Astronauts aren’t made in a day. To first qualify for a mission assignment in space, NASA’s astronaut candidates typically have to complete up to two years of training here on Earth. And that includes a rotating roster of activities, workouts, and assignments that change every single day.

Perhaps the biggest aspect of astronaut training is learning to work in simulated space environments, something we explore in the second episode of Space Craft. For NASA, a crucial asset is the Neutral Buoyancy Lab, a giant pool located at the Sonny Carter Training Facility in Houston, Texas. It measures 202 feet long and 102 feet wide — a little less than half the size of a football field. It also stretches 40 feet deep and houses a full-scale replica of the International Space Station inside. Working in the pool is one of the best ways to train for future spacewalks, since it’s a pretty fair representation of how it feels to work in microgravity outside the ISS.

Perhaps the biggest aspect of astronaut training is learning to work in simulated space environments

But there are other ways to simulate spacewalks apart from diving into the NBL. NASA was an early adopter of virtual reality, using the technology over the last decade to help astronauts train for upcoming space missions. NASA’s Johnson Space Center in Houston is home to the Virtual Reality Lab, where astronauts plan out their future excursions inside and outside the International Space Station.

VR is a useful tool for better understanding the scope of a spacewalk, for instance. It gives astronauts a sense of how far apart segments are going to be on the outside of the station, as well as how they’ll need to grip handrails or twist their arms to properly scale the ISS modules. Astronauts who are assigned to missions in space usually plan months to years in advance for any of their spacewalks. And at the Virtual Reality Lab, they can simulate the exact spacewalk scenario that they need to practice over and over, before doing the real thing in lower Earth orbit.

While VR is good for making plans in advance, it’s also critical for preparing astronauts for the remote possibility of those plans failing. In the VR Lab, astronauts can also experience virtually what it’s like to get disconnected from the ISS during a spacewalk. Such a scenario has never happened accidentally before; astronauts are always tethered to the station when they do their spacewalks, but NASA likes to prepare for the remote possibility of an astronaut floating away freely. To get back to safety, astronauts can operate a jet backpack called SAFER, which uses tiny thrusters to propel someone through space. It’s not the easiest tool to maneuver, however, and VR is great at demonstrating the difficulty of using SAFER in an emergency scenario.

The Johnson Space Center doesn’t train astronauts with just VR technology. It’s also home to the Systems Engineering Simulator, a facility that contains mock-ups of space vehicles that astronauts may be tasked to operate in the future. For instance, astronauts can train how to work in the future space capsules that SpaceX and Boeing are building, which will be carrying astronauts to the space station in the next couple of years. The facility also has mock-ups of rovers that can traverse other worlds, like Mars. It’s a vehicle that astronauts probably won’t be driving on Mars for decades, but thanks to the SES facility, at least they’ll be somewhat prepared.

Update March 12, 2019 10:00AM ET: This article was originally published on August 22, 2017 and has been updated to include video.