Roscosmos will launch an uncrewed Soyuz spacecraft to the ISS to return two Cosmonauts and an American astronaut after their spacecraft was damaged in a micrometeoroid strike.

Russian Cosmonauts Sergey Prokopyev, Dmitry Petelin, and US astronaut Frank Rubio were launched aboard the Soyuz MS-22 as a part of Expedition 67/68. The MS-22 crew was initially set to return in March, but their mission will be further extended for an indeterminate period after their replacement spacecraft arrives.

"They are ready to go with whatever decision we give them,” said Joel Montalbano, NASA's ISS program manager in a joint NASA-Roscosmos press conference. "I may have to fly some more ice cream to reward them."

Montalbano also made it clear that this launch should not be characterized as a rescue mission since the immediate return of the crew is not required.

“We're not calling this a rescue Soyuz. No immediate need for the crew to come home. I'm calling it a replacement Soyuz.”

On December 14, 2022, cosmonauts Sergey Prokopyev and Dmitri Petelin were preparing for a scheduled spacewalk when the mission control at Houston and Moscow noticed a leak from the aft portion of the Soyuz MS-22 spacecraft, docked to the Rassvet module on the Russian side of the ISS. The spacewalk was canceled as the ground teams at Moscow began an investigation to evaluate the nature of the leaking fluid, and its potential impact on the Soyuz spacecraft, which was due to return to Earth in March.

Ground controllers in Moscow said that there had been damage to the outer skin of an internment assembly compartment of the Soyuz, causing the coolant to leak. This was then confirmed as the teams noticed a drop in pressure in the external cooling loop of the spacecraft. To have a closer look at the source of the leak, Roscosmos made use of the cameras onboard the 17-meter-long robotic arm attached to the ISS, known as the Canadarm2.

High-fidelity images from Canadarm2 helped conclude that Soyuz’s cooling system was struck by a micrometeoroid, resulting in a puncture less than a millimeter wide and causing the coolant to leak out of the spacecraft. NASA and Roscosmos officials are certain that it was not caused by the Geminid meteor shower or space debris.

"Space is not a safe place and not a safe environment. We have meteorites, we have a vacuum and we have a high temperature and we have complicated hardware that can fail," said Sergei Krikalev, Roscosmos’ chief of crewed space programs.

"Now we are facing one of those scenarios ... we are prepared for this situation."

This is the first time a spacecraft has been declared unfit to return a crew to Earth in the 22-year span of continuous human inhabitation onboard the ISS. But a similar instance took place in 1979 when the soviets launched cosmonaut Nikolai Rukavishnikov and Georgi Ivanov onboard the Soyuz 33 mission to the Salyut 6 space station. It was the fourth international crew launch for the Soviet's Intercosmos program, which saw cosmonauts from the Soviet Union’s allies launching to space. This mission was also the first such flight to be commanded by a civilian, and the first Bulgarian to reach space.

However, as the Soyuz was rendezvousing with the Salyut, its onboard attitude control system failed and its engine automatically shut down after 3 seconds of a planned 6-second burn. This was the first in-orbit failure of the Soyuz propulsion system. After multiple troubleshooting attempts by ground control, the mission was ultimately aborted, and the crew returned safely back to Earth.

Because Soyuz 32 — the previously launched spacecraft — shared the same engine design, Soviet teams decided to not use that spacecraft for a return journey, and instead launched a fresh return vehicle to the Salyut, incorporating numerous engine design modifications.

The uncrewed Soyuz 34 mission was launched on June 6, 1979, successfully docking with the station by June 9. With a reliable return craft available, the resident crew undocked and returned to Earth on August 19, establishing a then-space-endurance record of 175 days.

As the teams concluded their investigation, engineers at Roscosmos back on Earth studied the data to determine the viability of MS-22. Utmost safety precautions are taken during any crewed mission to minimize risks, and the agency eventually certified MS-22 infeasible for crew return, deciding instead to launch a “replacement” uncrewed Soyuz to the ISS.

