NASA’s Lunar Reconnaissance Orbiter (LRO) has successfully pinged the Vikram lander of India’s Chandrayaan-3 mission using a laser instrument, demonstrating a new technique to locate targets on the lunar surface.
Introduction
The Vikram lander of India’s Chandrayaan-3 mission, which soft-landed on the Moon’s south pole region on November 14, 2023, has been detected by a laser instrument onboard NASA’s Lunar Reconnaissance Orbiter (LRO), the US space agency announced on January 23, 2024. The laser beam was transmitted and reflected between the LRO and an Oreo-sized device called a Laser Retroreflector Array (LRA) on the Vikram lander, opening the door to a new style of precisely locating targets on the Moon’s surface.
How it works
The LRA is a simple and durable device that consists of eight quartz-corner-cube prisms set into a dome-shaped aluminum frame. It can reflect light coming in from any direction back to its source, without requiring any power or maintenance. The LRA was developed by NASA’s Goddard Space Flight Center as part of a partnership between NASA and the Indian Space Research Organization (ISRO).
Sending laser pulses towards an object and measuring how long it takes the light to bounce back is a commonly used way to track the locations of Earth-orbiting satellites from the ground. However, using the technique in reverse—to send laser pulses from a moving spacecraft to a stationary one to determine its precise location—has many applications at the Moon, such as mapping, navigation and communication.
“We’ve showed that we can locate our retroreflector on the surface from the Moon’s orbit,” said Xiaoli Sun, who led the team that developed the LRA. “The next step is to improve the technique so that it can become routine for missions that want to use these retroreflectors in the future.”
Implications
Retroreflectors can be used for many applications in science and exploration and have been in use at the Moon since the Apollo era. By reflecting light back to Earth, the suitcase-size retroreflectors revealed that the Moon is moving away from our planet at a rate of 3.8 centimeters per year.
The LRA on Vikram is much smaller and lighter than the Apollo retroreflectors, making it easier to accommodate on future lunar missions. It can also serve as a fiducial point (precisely located marker for reference) on the Moon, which can help calibrate other instruments and improve lunar mapping.
The successful detection of Vikram by LRO also confirms the success of India’s Chandrayaan-3 mission, which aimed to demonstrate India’s capability to soft-land on the lunar surface and operate a robotic rover. The mission also carried scientific instruments to study the lunar terrain, mineralogy, elemental abundance, lunar exosphere and signatures of hydroxyl and water ice.