Why is it so hard to land on the moon?

Why is it so hard to land a spacecraft on the moon? And why are we struggling now when we did it in the 1960s and 70s with Apollo?

This is a really good question that a lot of people have been asking in the wake of Intuitive Machines’ moon lander Odysseus falling over after its soft landing. And it’s a good question. II absolutely understand that it seems ridiculous that it’s so hard to land on the moon when we were able to do it half a century ago.

The key issue here is that the physics of landing on the moon hasn’t changed. Yes it’s moved 80 inches (207 cm) away from us in the last 50 years, but generally speaking, the moon is the same. But the way we are doing it, where we’re going on the moon, the goals behind it, and the reasons we’re doing it are very different. And that’s why we’re having to redo all of this and it feels like NASA is starting from scratch.

It’s important to note that landing on the moon has always been hard. It was hard back then, and that hasn’t changed now. 

The moon’s atmosphere (or lack thereof)

Let’s start with the moon’s laughable atmosphere. The moon has what we call an exosphere, it’s extremely thin and the molecules are so spread out, they barely interact with one another. For the purposes of landing on the moon, let’s just say it has absolutely nothing. There is NO atmospheric drag to slow your spacecraft on the way down.

I’m going to use Apollo as an example because we’re going to talk about that a lot. The Apollo capsules didn’t have any engines on re-entry to Earth. The capsule just turned its blunt side into the atmosphere and used its ablative heat shield, which burned off in the heat of re-entry, to slow it down.

Earth’s atmosphere serves as a natural braking system. When the capsule passed through the outer atmosphere safely, the three parachutes deployed, and the spacecraft touched down gently in the ocean. For reference, Apollo 11 re-entered Earth’s atmosphere at almost 24,000 miles per hour (about 38 and a half thousand km per hour) and splashed down at probably 10-15 miles per hour (16-24 kph). (The video below is the re-entry of Apollo 15, taken from the command module.)

In comparison, Intuitive Machines had to slow their spacecraft down with just engines from 25,000 miles per hour (40,000 KM) to 6 miles per hour (about 9 kph). And you have to take the fuel with you. Yes, the moon has 1/6 of Earth’s gravity so there’s less pull on the spacecraft, but when you’re going that fast it doesn’t make a huge difference. You HAVE to slow down, and all you have are engines.

The lunar surface is a nightmare

The terrain of the moon is also a mess. It doesn’t have nice oceans to gently splash down in. It’s rocks and craters and regolith, or lunar dust, that gets everywhere. Not to mention the lunar south pole is a VERY different place than the landing sites of Apollo which were in brilliant sunlight. 

The lunar south pole is where we think the moon’s water ice is, a valuable resource if we want to stay there permanently. That’s why the Artemis missions are targeted towards that area. But there are permanently shadowed craters that may be the coldest places in the solar system. There are long shadows because the sun never rises over the horizon. That means you have to worry a lot about the orientation of solar panels and it makes it harder to see your landing site.

And there’s no GPS on the moon to be able to pinpoint where you are. You have to rely on the spacecraft’s computers to calculate exactly how much fuel to use and how long to burn the engine based on, and that presumes it can figure out exactly where the spacecraft is and what the terrain is like. And that doesn’t even bring into the discussion the fact that communications when you’re in orbit of the moon, and at the lunar south pole, aren’t necessarily reliable.

But still, we were able to do it 50 years ago, with less advanced technology. So what’s going on?

We’re not dumber than we were then. There are a few really good reasons we struggle now when we were able to do it before.

Astronauts on board makes a big difference

One of the big this is unlike in Apollo, robotic landers don’t have astronauts on board to make corrections in real time.

For example, during Apollo 11, on the way down to the moon’s surface, the LM, lunar module’s guidance computer threw a master alarm. Basically, the computer was overloaded and it couldn’t focus on the things it needed to for descent and landing because the rendezvous radar had been left on. Because of a programming error, the computer couldn’t process both the updates from that radar and descent and landing. It kept kicking back errors and rebooting. 

Obviously, the astronauts ended up proceeding with descent — but if it had been a fully robotic lander using algorithms and auto navigation, it’s very possible that the landing would have been aborted. But even after that, the auto navigation identified a crater as a safe landing site, and Neil Armstrong expended extra fuel to navigate away from it and land somewhere he thought was safer.

