The phases of lunar lander success, revisitedby Jeff Foust
|
| “What we can confirm, without a doubt, is our equipment is on the surface of the Moon and we are transmitting. So, congratulations IM team,” Crain said. |
The situation now involves another lunar lander, a case of history, if not repeating, at least rhyming. The Nova-C lander, named Odysseus by Intuitive Machines, was flying the IM-1 mission to the Moon, attempting a landing late in the afternoon (Houston time, where the company is headquartered) Thursday. Unlike the SLIM landing last month, which featured a webcast with detailed telemetry from the spacecraft—and which offered the first hint that something went wrong with the landing—the joint NASA/Intuitive Machines webcast provided only repeated computer animations and audio from mission control.
The spacecraft made its final descent towards the surface, with a landing planned for 6:23 pm EST. That time came and went with no confirmation that Odysseus was on the surface. Had the lander crashed in its final descent, or was there just a problem with communications. “We’re not dead yet,” quipped Tim Crain, chief technology officer of Intuitive Machines and flight director, as they tried to establish communications with the lander.
Finally, about 15 minutes after landing, the company said it had a signal from the lander. “What we can confirm, without a doubt, is our equipment is on the surface of the Moon and we are transmitting. So, congratulations IM team,” Crain said. “Houston, Odysseus has found his new home.”
The webcast cut away to a scene at company headquarters were employees and their guests cheered the news. The announcement was enough for the company, and for NASA, to declare the landing a success. “Today, for the first time in more than a half-century, the US has returned to the Moon,” NASA administrator Bill Nelson said in remarks on the webcast just minutes after Crain’s announcement. “Today is a day that shows the power and promise of NASA’s commercial partnerships.”
“What a triumph! Odysseus has taken the Moon,” he said. “Stay tuned.”
The last comment was more figurative than literal: NASA and Intuitive Machines ended the webcast moments later. For nearly 24 hours afterwards, there were only a few updates from the company, including one a couple hours after landing where the company said the lander was upright and would soon be returning images. Yet by late Friday afternoon, there were no images yet released from the company and few other details about the health of the spacecraft.
That’s when the company revealed the bad news. The lander “caught a foot in the surface, and the lander has tipped,” said Intuitive Machines CEO Steve Altemus. With no images from the lander yet, he illustrated the situation with a model of the lander, placing it on its side, resting the top of the lander on what appeared to be an even smaller model of the lander serving as a rock.
The problem, Altemus and Crain said, appeared to come in the lander’s final descent. Odysseus was supposed to come straight down at a velocity of about one meter per second. Instead, it was descending at about three times that rate, with a meter per second of lateral velocity as well. In that case, the foot of one of the six landing legs might have hit the surface first and tipped the lander. “If you catch a foot, we might have fractured that landing gear and tipped over gently,” Altemus said.
So why had the company said hours after landing that the spacecraft was upright? Altemus blamed “stale telemetry” from fuel tanks on the lander that initially indicated the lander was upright. Updated telemetry, he said, showed the lander was on its side.
In that configuration, Odysseus was having problems communicating with Earth. Some of its antennas are now pointing at the surface. “That really is a limiter in our ability to communicate and get the right data down so we get everything for the mission,” Altemus said.
Crain said engineers were working on reconfiguring communications equipment on the lander to optimize the performance of the other antennas. “We expect to get most of the mission data down once we stabilize our configuration,” Crain said.
He said the company expected to keep operating the lander until the end of the lunar day. “Best-case scenario, we're looking at another nine to ten days,” he said. The company, in a press kit published before the launch, projected a lifetime on the surface of about seven days.
| “Based on Earth and Moon positioning, we believe flight controllers will continue to communicate with Odysseus until Tuesday morning,” the company said in its update Monday. |
The company waited until Monday morning for is next update, which offered both good and bad news. The good news was that NASA’s Lunar Reconnaissance Orbiter spotted the lander in images taken over the weekend. It showed Odysseus had landed 1.5 kilometers from its planned location. At Friday’s briefing, Crain expected a landing precision of two to three kilometers based on the performance of the lander’s optical navigation system.
However, NASA, in a release about the images, noted that the landing location was within a “degraded” crater a kilometer across, with an estimated slope at the landing site of 12 degrees. Intuitive Machines hadn’t disclosed the maximum slope for a safe landing, but Crain said at Friday’s briefing that a higher slope than expected could have contributed to the lander’s toppling. A slope, he said, “would also explain a tip-over, if there was more slope than anticipated at touchdown.”
The company also said that mission operations would soon end. “Flight controllers intend to collect data until the lander’s solar panels are no longer exposed to light. Based on Earth and Moon positioning, we believe flight controllers will continue to communicate with Odysseus until Tuesday morning,” the company said in its update Monday.
 A low-resolution image from Odysseus after landing, showing part of the lander and the shadow it cast on the lunar surface. (credit: Intuitive Machines) |
Degrees of success
So does a spacecraft that made it to the surface intact, but on its side, and operating at less than full capacity for less than its planned lifetime, count as a success or a failure?
