Largest object ever jettisoned from ISS to make uncontrolled re-entry this week

The International Space Station’s (ISS) largest-ever discarded object, a hefty equipment pallet weighing 2.9 tons, is anticipated to make an uncontrolled descent back to Earth between March 8 and 9, 2024. Launched into space for a critical ISS power system upgrade, this pallet, loaded with nine old station batteries, will not fully disintegrate upon re-entry, with predictions indicating about half a ton of debris could survive the descent and impact the planet’s surface.

The International Space Station’s most massive object ever released—a 2 633 kg (5 800 pounds) equipment pallet—is expected to make an uncontrolled re-entry into Earth’s atmosphere this week.

According to official statements, the re-entry window is estimated between 12:30 UTC on March 8 and 08:30 UTC on March 9, 2024. Approximately 500 kg (1 100 pounds) of fragments are likely to impact the Earth’s surface.

The pallet, dispatched into the void by the station’s robotic arm, Canadarm-2, on March 11, 2021, was initially brought to the ISS by Japan’s HTV9 cargo ship in May 2020. Its mission was to assist astronauts in swapping out the station’s older nickel-hydrogen batteries for new, more efficient lithium-ion ones.

This equipment played a vital role in a series of operations that saw 48 old batteries replaced with 24 new ones across six years, involving four supply missions from the Japanese H-II Transfer Vehicle (HTV) cargo spacecraft, 13 astronauts, and 14 spacewalks.

“It was the largest object—mass-wise—ever jettisoned from the International Space Station,” NASA spokesperson Leah Cheshier said in March 2021. This jettison surpasses the previous record held by the Early Ammonia Servicing System tank released during the STS-118 mission in 2007.

The decision to dispose of the pallet in an uncontrolled manner was not part of the original mission plan. It resulted from logistical challenges and a backlog in equipment disposal caused by the failed launch of a Soyuz rocket in 2018.

This incident, which forced an emergency landing for NASA astronaut Nick Hague and Roscosmos cosmonaut Alexey Ovchinin, disrupted the schedule for spacewalks and subsequent equipment disposal. Typically, old batteries would be secured within an HTV and safely jettisoned to burn upon re-entry. However, due to the postponement of spacewalks and the phasing out of the old HTV design in favor of the new HTV-X cargo spacecraft, the pallet had to be discarded independently.

Featured image credit: NASA/ISS