Saturday, 5 January 2019

Fireball seen over New Zealand during cricket match was the reentry of Kosmos 2430 (2007-049A)

image from Fox News broadcast

The image above is a still image from TV-footage shot during the January 5th 2019 cricket match of Sri Lanka against New Zealand at Mount Maunganui, New Zealand. The camera captured a bright, very slow, copiously fragmenting fireball that occurred during the match. Here is the actual footage:

From the video footage, the event had a duration of at last 1 minute, and likely longer. The event was widely seen and reported from New Zealand: more images and more noteworthy video footage, as well as descriptions, can be found in this news article from the New Zealand Herald.

From the footage it is clear that this is a space debris reentry: the event is too slow and of too long duration to be a meteoric fireball.

From a Sri Lankan tv-broadcast of the cricket match, which features a clock in the imagery, the time of the event can be established as 5 Jan 2018 at 07:58 UT (Sri Lanka has a time difference of 5:30 with GMT):

image from Lotus TV broadcast

From the time and location, the event can be identified as the reentry of Kosmos 2430 (2007-049A), a defunct Russian US-K Early Warning satellite launched in 2007. Time and location match well with a near perigee pass of this object over New Zealand. The map below shows its predicted position for 08:00 UT on Jan 5 (movement is from top to bottom):

click  ap to enlarge

CSpOC at the time of writing (5 Jan 2019 14h UT) has a reentry TIP for 6:41 ± 4 m UT on its webportal Space-Track. This is 1h 47m, or one revolution, earlier than the New Zealand sightings.

Nevertheless, I am fully convinced that the event is Kosmos 2430 reentering - the match is too good, and the footage clearly suggests an artificial object reentering from earth orbit. So why the mismatch with the CSpOC TIP?

Kosmos 2430 was in a highly elliptical orbit with perigee over the southern hemisphere. In the diagram below, we see the apogee altitude (the blue line) quickly diminishing in the days before reentry, due to the drag experienced in perigee (diagram based on orbital tracking data from CSpOC):

click diagram to enlarge

The perigee altitude already is very low, near 90-85 km altitude, for days before the reentry and changes minimally untill the actual moment of reentry. The difference between apogee and perigee altitude remains significant up to the last few revolutions, with apogee still at 1000 km only two revolutions before reentry.

This means that, unlike typical objects reentering, Kosmos 2430 only briefly dipped into the upper atmosphere during each orbital revolution, experiencing drag only during brief moments. This is the kind of situation where an object can survive multiple very low perigee passes, and predicting the actual moment of reentry (i.e. during which perigee pass reentry will happen) is difficult. Looking at the CSpOC TIP bulletins for January 5th, this is clear as well as the CSpOC predictions significantly shifted forward in time with the addition of data from each new orbital revolution.

The sightings from New Zealand strongly suggest Kosmos 2430 survived one orbital revolution longer compared to the current (final?) CSpOC TIP estimate.

Note that with such brief but deep dives (well below 100 km) into the upper atmosphere, it is possible that the satellite already developed a plasma tail one or two perigee passes before actual reentry. The copious fragmentation visible in the footage from New Zealand shows that this event, at 7:58 UT was the actual moment of atmospheric reentry and complete disintegration.