Rise or Fall
2015 Jul 29
Wednesday, Day 210
Where Did Phobos-Grunt Re-enter?
Contrary to previous reports, as of Jan 16, 08:00 UTC, its re-entry point is not known - to the public at least. An initial report by the Novosti news agency gave a location over the southern Pacific Ocean. It was later retracted and replaced with 'not known' and a debate between, the Pacific, Brazil and the Atlantic. Unfortunately, the retraction was too late to stop it being brodcast by a plethora of other news-related sites.
Earlier Guesses As To Where
They were just that - Guesses. Unfortunately, a few weeks ago, Spacetrack inadvertently released a TIP Message giving an geographical location relating to the central time of the estimate it contained. A number of news sites found the location on a map and, led by RIA-Novosti, wrote many words on the subject of Phobos-Grunt coming down over Afghanistan. The fact that Spacetrack had given an error margin of ±11 days (equivalent to several millions of kilometres of ground track) was lost on the non-scientists as they became fixated on that one point on the globe, even naming the town.
When Spacetrack began issuing TIP messages in earnest, they were not in the usual format and omitted a latitude and longitude for the central time. A possibility is that it was an attempt to avoid the data becoming the trigger of another ill-informed frenzy among the 'cut and paste' web-reporters.
What Did We Know
As of Jan 13, the main sources of estimates - Spacetrack, Aerospace and the trusty amateurs of the Seesat-L observer group - were homing in on Jan 15 somewhere between 17:00 and 18:00 UTC. Even so, the error margins were many hours, representing several circuits of the Earth at 40,000+ kilometres per lap.
The map shows the ground track of Phobos-Grunt for the period covered by the significant majority of estimates. There was a very strong likelihood that re-entry would occur along this line but it was not certain. A small change in upper atmosphere density, or errors in assumptions made by the estimators would have moved the track eastwards in increments of 22° for an earlier re-entry, or westwards for a later one.
The yellow segments of line represent Phobos-Grunt in daylight. If the re-entry was to be seen visually, then it would have had occur on the darker-coloured segments of track.
Novosti originally reported the Russian Ministry of Defence saying that re-entry was 1250 km west of Wellington Island, Chile at 17:45 UTC. Later, it downplayed the statement, saying that the location was not known and Phobos-Grunt might have travelled as far as Brazil and the Atlantic Ocean.
Spacetrack was slightly enigmatic saying only that it had "Decayed Inside (the) Predicted Window" which was 16:59-17:47 UTC.
In the course of January 16, Roscosmos stated that the re-entry point was unknown but the event occurred between 16:40 and 17:10 UTC. This is the segment of track coloured red on the map. On January 18 ESA's Thomas Reiter was quoted as saying that it had occurred "....perfectly in line with ESA and Roscosmos predictions".
Unfortunately, the Russian Ministry statement did not have the hallmarks of being based on reality so it was a case of waiting. Eight days after the event, a full-format TIP Message appeared on the Spacetrack website giving 17:46 UTC ±1 minute as the re-entry time. The issue date was shown as January 15 at 17:53 UTC.
The final Phobos-Grunt orbit data is here.
There is a summary of re-entry estimates here.
Likely to be Dangerous?
The answer is "not particularly". Although Phobos-Grunt was large and has a high mass compared with most re-entering items, much of it was fuel that was expected to ignite as it heated up. RoSat, for example, was considered much more of a risk because of the amount of heat resistant material used to build it. Some fragments of Phobos-Grunt probably survived but they are not expected to be dangerously large. One interesting item though was the sample return container - did it do the job it was designed for and get through the atmosphere?
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