A Japanese robotic spacecraft successfully landed on the moon on Friday — but its solar panels failed to generate power, which will cut the amount of time it can operate to just a few hours.
With this achievement, Japan is now the fifth country to send a spacecraft that made a soft landing on the moon.
For JAXA, Japan’s space agency that currently conducts a variety of robotic science missions in space, this was the first time it had attempted to land on a planetary body elsewhere in the solar system. The spacecraft, the Smart Lander for Investigating Moon, or SLIM, was intended to demonstrate precision landings, within a football field of a targeted destination, rather than an uncertainty of miles that most landers are capable of.
The technology could also be useful for future missions like those in NASA’s Artemis program. Japan is a partner in this program, which will send astronauts back to the moon in the coming years.
At 10 a.m. ET on Friday — midnight Japan, early Saturday — SLIM fired its engines to begin its descent from lunar orbit. At 10:20, the main lander touched down near a small crater called Shioli in the equatorial region of the moon’s near side.
The surface there has an angle of about 15 degrees, which created difficulties in landing without a rollover. SLIM’s designers thus decided to tilt the spacecraft to one side just before landing, and then after initial contact with the ground, SLIM leaned forward on its front legs.
Immediately after landing, SLIM was able to send radio signals back to Earth. But the webcast commentator at the time repeatedly said, “We’re still monitoring the situation.” The webcast ended without revealing SLIM’s fate.
At a news conference a few hours later, JAXA officials said the smooth landing was successful but revealed the problem with the solar panel.
They said it was possible the panels were simply pointing in the wrong direction and could generate power later when the sun was shining at a different angle. The landing met the minimum requirements for mission success, officials said. If the landing was within 100 meters of the target, that would be a complete success, although it will take a month of analysis to determine how close SLIM was.
With no working solar panels, the spacecraft runs on its battery. To conserve energy, the spacecraft’s heaters have been shut down, JAXA officials said.
During the limited time, mission managers prioritized the recovery of navigation data acquired during the landing.
Two small rovers were successfully deployed from the lander shortly before landing.
Developing such precision landing capabilities in the future will allow spacecraft to aim closer to places of interest such as craters, rather than large flat plains.
Because the moon has no global positioning satellites or radio beacons, spacecraft must figure out exactly where they are on their own. Radar pings informed SLIM how high it was and how fast it was moving. A camera taking pictures of the landscape below helped the spacecraft determine its position by matching the pattern of craters it saw with maps stored in its memory.
Vision-based systems on spacecraft have been limited because they use special computer chips that are hardened against the powerful radiation of deep space. Such chips are generally a generation or two behind top-of-the-line chips, with only one-hundredth of the processing power, JAXA said in a press kit for the SLIM mission.
JAXA developed image processing algorithms that can run quickly on the slower space chips.
The images allowed SLIM to avoid dangerous rocks and other obstacles during its final approach.
The two rovers SLIM developed, called Lunar Excursion Vehicle 1 and Lunar Excursion Vehicle 2, were unconventional. One used a bounce mechanism and carried a thermometer, a radiation monitor, and an instrument for measuring inclination and elevation.
The second rover was spherical, about the size of a baseball and weighed half a kilogram. Its two halves were to detach, allowing the rover to crawl along the surface for a few hours until its battery died. JAXA developed this rover in collaboration with Doshisha University and Tomy, a toy company.
LEV-1 was able to communicate directly with Earth and LEV-2 communicated through LEV-1. Data from the two rovers was sent back to Earth, JAXA said.
Even with limited power, an instrument on the lander attempted to analyze the composition of the rocks around the craft.
For the past 11 years, a parade of spacecraft has headed for the moon. Less than half reached their destination intact.
China is the only country with a perfect record of landing its robotic spacecraft on the moon — three successes in three attempts. India succeeded last year after a previous attempt failed in 2019. Other efforts by Russia, a Japanese private company and an Israeli non-profit organization failed.
The latest failure, a spacecraft built by Astrobotic Technology of Pittsburgh, never reached the moon due to a malfunction in its propulsion system shortly after reaching orbit.
Other spacecraft will attempt to reach the moon this year. A second American company, Intuitive Machines of Houston, is contracted to carry NASA experiments to the moon. He plans to launch his aircraft in the middle of next month. China may also attempt a robotic landing mission on the lunar far side this year.
Japan has its own future lunar plans. It is working with India to launch a robotic rover, LUPEX, next year. Japanese astronauts may head to the moon in the future as part of NASA’s Artemis program.
Hisako Ueno contributed reporting from Tokyo.