AS the International Space Station continues to orbit Earth as it has for over a quarter of a century, the Expedition 75 astronauts aboard have been busy performing science and maintenance tasks, and preparing for new arrivals and a crew handover early next month.

Just before the end of August, the Cygnus XL cargo ship S.S. Steven R. Nagel reboosted the Station to prepare for the upcoming Progress MS-35 cargo flight, which at the time was scheduled to fly on Sept. 9. Following on from three spacewalks made from the US segment of the ISS in August, another EVA was carried out on Sept. 1.

Sophie Adenot, as EV1 with red stripes on her space suit, and Jessica Meir, as EV2, conducted US EVA-99, returning to the Station’s Quest airlock module after six hours and 49 minutes outside. The astronauts installed a new retroreflector on the Harmony node module’s forward port to support navigation for visiting vehicles.

Adenot and Meir also replaced a high-definition camera on the Station’s truss assembly and swabbed the Station’s exterior for microorganism samples. The astronauts began installing jumper cables for electrical systems and started work on replacing the Alpha Magnetic Spectrometer’s radiator assembly, tasks that will be finished on a future spacewalk.

During the spacewalk, Sophie Adenot experienced mobility issues in her left shoulder, which were traced to a joint heater harness getting caught in the shoulder joint. Meir unzipped the joint, which appeared to solve the issue. Various issues with the aging Shuttle-era suits have delayed Station spacewalks and forced repairs on various suit parts, which can be returned to Earth aboard Cargo Dragon spacecraft for evaluation and maintenance if required.

EVA-99 was the 248th spacewalk overall in support of the ISS, and marked Meir’s seventh and Adenot’s third spacewalk. Jessica Meir is now NASA’s third most experienced female spacewalker, behind only Peggy Whitson and Suni Williams. Two additional spacewalks are planned for Expedition 75 to install iROSA solar arrays on the 3B and 2A power channels, although scheduling of this work has not yet been announced.

A week after EVA-99, Progress MS-33 undocked from the Russian segment’s Poisk module to make room for the upcoming Progress MS-35 flight. Loaded with trash, MS-33 burned up on reentry on Sept. 7,  ahead of the planned launch of MS-35 on Sept. 9, although the launch was subsequently delayed by a hydraulic issue with the rocket.

NASA also announced that the upcoming Crew-13 flight to the Station would be delayed due to an oxidizer leak on Crew Dragon Grace. The flight is now set for Oct. 1, and Crew-13 astronauts entered quarantine on Sept. 17. When Crew-13 arrives, astronauts Jessica Watkins and Luke Delaney of NASA, Canada’s Joshua Kutryk, and Roscosmos’ Sergey Teteryatnikov will relieve their Crew-12 counterparts after a short handover period.

Progress MS-35 launched on Sept. 16, successfully docking with the Poisk module on Sept. 19 at 13:44 UTC. MS-35, also designated Progress 96 or 96P by NASA, delivered roughly 2,600 kg of cargo for the Station and its crew. As of Sept. 24, there are five visiting vehicles at the ISS: Progress MS-34 and MS-35, Soyuz MS-29, Dragon Freedom on the Crew-12 mission, and the NG-24 Cygnus S.S. Steven R. Nagel.

The Expedition 75 crew conducts a daily schedule of science and maintenance tasks. Recent science highlights have included a lead-free soldering experiment in the Harmony module. NASA’s Anil Menon set up a work area in Harmony and soldered components on a circuit board. His work will now be returned to Earth so it can be compared with another circuit board that was soldered on the ground. Soldering components in flight may reduce reliance on resupply flights during future space missions by enabling more repairs to be carried out in-situ.

Other science highlights included a 3D colloidal crystal experiment, observing particles suspended in liquids, with possible space-based manufacturing applications. Sophie Adenot set up the Kubik research incubator and centrifuge for remote operations by scientists on the ground. Many experiments on the ISS are controlled this way.

Adenot has been working extensively with the Advanced Resistive Exercise Device (ARED) in the Tranquility module, recording her workouts using a motion capture system. She is also evaluating the European Enhanced Exploration Exercise Device (E4D) set up in the Columbus science module, including rope-pulling exercises which had never been done in space before.

Astronauts are required to exercise for at least two hours per day to mitigate the effects of microgravity on the body, such as muscle atrophy and weakening of bones. Cosmonauts Andrey Fedyaev and Anna Kikina have been evaluating a Russian lower-body negative pressure suit. This suit forces blood back toward the lower body and feet, reversing the typical fluid shift toward the head that occurs in microgravity. Future crews may use these suits to assist with adaptation to Earth’s gravity as they prepare to return home at the end of their spaceflights.

While Crew-13 is due to arrive in October and Crew-12 will subsequently return to Earth, Expedition 75 will continue until the spring of 2027 and the planned departure of Soyuz MS-29.

While day-to-day operations continue on the Station, NASA signed a contract modification with SpaceX to fly the upcoming Crew-15, Crew-16, and Crew-17 missions. These missions have readiness dates in 2027 and 2028, as NASA prepares to end Station operations around 2030. NASA is continuing to work with Boeing to resolve outstanding issues with its Starliner spacecraft to support future commercial space station missions.

(Lead image: The International Space Station orbiting over Central Asia. Credit: NASA/Anil Menon)