Why Are Astronauts Making Daring Flights Through the Mountains?

Flying helicopters on Earth is a strong foundation for landing spacecraft on the moon.

Neil Armstrong was only 500 feet above the moon’s surface when he realized that he had a problem: the landing site, which had been selected by his onboard computer, was strewn with large boulders. With minutes to spare, he switched to semi-automatic control of the Eagle lunar lander, tilted the craft slightly forward, and coasted over the rocks to identify, by eye, a safe place to touch down. 

Armstrong attributed his safe landing to the hours he had spent flying NASA’s lunar landing research vehicle (LLRV) and its successor, the lunar landing training vehicle (LLTV). The vehicle had been an unwieldy open-cockpit, four-legged contraption the astronauts had nicknamed the “flying bedstead.” 

“I had made from 50 to 60 landings in the trainer, and the final trajectory I flew to the landing was very much like those flown in practice,” Armstrong later said. “That of course gave me a good deal of confidence—a comfortable familiarity.”

Still, NASA opted to ground the trainers after the Apollo program ended. The vehicles were notoriously difficult and dangerous to fly. Of the five built, three were destroyed in crashes, including one flown by Armstrong, who was forced to eject at the last moment (he landed safely via parachute). 

Today, the NASA astronauts training for the Artemis missions to land on the surface of the moon face their own challenges. This new generation of astronauts will be landing at the lunar South Pole, which is a region that offers exceptional opportunities for conducting scientific research and establishing a sustained presence on the moon. Notably, the South Pole is believed to have abundant water ice trapped in its permanently shadowed regions—water that could be broken down into its components to produce oxygen for breathing and hydrogen for rocket fuel. And, because of the moon’s tilt, certain ridges at the South Pole receive near-continuous sunlight, which is ideal for sustained solar power.

But the same terrain that makes the region attractive for exploration also poses multiple risks for the astronauts landing there. Although the Apollo astronauts explored flat, equatorial plains, the Artemis astronauts will have to navigate a rugged highland defined by mountains as high as 19,700 feet—along with deep impact craters—and a lighting environment that creates optical illusions and hazards. Since the sun never rises more than a few degrees above the horizon at the pole, the view will look like perpetual sunset. As such, the shadows are incredibly long: a boulder only 0.5 meters high (large enough to pose a hazard to landing gear but still difficult to see from orbit) can cast a shadow 20 meters long. These shadows not only impede size perception, they can also shroud landing hazards (craters or other rocks) in darkness.

That’s why, for hands-on experience prior to mission liftoff, astronauts are training to land on the lunar surface by piloting high-altitude helicopters in the snow-covered terrains of Colorado and the German Alps. This training helps the astronauts build proficiency in landing in environments that demand precision and adaptability. 

Back in the day, the Apollo astronauts also had some helicopter training. In fact, it was a prerequisite for being selected for LLTV training. “For airborne craft, the helicopter was the closest in terms of characteristics to the lunar lander,” said former Apollo astronaut Curt Michel in a 2009 interview. “So, if you didn’t get helicopter training, you knew you weren’t going. That sort of gave it away.”

But today’s helicopter training is more focused on preparing astronauts for the dynamics of planetary landings, which require capabilities such as vertical takeoff and landing, terrain-based decision-making, and high levels of situational awareness. 

Flying a helicopter closely mirrors these phases of a mission in space. Like Armstrong before them, the Artemis astronauts will spend weeks preparing for the crucial few minutes when they will execute one of the most perilous maneuvers in space exploration: landing a spaceship on the moon. 

Steep landings

In 1960, scientists knew that the moon had one-sixth the Earth’s gravity, no atmosphere, and a surface covered by a layer of lunar dust that some researchers believed might be thick enough to swallow an entire lander. 

“There was this clear recognition that to land on the lunar surface would be to land in an entirely alien environment, and that there would be numerous unknowns about that process that they would need to try to address through training,” says Teasel Muir-Harmony, a historian of science and technology and the curator of the National Air and Space Museum’s Apollo collection. “It quickly became apparent to the group that different aspects of the landing could be simulated individually but not simulated in their entirety. The Apollo landings required a whole system of different types of simulators and approaches to try to create that experience on Earth before the astronauts went to the moon. Helicopters were one of the technologies that they thought would be useful for training. A ground-based simulator was another, and there was also the idea of tethering a lunar lander to test free-flying techniques.”

“People realized at the outset that the hardest part of the entire Apollo mission was going to be the actual landing on the moon,” says Andrew Chaikin, author of A Man on the Moon: The Voyages of the Apollo Astronauts.“Helicopters were valuable to familiarize an astronaut with the lunar lander’s descent trajectory and the fact that, to change direction or forward or sideways speed, you had to tilt the entire vehicle. But the fact that a helicopter utilizes aerodynamics and flies in Earth’s gravity meant that it couldn’t precisely duplicate the lunar module’s flying characteristics in a vacuum and in the moon’s one-sixth gravity.”

