KH-12 USA 161 de-orbited? [updated 02/09/2011]

UPDATE 2 Sept 2011: USA 161 is Still Alive! It has not been deorbitted but made a large manoeuvre. Read more about the recovery here.

Negative observations on Wednesday and Thursday 24-25 and 25-26 August reported by Russell Eberst from Scotland on SeeSat-L and Pierre Neirinck from France (priv. com) suggest that the KH-12 Keyhole USA 161 (2001-044A), an advanced high resolution optical reconnaisance satellite launched on 5 October 2001, has either undergone a large manoeuvre or (more likely) has been de-orbited last week.

Earlier this year (January 20, 2011), USA 224 (2011-002A) was launched as NROL-49 and put in the same orbital plane as USA 161, probably as a replacement for the latter.

Below are two archive pictures I shot of USA 161 brightly flaring twice on 30 July 2009:

click image to enlarge

The remaining KH-12 constellation (if indeed USA 161 has been de-orbitted last week) now consists of three satellites: USA 129 (96-072A), USA 186 (05-042A) and USA 224 (2011-002A), the oldest of which (USA 129) is now 15 years in service.

USA 224 which replaced USA 161 represents the noon and midnight plane. USA 129 and USA 186 represent the morning and evening plane. Below diagram shows the satellite constellation as it is now USA 161 has presumably been de-orbitted:

click diagram to enlarge

An update on IGS-1B

Along the line of expectations, our tracking data show that the Japanese spy satellite IGS 1B (2003-009B) which malfunctioned in March 2007, keeps coming down (see earlier coverage here and here).

Early July 2011, the perigee had come down to 450 km and the Mean Motion (the number of orbital revolutions per day) is steadfastily increasing as the orbit becames more narrow:





The predicted decay date keeps shifting back and forth, being highly dependant on solar activity. Solar activity has been back to modest the past two months. As a result, the decay date forecast has shifted further away in time.

If solar activity does not increase, forecasted decay will be in late 2013 (SatEvo with current solar flux F10.7 cm = 85, elset 11184.15154535). If it does increase - which is likely, as we are on the approach to a solar maximum - it will be earlier, possibly as early as mid-2012.



Meanwhile, it is interesting to see how the still active sister-ship IGS 1A (2003-009A), launched in the same 2003 launch, is faring. Above diagram shows the evolution of the orbital inclination. IGS 1B's orbital inclination is clearly drifting, consistent with loss of control. IGS 1A's orbital inclination initially was allowed to co-drift with IGS 1B, but then altered in a manoeuvre mid-2008 that brought the inclination up again, to match the other IGS-es in the constellation. As of 2010, it is kept more or less steady, librating around a value of 97.39 degrees, the sun-synchronous value for a 487 x 498 km orbit.

More on the IGS 1B fuel tank, and the (reduced) risk of it re-entering

At the end of the previous weekend, I posted an extensive post on the malfunctioned Japanese spy satellite IGS 1B (03-009B). It malfuntioned in 2007, has subsequently lost orbital altitude, and is now expected to re-enter early 2012.

The concerns was, that it might have a still partly filled fuel tank - potentially creating a risk at re-entry, a concern similar to that for the re-entry of USA 193 in 2008 (which, for that reason, was destroyed on-orbit by a SM-3 missile). This greatly worried me, the more as no news on this was appearing from either the Japanese, or US Space Command (who no doubt must have been aware that IGS 1B was coming down - an object like this will certainly be tracked).

My assessment of a potentially still half-full tank, was, as I indicated, at best an "educated guess". Noted amateur observer Ted Molczan from Toronto has now made an independant assessment of the situation, notably on the absolute amount of fuel left. Below I quote from his analysis, in which he writes (after first noting that he gets similar results to mine as to the probable time of decay, i.e early 2012):

"I agree that IGS 1B could decay from orbit in 2012, with perhaps half of its initial fuel mass; however, I believe that its initial fuel mass probably was far less than that of USA 193 - between approximately 28 kg and nearly 100 kg, compared with the 450 kg of USA 193. If half of IGS 1B's fuel has been expended, then between 14 kg and 50 kg may remain - at most 10 percent of USA 193's fuel load. Only the Government of Japan knows for certain the quantity of fuel that remains, but if my estimate is in the ballpark, then the risk of an uncontrolled decay from orbit would be much less than for USA 193."

