Two Russian cosmonauts took an almost 8 hour spacewalk today to literally uncover the other side of a hole that was discovered in the Soyuz MS-09 spacecraft that is docked to the International Space Station (ISS). Soyuz MS-09 will return three ISS crew members to Earth next week and the hole is in a segment of the spacecraft that does not return to Earth. Any questions about how the hole got there must be answered before it undocks.

Cosmonauts Oleg Kononenko, who just arrived at ISS on December 3, and Sergey Prokopyev, who has been there since June, spent 7 hours 45 minutes on a risky extravehicular activity (EVA) to inspect the exterior of the Soyuz spacecraft. It is highly unusual to have to do an EVA at that location and it was difficult for them to work their way over to the right spot — a trip that placed them in some precarious positions.

And another spectacular shot of spacewalker Oleg Kononenko working outside the Soyuz orbital module preparing to begin inspection work as the Earth passes below. #AskNASA | https://t.co/yuOTrYN8CV pic.twitter.com/N2RnfETpIV — Intl. Space Station (@Space_Station) December 11, 2018

They used makeshift tools to cut through thermal insulation and micrometeroid and orbital debris (MMOD) shielding to expose the hole.

NASA and Roscosmos televised the expedition. Cameras mounted in the cosmonauts’ helmets provided a first hand view. NASA tweeted the “Eureka” moment when they finally found the hole.

The “eureka” moment. Spacewalkers find the “small black dot” where controllers believe the area of the fixed pressure leak is located on the Soyuz crew vehicle. #AskNASA | https://t.co/yuOTrYN8CV pic.twitter.com/NFNOIPTkW1 — Intl. Space Station (@Space_Station) December 11, 2018

The two kept removing material to expose the hole more fully. Roscosmos wanted samples of the area around the hole, which had been filled from the inside with gauze and epoxy. This NASA tweet shows the hole fully uncovered. The dark blemish is caused in part by epoxy that extrudes from the hole.

Spacewalkers spot the patched hole on the hull of the Soyuz crew vehicle where a pressure leak was detected and fixed in August. #AskNASA | https://t.co/yuOTrYN8CV pic.twitter.com/Rt37VmvVZ1 — Intl. Space Station (@Space_Station) December 11, 2018

The hole was discovered from the inside when the ISS suffered a very slight pressure drop on August 29-30. ISS crew members quickly traced it to the Soyuz and repaired it. The pressure has remained steady since then.

Close examination shows a 2 millimeter hole that clearly had been drilled, with scratch marks nearby.

Roscosmos General Director Dmitry Rogozin implied that it was sabotage by one of the ISS crew members rather than the more likely explanation of an error during manufacturing. Rogozin’s comments created some tension. After a September telecon with NASA Administrator Jim Bridenstine, agreement was reached on “deferring any preliminary conclusions” until the investigation was complete. Today’s spacewalk is part of that investigation.

Concern about the hole was temporarily overtaken by the October 11 launch failure of Soyuz MS-10, which was traced to an assembly error of the Soyuz rocket at the Baikonur Cosmodrome. Russia quickly identified and rectified that problem and a new ISS crew was launched on December 3 — the flight that delivered Kononenko.

Whether the results of today’s EVA will resolve the origin of the hole remains to be seen, but this segment of the Soyuz spacecraft, called the Orbital Module or Habitation Module, will disintegrate when Soyuz MS-09 returns to Earth next week. The Soyuz spacecraft has three compartments and only the Descent Module is designed to survive reentry. The other two, including the Orbital Module, are jettisoned and burn up in the atmosphere.