Still, Bob Gilruth, the first director of the Manned Spacecraft Center (now the Lyndon B. Johnson Space Center), was worried that use of the LLTVs would cause a fatality, and he wanted to end the risky training. Armstrong and Pete Conrad, however, were unequivocal in their support for continuing to use the trainer. “Conrad told Gilruth that NASA was banking the whole program on a fellow not making a mistake on his first landing, and that meant that you needed the LLTV,” says Chaikin. “Conrad said that if he were to go back to the moon, he personally would want to fly the LLTV again as close to flight time as practical.” 

The Apollo astronauts favored the unwieldy LLTV because it bridged the gap between the theoretical understanding of lunar conditions and the physical reality of landing a spacecraft in a vacuum under low gravity. The LLTV used a centrally mounted turbofan engine that was set to constantly support roughly 80 percent of the vehicle’s weight, effectively canceling out much of Earth’s gravity. The remaining 20 percent of the weight was controlled by the pilot using hydrogen peroxide lift rockets, which simulated how the lunar module would feel as it descended to the moon’s surface. 

As such, the LLTV forced astronauts to fly purely on thrust. If they tilted the vehicle to move forward, it wouldn’t fly forward like a helicopter; it would drift. To stop, they had to tilt backward and fire the thrusters again to cancel the momentum. And, despite the trainer’s flaws, “it gave the astronauts the confidence to know that during the descent, if they had to, they could move to a different landing point, particularly when they were flying semi-manually at a low altitude,” says Chaikin.

Such practical experience was all the more necessary given that NASA’s ground simulators relied on digital technology that was still in its infancy. Visual systems for simulators relied on cameras traversing physical scale models of the lunar surface, and these systems lacked the depth perception and response times required to simulate the final lunar descent.

And, from the perspective of the astronauts preparing to land on another world for the first time in history, the danger of flying the LLTV was one of its most valuable assets. The knowledge that a single mistake could be fatal forced a level of focus that a safe, indoor simulator never could—the feeling that military pilots refer to as the “pucker factor.” 

But a training vehicle with an attrition rate of 60 percent was not destined to be a viable option for today’s Artemis astronauts. The space shuttle tragedies of Challenger and Columbia have pushed NASA from a posture of risk acceptance to risk management. In fact, the risks of flying a vehicle like the 20th-century LLTV nowadays would be higher than the risks of flying a 21st-century lander, which has digital technology that can stabilize a spacecraft and control its hovering. 

Managing risk is the thinking that led NASA to partner with the Colorado Army National Guard at the High-Altitude Army National Guard Aviation Training Site near Gypsum, Colorado, to develop a specialized flight course—Zero to Helo—that places astronauts in a demanding environment with real world consequences, but without the extreme mechanical risk of the lunar landing training vehicle.

A helicopter’s aerodynamics differ from a moon lander, but the goal of the program isn’t to replicate lunar physics. Instead, it replicates the operational constraints of a lunar landing. When operating at altitudes as high as 14,000 feet, for instance, helicopter rotor blades generate less lift. This phenomenon forces pilots to operate within extremely thin power margins—the difference between the power required to hover and the maximum power available. This tight margin mimics the demands of flying a lunar lander, which has a finite supply of propellant and limited thrust-to-weight margins.   

Meanwhile, the sometimes snow-covered terrain of the Rocky Mountains and the German Alps mimics the lack of visual depth cues found at the moon’s South Pole. Flying their helicopters, astronauts must identify landing zones and commit to them or abort, which simulates the psychological pressure of a one-shot landing profile on the moon.

Lieutenant Colonel Kai Eggert, the designated project officer of the German Army Helicopter Command for the support of the European Space Agency, is the designer of Germany’s version of the Zero to Helo course. “We’ve been given a curriculum from NASA, and we transferred it and adapted it to our capabilities,” says Eggert. “We started off with a little bit of theory—okay, we’re talking to scientists and all this theoretical background was very easy to transfer. Then we went into the simulator and focused on building up their ability to manually control the helicopter, particularly for stabilized hovering. From there, we expanded this training to include a very easy flight pattern, and lastly the landing phase, which was the focus of our training for the astronauts. This included some flying in our specially created moon-like simulation.”

In the second week, the instructors and astronauts started flying in Eurocopter EC135s over central Germany. “We were really overwhelmed by their speed of learning,” says Eggert. “They progressed amazingly quickly and flew in the real training aircraft earlier than we expected.” The third week of training was spent flying over the glaciers, deep valleys, and high peaks of the German Alps near the border with Austria. The highest mountain is the Zugspitze, which has an elevation of 9,718 feet. 

Whether landing in the Alps or at the lunar South Pole, astronauts can experience the loss of their horizon line, as well as believing they are landing on a slope when in fact the ground is flat. The optical distortions that can be caused by ascending and descending slopes can create a false reality. The distortions can also make it appear to the astronauts that they are coming in to land at their target site too high or too low.  Says Eggert: “That is the experience that we want to provide them with by practicing landings in small areas, on very uneven and rocky terrain, or on sloping ground, especially in mountainous areas where they must deal with a lot of visual illusions and distractions.”