[...]

"USA 193 carried about 450 kg of fuel, none of which had been expended by the time of its impending decay, due to its failure soon after it reached orbit. I believe that IGS 1B may have considerably less fuel for the following reasons:

1. IGS 1B was designed to operate at a considerably higher altitude than USA 193 (485 km vs. 360 km), which means that it was subject to far less atmospheric drag, which would have decreased the quantity of fuel required for orbit maintenance.

2. IGS 1B's total mass is reportedly about half that of USA 193 (1200 kg vs. 2300 kg). For a given velocity change, the fuel expenditure varies in direct proportion to total spacecraft mass.

3. IGS 1B died four years into what was reportedly a five year mission, so might already have expended most of its fuel."  

[note from Marco Langbroek: but its sister ship IGS 1A is still maintaining orbit 8 years later, as I indicated in my original post, suggesting that these satellites carry more fuel than for a minimum 5 year mission]

"With respect to points #1 and #2, assuming that IGS 1B's ballistic coefficient (mass divided by cross-sectional area) is similar to that of USA 193, and that its fuel supply was designed to enable operating up to twice the reported 5 year design life, i.e. 10 years, then the total velocity change required to maintain 485 km altitude would have been about 53 m/s (metres per second). Assuming IGS 1B uses the same fuel as USA 193, then for its mass of 1200 kg, the required initial fuel mass would have been just 28 kg - far less than that of USA 193.

Factoring in point #3: assuming provision of fuel for 10 years operation, then IGS 1B might have consumed 40 percent of its fuel by the time it died, four years after launch. Considering that its first couple of years of operation coincided with the tail end of the  previous solar maximum, its fuel use could have been somewhat greater; assuming for the sake of argument that half its fuel has been expended, then 14 kg would remain.

I based this rough estimate on data found in the respected textbook/reference Space Mission Analysis and Design III, specifically the annual velocity change required to maintain low Earth orbits against decay, depending on altitude, ballistic coefficient and solar activity. I assumed that fuel for attitude control was negligible, and that IGS 1B was not designed to be de-orbited at the end of its useful life (the latter would have increased the initial fuel mass to nearly 100 kg, with perhaps 50 kg remaining after four years of operation, still far less than USA 193 carried.)"

I have high trust in Ted's assessment: and the result is somewhat of a reassurrance: 14 to 50 kg of fuel is an order of a magnitude less than the 450 kg of fuel of USA 193. While no uncontrolled re-entry is without danger, these figures from Ted's assessment lead me to think that IGS 1B is clearly less of a threath than USA 193 was.

Ted's assessement is exactly the kind of thing I called for in my earlier post, when I wrote:

Instead of watching this one quietly go down, I would prefer to see a good risk assessment done [...] a clear argument presented as to why it would not be a danger in this case, given all the fuzz created around falling fuel tanks with USA 193.

Ideally, this should of course have come from the Japanese themselves (which refused to say anything pertinent to one of the reporters that contected me over this, besides the simple statement that there was "no risk"). In absence of that, Ted's assessment is a good thing to have.

Yet another Japanese satellite failure!

The Japanese, already suffering from the major devastation of the recent earthquake, truely don't seem to catch a break.

Today news broke that yet another Japanese radar- and optical satellite has broken down on orbit. It concerns ALOS, a non-classified Earth Observation satellite including radar, visual and infrared sensing equipment.

This comes after the 2007 malfunction of the classified SAR satellite IGS 1B, which is now developing into a re-entry hazard concern for 2012 (as discussed extensively on this blog in a post from last weekend): and the 2010 malfunction of their other classified SAR satellite, IGS R2.

In the aftermath of the recent earthquake, losing their prized remote sensing satellites must really be a pain for the Japanese: this is all really at the most untimely of moments.

