Sunday 10 March 2024

The ISS EP9 battery pack observed on its last revolution before reentry

ISS EP9 battery imaged on 8 March 2024 18:17 UTC (click image to enlarge)

On 11 January 2021, a 2.6-tons car-sized container with old NiH batteries was detached from the International Space Station using the Canadarm2 robotic arm, and released into space. The object, called "ISS DEB (EP BATERRY)" by CSpOC, catalogue number47853, COSPAR 1998-067RZ, had since been slowly coming down for an uncontrolled reentry.

This reentry happened on 8 March 2024, at 19:29 +- 1 m UTC according to CSpOC, near 22 N, 85.5 W, over Yucatan and the western Caribean (the +-1 minute time uncertainty indicates that this is likely based on a SBIRS satellite detection of the reentry fireball).

Earlier similar packs of discarded NiH batteries were taken onboard visiting HTV supply spacecraft, to return and burn up in a controlled reentry with the HTV. For this last pallet, no HTV was available anymore, hence why it was unceremoniously tossed into space for a natural, uncontrolled reentry.


Canadarm2 releasing the container with NiH batteries into space (image: NASA)

In Germany, for some odd reason the news of the imminent reentry lead to a minor scare, with the German government issuing an alert through their cellphone civilian alert system, as the object would briefly pass over Germany within the (at that time almost a day wide!) reentry uncertainty window.

This alert was unnecessary in my opinion: yes, this was not a small object, and more solid than a rocket stage, but still, objects this size and mass and even bigger reenter several times a month - this was not an unusually large piece of space debris reentering. The very weekend following on this reentry for example, a 5-tons Chinese rocket stage, i.e. twice as heavy, would have an uncontrolled reentry as well. 

Chances of the pallet with discarded batteries coming down over Germany were less than 1%, and even if it would have done so, it would break up into much smaller pieces during reentry, and most of these would burn up in the atmosphere. Some pieces might survive and reach Earth surface, as with any reentry of a somewhat larger object, but the hazard is relatively small and is not of catastrophic proportions. Using the civilian alert system for catastrophies to issue alerts was panic-football, in my opinion, and it unnecessarily spread fear

Maybe it was meant to avoid panic in case of a reentry - with a spectacular light show in the sky and possible sonic booms - over Germany: but this alert reached the opposite I feel, creating unrest rather than avoiding it.

On its last orbit, slightly over an hour before reentry, I imaged the object passing over Leiden, the Netherlands around 18:17 UTC (March 8: 19:17 local time), as can be seen in the image above. This was in early twilight.

The object was moving very fast, zipping across the blue twilight sky, and bright: at magntiude -1 to -2 brighter than the brightest stars in the sky. I had no trouble seeing it naked eye. The image in top of this post is a 1/25th second exposure showing it passing through the constellation Auriga, almost right overhead (the bright twilight sky combined with a fast wide angle lensnecessitated a short exposure time).

A day earlier, on March 7th when all the anxiety in Germany erupted, I filmed it under terrible observing conditions (clouds came in just as the object was about to pass), where it was bright enough to shine through the clouds:

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