Zero to Helo

Flying a helicopter was completely new to European Space Agency astronaut Alexander Gerst. Until, that is, last September, when the German geophysicist, Antarctic explorer, and astronaut—and apparently the inspiration for a character in the 2015 film The Martian—found himself in the three-week training course at the International Helicopter Training Center in Bückeburg, Germany. Two hundred miles west of Berlin, among the rolling woodland and historic villages of Lower Saxony, the training center is the primary facility for instructing German military helicopter pilots. 

“I’m a fixed-wing pilot, so I know how to fly in general,” says Gerst, who has completed two six-month tours of duty on the International Space Station, becoming the youngest station commander in its history. “At first, in a simulator, I was drifting everywhere, and I couldn’t maintain my height. But by the end of the first week, I felt I had the simulator nailed. Still, I knew that the real vehicle would behave very differently.”

The instructors threw Gerst into the proverbial deep end, requiring him to land in small forest clearings and narrow mountain gorges. “In what they called Dead Man’s Gorge, there was a rock wall to the left, a rock wall to the right,” says Gerst. “I had to ask my instructor what the clearance was on the left, and he said, ‘Oh yeah, you’re good. You have five meters.’ I looked to the right, and then there were also five meters, and I thought, ‘Okay, wow. You trust me to do that?’ But I managed that landing, and it felt like, ‘Okay, I got this under control.’ ”

The challenges Gerst faced inside the helicopter cockpit grew harder still. “We had to fly high into the mountains to this glacier field and then land on a rock that looked like a pebble, and I thought, ‘You’ve got to be kidding me, it’s not possible,’ ” he says. “But the instructor just said, ‘let’s try it,’ and in the end, I realized, wow, that the pebble was a three-by-three meters rock, and just about big enough to put my skids down. By then, I couldn’t see the rock my helicopter was standing on anymore. All I could see was 15 meters of nothing below.”

Then there was the snow. Subjected to the downwash from a helicopter’s rotor blades during landing, snow behaves like lunar dust—degrading the visual environment for pilots and obscuring vital points of reference. 

“If you look at the recordings from some of the lunar landings, the astronaut who sat on the right of the lander saw the dust beneath him drifting to the right, and said, ‘Oh, I think we’re moving to the left,’ ” says Gerst. “And the guy who sat on the left saw it the other way around, and said, ‘I think we’re moving to the right.’ Our instructors had us put a skid down on a slope and just hover the helicopter there until we couldn’t see the horizon anymore. We wanted to fly away from where our brain thought the mountain should be. We had to train ourselves not to do this because potentially it could be a critical mistake for the mission.” In such a compromised visual environment, astronauts might not even be aware that their lander is tipping over, which could prove deadly. 

“What I found amazing was the confidence level they had built into us to control this two-and-a-half-ton machine with centimeter precision in just three weeks,” says Gerst.

The European Space Agency astronauts who complete the course qualify for advanced training in Colorado, where three different types of helicopters are used: the Airbus LUH-72 Lakota, the Boeing CH-47 Chinook, and the Sikorsky UH-60 Black Hawk. The Lakota, a light utility helicopter, enables astronauts to get a feel for power management without the complexity of a larger airframe. 

By contrast, the massive Chinook is a heavy-lift, tandem-rotor helicopter with high inertia: It takes a long time to get it moving and a long time to stop it. High inertia trains astronauts to “fly ahead of the aircraft,” anticipating maneuvers well in advance, which is critical when piloting a complex lunar lander.

The versatile Black Hawk, a medium-lift utility helicopter, is used in intermediate training for tricky approach paths. Astronauts fly both the Chinook and Black Hawk to practice landing on steep ridgelines and slopes that are similar to the landing zones at the lunar South Pole, which are riddled with craters and uneven terrain.

It isn’t exactly the same. Says Gerst: “While helicopters were valuable to understand the lunar lander’s trajectories, visual fields, rates of motion, and the flight paths you wanted to make, helicopter aerodynamics precluded NASA from exactly duplicating the lunar module’s characteristics.”

Still, Eggert believes the training is invaluable, not just in terms of what the astronauts learn, but in how they feel. “You then have to see the training in a more general way,” he says. “What we provide are experiences. It all comes down to their experience, especially in the mountainous areas they are forced into, that they have never been in before, that they must deal with, apply procedures to, and deal with aspects of fear. Our job is to make sure that they are not encountering this for the first time upon the approach to the moon.”

Alexander Gerst is now ready to go.

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Mark Piesing is an award-winning aviation journalist. He is the author of N-4 Down: The Hunt for the Arctic Airship Italia (Mariner Books, 2021).

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This article, originally titled "Astronauts in the Alps," is from the Spring 2026 issue of Air & Space Quarterly, the National Air and Space Museum's signature magazine that explores topics in aviation and space, from the earliest moments of flight to today. Explore the full issue.

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