Laser on NASA’s LRO successfully ‘pings’ Chandrayaan-3 Moon lander

For the first time on the Moon, a laser beam was transmitted and reflected between an orbiting NASA spacecraft and an Oreo-sized device on the Indian Space Research Organisation’s Vikram lander of India’s Chandrayaan-3 mission, the space agencies said in separate statements.

The successful experiment opens the door to a new style of precisely locating targets on the Moon’s surface, the American space agency said.

At 3 pm EST on December 12, 2023, NASA’s Lunar Reconnaissance Orbiter (LRO) pointed its laser altimeter instrument toward Vikram. The lander was 100 kilometers away from LRO, near Manzinus crater in the Moon’s south pole, when LRO transmitted laser pulses toward it.

After the orbiter registered light that had bounced back from a tiny NASA retroreflector aboard Vikram, scientists knew their technique had finally worked, the space agency said in a statement.

Sending laser pulses toward an object and measuring how long it takes the light to bounce back is a commonly used method to track the location of Earth-orbiting satellites from the ground.

But 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, scientists say.

The Laser Retroreflector Array (LRA) on the Vikram lander has begun serving fiducial points (precisely located markers for reference) on the moon, ISRO said in a statement. NASA’s Lunar Reconnaissance Orbiter (LRO) achieved a laser range measurement using the LRA by successfully detecting signals reflected by it on December 12, 2023, the Indian space agency said.

The ranging utilised the Lunar Orbiter Laser Altimeter (LOLA) on the LRO. The observation occurred during lunar night time, with the LRO ascending to the east of Chandrayaan-3.

NASA’s LRA was accommodated on the Vikram lander under international collaboration. It comprises eight corner-cube retroreflectors on a hemispherical support structure. This array facilitates laser ranging from various directions by any orbiting spacecraft with suitable instrument. The passive optical instrument, weighing about 20 grams, is designed to last for decades on the lunar surface.

Having landed near the lunar south pole on August 23, 2023, Vikram lander has been accessible for LOLA measurements since then.

While several LRAs have been deployed on the Moon since the beginning of lunar exploration, the LRA on Chandrayaan-3 is a miniature version and is the only one available near the south pole.

NASA’s LRA on Vikram lander will continue to serve as a long-term geodetic station and a location marker on the lunar surface, benefitting current and future lunar missions.

These measurements, apart from helping in precise determination of a spacecraft’s orbital position, will help refine the lunar geodetic frame, revealing insights into the Moon’s dynamics, internal structure, and gravitational anomalies.

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