After 10 years of trying, NASA finally bounced its first-ever laser beam off the lunar orbiter

• The National Aeronautics and Space Administration (NASA) was unsuccessfully bouncing laser beams off the Lunar Reconnaissance Orbiter (LRO) for over a decade — until today.
  
• For the first time, NASA hit its target and received a signal back from its lunar orbiter.
  
• It will help determine why the existing reflectors on the Moon are sending back weak signals, and hopefully, present a solution on how to solve the problem.
  

The National Aeronautics and Space Administration (NASA) has been bouncing lasers off the Moon since the 70s in its own version of the outer space disco. This time the US space agency was able to hit an even smaller, moving target — the Lunar Reconnaissance Orbiter.

Around the size of a car, moving around the move at 70 miles per hour, with a reflector that’s only the size of a paperback novel — NASA and its french partners at the Universite Cote D’Azur saw the signal came back for the first time in 10 years.

Why bounce lasers off the Moon?
Laser-ranging science has not only been critical in narrowing down the distance between the Moon and the Earth, but it’s also the reason scientists were able to determine that the Moon is moving around 3.8 centimeters or 1.5 inches further away every year.

There are currently five reflectors on the Moon, and the first two were delivered during the Apollo 11 mission. Each of these reflectors are made up of 100 mirrors. “Now that we’ve been collecting data for 50 years, we can see trends that we wouldn’t have been able to see otherwise,” said Erwan Mazarico, who coordinated the LRO experiment.

To continue building on those discoveries, NASA needs to figure out why the older panels are only returning a 10th of the signal that's expected from them.

Why are the reflectors on the Moon’s surface so weak?
One explanation for the existing reflectors being weak is that dust may have settled over the reflectors over time, considering that they have been on the lunar surface for around 50 years.

NASA’s lunar orbiter, on the other hand, was launched in 2009. Comparing the signal from the LRO to the ones sent back from the Moon’s surface can help scientists determine why there may be discrepancies between the two signals.

However, other factors have a role to play, as well. Each time, the scientists must figure out where each reflector is placed, which is continuously changing with the Moon’s orbit.

Once that has been pinpointed, the laser photons first travel through the Earth’s thick atmosphere on their way to the Moon. And then again, on their way back to Earth, which can scatter the light.

The light may start as being something that’s only around 10 feet wide, but by the time it reaches the Moon’s surface, it can spread out to nearly 2 kilometers. The light beam only gets wider on the return journey.

A little bit of luck and a little bit of precision
The odds of a laser photon reaching the moon’s surface are one-in-25 million. The odds of one of the photons that hit the moon, coming back to Earth is exponentially lower at around one-in-250 million.

Reaching the LRO’s reflector expands the odds even further. For one, it’s a moving target, and secondly, it’s one-tenth the size of the reflectors that are already on the moon.

Scientists use infrared light to beam at the LRO since it has a better chance of penetrating the Earth’s atmosphere with minimal distortion. Even so, only about 200 protons — out of tens of thousands — made their way to Earth.

The research team is hoping that this will be enough to help them answer the reflector dust question.

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