When Apollo astronauts landed on the moon, they brought devices with them, called retroflectors, which are essentially small mirror arrays. The plan was for scientists on Earth to target lasers and calculate the time it takes for the beam to return. It provides exceptionally accurate measurements of the Moon’s orbit and shape, including how it changed slightly depending on the Earth’s gravitational bridge.
Research continues with these Apollo-era lunar retirees, and scientists want to conduct similar experiments on Mars. NASA’s Perseverance Rover — scheduled to land on the Red Planet on February 18, 2021 — was a palm-sized laser retroflector array (LaRA). The agency’s Insight Lander also has a small one, called Laser Retroflector for Insight (LaRRI). And the ESA (European Space Agency) ExoMars Rover, to be launched in 2022, will have a retroreflector rider.
While there are currently no lasers in this type of Mars research work, the devices are headed for the future: Such reflectors may one day enable scientists to operate what they need to measure the position of the rover on the Martian Is called laser-rich research. Test Einstein’s theory of surface, general relativity, and help make future landings on the red planet more accurate.
“Laser retroreflectors are luminous, point-like markers,” said Simone Dell’Aglino, who led the development of the three retrofractors at Italy’s National Institute for Nuclear Physics, which manufactured the devices on behalf of the Italian Space Agency. “Because they are simple and maintenance-free, they can work for decades.”
A box of mirrors
The devices act very much like a bike reflector, bouncing light back in the direction of its source. The LaRA of solidity, for example, is a 2-inch-wide (5-cm-wide) dome, with half-inch holes containing glass cells. In each cell, the three mirrored faces are located at a 90-degree angle from each other so that the light entering the hole is directed back in the same direction from where it came.
LaRA is much smaller than the retroflectors present on the Moon. The first, delivered by the Apollo 11 and 14 missions, are about the size of a normal computer monitor and embedded with 100 reflectors; The ones distributed by Apollo 15 are also large and embedded with 300 reflectors. This is because lasers have to travel 478,000 miles (770,000 kilometers) to the moon and back. From the return trip, the beams faint, they cannot be detected by the human eye.
Those rays, which were created to reflect strongly and reflect the Insight’s LaRRI, would indeed be a short journey, despite Mars being 249 million miles (401 million kilometers) away from Earth. Rather than traveling forward and backward from Earth, which would require heavy retrofactors, the laser beam would simply need to travel back and forth from a suitable laser-equipped future Mars orbiter.
Such a circumambulation can determine the exact position of a retrofractor on the Martian surface. And since persistence will be mobile, it can provide many points of reference. Meanwhile, the position of the orbiter will also be tracked from Earth. This would allow scientists to test Einstein’s theory of general relativity, since they have retroreflectors on the Moon. The orbit of each planet is greatly affected by the bend in space-time created by the large mass of the Sun.
“This kind of science is important for understanding how gravity shapes our solar system, the entire universe, and ultimately the roles of Dark Matter and Dark Energy,” Del Agello said.
In the case of the Insight lander being touched on November 26, 2018, laser-ranging science can also assist the spacecraft’s main mission to study the deep interior of Mars. Insight relies on a radio instrument to detect subtle differences in the planet’s rotation. By learning from this tool how the planet staggers over time, scientists can eventually determine whether the core of Mars is liquid or solid.
And if the science team were able to use Lander’s retroflector, they could get more accurate position data than Insight’s radio could provide. LaRRI can also find out how the terrain insight sits over time and in which direction the Martian crust expands or shrinks.
Better landing on mars
The landing of Mars is difficult. To help bring firmness to the surface safely, the mission will rely on terrain-relative navigation, a new technology that compares images taken during descent to an onboard map. If the spacecraft sees itself too close to danger (like cliffside or sand dunes), it can go away.
But in such a mission-critical event, you can never have too many backups. Future missions leading to the surface of the red planet could use a series of reference points from laser retroreflectors as a test on the performance of their terrain relative navigation system – and perhaps even increase their accuracy by a few centimeters. When the difference between successfully landing near a seductive geological formation or the steep slope of a pit wall can only be measured in feet, retrofractors can be important.
Dell’Agnello said, “The laser range could open up new types of Mars exploration.”
More on mission
An important objective of the mission of persistence on Mars is astronomy, which involves the discovery of signs of life from ancient microorganisms. The rover will also portray the planet’s climate and geology, paving the way for human exploration of the Red Planet, and will be the first planetary mission to collect and cache Martian rock and regoliths (broken rock and dust). Later missions, currently under consideration by NASA in collaboration with the European Space Agency, will send the spacecraft to Mars to collect these cached samples from the surface and return them to Earth for in-depth analysis.
Managed for NASA by JPL, a division of Caltech in Pasadena, California, the Mars 2020 Perseverance Rover is part of a larger program that includes missions to the moon as a way to prepare for human exploration of the red planet. Accusing NASA of returning astronauts to the Moon by 2024, NASA will establish a continued human presence on the Moon by 2028 and through NASA’s Artemis lunar exploration plans.
NASA’s Perseverance Rover Attaches to Atlas V Rocket
Quotes: New Mars Rover is ready for Space Laser (2020, September 28). Https://phys.org/news/2020-09-mars-rover-ready-space-lasers.html from 29 September 2020
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