The Far Side of the Moon

For people who are interested in space exploration, 2019 is already becoming a historic year.

Just a few hours after the new year, the New Horizons probe did a fly by near a far far object named, Ultima Thule. A small and peanut-shaped object inside the Kuiper belt. Officially known as 2014 MU69, Ultima Thule orbits the sun every 298 years at the distance of 6.5 billion km from us. On the first day of January, it became the farthest object in the solar system that has been visited by an earthling spaceship.

Landing on the Far Side of the Moon

A few days later, this time in our own celestial neighborhood, another historic event took place. For the first time in the history of the space explorations, an unmanned robotic lander, successfully landed on the far side of the Moon.

Chang’e-4 (named after the goddess of the Moon) is the latest mission in the China lunar exploration program. After successfully orbiting and landing on the familiar and near side of the Moon, China took a step forward and successfully landed its lander on a crater called Von Kármán, inside the South Pole–Aitken basin which is one of the largest impact craters in the solar system.

This mission is an important one. For the first time, the Chinese space program is accomplishing a task that never has been done before by any other nations. No one ever landed on the far side of the moon. This mission also has scientific importance.

The lander accompanied by a small moon rover called, Yutu-2, equipped by several scientific instruments and a small bio-box to test the growth of seeds and insects in low gravity.

The Far Side or the Dark Side

The moon's orbital periods and its rotation are tidally locked with each other. In another word, the moon will rotate around its axis in the same time that it takes to complete one rotation around the Earth. As a result, from the Earth, we only can see one side of the Moon and the other side is hidden from us (except a small area that could be visible because of phenomena called libration).

That is why we call it the far side of the moon. Sometimes the far side of the moon is also called the dark side of the moon. It is a popular name (especially after the famous Pink Floyd album), but it is not accurate.

The far side of the moon is not always dark. It is experiencing days and nights like the near side of the moon but both days and nights of the far side are happening behind the moon and far from our eyesight.

The far side of the moon also has a different appearance from the near side.

There are no signs of the seas there (the flat areas in the front side of the moon that seems a little darker or greyish and you can see them any night that the moon is shining in the night sky.) The surface of the far side of the moon is more similar to the surface of Mercury and covered with many ancient, and new, craters.

It is a strange and undiscovered land, waiting to be discovered.

Calling Home from the Far Side of the Moon

One of the challenges in conducting any mission behind the moon are the communications problem. If you are on the surface of the far side of the moon or in a low orbit—like the command module of Apollo missions during their orbit around the Moon, the body of the Moon blocks your line of sight of the Earth. Which means there is no way to talk directly to the Earth from the surface or when you are in a low orbit behind the moon. During the Apollo missions, the communications with the command module (CM) disconnected for few minutes while the CM was orbiting the far side of the moon.

There are two major ways to keep in touch with Earth from the far side of the Moon.

First, to put a series of communications satellite around the Moon in medium height orbits. These multi propose satellite network can relay the communications and also play the role for some kind of positioning systems and mapping the surface. It is probably going to be the case in the future when we will establish proper infrastructure there.

The second way is the one that Chinese chose. They put a satellite in a specific point behind the Moon. This point called halo orbit or second Lagrangian point in the Earth-moon system. This is the place that sum of gravitational forces allows us to put an object there and it will keep its position fixed in regard to the Moon.

L2 is about 65,000 km behind the moon. In that distance, any satellite sees not only the surface of the far side of the moon, but also the Earth will be on its eyesight and therefore the line of communications is open with the lunar surface and the Earth at the same time.

China Space Agency has sent an orbiter, Quèqiáo, to this point a year earlier. In Chinese folklore, Quèqiáo means the bridge formed by birds to make it possible for the seventh daughter of the goddess of heaven to reach to her earthling lover. Quèqiáo is now the bridge between the Earth and its messenger on the moon.

This could be a first step toward the lunar communication networks that would be critical for any long-term project on the moon.

The Moon: The Forgotten Frontier

The Apollo program was the epic period of our history. When a nation put its will and resources to do something incredible. The space race was indeed the result of political dispute and advisory between the East and the West.

After Apollo missions, we lost our will to continue that way. The US defeated its ideological enemy in the space, and especially after the fall of USSR, there was no political justification and neither the will to continue this adventure.

Not only US, but most of the world are suffering from lack of long-term perspective in the space. Yes! The robotic exploration of the solar system is much cheaper and more fruitful than human explorations, but there could be an architecture that combines both components in a meaningful way. And the moon is one of the most important destination for us—both in robotic and manned missions, and it seems that we forgot it.

We already have been on the moon, and it is not being considered a sexy destination anymore. We love to explore Mars and send miners to asteroids. These destinations could grasp the attention of the public and even politicians. They love to invest something that could be described as the "first." But if we are going to have a sustainable plan for our future presence in the space, it would start with the moon.

Because of the short distance between the moon and Earth, any mission to the moon could benefit from the direct support from Earth. Remember, Apollo 13—three astronauts of that mission have survived because they had the support of a few hundred people back on Earth in mission control. If they were on their way to Mars, their chance of survival would have been decreased exponentially.

This proximity means that backup and rescue missions also could be a vital option.

The price tag for travel to the moon is far cheaper than any other destination in our solar system beyond the Earth's orbit.

If we are going to colonise another planet some time in the future, we should practice it somewhere with all the potential support, and that is the moon.

We can build our first research camps on the moon remotely, by using robots even before sending our astronauts there.

We can use all of our experience in the orbit of Earth to build an orbital station around the moon and also developing our techniques to use local materials for our needs and constructions.

The low gravity of the moon makes it a great shipyard, if anytime we decide to go boldly farther deep in our solar system.

And then there is a chance for tourism. When our technology advances enough and we master the art of construction and staying on the moon, the ticket price of wealthy tourists could bring back some of the investments.

But the importance of the moon is not limited to only a step for further exploration.

The moon, and especially far side of the moon, is the paradise for most of the astronomer and scientists.

On the far side of the moon, there is no atmosphere and no light pollution. Even the faint glow of the Earth would never reach this land and also there is no sign of the Earth’s infrared glow.

We can build really large telescopes, without the boundaries that the Earth atmosphere or a space telescope has to face. Just imagine an optical and near-infrared telescope in the class of four meters can discover and see on such condition.

And the scientific advantages of the far land of the Moon is not limited to the astronomy alone.

Of course, like any other adventure, this task requires overcoming many known and unknown challenges. But this is the step that we should take to go beyond.

The Chinese Lunar Exploration program could be a reminder for us about the importance of the moon. But the real step will only take place when we find our courage and will to explore again. When we realize that our problem here is not worthy of our intelligence and time—we could be explorers once again and become part of a great and shared dream to expand in the solar system and maybe beyond, To remember the glory and the joy of learning new things and go forward into the unknown, to face the problems and to find a way to overcome them.