Like throwing a dart and hitting the bullseye on a moving target in the next city over: that’s what it’s like trying to land a spacecraft on the moon. With an inhospitable surface of steep craters and inconvenient boulders, there are no landing pads, no GPS, no air traffic control, and no one to help if things go wrong.
This weekend, Firefly Aerospace will attempt to defy the odds and land its Blue Ghost spacecraft safely on the moon’s surface, touching down in the Mare Crisium region on the moon’s near side.
Only one other private company has ever successfully landed on the moon, and that landing was no cakewalk: the Intuitive Machines Odysseus lander caught a leg on the moon’s rough surface as it came down and ended up landing on its side, limiting its lifespan.
So the pressure is on for the Firefly team, who are aiming for a picture-perfect soft landing on Sunday — and we spoke to a member of that team to hear about how they’re hoping to pull it off.
Kevin Scholtes is Firefly’s Future Systems Architect, which means his job is to look to problems of the future. “I like to tell people that my job is to be perpetually dissatisfied with where we are, and pushing us to go further,” he told Digital Trends.
He and his colleagues are hotly anticipating this weekend’s landing attempt, waiting to see if their years of hard work have equipped their beloved lander to tackle the many challenges that landing on the moon has to offer.
“Everyone is definitely on pins and needles in anticipation of what’s gonna happen,” he said.
Trusting the engineering
Of all the scary things about trying to land on an object more than 200,000 miles away is that you can’t control a lunar spacecraft manually. Once the landing process begins, the spacecraft has to navigate itself — which is why the Japanese space agency referred to this period as the 20 minutes of terror.
“Once we commit to descent, then at that point it’s fully autonomous,” Scholtes explained. Because of the distance to the moon and the limitations of the speed of light, there’s an inevitable communications delay of a few seconds between Earth and the spacecraft.
“So it’s not even possible to do real time commanding and communication with the lander. So we’re trusting the engineering. We’re trusting the analysis. We’re trusting the guidance and the navigation on board the vehicle. We’re very conscious that we’ve made the decision to commit, and we’re going to see that through to the end.”
Looking out the window
Humanity might have successfully landed on the moon over 50 years ago, but don’t be fooled into thinking a lunar landing is easy.
“Counterintuitively, one of the biggest challenges about doing this is simply knowing where you are,” Scholtes said.
Without the benefit of GPS to give accurate positioning, or astronauts on board to look out the window, a spacecraft must slow itself from traveling at a mile per second to an eventual landing speed of just one meter per second, and accurately calculate its own location with meter-level accuracy.
“That can be terrifying because we have to generate all of that internally,” Scholtes explained. “We have to do that the way that a pilot would do that, by visually looking out the window, so to speak, and saying, I recognize those features and I can tell approximately how fast I’m going based on that.”
Recognizing those features isn’t easy either, because the moon’s surface is covered in craters both large and small. These look similar from different altitudes, which makes it hard to know if you’re seeing a large crater up close, or a small crater from further away.
“A hundred kilometers up, one kilometer up, or 10 meters up — when you look at the surface, you see craters,” Scholtes explained.
That means that even with ideal navigational data, it’s still hard to tell how far away the surface is as you get closer to it.
“Make no make no mistake,” Scholtes said, “landing on the moon is an incredibly difficult challenge.”
Picking the perfect spot
With modern technology and cameras on spacecraft like NASA’s Lunar Reconnaissance Orbiter, we’re lucky to have impressive imagery of the moon’s surface captured from orbit. And that imagery is invaluable for picking a landing site, but at a resolution of a few meters per pixel, images can’t show all of the hazards that a lander needs to avoid.
“That’s a pretty low resolution for detecting a big rock that you’re about to land on,” Scholtes said.
There is an advantage of the lunar environment though, which is that its lack of atmosphere means that there are no winds and no motion, so there aren’t any objects like clouds which cast shadows on the surface. That static environment means that if you know where the sun is, then the length of a shadow gives you a very good idea of how large an obstacle is.
So Blue Ghost is equipped with a technology called terrain relative navigation, which uses a camera mounted to the underside of the spacecraft to take images of the terrain below, and matches these to an onboard map of the surface. This kind of navigation has only recently become possible thanks to advances in computer processing, which allows an onboard computer to rapidly compare images coming in to its internal map.
“We synthesize what the moon is supposed to look like,” using the onboard computer, Scholtes explained, “and essentially do a comparison between that and what the cameras are showing us.”
Differences between the onboard map and the actual camera images can tell the spacecraft how fast it is travelling and its orientation, and that lets the system figure out where exactly the lander is.
Then a second system called hazard avoidance can use the same camera data to highlight any potential dangers like boulders or craters, creating hazard maps which show which areas are potentially dangerous to attempt a landing in, and which are safer.
Crushable honeycombs
Along with a method for calculating distance from a surface using lasers, called laser altimetry, and data on relative altitude and acceleration collected by onboard sensors, these systems can figure out where the spacecraft is relative to the surface and help set it down gently.
If the spacecraft does come in faster than expected though, it has one last trick up its sleeve: its legs contain a crushable honeycomb core material which can crumple and absorb impacts like the crumple zones on a car.
Sensors on the lander’s feet indicate when they have made contact with solid ground and send a cutoff signal to the engine — at which point, hopefully, the lander is standing safely upright on the moon’s surface and ready to begin its operations.
Race to the moon
Blue Ghost is just one of the private moon missions currently underway. In addition to Firefly’s lander, two other lunar landers are currently on their way to the moon, with another set to launch next year.
But that doesn’t mean there’s negative feelings between the competing companies. Rather, Scholtes said, they were hoping for success for all.
“We’re very encouraging of each other,” he said. “We’re very much rooting for Intuitive Machines, we’re rooting for ispace and Astrobotic. We really want to see them successful — partially for the reason that their success is our success. What we really want to do is to inspire American taxpayers and people around the globe that the moon is worthy of going back to.”
The companies do share information and several are part of a NASA program called Commercial Lunar Payload Services, or CLPS. But each company takes its own direction and makes its own decisions, with the hope of finding which approach works best.
For now, “we’re trying to focus on successfully sticking the landing for us,” Scholtes said, “and then hopefully getting a good friend on the other side of the moon sticking their landing shortly thereafter.”
This weekend, everyone will be keeping their fingers crossed in anticipation of this ambitious feat, which has taken years of preparation and work. “Everything about the process is quite frankly terrifying,” Scholtes said. “It’s a terrifying and incredibly audacious thing to attempt.”
