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– Last Thursday was apparently a garbage day at the International Space Station, which freed itself from a 2.9-ton pallet of used nickel-hydrogen batteries. It is the largest mass of space debris released by the ISS, and NASA wrote that the pallet “moves safely away from the station and orbits between two and four years before burning harmlessly in the atmosphere.” As for how big, a NASA representative tells Gizmodo that the hunk is “more than twice the weight of the Early Ammonia Servicing System tank dropped by spacewalker Clay Anderson during the 2007 STS-118 mission.” Syfy explains that this was not the original plan. Japan’s H-II Transfer Vehicle (HTV) disposables were in the process of replacing those old batteries with lithium-ion batteries, and each HTV would fall back to Earth with a battery pallet on board. The items would burn on the return, with all remains falling into the South Pacific.
As for why this pallet was instead jettisoned from the ISS, blame the “ripple effect” of an emergency landing in 2018 that violated the ISS’s removal schedule, Syfy reports. Spaceflight Now explains that astronaut Nick Hague would participate in the battery changes, but failing to reach the ISS at the time ultimately resulted in one pallet of batteries not being picked up by an HTV. However, “Bad Astronomy” blogger Phil Plait is not convinced of the long-term success of this plan, and tweeted Thursday: “This seems (haha, a pun given the circumstances) to be dangerous. It looks big and compact, so it’s unlikely to burn out completely.” Astronomer Jonathan McDowell agreed, tweeting“Yes. On the other hand, the Tiangong-1, for example, was 7,500 kg, much bigger. But given the density of EP9, it’s alarming, albeit on the low side of troubling.” The US Space Command will keep an eye on things. (Read more stories about the International Space Station.)