Explainer: Why it's so difficult to land on the moon, even five decades after Apollo

Buzz Aldrin on the moon, by the leg of the Lunar Module, Apollo II mission, July 1969.
Buzz Aldrin on the moon, by the leg of the Lunar Module, Apollo II mission, July 1969. Photo credit: Heritage Images / Getty Images

Hundreds of thousands of miles beyond Earth, a phone booth-size spacecraft has just achieved something no vehicle launched from the United States has attempted in more than 50 years.

The lunar lander called Odysseus or IM-1, created by Houston-based company Intuitive Machines, has landed the moon. The robotic explorer had to prepare for terrifying moments of uncertainty as it attempted to slow its speed by about 4026 miles per hour (1800m per second) in order to gently touch down on the moon's surface.

Success was not guaranteed. If it failed, Odysseus would have been the third lunar lander to meet a fiery demise on the moon in less than a year. Russia's first lunar lander mission in 47 years, Luna 25, failed in August 2023 when it crash-landed. Hakuto-R, a lander developed by Japan-based company Ispace, met a similar fate last April.

Overall, more than half of all lunar landing attempts have ended in failure - tough odds for a feat humanity first pulled off nearly 60 years ago.

The Soviet Union's Luna 9 became the first spacecraft to make a controlled, or 'soft', landing in February 1966. The United States followed shortly after when its robotic Surveyor 1 spacecraft touched down on the moon's surface just four months later.

Since then only three other countries - China, India and Japan - have achieved such a milestone. All three reached the moon with robotic vehicles for the first time in the 21st century. India and Japan each pulled off the monumental feat just within the past six months, long after the US-Soviet space race had petered out. The US remains the only country to have put humans on the lunar surface, most recently in 1972 with the Apollo 17 mission.

But the US government hasn't even tried for a soft landing - with or without astronauts onboard - since then. Private space company Astrobotic Technology had hoped its Peregrine lunar lander would make history after its recent January launch, but the company waved off the landing attempt mere hours after liftoff because of a critical fuel leak and brought the spacecraft back to burn up in Earth's atmosphere.

Regaining past knowledge and experience is a big part of the challenge for the US, Scott Pace, director of George Washington University's Space Policy Institute, told CNN.

"We're learning to do things that we haven't done in a long time, and what you're seeing is organizations learning how to fly again," Pace said. "Going to the moon is not a matter of just a brave or brilliant astronaut. It's a matter of entire organizations that are organized, trained, and equipped to go out there. What we're doing now is essentially rebuilding some of the expertise that we had during Apollo but lost over the last 50 years."

Technical know-how, however, is only part of the equation when it comes to landing on the moon. Most of the hurdles are financial.

A new model

At the peak of the Apollo program, NASA's budget comprised over 4 percent of all government spending. Today, the space agency's budget is one-tenth the size, accounting for only 0.4 percent of all federal spending, even as it attempts to return American astronauts to the moon under the Artemis program.

"There were literally hundreds of thousands of people working on Apollo. It was a US$100 billion program in 1960s numbers. It would be a multi-trillion-dollar program in today's dollars," said Greg Autry, director of space leadership at Arizona State University's Thunderbird School of Global Management. "There's simply nothing that compares to it."

The lunar landers of the 21st century are attempting to accomplish many of the same goals at a small fraction of the price.

India's Chandrayaan-3 lander, which became the first spacecraft from the country to safely reach the lunar surface in August 2023, cost about US$72 million, according to Jitendra Singh, the Minister of State for Science and Technology.

"The cost of Chandrayaan-3 is merely Rs 600 crore (US$72 million USD), whereas a Hollywood film on space and moon costs more than Rs 600 crore," Singh told The Economic Times, a media outlet in India, in August.

In the US, NASA is attempting to drastically reduce prices by outsourcing the design of small, robotic spacecraft to the private sector through its Commercial Lunar Payload Services program, or CLPS.

Astrobotic was the first company to fly under the CLPS initiative, and after its January setback, Intuitive Machines has picked up the torch - aiming to soft-land Odysseus near the lunar south pole on Thursday.

"We're going a thousand times further than the International Space Station," Intuitive Machines President and CEO Steve Altemus told CNN. "And then, on top of that, you set the target: Do it for $100 million when in the past it's been done for billions of dollars."

