Here’s the secret to how Firefly was able to nail its first lunar landing

Darkness fell over Mare Crisium, ending a daily dose of dazzling images from the Moon.

Firefly Aerospace's Blue Ghost science station accomplished a lot on the Moon in the last two weeks. Among other things, its instruments drilled into the Moon's surface, tested an extraterrestrial vacuum cleaner, and showed that future missions could use GPS navigation signals to navigate on the lunar surface.

These are all important achievements, gathering data that could shed light on the Moon's formation and evolution, demonstrating new ways of collecting samples on other planets, and revealing the remarkable reach of the US military's GPS satellite network.

But the pièce de résistance for Firefly's first Moon mission might be the daily dose of imagery that streamed down from the Blue Ghost spacecraft. A suite of cameras recorded the cloud of dust created as the lander's engine plume blew away the uppermost layer of lunar soil as it touched down March 2 in Mare Crisium, or the Sea of Crises. This location is in a flat basin situated on the upper right quadrant of the side of the Moon always facing the Earth.

Other images from Firefly's lander showed the craft shooting tethered electrodes out onto the lunar surface, like a baseball outfielder trying to throw out a runner at home plate. Firefly's cameras also showed the lander's drill as it began to probe several meters into the Moon's crust.

The first Blue Ghost mission is part of NASA's Commercial Lunar Payload Services (CLPS) program established in 2018 to partner with US companies for cargo transportation to the Moon. Firefly is one of 13 companies eligible to compete for CLPS missions, precursors to future astronaut landings on the Moon under NASA's Artemis program.

Now, Firefly finds itself at the top of the pack of firms seeking to gain a foothold at the Moon.

Blue Ghost landed just after sunrise at Mare Crisium, an event shown in the blow video captured with four cameras mounted on the lander to observe how its engine plume interacted with loose soil on the lunar surface. The information will be useful as NASA plans to land astronauts on the Moon in the coming years.

“Although the data is still preliminary, the 3,000-plus images we captured appear to contain exactly the type of information we were hoping for in order to better understand plume-surface interaction and learn how to accurately model the phenomenon based on the number, size, thrust and configuration of the engines,” said Rob Maddock, project manager for NASA's SCALPSS experiment.

One of the vehicle's payloads, named Lunar PlanetVac, dropped from the bottom of the lander and released a blast of gas to blow fine-grained lunar soil into a collection chamber for sieving. Provided by a company named Honeybee Robotics, this device could be used as a cheaper alternative to other sample collection methods, such as robotic arms, on future planetary science missions.

After two weeks of pioneering work, the Blue Ghost lander fell into darkness Sunday when the Sun sank below the horizon, robbing it of solar power and plunging temperatures below minus 200° Fahrenheit (148°Celcius). The spacecraft's internal electronics likely won't survive the two-week-long lunar night.

A precoded message from Blue Ghost marked the moment Sunday afternoon, signaling a transition to "monument mode."

"Goodnight friends," Blue Ghost radioed Firefly's mission control center in Central Texas. "After exchanging our final bits of data, I will hold vigil in this spot in Mare Crisium to watch humanity's continued journey to the stars. Here, I will outlast your mightiest rivers, your tallest mountains, and perhaps even your species as we know it."

Blue Ghost's legacy is now secure as the first fully successful commercial lunar lander. Its two-week mission was perhaps just as remarkable for what didn't happen as it was for what did. The spacecraft encountered no significant problems on its transit to the Moon, its final descent, or during surface operations.

One of the few surprises of the mission was that the lander got hotter a little sooner than engineers predicted. At lunar noon, when the Sun is highest in the sky, temperatures can soar to 250° F (121° C).

"We started noticing that the lander was getting hotter than we expected, and we couldn't really figure out why, because it was a little early for lunar noon," Ray Allensworth, Firefly's spacecraft program director, told Ars. "So we went back and started evaluating and realized that the crater that we landed next to was actually reflecting a really significant amount of heat. So we went back and we updated our thermal models, incorporated that crater into it, and it matched the environment we were seeing."

