A NASA technology demonstration may still be viable on the lunar surface.
When Beresheet, the lunar lander built by the Israel-based company SpaceIL, crashed into the Moon, it was carrying more than the hopes and dreams of the first private company to reach the Moon.
It also happened to be shuttling a small piece of NASA equipment. But the device may have survived the crash, according to Space.com — a remarkable testament to the hardiness of the space agency’s equipment.
In a serendipitous twist, the device — called a Lunar Retroreflector Array (LRA) — happens to function as a sort of beacon. The spherical gadget, full of cubic quartz mirrors, is meant to help guide spacecraft into precise landings, sort of like the lights illuminating an airport runway. That means that NASA scientists could feasibly go find it in a followup mission.
The NASA piggyback experiment may have survived the April 11 crash of Israel’s Beresheet moon lander, experts said.
The NASA payload, known as the Lunar Retroreflector Array (LRA), is a technology demonstration composed of eight mirrors made of quartz cube corners that are set into a dome-shaped aluminum frame. These mirrors are intended to serve as markers for other spacecraft, which can use them to orient themselves for precision landings.
The entire instrument is smaller than a computer mouse and lightweight. But it’s tough, radiation-hardened and designed to be long-lived, so the LRA may not have been destroyed by Beresheet’s hard landing.
“Yes, we believe the laser reflector array would have survived the crash, although it may have separated from the main spacecraft body,” said David Smith of the Massachusetts Institute of Technology, principal investigator of the Lunar Orbiter Laser Altimeter (LOLA) instrument aboard NASA’s Lunar Reconnaissance Orbiter (LRO) spacecraft.
“Of course, we do not know the orientation of the array,” Smith, who’s also an emeritus researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, told Inside Outer Space. “It could be upside down, but it has a 120-degree angle of reception, and we only need 1 of the 0.5-inch cubes for detection. But it has certainly not made it any easier.”
The LOLA team will begin planning LRA-hunting observations soon, he added.
Laser beams generated by LOLA hit the lunar surface and bounce back to the instrument. For each beam that returns, LOLA measures its time of flight, or range.
And if LOLA manages to bounce some light off the LRA reflector, the team should know about it.
NASA is interested in dotting the moon with many such retroreflectors in the future. These would serve as permanent “fiducial markers” on the moon, meaning future craft could use them as points of reference to make precision landings.
In addition, LRO is attempting to image Beresheet’s crash site with its Lunar Reconnaissance Orbiter Camera system, or LROC for short, Smith said.
LRA is a passive instrument. It will be used in conjunction with LRO’s Lunar Orbiter Laser Altimeter, or LOLA. That altimeter’s laser beams strike and are backscattered from the lunar surface. For each laser beam, LOLA measures its time of flight, or range.
There won’t be any attempts to range the reflector from LRO until Beresheet is no longer active on the moon. Doing so ensures that the LRO laser would not damage any sensitive detectors on the Israeli lander, said the Massachusetts Institute of Technology’s David Smith, the principal investigator for LOLA and an emeritus researcher at NASA Goddard in Greenbelt, Maryland.
[NOTE: Beresheet is no longer active now.]
Subsequently, LOLA will attempt to make range measurements to the lander from LRO.
“This is an experiment to determine feasibility, and it will be possible to continue to make measurements to the array for an indefinite time, or as long as the LOLA instrument on LRO continues to operate, which is approaching 10 years in June 2019,” Smith told Space.com.
The laser array was conceived and designed by Smith and Xiaoli Sun at NASA Goddard about 15 years ago for NASA’s Phoenix Mars lander.
“It was intended that it would work with the laser altimeter that we had on NASA’s Mars Global Surveyor spacecraft. By the time the lander arrived at Mars, however, the instrument was no longer active,” Smith said. The purpose of the Mars and the moon arrays is to try and locate the position of landers from an orbiting spacecraft carrying a laser system, he said.
In principle, ranging to the reflector array many times will enable NASA to determine the location of the lander. But the accuracy of this method is limited by the size of the spot illuminated by the laser on the surface, Smith said.
A laser generating a 16.5-foot (5 meters) spot on the surface requires very precise pointing of the laser, Smith said. It will be easier for a wide-beam laser to detect the reflector array, but knowledge of the array’s location on the surface will be more uncertain, he said.
Lonely lunar laser
“A properly designed ranging system could solve this problem,” Smith said. “LOLA was designed to do altimetry, not range to a small reflector array. But it is the only laser at the moon for the immediate future.”
Imagery taken by the high-flying LRO can clearly identify where Israel’s Beresheet sits on the moon. So the Laser Retro-reflector Array is an experiment to see how difficult it will be for LRO to make the range measurements to the lander, Smith said.
“A small grouping of these small arrays placed around a landing site, for example, could assist in a lander returning to a location at some future time,” Smith said. “Requiring no power, the arrays could be used for decades, possibly longer.”
Smith said there are also potential applications for these small reflectors on other celestial bodies, such as asteroids. Placing — perhaps dropping — a number of small arrays on the surface of a body would allow nearby probes to monitor the object’s rotation and position, as well as determine its shape.
“Since the reflectors could last for decades, the object could be monitored by other spacecraft on subsequent visits, and of course, would assist in landing on the object if desired,” Smith added.
Of course, the reflectors’ small size limits the range from which they can be detected. Present buildable laser concepts at NASA Goddard could enable measurements from over 6,000 miles (10,000 kilometers) away, Smith said.
“These small reflectors only weigh roughly 20 grams [0.7 ounces] but could be much larger and capable of being detected from even greater range,” Smith said. “But larger would mean heavier, and one of the attractions of these small reflectors is that they are very low-mass, so almost any lander can carry them.”