Unlike IGS 1B, ALOS is not a direct re-entry hazard for the near future. In a 697 x 694 km orbit (notably higher than that of the IGS-es), it will take a considerable time for it to decay.

KH-12 USA 129 flaring: and IGS 1B again

A period of sunny weather commenced the past week, albeit with a trend towards increasing hazyness. I observed on the 19th, 20th and 21st of April, targets being the evening KH-12's USA 129 (96-072A) and USA 186 (05-042A), as well as IGS 1B (03-009B). An attempt to locate the geostationary satellite Mentor 2 (98-029A) on the 20th failed, probably because of the poor observing conditions.

Yesterday evening (21st April) the sky was quite hazy with, during twilight, abundant whisps of thin clouds. USA 129 (96-072A) slowly flared to mag. 0 at about 19:56:15 UTC, and the resulting picture of the flare amidst thin clouds in a still bluish twilight sky, looks very eerie:

click image to enlarge

Some what later, I made this shot of IGS 1B (03-009B) gracefully sailing through Bootes:

click image to enlarge

My story about the re-entry of the above pictured malfunctioned IGS 1B satellite in about a year from now, has been picked up, notably after Jim Oberg reposted it on the NASA Spaceflight Forum here. Two journalists contacted me with questions, and my post itself attracted some US Government attention (when the Executive Office of the President visits your weblog, you know it is being taken serious). So I guess some people have woken up now, and hopefully we will soon see a serious risk assessment and more pertinent information by the Japanese as to the tank content of the satellite.

[UPDATED] Another Malfunctioned Spy Satellite is Coming Down - with Hydrazine onboard

UPDATE (24 Apr 2011): in a separate post, I discuss a new analysis by Ted Molczan, who has done an independent assessment on the absolute amount of fuel left in the tank of IGS 1B. This assessment, in which I have a large degree of trust, suggests that the absolute amount of fuel carried by IGS 1B is substantially lower than was the case with USA 193. This is somewhat of a reassurance. Read more about it in the separate post here.

Summary - this long post discusses the imminent uncontrolled re-entry of the malfunctioned Japanese spy satellite IGS 1B (2003-009B) in the first half of next year (2012): and points out that there might be a potentially hazardous half-full tank of fuel still in the defunct satellite, mimicking the situation with USA 193 in 2008.

Prologue - Three years ago: USA 193 and 'Operation Burnt Frost'

Three years ago, a malfunctioned US Spy Satellite called USA 193 (2006-057A) made headlines, when it was destroyed by a modified SM-3 missile fired from the USS Lake Erie near Hawaii. This was done in order to avoid a potentially dangerous uncontrolled re-entry early 2008 (see my coverage of the story here). According to US Government officials, the tank with toxic Hydrazine fuel onboard the satellite was the main reason for this unusual and spectacular pre-emptive destruction code-named "Operation Burnt Frost", although a few independant analysts (e.g. Yousaf Butt) maintain that the real motives were instead to prevent cutting edge technology from falling in the wrong hands, and perhaps also to provide a symbol warning to the Chinese. The Chinese had conducted a succesfull anti-satellite test (ASAT) a year earlier which greatly worried the USA. The suggestion that it was not the potential hydrazine hazard but another motive that prompted the decision to destroy USA 193, was hotly debated, notably by noted Space journalist Jim Oberg who strongly defended the official position (for more examples of the heated discussion, see here).


2012: IGS 1B, Another Spy Satellite Coming Down

Now, three years later, another malfunctioned spy satellite is coming down. And like USA 193, it likely too has a significant reserve of fuel left in it's onboard tank.

Image below: the doomed malfunctioned satellite IGS 1B, a bright naked-eye object, photographed by the author from Leiden (the Netherlands) on 21 April 2011

click image to enlarge

The satellite in question is a Japanese spy satellite, IGS 1B (2003-009B), believed to weigh 1.2 tons (about one-third of the weight of USA 193). It was launched on a H-2A rocket on 28 March 2003 together with a sister satellite, IGS 1A (2003-009A). IGS stands for Intelligence Gathering Satellite, an English translation of the Japanese designation joho shushu eisei.

