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
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):
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:
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
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.