Underwater Moonwalk

You’re an astronaut walking across a desolate lunar landscape for the first time. With each step, your boots sink into the gritty surface underfoot. Even though you’re wearing a heavy spacesuit, you bounce forward in what seems like slow motion. That’s because the pull of the moon’s gravity is so weak. Or it would be . . . if you were actually on the moon. In reality, you’re on Earth at the bottom of a massive indoor pool.

This pool—12 meters (40 feet) deep and roughly the size of 10 Olympic swimming pools—is found at NASA’s Neutral Buoyancy Lab (NBL) in Houston, Texas. For the past 30 years, it’s been used to help train astronauts for space exploration. The surface of the water is good for practicing the recovery mission. That’s the final stage of spaceflight, when the capsule carrying crew members returns to Earth and splashes down into the ocean. Beneath the surface, the pool contains a replica of most of the International Space Station (ISS). Moving on and around this model, astronauts practice working in microgravity—the reduced pull of gravity that creates a sense of weightlessness in space. Most recently, NASA and an aerospace company called V2X have transformed the bottom of the pool into a realistic copy of the moon’s surface.

The simulation will be used as a training ground for NASA’s upcoming Artemis program. The astronauts flying this series of missions will include the first woman and person of color to visit the moon. It will mark humanity’s first return to the moon in more than half a century (see “Shooting for the Moon,” Science World, March 12, 2023). The crew will land near the moon’s south pole, an entirely unexplored region. There, they’ll encounter huge craters, extreme temperatures, and areas of permanent darkness. “It’s a fascinating and challenging environment to try to reproduce,” says Clay Tomlinson, a program manager at V2X.

You’re an astronaut on a barren lunar landscape. This is your first time walking across it. With each step, your boots sink into the gritty surface. You’re in a heavy spacesuit, but you bounce forward, like you’re in slow motion. That’s because the pull of the moon’s gravity is so weak. Or it would be . . . if you were actually on the moon. Really, you’re on Earth at the bottom of a massive indoor pool.

This pool is 12 meters (40 feet) deep and about the size of 10 Olympic swimming pools. It’s found at NASA’s Neutral Buoyancy Lab (NBL) in Houston, Texas. For the past 30 years, astronauts have used this pool to train for space exploration. The surface of the water is good for practicing the recovery mission. That’s the final stage of spaceflight, when crew members return to Earth. They ride inside a capsule that splashes down into the ocean. Under the surface, the pool contains a model of most of the International Space Station (ISS). Astronauts move on and around this model to practice working in microgravity. That’s the reduced pull of gravity in space. It creates a feeling of weightlessness. Recently, NASA worked with an aerospace company called V2X. They turned the bottom of the pool into a realistic copy of the moon’s surface.

The simulation will be a training ground for NASA’s upcoming Artemis program. This series of missions will include the first woman and first person of color to visit the moon. It will mark humanity’s first return to the moon in more than half a century (see “Shooting for the Moon,” Science World, March 12, 2023). The crew will land near the moon’s south pole. That’s an entirely unexplored region. They’ll come across huge craters, extreme temperatures, and areas of permanent darkness. “It’s a fascinating and challenging environment to try to reproduce,” says Clay Tomlinson, a program manager at V2X.

Astronauts heading to the moon will need to be comfortable moving in lunar gravity, which is about one-sixth that on Earth, says Scott Wray, a lead training instructor on the Artemis program. That’s where the NBL comes in. Before entering the pool, astronauts are outfitted with weights and floats to wear underwater. These alter the astronauts’ buoyancy—the upward force that acts on objects in a fluid—to mimic the moon’s gravity. “The idea of using buoyancy to simulate the effects of reduced gravity has been around since the earliest spacewalks,” says Wray.

In the pool, astronauts test out the spacesuits they’ll wear during moonwalks (see Spacesuit Design). The newest spacesuits are easier to move around in than any past design, including those worn by astronauts who visited the moon during the Apollo missions of the 1960s and 1970s. Still, Artemis astronauts need to get used to walking, kneeling, and using tools while wearing them. And since the suits weigh roughly 181 kilograms (400 pounds) on Earth, it’s much easier to practice those movements in the simulated reduced gravity of the pool.

The moon’s gravity is about one-sixth Earth’s gravity. Astronauts on the moon will need to be comfortable moving in lunar gravity, says Scott Wray. He’s a lead training instructor on the Artemis program. That’s where the NBL comes in. Before they enter the pool, astronauts are outfitted with weights and floats. Underwater, these alter the astronauts’ buoyancy. That’s the upward force on objects in a fluid. The result feels like the moon’s gravity. “The idea of using buoyancy to simulate the effects of reduced gravity has been around since the earliest spacewalks,” says Wray.

