Tonight at 8:40 p.m. EST, Expedition 57 Commander Alexander Gerst and Flight Engineers Serena Auñón-Chancellor and Sergey Prokopyev will end their 197-day mission in space and return home inside the Soyuz MS-09 spacecraft.
The astronauts will undock the spacecraft from the International Space Station, travel back toward Earth, and ultimately parachute down to Kazakhstan three-and-a-half hours later. Prokopyev will command the Soyuz flight which will be live-streamed on NASA TV. But, just a few days ago, this same spacecraft had a large hole cut into it by Prokopyev and Oleg Kononenko during a spacewalk.
The cosmonauts cut out pieces of the external hull of the craft’s orbital module to bring back to Earth for analysis. These pieces will be studied as part of an ongoing investigation to find the cause or culprit behind the hole that appeared in the spacecraft this past summer. The hole was discovered after astronauts noticed a pressure dip inside the space station. After initially investigating and patching it up, drill marks near the hole led some to speculate that it could have been created intentionally. After cutting out samples for analysis and taking photos of the site, the hole was once again patched up during the spacewalk.
But will it be safe for these astronauts to travel back to Earth on a spacecraft that was recently cut apart with a knife? According to Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics who tracks the objects that launch into space and back, “I think it’s gonna be just fine.”
The patched-up hole in the Soyuz craft is located in its orbital module. The trip that astronauts take to the space station lasts anywhere from 6 hours to two days. Comparing the ride to an airplane flight, McDowell explained that astronauts use this orbital module on the way up so they can float around and stretch their legs, which makes the trip more comfortable. But the journey back down to Earth is significantly shorter, lasting just a few hours. That’s why the orbital module is closed off and the astronauts travel only in the descent module on their way back down to Earth.
Because of this, even if the patch job doesn’t hold and the orbital module springs another leak, the astronauts on board will almost certainly land safely. The only danger, according to McDowell, is if the module springs a leak at the wrong time, the leak could act almost like a rocket engine and provide thrust that could push the craft in the wrong direction. If this happened early in the journey, the thrust could be counteracted with additional thrust from the craft. But if it happened later on in the trip, it could be dangerous.
“Worst case I can see is if it springs a leak during the deorbit burn because while you’re decelerating the spacecraft to bring it down out of orbit you really want your thrust to be in the correct direction,” McDowell said. But, so far, the first and now second patch jobs have both held up without issue.
“I’m not concerned, it’s really hard for anything in the orbital module to make things go badly in the descent module where the astronauts are,” McDowell said. “I’ll still be very glad when they get down,” he added.
This article originally appeared on discovermagazine.com.