Laser Instrument on NASA’s LRO Successfully ‘Pings’ Indian Moon Lander

 In a significant breakthrough, NASA achieved the transmission and reflection of a laser beam between its Lunar Reconnaissance Orbiter (LRO) and a small retroreflector on ISRO's Vikram lander on the lunar surface. This successful experiment, conducted near the moon's south pole, introduces a new method for precisely locating targets on the lunar surface.

On December 12, 2023, at 3 p.m. EST, the LRO pointed its laser altimeter instrument toward Vikram, which was approximately 62 miles away near the Manzinus crater. After LRO transmitted laser pulses toward Vikram, the orbiter registered light bouncing back from a tiny NASA retro reflector aboard Vikram, confirming the success of the experiment.

While tracking Earth-orbiting satellites with laser beams from the ground is a common practice, the reverse technique—sending laser pulses from a moving spacecraft to a stationary one to determine its precise location—has diverse applications on the moon. Xiaoli Sun, leading the NASA team at Goddard Space Flight Center, stated, "We've shown that we can locate our retro reflector on the surface from the moon's orbit," emphasizing the potential for routine use in future missions.

Measuring only 2 inches in width, NASA's retro reflector, named the Laser Retro reflector Array, boasts eight quartz-corner-cube prisms in a dome-shaped aluminum frame. This compact yet durable device requires no power or maintenance and can last for decades. Its unique configuration allows it to reflect light back to its source from any direction.

Retro reflectors have a rich history of applications, dating back to the Apollo era, where larger versions revealed the moon's gradual movement away from Earth. The new generation of tiny retroreflectors holds even more potential, serving as precision markers on the International Space Station and potentially guiding Artemis astronauts during lunar surface missions.

Despite these advancements, challenges persist. The primary hurdle is that LRO's altimeter, operating beyond its primary mission for 13 years, is the sole laser instrument orbiting the moon. However, its original design focused on mapping the moon's topography, not pinpointing small targets. The altimeter, called LOLA, took eight attempts to contact Vikram's retro reflector.

LOLA functions by dispatching five laser beams toward the moon and measuring the time it takes for each to bounce back, providing elevation data. However, its wide coverage area and large gaps between beams make pinpointing small retro reflectors challenging. A future laser designed for continuous coverage without gaps could enhance the accuracy of retro reflectors.

The NASA team intends to use LRO's laser altimeter to refine target positions, especially for landers, while several retro reflectors are planned for deployment on upcoming moon landers. These include one on JAXA's SLIM lander, set to land on January 19, 2024, and one on an Intuitive Machines spacecraft launching in mid-February, underscoring the continued integration of innovative technologies in lunar exploration.