NASA’s Innovative Use of Laser Retroreflective Arrays (LRAs) for Precise Lunar Navigation

NASA, the National Aeronautics and Space Administration, is known for its groundbreaking discoveries and technological advancements in the field of space exploration. One such innovation is the use of Laser Retroreflective Arrays (LRAs) for lunar missions. These simple yet effective devices have revolutionized the way NASA determines the locations of lunar landers, enabling more accurate navigation and scientific exploration.

LRAs consist of a small aluminum hemisphere, 2 inches (5 centimeters) in diameter and 0.7 ounces (20 grams) in weight, with eight 0.5-inch-diameter (1.27-centimeter) corner cube retroreflectors made of fused silica glass. These devices are designed to reflect laser light shone on them from a wide range of angles, making them similar to reflective strips on road signs. By measuring the time it takes for the laser beam to travel to the LRA and back, scientists can determine the distance between the two objects.

NASA has been using LRAs on satellites for years, ranging to them from ground-based lasers. However, the idea of attaching them to lunar landers came about twenty years ago. This innovation allows scientists to range to the landers from orbit and know their exact location on the lunar surface. This is crucial for establishing a navigation aid similar to the Global Positioning System (GPS) we use on Earth.

Laser ranging is also used for docking spacecraft, such as cargo spacecraft for the International Space Station. The LRAs light up when illuminated, helping to guide precision docking. They can also be detected by lidars on spacecraft from a distance, determining their range and approach speed with high accuracy ratings. This feature allows docking to occur at nighttime, free from the need for illumination from the Sun.

Moreover, LRAs can help spacecraft accurately range-find their way to a landing pad, even without external light to guide the approach. This means that LRAs can eventually be used to help spacecraft land in otherwise pitch-dark places close to permanently shadowed regions near the lunar South Pole, which are prime target areas for crewed missions due to the resources that might exist there, such as water ice.

Since LRAs are small and made of simple materials, they can be added to scientific missions as a beneficial but low-risk add-on. They will survive the harsh lunar environment and continue to be usable on the surface for decades. Furthermore, besides navigating and finding out where your landers are, you can also use laser ranging to tell where your orbiter is around the Moon.

As more landers, rovers, and orbiters are sent to the Moon bearing one or more LRAs, our ability to accurately gauge the location of each will only improve. This growing network of LRAs will allow scientists to gauge the location of key landers and other points of interest more and more accurately, enabling bigger, better science to be accomplished.

Currently, NASA’s Lunar Reconnaissance Orbiter (LRO) is the only NASA spacecraft orbiting the Moon with laser-ranging capability. LRO has already succeeded in ranging to the LRA on the Indian Space Research Organization’s Vikram lander on the lunar surface and will continue to range to LRAs on future landers.

Under Artemis, NASA’s Commercial Lunar Payload Services (CLPS) deliveries will perform science experiments, test technologies, and demonstrate capabilities to help NASA explore the Moon and prepare for human missions. With Artemis missions, NASA will land the first woman and first person of color on the Moon, using innovative technologies to explore more of the lunar surface than ever before. The agency will collaborate with commercial and international partners and establish the first long-term presence on the Moon. Then, NASA will use what we learn on and around the Moon to take the next giant leap: sending the first astronauts to Mars.

In conclusion, NASA’s use of Laser Retroreflective Arrays (LRAs) for lunar missions is an innovative and effective solution for precise lunar navigation. These simple devices have revolutionized the way we determine the locations of lunar landers, enabling more accurate navigation and scientific exploration. As we continue to send more landers, rovers, and orbiters to the Moon bearing LRAs, our ability to accurately gauge their locations will only improve, leading to bigger, better science and paving the way for human missions to the Moon and beyond.