Why we can't just repeat Apollo

It's also unrealistic to expect that NASA or one of its partners could simply drag out the blueprints of a 1960s lunar lander and recreate it from scratch. Most of the technology used on those missions has long been retired, cast aside by the massive leaps in computing power and material sciences made in the past half-century.

Flight controllers gather around NASA Flight Director Glynn Lunney (seated, foreground) in the control room at what's now called Johnson Space Center in Houston during the Apollo 13 aborted lunar landing mission, on April 15, 1970.
Flight controllers gather around NASA Flight Director Glynn Lunney (seated, foreground) in the control room at what's now called Johnson Space Center in Houston during the Apollo 13 aborted lunar landing mission, on April 15, 1970. Photo credit: Space Frontiers/Archive Photos/Getty Images via CNN Newsource

Each piece of hardware on a lunar lander must be sourced from modern supply chains - which look far different than those of the 20th century - or designed and manufactured anew. And every sensor and electronic component on the spacecraft must be created to withstand the harsh environment of outer space, a process the industry calls "hardening".

The Apollo missions were famously controlled by computers less powerful than modern smartphones. But spaceflight is far too complex and dangerous to directly translate computing advancements to easier, cheaper moon missions.

"Landing on the moon is very different than programming a game. The thing about the iPhone in your pocket is that there are millions and millions of these things. Whereas with space launches, there's maybe only a handful of them," Pace said.

"The iPhone is, of course, a wonderful innovation with hundreds if not thousands of innovations buried within it, but it also benefits from just raw numbers. And so we really haven't had that kind of repetition in lunar landings."

A perilous descent

And while technology has advanced in the past five decades, the fundamental challenges of landing on the moon remain the same. First, there is the sheer distance - it's roughly a quarter of a million-mile (402,000km) journey from Earth to the moon. If you could drive a car to the moon at a constant speed of 60 miles per hour (97km/h), it would take more than five months.

"Some people have likened it to hitting a golf ball in New York and having it go into a specific hole in Los Angeles. That kind of precision in long distance is unbelievably difficult to do," Pace said.

Then, there is the tricky lunar terrain. The moon is covered in dead volcanoes and deep craters, making it difficult to find flat landing zones.

"Apollo 11 would absolutely have crashed and been destroyed if it had landed on the spot it originally came down on," Autry said. "Neil (Armstrong) was literally looking out the window. He maneuvered the lander over a boulder field and a big crater and found a safe spot to land with just barely enough fuel left. If there wasn't a skilled pilot that could control it, the lander certainly would have wrecked."

Without the assistance of human eyes inside the spacecraft, modern-day robotic lunar landers use cameras, computers, and sensors equipped with software and artificial intelligence to safely find their landing spot - and avoid boulders and craters - during the final descent. And even humans in mission control rooms back on Earth can't help the spacecraft in those final, critical seconds before touchdown.

"It takes time for a signal to go up and come back, about three seconds total round trip," Pace said. "A lot can go wrong in that time. So when the vehicle is actually landing, it's pretty much on its own."

Failure is an option

In the early days of the 20th century space race, far more spacecraft failed than safely touched down on the moon. The companies and governments dashing for the moon today - aiming for cheaper price points as they implement modern technology - acknowledge that legacy.

And NASA's commercial partners may be even more willing to embrace risks as they take their moonshots.

"(Commercial companies) brought that iterative, fail fast model with them. Get the product out there, let it blow up, figure out what you did wrong, fix it, and go again," Autry said. "That is not the way the US government operates. Because if your project dies, your government career is screwed."

For its part, even NASA recognizes that a 100 percent success rate is not guaranteed for its partners.

"We've always viewed these initial CLPS deliveries as being kind of a learning experience," said Joel Kearns, the deputy associate administrator for NASA's exploration, science mission directorate, during a February 13 briefing. "We knew going into this … we didn't believe that success was assured."

The hope, however, is that failures early on will lead to repeatable successes down the road. It's already clear many of the modern moon race participants are prepared to bounce back from their initial failures.

Both Ispace - the Japanese company that encountered a mission-ending software glitch last year - and Astrobotic, which lost its Peregrine lander to a propellant issue, have second attempts already in the works.

"Everybody on those missions was a rookie. These are people doing it for the first time and there's no substitute for that experience. It's like taking your first solo flight," Pace said. "Yes, they're failing, and some companies will go out of business. But if they learn from that failure and come back, now you're going to have a strong team. This is really about educating a new generation."