The Dark Side of the Moon
No this is not a review of Pink Floyds album.... What is the dark side of the moon and why is it so hard to get there.
Looking out at the stars
To the people who have looked up at the moon when its shining the brightest, you may have noticed something. It looks exactly the same, all year round. Now for the astronomers in the crowd you may know why this is. Its to do with something called synchronous rotation and is illustrated well below.
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Simply said, synchronous rotation is when the time it takes for a celestial object to orbit another is the same as the time it takes to rotate about its own axis. Now, for the moon this takes approximately 27 days to happen. Its orbit is also why we have the different phases of the moon, where its to do with the angle of light coming from the sun. Now you may expect the dark side of the moon to be dark right? Well actually it experiences light as much as the side facing Earth other than when its the full moon where its fully dark. It will have lunar days and nights like we have on Earth.
Now that we have established where the dark side comes from lets go through a short history of the Space Age and its missions to do with the moon.
The Luna Missions
The Luna Missions are comprised of 24 individual missions carried out by the Soviet Union from 1959 - 1976. They achieved a lot of milestones, beating the Americans to pretty much everything other than the first humans on the Moon. Noticeably though, is the fact that despite completing the first soft landing, the first flyby and images from the dark side they didn’t manage to land on that side. Despite this, they did manage to land 7 out of the 9 missions that were launched.
Ranger, Lunar Orbiter & Apollo Missions
The Ranger program had the intent on relaying pictures back to the US before crashing into the moon. Coincidentally, even though failing, Ranger 4, having issues with deploying its solar panels, crashed on the far side of the moon, making the first spacecraft to land on the far side.
The Lunar Orbiter missions were the preparation for the Apollo program, where over the 5 missions they had to get all the data they required. This included photographing and mapping the surfaces as well as getting accurate gravitational force readings. You have to remember the data that the Soviets captured wasn’t accessible to the Americans due to the heightened tensions between the countries.
With the aid of the previous programs as well as the Mercury one, the Apollo program set 12 individual people on the near side of the moon with all but 2 going to plan: Apollo 1 & Apollo 13. This has since not been done.
Key problems
Over the coming decades no country has ever landed on the far side of the moon intentionally. In general, it has been quite difficult to land on the moon to begin with, but landing on the far side is another mountain to overcome. Even the veteran space agencies haven’t managed to climb it. The main issue isn’t the mapping of the far surface, it is rather the communication to the far side. The moon acts like a radio wave sponge meaning that it is impossible to directly relay information from the far side of the moon to Earth and vice versa. This has made it impossible for corrections during the final descent and touchdown phases of a mission.
The next reason is the terrain. Just like the side facing us, the far side has a lot of boulders and craters, which limit the suitable landing spots. Another reason is the varying degree of sunlight, which makes that rocky terrain even harder to see.
Recent success
Until recently, the far side of the moon has only been mapped and observed but never landed on. In 2019, the China National Space Administration (CNSA) landed Chang’e 4 on the far side of the moon. Its success is an impressive feat and is partly due to a geologist who became the last human to ever step on the moon. Back in the 1970s when Apollo 17 was in development, the geologist, Harrison Schmitt proposed an idea to land on the far side of the moon. This was envisaged by sending a communications relay satellite in an orbit far from Earth, where a special balance of forces, would allow it to ‘hover’ in space. This orbit would be at L2 (Lagrange point 2)
The Lagrange Points are 5 different points in space near Earth where the gravitational forces and orbital motion of the body, balance each other perfectly. In this case Lagrange point 2 would sit 1.5 million km from Earth, around 4 times further than the moon is. A satellite at this point would allow communication to a spacecraft that would land on the far-side of the moon. The CNSA utilised this idea in 2018 with the Queqiao satellite, which ultimately made it possible to land on the far side.
Another impressive achievement was done by the Indian Space Research Organisation (ISRO). Chandrayaan - 3 was the first spacecraft that landed on the south pole of the moon just last year, in 2023.
Looking to the Future
For now there is only one mission to land on the far side of the moon in the near future, in 2025! LuSEE-Night will be launched by NASA to detect radio waves from 13.4 billion years ago (just after the big bang).
There are also a lot of moon missions planned over the coming years most noticeably, the Artemis program. This is where humans will return to the moon in hopes of establishing a more permanent base.
So keep an eye out for those missions to the moon and stay tuned to keep up to date to the following stories up ahead.
See you next week,
Maxime