Leonard David's INSIDE OUTER SPACE

Image credit: ISRO

India’s Moon-bound Chandrayaan-3 lunar lander/rover is toting a NASA laser retroreflector array. In NASA acronym-land, better known as an LRA.

The device, mounted atop the lander, is from the LRA project based at NASA’s Goddard Space Flight Center.

NASA LRA mounted on Chandrayaan-3 lunar lander.
Image credit: ISRO/NASA

Daniel Cremons and Xiaoli Sun are leading the LRA project for the Chandrayaan-3 lander. They are also supplying LRA hardware for NASA’s Commercial Lunar Payload Services missions and the Smart Lander for Investigating Moon (SLIM) mission to be staged by the Japan Aerospace Exploration Agency, Cremons told Inside Outer Space.

At NASA Goddard there is a small team dedicated to designing, building, and flight-qualifying miniature LRAs.

Cremons also helped integrate the LRA on the SpaceIL Beresheet lander in November 2018. Beresheet was Israel’s first lunar mission and the first attempt by a private company to land on the Moon. That craft, however, was lost during an April 2019 landing attempt.

Small and compact, the laser retroreflector array.
Image credit: NASA/Goddard Space Flight Center

Tiny retroreflectors

The Laser Retroreflector Array (LRA) is too small to be used from Earth. They are designed to use reflected laser light from a laser altimeter or lidar on a spacecraft orbiting the Moon or landing on the Moon.

An LRA consists of eight tiny retroreflectors mounted on a small, high hemispherical platform. Total mass of the LRA is 20 grams, and requires no power.

According to LRA documentation, “retroflectors, unlike simple plane mirrors, reflect radiation from a broad range of incident angles back to its source, with minimal scattering, and brighter reflection.”

Intuitive Machines’ Nova-C lander undergoes testing. It is a NASA Commercial Lunar Payload Services mission.
Image credit: Intuitive Machines

Lander location

Another LRA is being carried by the Intuitive Machines’ Nova-C lander, scheduled to drop in on the crater rim of Malapert A near the south pole of the Moon. The Nova-C lander is expected to launch on a Falcon-9 rocket on its IM-1 mission later this year.

Mounted to the lander, the LRA reflects laser light directly backward to the orbiting spacecraft that emitted the laser light to precisely determine the lander’s location on the surface of the Moon.

As noted by Intuitive Machines, LRAs continue to be used as precision landmarks for guidance and navigation during the lunar day or night. “A few LRAs surrounding a landing site can serve as precision landmarks to guide the arriving landers by aiding in autonomous and safe landing,” the company explains.