite's flight path.

***

Main background story

The weekend of 25 January, after what appeared to be an "organized leak" by a US government agency, the imminent decay of the failed reconnaisance satellite USA 193 (06-057A) gathered press attention.

USA 193 was launched on 14 December 2006 as NROL-21 with a Delta II rocket from Vandenberg Air Force Base in California. It somehow failed and went "dead" shortly after launch. There is no sign that its orbit has been under control since, and amateur satellite trackers were already long aware that the satellite orbit was decaying and the satellite doomed due to this.

Some sources suggest failure of an onboard computer as the problem with the satellite. Imaging by John Locker shows no sign of solar panels, which brings in the option of a power failure due to a failure to deploy the panels. Ted Molczan has suggested that an onboard computer boot failure prevented the panels from deploying, causing a loss of power when the batteries ran down, and notes that this tallies with the fact that radio signals from the satellite were logged by amateur radio trackers for 1.5 days after launch but then died down.

Orbital plane of USA 193 (06-057A)

The orbital inclination of the satellite was 58.5 degrees meaning it roughly covered all locations between 60 degrees north and south latitude. It was probably intended as a test platform for a new generation reconnaisance sats about the purpose and construction of which little is known. Sources differ on whether it could have been an optic or radar reco platform, or maybe both. According to the usually knowledgeable globalsecurity.org, it was a radar reco sat intended to replace the Lacrosse system and probably weighing about 3300 kg (which is only 1/3rd of the 9000 kg reported in the press for the object). Imaging by John Locker from September 2007 suggests the satellite was about 4 meters large. The official NRO press release at the time of the launch only stated that "the satellite launched will provide invaluable intelligence data to support the war on terrorism".

USA 193 was a satellite which was part of my regular observing program, observed and imaged by me several times. It was a bright naked eye target, reaching magnitude +1 under favourable illumination conditions, zipping across the sky at a spectacular high speed due to it's low orbital altitude. At the end of it's one year "life", it's perigeum was already below 250 km above earth surface and in its last weeks it was coming down fast (see diagram below).

Below diagram shows the altitude decay of the perigee (and apogee) of the orbit over time, and how the decay rate was accelerating. The final rate of decay was over 1 km/day.

(data in the diagram are derived from published orbits
based on amateur observations including mine,
calculated by McCants and Molczan:
last updated 23/02 with final epoch 08052 orbit)

The last orbit calculated by Molczan (08052.017 epoch) measured 242 x 257 km and provided a nominal value of the expected decay date of March 12th, but this value has an uncertainty of many days. On February 21st at 3:29 GMT, the satellite was destroyed by an SM-3 missile, making the subject of the expected decay date moot.

The large media attention to the imminent satellite decay was somewhat surprising, and the same goes for the fact that the US government itself has brought the imminent decay to the attention. We failed to see the reason for this. Among (amateur) satellite observers it was already known for a long time that this decay was about to happen. Moreover, the question is how much of an extra risk this decay really posed compared to other decays happening several times a year. Chances that the impact of remains, if any, posed damage to property or persons are minimal. Only if someone comes into direct contact with hydrazine fuel remnants, risks are involved. With several earlier occasions of satellite or rocket fuel tanks reaching earth surface intact in the past, this so far never has happened. In fact, the chances that a random passenger aircraft with fuel tanks will drop on your head today, are considerably bigger than the chance that USA 193's fuel tank would have done.

The whole situation as to the "why?" of bringing the satellite decay (and later the ASAT-attack on it) so prominently into the news definitely has open questions.

Some wild speculation about the potential presence of a nuclear (Plutonium based) power system on board has been popping up here and there, e.g. in the discussion on Slashdot, in The Observer and here. There is no reason to think the latter is really likely according to several specialists.

*** "Shooting it down" ***

On February 14th, the US military announced that they had plans to shoot the satellite down with a missile, "to reduce the danger to human beings". This gives a new twist to the story.

Official sources state that here is about 450 kg of hydrazine fuel (a very toxic substance) on board, and an expected 1100 kg (about one tonne) of debris of the satellite itself might reach earth surface intact.

The plan was (and we now know they did it too) to intercept the satellite in the week following February 20, using one or more SM-3 intercept missiles fired from naval vessels in the North Pacific. The SM-3 missiles need to be modified for this task as they normally target object at lower altitude on a ballistic trajectory instead of a true orbit.

The term "shooting it down" is, by the way, a bit misleading here. In reality, what happened is that the impact of the ASAT weapon broke up the satellite in many pieces, which will continue their orbit around the earth as a debris cloud. Due to their higher surface-to-mass ratio, smaller debris pieces will experience increased drag, which will make them decay earlier than the intact satellite would have.

