NASA Strikes Laser at a Cookie-Sized Reflector aboard JAXA’s Lunar Orbiter And Received a Return Signal

A laser beam from NASA’s Lunar Reconnaissance Orbiter (LRO) altimeter in lunar orbit twice reached a cookie-sized retroreflector mounted on the JAXA Smart Lander for Investigating Moon (SLIM) on the lunar surface and received a reflected signal. This marks a significant advancement in lunar navigation and communication technology.

NASA’s successful experiment for future connectivity with the Moon

We previously reported that the Laser Retroreflector Array arrived on the Moon with the SLIM spacecraft on 20 January this year. It is one of six that NASA has sent to the Moon aboard private and government vehicles and the second to reflect the signal back to the LRO altimeter.

The first two were delivered to the satellite’s surface during the Apollo 11 mission 55 years ago. Each of these reflectors consists of 100 mirrors, but is only able to reflect a 10th of the signal, due to dust that may have settled on the reflectors over time.

According to NASA scientists, the experiment was not successful the first time, and it took eight attempts to make contact.  

The first time a laser beam was transmitted from LRO to NASA’s retro-reflector was on 12 December 2023, when LRO beeped at ISRO’s Vikram landing vehicle. Since then, LRO has exchanged laser signals with Vikram three more times.

Then, on 24 May 2024, during two consecutive overflights at an altitude of 44 miles above the SLIM spacecraft, LRO pointed its laser altimeter at it.

However, only in the last two attempts did the signal return to LRO’s detector.

A great milestone was achieved

NASA considers this an important achievement because the retroreflector on SLIM is not in the optimal position. Such retroreflectors are typically attached to the top of landing modules, giving the LRO spacecraft a 120-degree range of angles that can be navigated by sending laser pulses to the approximate location of the retroreflector. However, the SLIM lander did not descend to the surface as planned, and its top is now facing sideways, limiting the range of LRO’s capabilities.

As Xiaoli Sun, leader of the team that built the SLIM retroreflector at NASA’s Goddard Space Flight Centre, stated, ‘The LRO altimeter was not designed for such a purpose, so the chances of accurately detecting a tiny retroreflector on the surface of the Moon are already slim.’ The primary purpose of the LRO laser altimeter is to map the Moon’s topography to prepare for missions to the surface, not to aim with 1/100th of a degree of accuracy at a retroreflector.

NASA’s LRO Spots Japan’s Moon Lander 

As for the retroreflector aboard the Japanese lander, this tiny but powerful device consists of eight quartz corner cubic prisms mounted in a 5 cm wide domed aluminium frame. The device is simple and durable, the scientists say, requiring neither power nor maintenance, and can last for decades. Its configuration allows the retroreflector to reflect light from any direction back to its source. Such instruments can operate on the lunar surface for decades and become reliable beacons for future missions.

The success of this experiment demonstrates that laser-based communication and navigation systems could play an essential role in future space missions, including to Mars and beyond.