Many hailed the success, including NASA, the biggest customer for the IM-1 mission through its Commercial Lunar Payload Services (CLPS) program. Intuitive Machines had a CLPS award that, after amendments, was valued at $118 million for the mission.
“Let me congratulate Intuitive Machines for three major accomplishments,” said Joel Kearns, NASA deputy associate administrator for exploration in the Science Mission Directorate, at Friday’s briefing. Those accomplishments were the first soft-landing on the Moon by the US since Apollo 17 in 1972, the first soft-landing by any non-governmental entity, and the landing that was the closest yet to the south pole, at about 80 degrees south latitude. “This is a gigantic accomplishment.”
Kudos also came in from the White House. “I congratulate the Intuitive Machines team who successfully landed Odysseus, as well as their partners at NASA who are shaping the future of human space exploration,” President Biden said in a statement Saturday. “America is leading the world back to the Moon.”
The stock market, though, was less congratulatory. Shares in Intuitive Machines, which have traded on the Nasdaq for a little more than a year after the company went public through a merger with a special purpose acquisition company (SPAC), fell nearly 35% in trading Monday, giving up most of the gains it recorded in the days since the IM-1 launch early February 15.
So who’s right: Wall Street or Pennsylvania Avenue? The truth, as you might have already guessed, is somewhere in between. One way to examine mission success is to look at how well Intuitive Machines served its customers. The lander carried six NASA payloads and six for other customers, ranging from individuals to companies to a university.
| “No matter what happens, I’m extremely proud of this team,” ERAU’s Henderson said of his EagleCam student team. |
Four of the payloads were passive, and just getting to the Moon was enough. That included a laser retroreflector from NASA, an artwork from Jeff Koons (famous, or maybe infamous, for his “balloon animal” sculptures), a data archive in the form of a disc from Galactic Legacy Labs, and insulation from Columbia Sportwear that was used in a closeout panel to protect a cryogenic propellant tank. They wanted to get to the Moon, and now they’re there.
Some payloads were able to operate during the transit to the Moon, achieving some, if not all, of their objectives. That included a radiofrequency mass gauge from NASA, designed to use radio waves to measure the amount of propellant inside, and an S-band navigation beacon, also from NASA. A startup, Lonestar Data Holdings, said it planned a series of in-flight tests of a data archive, transmitting and receiving documents as a proof-of-concept of future lunar data centers for “disaster recovery as a service.”
The jury is out on a few payloads. It appears unlikely that a NASA radio astronomy experiment called Radio Observations of the Lunar Surface Photoelectron Sheath (ROLSES) will be able to operate as expected. It planned to use four antennas to measure low-frequency radio waves from various sources, including a sheath of electrons just above the lunar surface. It’s not clear that ROLSES can operate in a useful way with Odysseus on its side.
Another NASA experiment, Stereo Cameras for Lunar Plume-Surface Studies (SCALPSS), was supposed to take images of the dust plume kicked up by the landing, but communications issues may prevent it from returning more than a few images. The same issue may also hinder a commercial payload, ILO-X from the International Lunar Observatory Association (ILOA), which included two cameras to take astronomical images from the Moon. “Our international dedicated ILOA team, including the ILO-X payload developer Canadensys Aerospace, are working hard and remain hopeful to receive other images from the Moon surface,” the organization said in a statement after Friday’s briefing.
One of the most intriguing payloads on IM-1 was EagleCam. The payload, a camera system developed by students at Embry-Riddle Aeronautical University (ERAU), was intended to separate when the lander was about 30 meters above the surface, falling to the surface ahead of the lander. With several wide-field cameras, EagleCam was intended to provide a third-person perspective of the landing.
A change in flight software made hours before the landing kept EagleCam from being deployed, but ERAU students and others worked over the weekend to see if the camera, about the size of a 1.5U cubesat, could be deployed while on the surface. In a statement Sunday, Troy Henderson, faculty lead of the EagleCam team at ERAU, said the analysis showed the device should be able to get three to five meters from the lander, good enough to take some images—if there is time and bandwidth to do so.
But like many student projects, just getting the spacecraft built and flown can be considered a success. “No matter what happens, I’m extremely proud of this team,” Henderson said in a briefing before the launch. “Just being able to see students be mentored, trained, learn new skills outside of the classroom, take everything they had learned in the classroom, and apply it to real hardware has been a really cool thing.”
The one payload that stands out is NASA’s Navigation Doppler Lidar (NDL) instrument, which was designed to measure velocity and altitude independent of the lander’s own systems. NDL, it turns out, may have saved the landing.
| “I said, ‘Tim, we’re going to have to land without a laser rangefinder.’ And his face got absolutely white,” Altemus said. “It was like a punch in the stomach. We were going to lose the mission.” |
Intuitive Machines found out after Odysseus went into orbit around the Moon Wednesday, a day before the landing, that the lander’s laser rangefinders were not working. Engineers determined that a safety switch, designed to protect people from the lasers (which are not eye-safe) was not flipped before launch so the lasers could operate normally: the equivalent of forgetting a “remove before flight” tag.