On Feb 18th Ted Molczan has drawn attention to a NOTAM, issued by the US Government, that pointed to a possible ASAT attempt on USA 193 on Feb 21, 3:30 GMT.

PHZH   HONOLULU CONTROL FACILITY

02/062 (A0038/08) - AIRSPACE CARF NR. 90 ON EVELYN STATIONARY RESERVATION WITHIN
AN AREA BNDD BY 3145N 17012W 2824N 16642W 2352N 16317W 1909N 16129W 1241N 16129W
1239N 16532W 1842N 17057W 2031N 17230W 2703N 17206W SFC-UNL. 21 FEB 02:30 2008
UNTIL 21 FEB 05:00 2008. CREATED: 18 FEB 12:51 2008

The NOTAM excluded an area just west of Hawaii over which USA 193 would pass near the time above (see below map, showing USA 193's approximate position at 21 Feb 3:30 UTC):

(click map to enlarge)

An ASAT attack at this moment in this ground track would mean that within minutes the resulting debris cloud would come into range of ground tracking stations at the US West coast, where twilight would just have ended (and with the full moon being in eclipse at that moment (!) and low in the sky anyway, it woild be no hindrance to optical tracking facilities for tracking faint fragments). Next the debris cloud would pass over the arctic region of North America, where several radar tracking facilities exist.

Also, any quickly re-entering fragments would come down over the barren Canadian Arctic, rather than pass over highly populated areas. For a full orbit following an attack at this location, debris will not pass over significant inhabited land, as can be seen in the map below showing the trajectory of the satellite.

The marked position in the map below near Hawaii is for 3:30 GMT (Feb 21st), the moment of intercept, and the satellite (and its fragments after intercept) moves "up" along the marked line in the map, towards North America, over the Canadian arctic and then the Atlantic Ocean:

(click image to enlarge)

Hawaii itself would provide valuable tracking facilities prior and after the intercept.

On February 21st 2008 at 3:29 GMT (and quite along the anticipation described above), the satellite was indeed successfully destroyed with a SM-3 missile shot at 3:26 am GMT from the USS Lake Erie.

Link: Missile Intercept. Video released by the Pentagon

Amateur observers on the Canadian west coast report observing a spectacular shower of fragments re-entering in the atmosphere over Canada within 10 minutes after the successful attack. More fragments might come down today elsewhere along the former satellite's flight path.

As mentioned, there are questions as to the "why?" of the high profile media publicity of this all. Some observers have started to wonder whether it might all be a very cleverly orchestrated setup by the US Government, designed to get maximum global attention to an ASAT demonstration. Indeed, Russia has publicly accused the USA of covering-up a true ASAT-test with this.

If we entertain that notion for a moment: with this ASAT demonstration, they would hit three birds with one stone:

a) They send a high profile geopolitical message to China, and to the homefront, in answer to last year's Chinese ASAT test on Fengyun 1C. Basically, this message says: "you/they can shoot satellites out of the sky, okay. But remember we can too, so don't even dare to try ours or we will do the same to yours/theirs..."

b) They give some rendement to an otherwise worthless assemblage of several millions of Dollars worth of inoperative scrap metal now uselessly orbiting this planet.

c) it is an ideal opportunity to test their anti-satellite and anti-ICBM weaponry

I can't really comment on the value of this speculation, as I am not an expert on military geopolitics. A valid argument against (a) raised by some is however, that shooting down USA 193 at 250 km altitude is not quite the typical situation for an ASAT attack as this is much lower than the normal operational altitude of satellites. It is known from the succesfull ASAT test on the Solwind satellite (which orbitted at 550 km altitude) which the USA carried out in September 1985 however, that the USA does possess the capability to reach higher altitudes. The problem with ASAT attacks is moreover not so much the altitude to reach, but rather to hit the (small, fast moving) target.

As a reminder that the USA is capable of this, the demonstration would suffice, and USA 193 is the ideal target for it. Because of its low orbit, the formation of a debris cloud such as happened with the Chinese ASAT demonstration early last year isn't such a concern. Because of the low altitude, and unlike with the Chinese ASAT test, most if not all debris pieces would re-enter into the earth atmosphere within days after the ASAT attack, and therefore will not propose a real hazard to other satellites. This means the USA can use this object as a target without fear of being called hypocrits after their fierce criticism of the Chinese ASAT test last year, which created a high altitude, long lasting debris field which does provide a threath to other satellites.

Here's an archive picture of a USA 193 pass over Cospar 4353, which I shot on April 3 2007:

(note: all images in this post may be used for informational purpose, provided the source is acknowledged)

(click image to enlarge)