In the days before Harvey hit Texas, flight controllers at NASA’s Johnson Space Center outside of Houston had a decision to make: should they evacuate or ride out the storm at the agency’s Mission Control Center? The dilemma wasn’t just about the safety of the flight controllers. These personnel are tasked with flying the International Space Station — a round-the-clock job that can’t be done just anywhere. If there’s a gap in ground communication, it could put the astronauts in danger.

“It’s 100 percent the flight controllers on the ground flying the space station,” Zebulon Scoville, NASA’s lead flight director of Expedition 52 for the International Space Station, tells The Verge. “If that capability is lost, then that can be a risk to the mission.”

“It’s 100 percent the flight controllers on the ground flying the space station.”

There are many tasks that flight controllers can do remotely, such as monitoring ISS data that’s sent down to Earth. But when it comes to sending commands to the orbiting lab, that has to be done on site at JSC. Flight controllers have to be in the Mission Control Center and logged in to do so, primarily for safety reasons. In any given month, somewhere around 50,000 commands are sent to the ISS — including things like orbit correction maneuvers to keep the vehicle in a stable position around Earth or to put the station out of harm’s way from space debris.

Of course, JSC is no stranger to storms and NASA does have its backup plans for disaster scenarios on the ground. There’s the option of moving Mission Control temporarily to a hotel in Round Rock, Texas, before transitioning control more permanently to NASA’s Marshall Space Flight Center in Huntsville, Alabama. This facility has a lot of spaceflight infrastructure and could potentially support operations for weeks.

Putting exclamation marks on "tough and competent!!", this team riding out #Harvey in MCC to keep @Space_Station safe pic.twitter.com/Jns7YAb9Xj — Zebulon Scoville (@Explorer_Flight) August 25, 2017

On August 22nd, three days before the storm hit, the mission team was briefed by the National Oceanic and Atmospheric Administration, and decided the best plan was to stay put. They realized that whatever hit Texas would likely hit Round Rock, too, which is located outside of Austin. Plus, Harvey’s real danger looked to be the water rather than the winds. The building containing the Mission Control Center is designed to withstand flooding incredibly well.

“It was interesting to see these rooms usually lit up with all these screens blacked out for people to sleep.”

But the team also knew they had to prepare. “Where you don’t want to find yourself is just a single flight controller in any position who can’t leave because there’s no one to replace them,” says Scoville. So the flight controllers were told to come into work early and to make sure they had a way to both enter and leave the center safely. Many showed up Friday night with “big, monstrous climbing backpacks,” says Scoville. Meanwhile, cots were set up in a nearby room and in a building that serves as an astronaut quarantine facility, where astronauts quarantine before launch to avoid getting sick in space. “We have training rooms that are a mere copy of the flight control room,” says Scoville. “They have the same consoles and same screens, but we turned off the lights and put some cots in there. It was interesting to see these rooms usually lit up with all these screens blacked out for people to sleep.”

Throughout the weekend, Mission Control operated with the bare minimum essential personnel needed to keep the ISS working safely. Normally, flight controller teams work in nine-hour shifts, swapping out three times a day. During the storm, only about six flight controllers worked each shift, and some stretched their shifts to 12 hours. Because the flooding made the roads impassable, everyone had to spend a couple of nights at NASA.

Congrats to @NASA_Johnson teams entrenched in Mission Control, weathering the storm to keep @Space_Station flying! You will endure #Harvey pic.twitter.com/K7u1Xs6ZpP — Thomas Pesquet (@Thom_astro) August 31, 2017

Even with a skeleton crew, things have been more or less normal at the center. “In terms of operations of the vehicles, it’s been going exceedingly smoothly,” says Scoville. The controllers boosted the station slightly last week to prepare for the arrival of a new Russian Soyuz spacecraft, which will bring three new crew members to the ISS in mid-September. The crew currently aboard the station has been fully occupied with their normal schedules, too, and NASA made sure to reach out to their families, many of whom live in the Houston area, to see if they did well throughout the storm. But very little work was lost. “From an astronaut perspective, it’s business as usual,” says Scoville.

Scoville says he spent most of the storm working remotely, so that he didn’t become a liability to the flight controllers. It was a tough decision: he wanted to be there with his co-workers. “There was a feeling of helplessness, where you want to get down and help,” says Scoville. “But in many cases the roads were just impassable unless you had a truck or boat. So you sort of had to watch as people play their parts and coordinated for replacement flight controllers and had access to food.”

“We fly the space station not only when it’s easy but when it’s hard.”

But when he showed up to JSC on August 29th, he was met by enthusiastic employees. “These men and women were just in good spirits,” he says. “They were looking in great shape with good morale and they could have kept going if we hadn’t swapped them out.”

JSC is still closed and will continue to operate with only essential personnel until September 5th. Scoville says there’s been an outpouring of support for the flight controllers, but to him that’s not the story. He says the focus should be on the first responders and people rescuing others from their homes with boats and pickup trucks. For the people of NASA, it’s all about doing their jobs. “This is what we do and what the American people have trusted us to do,” he says. “We fly the space station not only when it’s easy but when it’s hard.”