Moonlight Magic
This was the ninth attempt to "get through" to the Japanese lunar module. Getting a return signal was complicated by the fact that SLIM landed on the Moon at an angle.
NASA's Lunar Reconnaissance Orbiter (LRO) has twice beamed a laser pulse to the cookie-sized SLIM reflector on the JAXA (Japan Aerospace Exploration Agency) lunar rover and received a reflected signal, Phys.org reports .
While flying over the SLIM lunar module on May 24, 2024, at an altitude of about 70 km, the LRO spacecraft tried for the ninth time to “knock” on it with a laser beam. Finally, two attempts ended successfully: the laser signal returned back to the LRO detector, confirming contact with the lunar surface.
This achievement by NASA is especially significant given the unusual position of the device. Typically, reflectors are mounted on top of landers, which gives LRO a wide range of angles (120 degrees) to direct laser pulses to the intended reflector location. However, the SLIM lander landed unevenly. This greatly limited LRO's ability to accurately point the laser.
To increase the likelihood of hitting the target, the LRO team worked with JAXA to determine the precise coordinates and orientation of the SLIM lander. NASA engineers then calculated LRO's orbital trajectory to provide the optimal angle for directing laser pulses to the retroreflector as it flew over the target area.
According to experts, the LRO altimeter was not designed for this type of application, so the chances of finding the tiny retroreflector on the lunar surface are already slim. It was originally designed to map the lunar relief. The fact that the LRO team managed to reach the reflector on its side, rather than up, speaks to the stability of these small devices.
SLIM landed on the lunar surface on January 20. The retroreflector that went to the moon with the lander, called the Laser Retroreflector Array, is one of six NASA has sent to the moon on private and government landers, and the second to reflect a signal back to LRO's altimeter.
The first time a laser beam was transmitted from LRO to NASA's retroreflector was on December 12, 2023, when LRO sent a signal to India's Vikram rover. Since then, LRO has exchanged laser signals with Vikram three more times.
NASA's retroreflector is a 2-inch-diameter aluminum dome that houses eight quartz angle prisms. Requiring no power or maintenance, retroreflectors could last for decades on the lunar surface, providing reliable beacons for future missions.
For example, retroreflectors could guide Artemis astronauts to the surface in the dark, or mark the location of spacecraft already on the surface to help astronauts and unmanned spacecraft land near them.
Earlier, JAXA stopped receiving signals from the SLIM lunar module.
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