The switch was a physical one, Altemus said, that could not be flipped with software. He recalled going into the control room early Thursday as Crain and his team were preparing for landing. “I said, ‘Tim, we’re going to have to land without a laser rangefinder.’ And his face got absolutely white. It was like a punch in the stomach. We were going to lose the mission.”
However, Crain said that he and company engineers found it would be possible to use two lasers on NDL in place of the lander’s own laser rangefinders. The company had been working closely with the NASA Langley Research Center team that developed NDL and had already “plumbed” data from NDL into the lander’s software.
“It sounds easy in retrospect,” Crain said, but required extensive modifications to the lander’s software to incorporate the NDL data, converting it into a form that could be used during the landing and compensating for different angles between the NDL’s lasers and the laser rangefinder. Intuitive Machines delayed the landing by one orbit, or two hours, to give engineers more time to make that change.
“In normal software development for a spacecraft, this is the kind of thing that would have taken a month,” he said. “Our team basically did that in an hour and a half.”
NASA was pleased that NDL could ride to the rescue and not only save the mission, but advance the technology beyond expectations. Prasun Desai, NASA deputy associate administrator for space technology, said that by flying NDL on the IM-1 mission, the agency hoped to raise the technology to a technology readiness level (TRL) of 6 on a scale of 1 to 9, proving a prototype of the technology in a relevant environment.
Instead, he concluded at Friday’s briefing, “we were able to get an operational system now, TRL 9. It’s ready to be used from now on.”
That solution was linked, though, to another problem with the mission. Altemus said they turned on the laser rangefinder earlier than planned because they noticed that Odysseus appeared to be in an elliptical orbit, rather than the circular one planned. In normal operations, Crain said, the laser rangefinder would only have been active in the final descent: “We would have probably been five minutes to landing before we realized those lasers weren’t working.”
Why the lander was in an elliptical orbit wasn’t clear. The company had announced a landing time of 5:49 pm EST initially, then moved it up to 5:30 pm and again to 4:24 pm before the two-hour delay. That jumping around of times led to speculation there were navigation or propulsion issues that put the spacecraft into a different orbit than expected.
While Intuitive Machines had not reported any major issues during the transit to the Moon, and had even skipped the last of three planned trajectory correction maneuvers, Altemus had hinted at Friday’s briefing of other problems with the mission. “It was quite a spicy seven-day mission to get to the Moon,” he said early in the briefing. Asked later what the mission’s “Hail Mary moment” was, he said there were several: “like I said, it was a spicy mission.”
He didn’t elaborate much on what made the mission “spicy” but Crain said one issue came after the first trajectory correction maneuver when engineers found an error in the engine pointing geometry. He didn't go into details about that issue other than it was difficult to test on the ground and required changes to flight software.
“This is a serious business that’s fraught with risk,” Altemus said in an interview before launch. “It’s a daunting challenge to land on the Moon. It doesn’t come easy, especially when you’re trying to break the barrier of a price point, a fixed price point—say, roughly $100 million. We’ve pushed to the bottom of the cost for lunar access.”
| “You're never going to build a spacecraft the first time off that's perfect. Never,” Altemus said before launch. |
He said then that the company would celebrate every milestone on the way to the surface of the Moon. “Whether its acquisition of signal or whether it's the commissioning maneuver, or entering low lunar orbit, every one of those is a success that we ought to really celebrate,” he said. “What I'm looking for in terms of managing expectations is really a sense of resiliency in the community. That let's keep trying, even if we have a failure in the mission.”
The company expected there would be issues with the first mission, he said, and planned to incorporate those lessons into a second Nova-C lander being built for the IM-2 mission, slated to launch in the fall, and a third for IM-3 the company wants to launch by early next year. “Learning between one mission to the next is vital for our success, and that's one of the reasons why we wanted to build the same vehicle three, four times in a row,” he said. “You're never going to build a spacecraft the first time off that's perfect. Never.”
Crain said at Friday’s briefing that once the lander lost solar power, the mission would be over: the electronics on board will likely not survive the cold temperatures during the two-week lunar night. “Of course, the next time the Sun illuminates the solar arrays, we’ll turn our dishes to the Moon, just to see,” he said. “We’ll take a look, we’ll take a listen.”
But maybe there’s reason for hope. On Monday, the Japanese space agency JAXA said that it received a transmission from SLIM on Sunday after it had unexpectedly survived the lunar night. The lander was also able to transmit images back as well, suggesting it made it through the cold lunar night in good condition. The odyssey of Odysseus may not yet be over.
Note: we are now moderating comments. There will be a delay in posting comments and no guarantee that all submitted comments will be posted.