With Expedition 73 now underway, the International Space Station is hosting seven crewmembers again. Thursday saw the astronauts complete the Station’s third spacewalk of the year. The ISS crew is also getting ready for the upcoming arrival of the commercial Axiom-4 mission as well as conducting the usual science and maintenance tasks.
Visiting Vehicles
The latest series of crew handovers on ISS started in March with the launch of the Crew-10 mission aboard SpaceX’s Dragon Endurance followed by Crew-9’s return to Earth aboard Freedom. Soyuz MS-27 launched on April 8 from the Baikonur Cosmodrome in Kazakhstan, docking with the Russian segment’s Prichal module just over three hours after liftoff. Its crew: commander Sergey Ryzhikov, flight engineer Alexey Zubritsky, and NASA astronaut Jonny Kim boarded the Station just over half an hour after the docking.
After the Russian segment’s handover period, Soyuz MS-26 undocked at 21:57 UTC on April 19. Its departure marked the end of Expedition 72, with Expedition 73 – commanded by JAXA’s Takuya Onishi – beginning as MS-26 backed away from the Station’s Rassvet module. The crew currently aboard the Station consists of Onishi, Anne McClain, Nichole Ayers, Jonny Kim, Sergey Ryzhikov, Alexey Zubritsky, and Kirill Peskov.
Soyuz MS-26 about to touch down on the Kazakh steppe after 220 days in space. (Credit: NASA)
Soyuz MS-26 and its crew, commander Aleksey Ovchinin and Ivan Vagner of Roscosmos along with NASA’s Don Pettit, landed safely in Kazakhstan at 01:20 UTC on April 20 after 220 days in space. Pettit celebrated his 70th birthday on the day of the landing, though he acknowledged that he needed some time to recover from encountering Earth’s gravity for the first time in over seven months.
A few days into Expedition 73, the Station received an important cargo delivery in the form of the CRS-32 mission, utilizing Cargo Dragon C209 on its fifth flight. This launched on Monday, April 21 at 08:15 UTC and docked to the zenith port on the Harmony module at 12:40 UTC the following day.
The significance of CRS-32, which was loaded with 3,021 kg of cargo including food, science experiments, and other supplies, was increased by the cancellation of Northrop Grumman’s NG-22 mission. The Cygnus cargo ship that was to have flown NG-22 incurred damage during shipping to Port Canaveral ahead of a planned midyear launch. NG-23, due to lift off later this year, will be the next Northrop Grumman cargo mission to the ISS.
CRS-32 approaching the ISS on April 22, 2025. (Credit: NASA)
Some science had to be taken off CRS-32 to be replaced by additional food supplies to keep the Station stocked after hosting an increased crew of nine astronauts for a few months last year. The additional food included 1,262 tortillas, which are used in place of bread aboard ISS to reduce the possibility of floating crumbs that could get into equipment.
Despite these changes to its cargo manifest, CRS-32 still delivered 255 kg of scientific equipment and experiments. These included six instruments to measure solar radiation, an instrument to obtain imagery of the Earth, as well as remote sensing, astrophysics, and materials exposure experiments. Two atomic clocks also were flown to the Station which will be mounted on an external pallet on the Columbus module.
Crew Dragon Endurance is currently docked at Harmony’s forward port, with CRS-32 at its zenith port. Soyuz MS-27 is docked to the Prichal module on the Russian segment, while the Russian Progress MS-29 cargo craft is docked to the Poisk module.
Illustration of the current visiting vehicles at the ISS. (Credit: NASA)
Progress MS-30 is docked at the Zvezda aft docking port, which enables it to conduct periodic burns to reboost the Space Station’s orbit. The Progress spacecraft was also used to conduct a debris avoidance maneuver on Wednesday, April 30, to increase the Station’s distance from debris associated with a Chinese Chang Zheng launch vehicle that flew in 2005.
US EVA-93
Following the resumption of US Orbital Segment (USOS) spacewalks in January, the first EVA of Expedition 73 took place on Thursday, May 1. EVA-93, which was originally supposed to take place last year before issues developed with the Shuttle-era Extravehicular Mobility Units (EMU) that forced a halt to USOS spacewalks for months, started at 13:05 UTC.
EVA-93 by the numbers. (Credit: NASA)
EVA-93 was performed by NASA astronauts Anne McClain and Nichole Ayers. McClain wore the suit with the red stripes as EV1, while Ayers was EV2 without stripes. EVA-93’s main tasks were to install a modification kit for the future installation of International Space Station Roll-out Solar Array (iROSA) solar panels at the 2A location on the port side’s P4 truss as well as the relocation of the Common Communications for Visiting Vehicle (C2V2) communications antenna boom.
After being assisted by Takuya Onishi and Jonny Kim; McClain and Ayers officially began EVA-93 when their spacesuits were transitioned to internal power, but only after Mission Control evaluated minor damage to one of McClain’s gloves. After exiting the Quest airlock, they translated to the iROSA modification kit work site with McClain holding a tool bag and Ayers carrying a 2.5-meter-long bag carrying struts. McClain was told to perform additional glove checks during the EVA.
