Enlarge / Three hours after the coolant leak was initially detected Wednesday night, it remained ongoing. (credit: NASA TV)

Four weeks ago, as two Russian cosmonauts were preparing to conduct a spacewalk, a Soyuz spacecraft attached to the International Space Station started to leak uncontrollably .

The spacewalk was canceled, and since then, Russian and US spaceflight engineers have been analyzing the cause of the leak and its implications for future travel to and from the large laboratory in low-Earth orbit. They have now deduced that a micrometeoroid or small piece of orbital debris struck the external cooling loop of the Soyuz spacecraft, causing all of its coolant to vent into space, and put a recovery plan into place.

Although there were no immediate threats to the seven astronauts on board the space station, there was the not-insignificant question of how the three people who had ridden on board this Soyuz MS-22 spacecraft into orbit— cosmonauts Sergey Prokopyev and Dmitri Petelin and NASA's Frank Rubio—would subsequently get home.

Enlarge / Three hours after the coolant leak was initially detected Wednesday night, it remained ongoing. (credit: NASA TV)

After working through the weekend to better characterize damage to its Soyuz spacecraft attached to the International Space Station, Russian specialists have decided to take no immediate action.

In a lengthy statement published Monday morning by Roscosmos (a VPN is required to access the site from Western nations), the Russian space corporation said it believed that a tiny piece of debris ruptured an external cooling loop that radiates heat from inside the Soyuz into space.

Working with NASA on Sunday to operate the long Canadarm2 manipulator arm, Russian specialists were able to get a clear look at the damaged area on the aft end of the Soyuz spacecraft. The area of the hole is about 0.8 mm across, which, although small, allowed all of the coolant in the external loop to be dumped into space last Wednesday. Importantly, the visual inspection discovered no other notable damage to the Soyuz vehicle from the debris strike.

Enlarge / The European robotic arm is seen investigating Soyuz MS-22 after a leak occurred Wednesday night. (credit: NASA TV)

Since a Soyuz spacecraft began to leak coolant uncontrollably on Wednesday night, flight controllers at Roscosmos, NASA, and other International Space Station partners have been closely studying data from the incident.

Although there is no immediate danger to the seven astronauts on board the space station, this is one of the most serious incidents in the history of the orbiting laboratory, which has been continuously occupied for nearly a quarter of a century. Among the most pressing questions: Is the Soyuz MS-22 spacecraft safe to fly back to Earth? If not, when can a replacement, Soyuz MS-23, be flown up? And if there is an emergency, what do the three crew members slated to fly home on MS-22 do in the meantime?

NASA has not held any briefings since the incident and has only released a fairly bland update on its blog. But there is a lot happening behind the scenes, and this story will attempt to summarize what is known—and what is not—at this time.