Scientists Are Sending Signal to the Moon. Finally, A Signal Is Back.

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Ever since NASA’s Lunar Reconnaissance Navigator (LRO) entered the lunar orbit in 2009, scientists have been firing lasers continuously.

To be more precise, they were sending a laser to a small array of reflectors roughly the size of a paperback book. Their goal was to bounce the rays into the world, and 10 years later they finally succeeded.

Photons were successfully projected onto Earth from the lunar orbit for the first time, and this not only gives us a new way to make measurements on the Moon and its surroundings, but it can also help us understand conditions on the Moon’s surface and downgrade the instruments placed there 50 years ago.

During the Apollo program, many astronauts went to the moon from 1969 until 1972. They didn’t just take a short journey. They left a lot of equipment behind them, like a seismometer and three laser reflectors. The Soviet space program has placed two reflectors on robotic rovers for a total of five people from two space agencies.

So why a laser reflector?

Well, if you send a really powerful laser beam to the Moon and know how long it will reflect from there and come back, you will make very accurate measurements between the two points, with the help of the speed of light. In this way, we can know to the millimeter how far the Moon is from us.

Over time, these measurements allowed us to paint the motions of the Moon. In this way, we know that the Moon has a fluid core by observing the rotational movements of the Moon. If it had a solid core, the movements of the Moon would show us how strong a magnetic field it has.

Thanks to such precise measurements, we know that the Moon is 3.8 cm away from us annually. If we are patient, distance measurements can tell us a lot.

NASA Goddard Space Flight Center Planetary Scientist Erwan Mazarico said, “We’ve been collecting data for 50 years, and seeing many approaches that we wouldn’t otherwise see, laser comprehensive science is a long game.”

But there is a problem. Over time, the reflected rays from the Moon reflectors dimmed, 10% less than they should be, and why it is still unclear.

However, if there is a reason, it is because of the abundant dust on the Moon. Although there is no wind to mix the atmosphere and this dust, small micrometeorites may have covered them enough to block the reflectors.

This is where the LRO reflector comes in. If we can get the reflected signals from these reflectors, scientists can compare the results with surface reflectors.

With the help of modeling, we can determine the reason for the reduced efficiency of surface reflectors and perhaps reveal how many micrometeorites was bombarded by the Moon and how much dust this bombardment generated.

Still easier said than done.

Bouncing signals from lunar surface reflectors are very difficult due to the atmospheric effects of the Earth and the weakening of signals. LRO reflectors are more challenging. These fast and moving reflectors measure 15x18x5 cm and are at an average distance of 384840 km from Earth.

The team’s initial attempts to reach the reflector using the green visible light failed. They then teamed up with scientists from Côte d’Azur University in France, who developed the infrared laser. This laser was more efficient with few losses when traveling through gas and clouds.

On September 4, 2018, the Laser Measuring Station in Grasse, France detected an infrared laser bouncing off the LRO for the first time. Then, the results were repeated in both trials, on 23rd and 24th August 2019. This time around, the team also rotated the spacecraft, pointing the reflector toward Earth, instead of waiting for the LRO to spin correctly, and showed how the bi-directional laser range could create an opportunity.

The return beam was small, only a few photons came back. It was not yet sufficient to understand what was blocking the reflectors on the lunar surface. But over time, even a few photons would give us too much information.

LRO measurements were not the team’s sole interest. The team’s work demonstrates improvements that can be made by using an infrared laser instead of optics, penetrating farther and potentially enabling the use of much smaller reflectors.

The researchers told their paper, “This experiment provides a new method for verifying decades of theories of dust accumulation on the lunar surface. It also showed that the use of similar arrays in future Lunar landing gear and orbits could support LLR Lunar science targets, especially in landing zones near the Moon’s limbs and poles, to be more sensitive to Lunar orientation. ” Wrote.

The research has been published in Earth, Planets, and Space.