Both satellites, placed in similar ~488 km, 97.3 degree inclined Polar orbits, were meant to work in tandem, the IGS-A object being an optical imaging reconnaissance satellite, the IGS-B object a Synthetic Aperture Radar (SAR) reconnaissance satellite with imaging resolutions believed to be in the order of 1 meter. Their mission -and that of subsequent similar IGS satellites launched- probably was and is primarily to keep an eye on North Korea's Ballistic Missile program, as well as providing an imaging aid in case of natural disasters occuring in Japan.

In order to carry out their mission, these satellites carefully maintain a very stable sun-synchronous orbit by means of frequent small manoeuvres. While some sources (including the CIA) list an intended life-span of 5 years, the optical satellite of the pair (IGS 1A) appears to be still actively maintaining its orbit as of April 2011, over 8 years after launch of the pair, indicating that these satellites probably have a significant amount of fuel onboard to enable these orbit maintenance manoeuvres.

Both objects in question are classified, meaning that neither the Japanese government nor the US Government make orbital elements available. Amateur trackers, including this author, have however kept track of both objects since their launch, determining and updating their orbits (periodically published here).


March 2007: Loss of power, and loss of altitude, by IGS 1B

In the spring of 2007, the Japanese government made public that the radar satellite of the pair, IGS 1B, experienced a serious malfunction involving loss of power on or near March 25, 2007.

Indeed, amateur tracking data show that since March 2007 the satellite has stopped the careful maintainance of its orbit and instead has started to lose altitude. In addition, amateur trackers (including this author) started to report an irregular brightness behaviour of the satellite, including some spectacular flares not seen prior to 2007 (e.g. reports here, here, here, here, here and here), indicating a loss of attitude control.

The following diagram, created by this author based on published orbital updates calculated by Mike McCants from amateur tracking data (including data by this author) shows how the Mean Motion of the satellite, initially constant near 15.26 revolutions/day (the sun-synchronous value for inclination 97.37 degrees), has gone up steadily since late March 2007 (this date, the date of the reported malfunction, indicated by a vertical dashed grey line), indicating a loss of altitude. For comparison, the values of IGS 1B's still operational optical sister satellite IGS 1A, are shown as well (note how they remain constant due to the constant orbital maintenance manoeuvres this satellite continues to make):

click diagram to enlarge

Indeed, the perigee and apogee altitudes of the satellite as derived from the published amateur orbits, show a clear and increasing drop in altitude from March 2007 onwards (unlike the constant values of its still operational sister craft IGS 1A, shown as a reference in the diagram as well). Since the 2007 malfunction, the orbital altitude has already decreased by over 30 km, and the decrease is continuing at an increasingly fast pace:

click diagram to enlarge

As the loss of altitude starts right at the moment of the reported malfunction (late March 2007), it appears to be a malfunction affecting control of the satellite itself, not just it's radar system. With this is meant that the loss of altitude and start of orbital decay does not appear to be due to a controlled shut-down sometime after the remote sensing equipment malfunctioned. Instead, it appears that the Japanese operators have indeed truely lost control over the satellite.


When will it re-enter?

At the current increasing rate of orbital decay, it is clear that the satellite is now entering its last year of existence. Using Alan Pickup's orbital evolution software SatEvo and the latest IGS 1B orbit updates by McCants, IGS 1B's re-entry into the atmosphere is predicted to occur in about a year from now, around March, April or May 2012.

These predictions will probably shift a bit back or forth in the future, as the orbital evolution depends on a.o. solar activity (which is not constant and not well-predictable). But it is clear that somewhere in the first half of 2012, IGS 1B will come down.


Issues connected to the uncontrolled re-entry of IGS 1B

Similar to what was the case with the now infamous USA 193 satellite, the situation is that we have a satellite in a Polar orbit and likely containing a still significant reserve of fuel about to come down in an uncontrolled fashion.

