Why landing a NASA spacecraft on the moon is still so difficult

Only about 1,600 feet above the lunar surface, Neil Armstrong took control of the Apollo lunar lander. The starship’s computer had directed the crew to a boulder-strewn field, forcing the legendary pilot to make a quick distraction. Meanwhile, erroneous alarms sounded in the module and an indicator showed they were about to run out of fuel.

Luckily, in the summer of 1969, Armstrong and Buzz Aldrin landed and walked on the moon. Five more Apollo missions would land on the lunar surface in quick succession over the next few years. Now, half a century later, NASA aims to return astronauts to the moon soon, potentially as early as 2025. The space agency recently successfully launched its powerful new rocket, the Space Launch System, and in a crucial test mission, an unmanned Orion spacecraft orbits the moon before returning safely to earth.

However, landing humans and robots on the moon still remains an extremely ambitious task.

“Just because we went there 50 years ago, it’s not a trivial undertaking,” Csaba Palotai, program director for space science in the Department of Aerospace, Physics and Space Sciences at the Florida Institute of Technology, told Mashable.

(It was not until 2023, for example, that an unmanned Japanese lander and the unmanned Russian Luna-25 spacecraft crashed on the moon.)

“It’s challenging – like a lot of what we do.”

NASA has already commissioned space exploration company SpaceX to build its first lunar lander, and in 2022 asked other companies to propose more landers. Whatever spacecraft eventually land on the moon will face daunting but surmountable challenges.

“It’s challenging — like a lot of what we do,” Tom Percy, a senior human landing system engineer at NASA’s Marshall Space Flight Center, told Mashable.

NASA astronaut Buzz Aldrin stands in front of the Apollo 11 Lunar Module in 1969.
Photo Credit: NASA/JSC

The moon has practically no atmosphere

When spacecraft land on Earth, they use the atmosphere to slow down, as we’ve seen with the return of space shuttles and Apollo capsules. But the moon’s atmosphere is extremely thin, comparable to the outermost edges of Earth’s atmosphere where the International Space Station orbits. This means that the slowdown depends on amounts of fuel being fired.

“There’s no atmosphere, so we can’t float down,” Palotai explained. “Nothing slows you down but your engine.”

Crucially, this gives the astronauts less room for error. Fuel is limited. NASA provides enough fuel to handle the unexpected — like a critical flight fix — Percy said. But the mission generally cannot afford major glitches.

“It’s literally a one-time thing,” Palotai said.

An artist’s conception of an Artemis astronaut stepping onto the lunar surface.
Photo credit: NASA

No GPS on the moon

On Earth, airplanes rely on GPS, the US government-operated satellite navigation system, to provide precise landing coordinates as planes and other spacecraft move through the sky. But there is no such satellite network orbiting the moon.

“GPS doesn’t work on the moon,” NASA’s Percy said.

So, in general, NASA still has to navigate as it did on the Apollo missions over fifty years ago. They will rely on the lunar lander’s computers to calculate how the spacecraft must fire thrusters to stay on course for a specific landing point on the moon. Importantly, astronauts like Neil Armstrong have the ability to take control of the spacecraft if the system goes wrong.

But today’s astronauts will have significantly more help on their final approach. This advanced technology, called “Terrain Relative Navigation,” uses a camera to map the ground during descent. This ensures that the astronauts get to the right place and the lander can avoid craters or boulders.

Accidentally landing on a boulder could be disastrous. “There’s a pretty good chance you’re having a bad day,” Percy said.

An example from an aerial photograph of the Mohave Desert of how NASA’s “terrain relative navigation” will work on the moon. The technology compares camera images with known satellite images of the lunar surface.
Photo Credit: Draper/NASA

The south pole of the moon is a strange, shadowy place

Apollo astronauts landed on the moon’s bright, sunlit side. But for NASA’s new moon effort, a mission called Artemis, astronauts will land in a crater at the moon’s south pole. Planetary scientists suspect that ice and other valuable resources reside in this deeply cold, dark region.

The sun never goes over us there. It is always near the horizon and can cast long shadows across the ground. These shadows distort the view of what is underneath when they land. “The long shadows make it difficult to see what the surface looks like,” Percy noted. “It’s especially challenging when you’re trying to land.”

“It’s going to be a very different environment than what astronauts experienced at Apollo,” Percy added.

In preparation for astronaut training, divers at NASA’s Johnson Space Center simulate the dark environment at the moon’s south pole.
Photo Credit: NASA/Johnson Space Center

NASA astronauts have walked and driven on the moon. But that was a long time ago. Our journey to and exploration of the moon is still in its infancy. Eventually NASA plans to colonize our satellite covered in limestone and craters. “We’re still in the early stages of lunar exploration,” Palotai said.

“We’re still in the early stages of lunar exploration.”

Therefore, landing on shady ground is not easy without GPS or the help of an atmosphere. But the space agency is gearing up for a steady series of annual moon landings, scheduled to begin around 2027. These ventures, beginning with a thunderous blast off the Florida coast, will undoubtedly captivate the world, as did the successful Apollo missions.

“Apollo inspired a generation of people to do something in science,” Palotai marveled. “I think this will have a similar boost.”

This article has been updated with information on recent moon landing attempts.