“[MS-22 Soyuz] will bring back some experiments, they'll monitor temps inside. Expect it to be OK — just not suitable for carrying people,” said Krikalev.

Originally designated for the crew of MS-23, the replacement Soyuz will launch on February 20, 2023. Normal handover procedure will be followed and the MS-22 spacecraft will be undocked for re-entry. The teams will continue to monitor the spacecraft and inspect the damage once it returns back to Earth.

The safety protocol of the ISS states that crew members should return to their spacecraft (either Soyuz or Crew Dragon) in case of an emergency that requires total evacuation. But since the extent of the damage to the cooling system is still unknown, it’s still not clear if MS-22 would be useable for an emergency return to Earth. Krikalev said the decision would be made by accessing the risks of various options as temperatures in the capsule could reach unhealthy levels of 30-40 degrees Celsius (86-104 degrees Fahrenheit) during re-entry.

"In case of an emergency, when the crew will have a real threat to life on the station, then probably the danger of staying on the station can be higher than going down in an unhealthy Soyuz," said Krikalev.

Ever since the incident, NASA has been in constant talks with SpaceX about how Crew Dragon can accommodate more people in case of emergency. The spacecraft was developed to launch and return up to 7 astronauts but NASA preferred to limit the configuration to accommodate only 4.

The upcoming NASA and SpaceX crewed launch to the orbiting laboratory, Crew-6 will be launched just after the Soyuz MS-23 to incorporate the manifest changes and a direct handover between Crew-5 and Crew-6.

Micrometeoroids are small tiny extraterrestrial rocks, measuring between 10 micrometers to 2 millimeters in size. While incredibly small, they travel at very high velocities and can pose a significant threat to space exploration and operations. Mitigations to their strikes are a significant design challenge for not only spacecraft but also space suit designers. Numerous high momentum impacts degrade the outer casing of the spacecraft and long-term exposure threatens its functionality.

The impact of such minute, yet high-velocity objects is heavily researched under terminal ballistics, which also includes the study of mitigation techniques to minimize damage. Such work — conducted by Harvard astronomer Fred Lawrence Whipple — predates the space race but only proved useful when space exploration later boomed after the 1960s. Whipple had demonstrated that the chance of being hit by a meteoroid large enough to destroy a spacecraft was extremely minute, but it will be constantly struck by meteoroids the size of dust grains, now referred to as micrometeoroids.

Whipple developed a solution to this problem in 1946 by designing a thin foil film that is held a short distance away from the spacecraft. Known as the Whipple shield, it vaporizes the micrometeoroids into plasma when it strikes the foil. This plasma quickly spreads and is diffused before it can penetrate the structure of the spacecraft.

Subsequent research and development led to new lighter and stronger materials to be used as the Whipple shield. Ceramic fiber woven shields were proven to provide better protection from particles traveling more than 7 kilometers per second than aluminum of the same weight.

NASA also developed a multi-layer flexible fabric for its inflatable space station module named TransHab. Although it never ended up flying, the technology was later reused to build the Bigelow Expandable Activity Module, which was launched to the ISS in 2016 and is still operational.

Even with such extensive research, spacecraft launched in space still sustain damage from micrometeoroid strikes. One of the mirrors onboard the recently-launched James Webb Space Telescope was hit by a micrometeoroid and the damage caused was significantly more than NASA expected. According to a report on the telescope's performance, the strike will have a lasting impact on its observation.

These strikes have raised an important question. Is Soyuz, and other spacecraft that have absorbed micrometeoroid strikes — just unlucky? Or are our spacecraft far more susceptible than originally thought? And will we find that these objects are more common and more dangerous than we expected? Observing the rate and characteristics of future impacts will be an important factor in answering these questions, and will be critical for ongoing advances in terminal ballistics. 

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