Early Friday morning, the Blue Ghost spacecraft captured the first high-definition views of a total solar eclipse from the Moon. At the same time that skywatchers on Earth were looking up to see the Moon turn an eerie blood red, Firefly's cameras were looking back at us as the Sun, Earth, and Moon moved into alignment and darkness fell at Mare Crisium.

Diamond ring

The eclipse was a bonus for Firefly. It just happened to occur during the spacecraft's two-week mission at the Moon, the timing of which was dependent on numerous factors, ranging from the readiness of the Blue Ghost lander to weather conditions at its launch site in Florida.

"We weren't actually planning to have an eclipse until a few months prior to our launch, when we started evaluating and realizing that an eclipse was happening right before lunar sunset," Allensworth said. "So luckily, that gave us some time to work some procedures and basically set up what we wanted to take images of, what cameras we wanted to run."

The extra work paid off. Firefly released an image Friday showing a glint of sunlight reaching around the curvature of the Earth, some 250,000 miles (402,000 kilometers) away. This phenomenon is known as the "diamond ring" and is a subject of pursuit for many eclipse chasers, who travel to far-flung locations for a few minutes of totality.

The Blue Ghost spacecraft, named for a species of firefly, took eclipse chasing to new heights. Not only did it see the Earth block the Sun from an unexplored location on the Moon, but the lander fell into shadow for 2 hours and 16 minutes, about 18 times longer than the longest possible total solar eclipse on the Earth.

The eclipse presented challenges for Firefly's engineers monitoring the mission from Texas. Temperatures at the spacecraft's airless landing site plummeted as darkness took hold, creating what Allensworth called a "pseudo lunar night."

"We were seeing those temperatures rapidly start dropping," Allensworth said Friday. "So it was kind of an interesting game of to play with the hardware to keep everything in its temperature bounds but also still powered on and capturing data."

Shaping up

Using navigation cameras and autonomous guidance algorithms, the spacecraft detected potential hazards at its original landing site and diverted to a safer location more than 230 feet (70 meters) away, according to Allensworth.

Finally happy with the terrain below, Blue Ghost's computer sent the command for landing, powered by eight thrusters pulsing in rapid succession to control the craft's descent rate. The landing was gentler than engineers anticipated, coming down at less than 2.2 mph (1 meter per second).

According to preliminary data, Blue Ghost settled in a location just outside of its 330-foot (100-meter) target landing ellipse, probably due to the last-minute divert maneuvers ordered by the vehicle's hazard avoidance system.

"It looks like we're slightly out of it, but it's really OK," Allensworth said. "NASA has told us, more than anything, that they want us to make sure we land softly... They seem comfortable where we're at."

Firefly originally intended to develop a spacecraft based on the design of Israel's Beresheet lander, which was the first private mission to attempt a landing on the Moon in 2019. The spacecraft crashed, and Firefly opted to go with a new design more responsive to NASA's requirements.

"Managing the center of gravity and the mass of the lander is most significant, and that informs a lot of how it physically takes shape," Allensworth said. "So we did want to keep certain things in mind about that, and that really is what led to the lander being wider, shorter, broader. We have these bigger foot pads on there. All of those things were very intentional to help make the lander as stable and predictable as possible."

These design choices must happen early in a spacecraft's development. Landing on the Moon comes with numerous complications, including an often-uneven surface and the lack of an atmosphere, rendering parachutes useless. A lander targeting the Moon must navigate itself to a safe landing site without input from the ground.

The Odysseus, or Nova-C, lander built by Intuitive Machines snapped one of its legs and fell over on its side after arriving on the Moon last year. The altimeter on Odysseus failed, causing it to come down with too much horizontal velocity. The lander returned some scientific data from the Moon and qualified as a partial success. The spacecraft couldn't recharge its batteries after landing on its side, and Odysseus shut down a few days after landing.

The second mission by Intuitive Machines reached the Moon on March 6, but it suffered the same fate. After tipping over, the Athena lander succumbed to low power within hours, preventing it from accomplishing its science mission for NASA.