Illustration of the iROSA modification kit installation. (Credit: NASA)
The iROSA modification kit consists of a triangle formed by two small struts and a mounting bracket, with four larger struts connected to this. The astronauts installed the triangle and the right lower and mid struts as well as multi-layer insulation on the middle strut to help protect them against temperature swings and debris impacts. The astronauts also rolled out electrical wiring for the iROSA arrays to be installed on a future spacewalk.
There have been six prior installations of the iROSA modification kit, and McClain and Ayers were trained on this task on the ground in Houston. After the array installation at the 2A location, the final iROSA modification kit will be installed in a future EVA at the 3B location on the S6 truss on the starboard side of the Station. By the time the ISS ends its career, all eight solar array locations will have iROSA panels along with their original, degraded solar arrays.
Anne McClain and Nichole Ayers performing the relocation of an antenna during EVA-93. (Credit: NASA)
The iROSA kit installation was not completed during Thursday’s spacewalk, with Mission Control electing to have the astronauts move to the higher-priority task of relocating the C2V2 antenna boom instead. The EVA was at the two-hour, 30-minute mark when this decision was taken. Installation of the left-mid and lower struts will be left for a future spacewalk. At this point in the EVA, McClain’s consumables were the limiting factor for its duration, with a total of six hours and 30 minutes available.
The astronauts moved to the P3 truss, also on the port side of the Station, to begin the work of relocating the C2V2 antenna boom. They shifted the boom by about 46 cm (18 in) and mounted it onto an extension, clearing a structural blockage that affected one of the antennas during a previous rendezvous with a Cygnus cargo spacecraft.
Illustration of the C2V2 antennae. (Credit: NASA)
The C2V2 assembly, which features two antennae, is used to communicate with visiting vehicles, and moving the antenna will help support future visitors, including Cygnus NG-23 and Japan’s first HTV-X mission later this year. After the C2V2 relocation was complete, the astronauts returned to the airlock and the spacewalk ended after five hours and 44 minutes, at 18:49 UTC. It had originally been scheduled for six and a half hours.
During EVA 93, Diana Trujillo served as the spacewalk flight director in Mission Control. Astronaut Marcos Berrios was the spacewalk communicator and Sandy Moore was the capsule communicator, or CAPCOM. Faruq Sabur, Lucas Widner, Bailey Vega, and Steven Vilano were also part of the EVA-93 team at the control center in Houston.
EVA-93 was Anne McClain’s third spacewalk and Nichole Ayers’ first. McClain’s two previous spacewalks lasted a total of 13 hours and eight minutes. This was the 275th spacewalk in support of ISS assembly, maintenance, and upgrades as well as the fifth EVA to be carried out by only female astronauts.
Axiom-4 crew portrait. (Credit: Axiom Space)
Upcoming Activities
The Station will receive its next visitors later in May. The privately-operated Axiom-4 mission is currently scheduled for liftoff on Thursday, May 29 aboard a new Crew Dragon spacecraft. Crew Dragon C213, the fifth Crew Dragon to fly with people aboard, will be making its first flight and the Axiom-4 crew will get the honor of naming this spacecraft.
Axiom-4 is commanded by Peggy Whitson, a former NASA astronaut and ISS veteran. Whitson is the only US astronaut and the only spaceflight veteran on the Axiom-4 crew. India’s Shubhanshu Shukla, Poland’s Slawosz Usnanski, and Hungary’s Tibor Kapu will also be aboard, with Shukla and Usnanski the first of their nationalities to visit the ISS. Usnanski is an ESA astronaut, while Shukla will be the first of India’s new astronaut corps to fly into space.
Other Axiom missions to the ISS have spent between nine and 21 days in space, with Axiom-4 scheduled to last two to three weeks. After C213’s return to Earth, no other visiting vehicles are scheduled to fly to the Station until Progress MS-31 arrives in July. Cygnus NG-22 was supposed to have flown within this timeframe, but its cancellation created urgency for a successful CRS-32 flight.
Expedition 73 commander Takuya Onishi is seen working on the Advanced Space Processor Experiment-4 for a biotechnology study. (Credit: NASA)
The Expedition 73 crew has been busy this month with spacewalk preparations, maintenance activities, and various experiments including the ones recently sent up aboard CRS-32. An experiment to create DNA-like nanomaterials is operating in the Japanese Kibo module, while an ultrasound machine has been used to image crewmembers’ blood vessels.
Many other experiments are being conducted on both the USOS and the Russian segment of the Station, ranging from an investigation into how cells detect gravity, research on cognition in space, photography of glaciers, and research in other disciplines. While the Expedition 73 crew is working in space, NASA is preparing to mark the 25th anniversary of continuous human occupation of the ISS in November.
(Lead image: NASA astronaut Anne McClain during her recent spacewalk. Credit: NASA)