In the pool, astronauts test their spacesuits. They’ll wear these suits during moonwalks (see Spacesuit Design). The newest spacesuits are easier to move around in than older ones. That includes the spacesuits from the Apollo missions of the 1960s and 1970s, when astronauts visited the moon. Still, Artemis astronauts need to get used to the spacesuits. They’ll have to walk, kneel, and use tools while wearing them. But the suits weigh about 181 kilograms (400 pounds) on Earth. So it’s much easier to practice those movements in the pool, with its simulated reduced gravity.

The south pole of the moon—where future astronauts plan to land—is even more inhospitable than the areas Apollo astronauts explored. The angle of the sun keeps low-lying areas in permanent darkness and bitter cold. Craters make the ground uneven and hard to navigate.

To mimic aspects of this environment, Tomlinson and his team from V2X placed huge natural and manufactured boulders at the bottom of the NBL pool. They built sloped panels into the floor so astronauts can practice navigating the region’s uneven terrain. Programmable LED lights simulate the movement of the sun and the region’s extreme shadows. Engineered sand mimics the lunar regolith—the layer of dusty debris that covers the moon’s surface. With no wind or flowing water on the moon, there’s no weathering to wear and smooth regolith particles. So they tend to be jagged. Regolith can stick to surfaces and make them slippery. Astronauts must practice moving around and using tools in it, explains Tomlinson.

For the V2X team, the goal is to make the environment as close as possible to the real thing. “There’s no room for surprises in an extreme environment like space,” says Tomlinson. “The realism of our simulations is directly tied to crew safety and mission success.”

Future astronauts plan to land near the moon’s south pole. That area is even harsher than the ones Apollo astronauts explored. The sun’s angle keeps low-lying areas in permanent darkness and bitter cold. Craters make the ground uneven and hard to navigate.

Tomlinson and his team from V2X needed to mimic this environment. So they placed huge natural and manufactured boulders at the bottom of the NBL pool. They built sloped panels into the floor. This allows astronauts to practice moving over uneven ground. The team also programmed LED lights. They simulate the movement of the sun and the region’s extreme shadows. Engineered sand mimics the lunar regolith. This layer of dusty debris covers the moon’s surface. No wind or water flows on the moon. So there’s no weathering to wear and smooth regolith particles. They tend to be jagged. Regolith can stick to surfaces and make them slippery. Astronauts must practice moving around and using tools in it, explains Tomlinson.

The V2X team has a goal. They want to make the pool environment as close as possible to the real thing. “There’s no room for surprises in an extreme environment like space,” says Tomlinson. “The realism of our simulations is directly tied to crew safety and mission success.”

While on the moon, Artemis astronauts will collect samples of rocks more ancient than the oldest ones scientists have uncovered on Earth. They also plan to study permanently shadowed areas within the crater basins, where temperatures hover around -203°C (-333°F). That’s cold enough to freeze certain gases and potentially keep them preserved for billions of years. Scientists hope these ancient rocks and gases can help them better understand the history of both the moon and Earth. Some researchers suspect that the moon may have formed when something large smashed into the young Earth, knocking off a chunk of material—which became the moon.

This exploration could require astronauts to walk on the moon for more than six hours at a time. In the NBL’s lunar environment, astronauts can practice these missions from beginning to end, simulating entire spacewalks in real time. During training, instructors can observe the crew through live video feeds and communicate through a tethered cable, helping astronauts become familiar with procedures and learn what to do if something unexpected happens.

The goal, says Wray, is to anticipate every situation the crew might encounter on the lunar surface and enable them to respond quickly. “We do everything we can to prepare them,” he says, “so that these procedures become second nature.”

On the moon, Artemis astronauts will collect samples of rocks. These are older than the oldest rocks scientists have found on Earth. They also plan to study areas with permanent shadows inside the craters. There, temperatures are around -203°C (-333°F). That’s cold enough to freeze certain gases and possibly preserve them for billions of years. Scientists want to study these ancient rocks and gases. This may help them better understand the history of both the moon and Earth. Some researchers suspect that a large object smashed into the young Earth. It knocked off a chunk of material, and that became the moon.

This exploration will take time. Astronauts might walk on the moon for more than six hours straight. In the NBL’s lunar environment, astronauts can practice these missions from beginning to end. They can simulate entire spacewalks in real time. During training, instructors can watch the crew with live video feeds. They communicate through a tethered cable. That helps astronauts learn procedures and how to handle unexpected situations.

Wray says the goal is to think of every situation the crew might find on the lunar surface. Then train them to respond quickly. “We do everything we can to prepare them,” he says, “so that these procedures become second nature.”