If that had been a robotic lander, without an astronauts on board, the landing might not have taken place. The lander might have crashed. It might have landed on the side of a crater and fallen over. Having astronauts on board to do the piloting and correct errors in real time makes a huge difference. 

The money question

There’s also money. At the peak of the Apollo program, NASA’s budget was 4 percent of the entire federal budget. The United States spent around $25.8 billion on the Apollo program. Adjusted for inflation, that’s around $257 billion today, according to The Planetary Society. In addition to that, the US spent $907 million on their robotic lunar program, which would be around $10 billion today.

NASA paid Intuitive Machines, a company with about 250 employees, $118 million for IM-1. They spent about $100 million of their own money as well. It’s easy to accomplish a Moonshot when you have all the money you need to get it done. It’s significantly harder when you don’t. 

Apollo was a huge risk. Astronauts died, literally, because of bad judgment calls and mistakes. But NASA had the money to test, test, and test again. They also had the money to build redundancies into every system they could. Sure, there were some things that couldn’t be tested: the LM’s ascent engine had been fired in space and around the moon, but on Apollo 11, if it didn’t fire on the surface, that was it. Neil Armstrong and Buzz Aldrin would have died on the moon. (To be clear, the ascent engine was designed as simply as possible to prevent this from happening.)

It seems unreal to think of it now, but the amount of testing they did of every component was very careful and intentional. And they had the money for it. 

I just can’t emphasize enough how much Apollo succeeded because of governmental and public support and money, even through failure and adversity. Neil Armstrong and Dave Scott almost died on Gemini VIII trying to test rendezvous and docking procedures because a thruster was stuck in the open position. So we tried again with Gemini IX and accomplished the mission.

Why we went to the moon with Apollo

The thing is, the support (and money) started tapering away after we landed because there was an appetite for Apollo as long as we were trying to beat the Russians to the moon. People—NASA internally, but also the general public—were willing to tolerate a lot more risk because we wanted to beat the Soviet Union. It was not about space exploration or science, it was about triumphing over communism. That’s why Apollo had so much support (and why, after we accomplished a few landings we haven’t been back to the moon in 55 years), but also we can’t do things now like we did during Apollo because we have higher safety standards and less tolerance for risk. 

Apollo failed many times before it succeeded. Three astronauts died in a fire when the rocket was on the launch pad during a routine test before Apollo ever got off the ground. 

There were so many failures, so much human error, so many mistakes, so much miscalculation and things going wrong. But also, we powered through and did the thing. We made it to the moon.

Now, if you look at Artemis, which is NASA’s program to go back to the moon’s surface, NASA is getting criticized from every angle. People say we don’t need to explore space. People say the money should be spent closer to home. People say it’s too expensive. People don’t like that NASA is partnering with private companies like SpaceX and Astrobotic and Intuitive Machines, and often people are saying those two things in the same sentence (that it’s too expensive and it shouldn’t involve commercial spaceflight) when one of the reasons NASA is partnering with these private companies is to keep costs down. Yeah, NASA did it all in-house and it was astronomically expensive during Apollo, and they’re doing some of it differently this time. 

And also to be frank, NASA has a ton more bureaucracy now than they did during the 1960s and 70s. That certainly doesn’t make matters any easier, nor does the fact that we took so long to go back that we lost a lot of generational knowledge of how we did it. So yeah, the technology is better, and we’ve already been there, but in some ways, we’re having to learn things all over again.

One key thing here is we’re not just trying to go there, walk around, maybe drive a car for a day or two, and then come home. Apollo was about getting there first. Artemis, and the CLPS program, which Intuitive Machines is part of, is about staying on the moon. That’s a key issue here. 

The challenge is just different. Yes we went to the moon successfully. Now we’re trying to build infrastructure there so we can explore the rest of the solar system. That means making delivery of payloads to the moon sustainable, which is why the CLPS initiative, which is NASA partnering with private companies to put stuff on the moon’s surface, exists.

And the end of the day, as I said at the beginning of the video, it’s complicated. I think it’s absolutely fair to wonder why this is so hard, when we’ve done it before, but I hope I shed some light on what really is going on.