The landers designed by Intuitive Machines are tall and skinny, towering more than 14 feet (4.3 meters) tall with a width of about 5.2 feet (1.6 meters). The Blue Ghost vehicle is short and squatty in shape—about 6.6 feet tall and 11.5 feet wide (2-by-3.5 meters). Firefly's approach requires fewer landing legs than Intuitive Machines—four instead of six.

Steve Altemus, co-founder and CEO of Intuitive Machines, defended the design of his company's lander in a press briefing after the second lunar landing tip-over earlier this month. The Nova-C lander isn't too top-heavy for a safe landing because most of its cargo attaches to the bottom of the spacecraft, and for now, Altemus said Intuitive Machines is not considering a redesign.

Intuitive Machines stacked its two fuel and oxidizer tanks on top of each other, resulting in a taller vehicle. The Nova-C vehicle uses super-cold methane and liquid oxygen propellants, enabling a fast journey to the Moon over just a few days. The four propellant tanks on Blue Ghost are arranged in a diagonal configuration, with two containing hydrazine fuel and two holding an oxidizer called nitrogen tetroxide. Firefly's Blue Ghost took about six weeks to travel from launch until landing.

The design trade-off means Firefly's lander is heavier, with four tanks instead of two, according to Will Coogan, Blue Ghost's chief engineer at Firefly. By going with a stockier lander design, Firefly needed to install four tanks because the spacecraft's fuel and oxidizer have different densities. If Firefly went with just two tanks side-by-side, the spacecraft's center of mass would change continually as it burns propellant during the final descent to the Moon, creating an unnecessary problem for the lander's guidance, navigation, and control system to overcome.

"You want to avoid that," Coogan told Ars before Blue Ghost's launch. "What you can do is you can either get four tanks and have fuel and oxidizer at diagonal angles, and then you're always centered, or you can stay with two tanks, and you can stack them."

The four landing legs on the Blue Ghost vehicle have shock-absorbing feet, with bowl-shaped pads able to bend if the lander comes down on a rock or a slope.

"If we did come in a little bit faster, we needed the legs to be able to take that, so we tested the legs really significantly on the ground," Allensworth said. "We basically loaded them up on a makeshift weight bench at different angles and slammed it into the ground, slammed it into concrete, slammed it into regular simulant rocks, boulders, at different angles to really characterize what the legs could do.

"It's actually really funny, because one of the edge cases that we didn't test is if we came down very lightly, with almost no acceleration," she said. "And that was the case that the lander landed in. I was joking with our structural engineer that he wasted all his time."

Proof positive

Firefly delivered 10 NASA-sponsored science and technology demonstration experiments to the lunar surface, operating under contract with NASA's CLPS program. CLPS builds on the commercial, service-based business model of NASA's commercial cargo and crew program for transportation to the International Space Station.

NASA officials knew this approach was risky. The last landing on the Moon by a US spacecraft was the last Apollo mission in 1972, and most of the companies involved in CLPS are less than 20 years old, with little experience in deep space missions.

A Pittsburgh company named Astrobotic failed to reach the Moon on its first attempt in January 2024. The next month, Houston-based Intuitive Machines landed its Nova-C spacecraft on the lunar surface, but it tipped over after one of its legs snapped at the moment of touchdown.

Firefly, based in Cedar Park, Texas, was the third company to try a landing. Originally established as a rocket developer, Firefly signed up to be a CLPS provider and won a $101 million contract with NASA in 2021 to transport a government-funded science package to the Moon. NASA's instruments aboard the Blue Ghost lander cost about $44 million.

The successful landing of Firefly's Blue Ghost earlier this month buoyed NASA's expectations for CLPS. "Overall, it's been a fabulous, wonderful proof positive that the CLPS model does work," said Brad Bailey, assistant deputy associate administrator for exploration in NASA's Science Mission Directorate.

NASA has seven more CLPS missions on contract. The next could launch as soon as August when Blue Origin plans to send its first Blue Moon lander to the Moon. NASA has booked two more Blue Ghost missions with Firefly and two more landing attempts with Intuitive Machines, plus one more flight by Astrobotic and one lander from Draper Laboratory.

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