Normally, when a spy satellite in Low Earth Orbit is at the end of its life, the last reserve of fuel is used to make the satellite deliberately re-enter in a controlled fashion, over a carefully chosen spot: usually the Pacific Ocean, where the re-entry can do no harm. This was recently done with the US radar spy satellite Lacrosse 2 for example (see here).

With a satellite that is out of control, like the infamous USA 193 and now this Japanese IGS 1B, that is however not possible. The satellite can basically plunge down anywhere on earth, and when remnants survive this re-entry, they can become a danger if the re-entry happens to occur over an inhabited area.

The latter danger was the official rationale behind the decision to destroy USA 193 in 2008 by means of a missile fired from the USS Lake Erie, just before the satellite would have come down on its own. Especially the fact that, due to the early malfunction of this satellite, there still was a tank with a considerable reserve of toxic hydrazine fuel on board, was given as a reason for the "shoot-down" (actually more of a "shoot-to-pieces"): the operation was called "Operation Burnt Frost" because the stated objective was to destroy the hydrazine reserve which, after two years of inactivity of the satellite, was likely frozen.

With IGS 1B, we might be facing a similar hazard in 2012. The satellite is bound to have a fuel reserve left, and quite likely a considerable reserve at that. (note added 24/04/2011: see however the post here, featuring an independant re-assessment by Ted Molczan)

IGS 1B passing through Canis venatici and the tail stars of the Big Dipper on 9 April 2011

click image to enlarge

As mentioned earlier, some sources list an intended life-span of 5 years for IGS 1B (and IGS 1A). It malfunctioned after 4 years, so one can expect that as a minimum there is at least enough fuel for a year left in the spacecraft.

But there are reasons to believe that the reserve of fuel left could in fact be considerably more than that.

The reason to think so is that, as mentioned earlier in this post, eight years after launch the IGS 1B sister craft IGS 1A is still actively maintaining it's orbit (see diagrams above). Mid-2008, the spacecraft manoeuvred to re-allign it's inclination to the 97.37 degree inclination orbital plane of subsequent IGS satellites launched from 2006 onwards. This indicates that 5 years after launch, it was (and up to this day probably is) still fully operational, and being primed for continued tasks. A CIA summary suggests an operational replacement by another IGS satellite was not effected untill at least mid 2010, over 7 years after its launch. As mentioned, amateur tracking data show that IGS 1A is still actively maintaining it's orbit as of April 2011, 8 years after its launch.

The implication is, that these IGS spacecraft actually have enough fuel reserves onboard for over 8 years of operation. As IGS 1B malfunctioned after only 4 years in operation, the implication of that in turn is that half or more of the original fuel reserves could still be left in the spacecraft (one factor however not easily calculated in with this, is the amount of fuel spent in the initial manoeuvering to obtain the desired orbit directly after launch).

That, a tank potentially still half full, is a considerable amount of fuel. (note added 24/04/2011: see however the post here, featuring an independant re-assessment by Ted Molczan)


Should action be taken?

The potential hazard of the onboard reserve of hydrazine fuel upon impact on earth was given as the primary reason to mount "Operation Burnt Frost" with USA 193 in 2008. As we might now be facing a similar situation with IGS 1B, it will be interesting to see if a similar drastic measure is taken, either by the Japanese (who own the same SM-3 missile system used for 'Operation Burnt Frost') or it's ally the USA, given that the latter has previous experience with such a complicated exercise. And if not, then the question will be: why in the case of USA 193, but not in the case of IGS 1B?




As was the case with USA 193 in 2008, the doomed IGS 1B satellite is in a polar orbit. It has a 97.3 degree inclined orbit, meaning that it is a potential danger to every latitude between 82.7 degree North and 82.7 degree South. This range of latitudes covers every inhabited spot on Earth, including all of the USA, Canada, Europe, Australia, Africa, Asia, South America and Japan.

