On Wednesday a planned Russian spacewalk in low orbit space was canceled. The Soyuz MS-22 spacecraft docked at the International Space Station (ISS) was leaking coolant. And three space travelers are temporarily stranded on board with no ride home.

The spacecraft was launched from Kazakhstan’s Baikonur Cosmodrome, on September 21st. It carried two cosmonauts and a NASA astronaut Frank Rubio to the ISS.

The Russian space agency Roscosmos posted a preliminary report. And the damage seems to be primarily to the spacecraft’s external casing. The outer skin of the Soyuz MS-22 instrumentation and equipment compartment was essentially experiencing melting.

NASA blog post details that “the external radiator cooling loop of the Soyuz is the suspected leak source.”

Russian Soyuz MS-22 international crew

Cosmonauts Sergey Prokopyev and Dmitry Petelin were already in their spacesuits. And preparation for a seven-hour spacewalk had begun when low-pressure readings were discovered by ground crews. 

After the first was cancelation a planned December 21 spacewalk is also being indefinitely postponed.

Experts claim a micrometeorite may be responsible for the damaged craft.

Micrometeorites are small pebbles which zip around space at extremely high speeds. They are usually the size of a grain of sand.

In May, a micrometeorite hit the Webb Telescope’s primary mirror. And created damage which impacted its performance. 

The cosmonauts were never directly exposed to the coolant. “Roscosmos is closely monitoring Soyuz spacecraft temperatures, which remain within acceptable limits,” NASA said. 

“NASA and Roscosmos continue to coordinate external imagery and inspection plans to aid in evaluating the external leak location.” The crew is safe and are conducting normal operations.

Russian cosmonaut Anna Kikina performed an investigation using the station’s robotic arm on the exterior of the space station. She sent images of the spacecraft to ground teams to assess.

According to NASA the photos show a “significant leaking of an unknown substance” from the Soyuz MS-22.

NASA used the livestream planned for the interrupted spacewalk to get a closer look. Particles can be seen bursting out of the spacecraft into space. And are visible for over three hours.

Recently a SpaceX launch was delayed from November 22 to November 26 due to an onboard coolant leak in the company’s cargo capsule.