Why does Danuri go back to four months for 3-4 days

The distance from Earth to the moon is about 380,000 km. Apollo 11 arrived in the moon in the Saturn V rocket in 1969.


Danuri, on the other hand, turns around 5.95 million km for four and a half months and goes to the moon. Why did Danuri in the 21st century chose to go around so far?

Danuri moves to the moon by Ballistic Lunar Transfer (BLT). Separate the propulsion from the projectile and move through the moon and the earth to the sun. After going to the Laglang tavern, where the gravity of the sun and the earth is balanced, the orbital is orbited in the direction of the earth. At this time, thanks to the gravity of the earth, acceleration can be easily obtained.

In this way, the track will be modified and about 54 days after the launch, it goes to the point of 1.55 million km from the earth. Afterwards, the Earth gravity will be used to move to the moon orbit, and in mid-December, it will be used to enter the moon orbit.

Another way other than the BLT is a phase transition method that gradually enters the moon track, gradually entering the moon orbit, with a long elliptical orbit near the direct transition and near Earth.

Incident missions, such as the Apollo plan, chose to transfer directly to reduce the time as much as humans exposed to harmful space environments. However, the fuel consumption is high because it is necessary to reverse the moon gravity after entering the moon orbit.

Phase transition takes about one month to enter the moon track. During this period, you can check whether the main parts are working normal, and if you have a problem, you can get time to modify. So Japan and India used this method when they first explored the moon. Korea originally chose this method.

However, the situation changed when the US NASA requested their permanent shades of cameras (shadow cam). As a result, the weight of Danuri increased from 550 kg to 678 kg.

In consideration of the size, weight, and performance of the satellite and the board, Hang Woo-yeon decided to change the navigation method by the BLT method, which has a longer operation period instead of reducing fuel. BLT can reduce fuel consumption by 25% compared to other methods.

Instead, the movement of the probe should be precisely controlled. Even if you move a little wrong, you can get out of the target trajectory. Hang Woo-yeon plans to modify Danuri’s trajectory up to nine times.

By accepting the US proposal and adopting the BLT method, Korea has been provided with space data from NASA, collaborated with the United States, and gains know-how related to space development. It was also helped by the United States for the BLT trajectory design.

We have a lot of areas to cooperate with Korea in the future. We hope that Korea will be able to exercise its capabilities while developing Danuri. I look forward to cooperation in.