While the amount of fuel left in IGS 1B is probably not as large (in the sense of amount of gallons) as it was in USA 193, a considerable amount of it nevertheless is very likely there, in the shape of what could be (note: in a "worst case scenario") up to a half full (and frozen) tank that might survive re-entry. Here, I should however mention that of course my assessment on the tank content is at best an "educated guess", and I could of course be wrong (only the Japanese can answer that point). (note added 24/04/2011: see however the post here, featuring an independant re-assessment by Ted Molczan)

Instead of watching this one quietly go down, I would prefer to see a good risk assessment done and either mitigating action taken, or a clear argument presented as to why it would not be a danger in this case, given all the fuzz created around falling fuel tanks with USA 193.



Note added: according to the Japanese press, a second IGS radar satellite (IGS R2, 2007-005A) suffered a system failure in August 2010, 3.5 years after launch.

note: this post has been slightly edited in the afternoon of April 20, to better reflect the point that the "tank half full" assessment for IGS 1B is a "worst case scenario". Japan should give some openness in information to replace these "educated guesses" by more solid facts.

Mexican "impact" / fireball event is NOT due to Kosmos 2421 debris

News is doing the rounds of a spectacular fireball/sonic boom near Mexico city on 10 Feb, 18:30 local time (= 11 Feb, 00:30 UTC).

Initial reports talked about an actual impact with a 30 meter wide crater and damage to a bridge and road. That seems not to be the case.

Subsequent news releases suggested that it was a piece of Komsos 2421 debris impacting (06-026 HK, #33006).

For a summary, see Phil Plait's Bad Astronomy blog post here.

However, this event was certainly NOT due to the mentioned piece of space debris. The object in question was, contrary to apparent statements by a spokesman of the Mexican Space Agency (?), no way near passing over Mexico in a window of several hours around the reported time:

click image to enlarge

In addition, there are elements available with an epoch 0.75 days after the event, suggesting it indeed was still in orbit after that time. I used Alan Pickup's fine SatEvo software with the current F10.7 solar flux parameter (94) to predict a decay near 12 Feb 9h UTC, 1.25 days after the Mexican event.

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.

(click images to enlarge)

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).

A decaying tank that is not shot down

Somewhere today, the Early Ammonia Servicer (EAS) will plunge into our atmosphere and decay. The EAS is a large refridgerator-sized tank filled with ammonia, that once was part of the International Space Station. It was never used, and finaly jettisoned during an EVA on July 27th, 2007. I observed it several times, and photographed it on July 20 this year.

Interestingly, some pieces of the EAS are thought to probably survive re-entry. Plus, it is filled with a large amount of Ammonia, a rather agressive substance.

Remember all the fuss about the hydrazine tank of USA 193 early this year? The danger of anyone coming into contact with the agressive hydrazine, was the official "argument" to shoot the decaying spy satellite USA 193 down with a missile. Subsequently, fierce debate erupted about whether this really was the reason or not (see here and here).

Now, here we have another tank with an agressive substance, the EAS, decaying. And does anyone really bother? No, apparently. Even though a NASA spokesperson is quoted in this Space.com story as saying:

NASA expects up to 15 pieces of the tank to survive the searing hot temperatures of re-entry, ranging in size from about 1.4 ounces (40 grams) to nearly 40 pounds (17.5 kg).

and:

"If anybody found a piece of anything on the ground Monday morning, I would hope they wouldn't get too close to it," Suffredini said.

Wasn't the last thing exactly what all the hu-ha was about with USA 193?! I again conclude that the whole fuss about the hydrazine in USA 193 was not the primary reason to shoot it down....

(Click image to enlarge)

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

Two satellite fuel tanks survive re-entry

Two recent finds of satellite fuel tanks - both of carbon-wrapped titanium fuel tanks from the Atlas Centaur upper stages of two US military satellite launches probably - are in the news at the same time. One came down a week ago in Brasil, the other was found in the autumn of 2007 in Australia.

The Brasilian tank (source):




The Australian tank (source):




The Brasilian fuel tank is very likely part of the upper Centaur stage of the rocket that launched a US military communications satellite (Global SATCOM, 2007-046B) in October 2007. The Australian fuel tank could be a part of the upper Centaur stage of the rocket that launched another military satellite, USA 138 (1998-016A) in 1998.

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)