by In the future, precision landing on the rocky, rocky face and crater of the moon will not be so difficult.
At least that’s the goal of NASA’s Lunar Retroreflector Array (LRA) program, an initiative that is in dialogue with US and foreign lunar land initiatives. LRA consists of a dome-shaped device, topped with small glass prism retroreflectors. That object is then landed on the moon and delivered to the surface of the moon.
The LRA can bounce laser light from other orbiting and incoming spacecraft, acting as a permanent position marker on the moon for years to come.
But it was difficult to plot the lunar landscape with these devices.
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High-stakes, hit-or-miss missions
The privately built Astrobotic lander, called Peregrine, is one of NASA’s Commercial Lunar Payload Services (CLPS) partnerships, which enable commercial companies to fly the space agency’s scientific instruments to the moon.
On board the Lunar Lander Astrobotic was now having trouble a NASA LRA. That lander ran into problems shortly after launch, curtailing any hope of a firm landing on the moon.
But the upcoming attempt is expected to land Japan’s Smart Lander for Lunar Investigation (SLIM), another on course for a January 20 landing. It also has a NASA-supplied LRA.
Several upcoming CLPS-supported lunar missions, such as the Intuitive Machines Nova-C lander, will carry LRAs. Then there’s the Griffin Astrobotic Lander, which will also be carrying LRA—a very high-stakes undertaking as it carries NASA’s Volatiles by Exploration Polar Investigation Rover, or VIPER.
But don’t forget the LRA that was already on the scene and India was very successful Chandrayan-3 lunar lander in August last year.
Numerous landmarks
The LRA payloads are under the CLPS program, but the LRA units provided to international partners were made under international memoranda of understanding communicated between NASA and the respective space agencies, explains Daniel Cremons, deputy principal investigator for Laser Retroreflector Array at NASA Goddard Space Flight Center in Greenbelt, Maryland.
Cremons says each LRA is a unique location marker on the surface.
“Just as we use numerous landmarks to navigate in our daily life on Earth,” Cremons says, having distributed a greater number of location markers on the surface of the moon “will make it easier and faster to determine your own location in the orbit of the moon.”
The project defines an “operational” LRA as the lander carrying an LRA landing safely on the lunar surface, Cremons says, “that [India’s] Chandrayaan-3 is currently the only operational unit.”
Cremons also helped integrate 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. However, that spacecraft was lost during a landing attempt in April 2019.
LRA needs no power
At NASA’s Goddard Space Flight Center a small team is dedicated to the design and construction, as well as the flight quality of the tiny LRA.
The LRA units already flown and demonstrated on upcoming CLPS missions in 2019 were made as one lot, Cremons says. “The LRA design was optimized for a laser from orbit to a lander or rover on the surface of a planet.”
The Laser Retrieval Array (LRA) is too small to use World. They are designed to use laser light reflected from a laser altimeter or Light Detection and Ranging (LIDAR) device on a spacecraft orbiting the moon or headed for a full stop on the lunar terrain.
LRA consists of eight tiny retro-reflectors mounted on a small hemispherical platform. The total mass of the LRA is 20 grams, and it requires no power.
Lascent degree
According to LRA documentation, “reflectors, unlike simple plane mirrors, reflect radiation from a wide range of incident angles back to its source, with minimal scattering, and brighter reflection.”
On the US side, Intuitive Machines’ Nova-C Lander is carrying another LRA, which is scheduled to crash into the rim of the Malapert A crater near the moon’s south pole. The Nova-C lander is expected to be launched on a Falcon-9 rocket on its IM-1 mission later this year.
As noted with Intuitive machines, LRAs are useful as precision landmarks for guidance and navigation during the lunar day or night. “A few LRAs associated with a landing site can act as precise landmarks to guide the incoming landers by assisting in an autonomous and safe landing,” the company explains.
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— For an Astrobotic trip, big risk (and bigger reward) on the private launch of Peregrine’s moon landing on January 8
Cremons says the vision is for future orbiters to be equipped with a laser ranging system for regular ranging to LRA units to refine spacecraft orbits around the moon or calibrate pointing control.
“LRA will be particularly useful at or near the lunar south pole where image-based navigation is difficult due to lighting conditions,” says Cremons. “Since the LRA is designed to operate for years, I’m sure there are opportunities to use the LRA ‘network’ that we haven’t considered even at this new stage.”
