[Jeonseungmin's Science World] Why Danuriho Flies for Four and a Half Months

[Asia Economy] Korea's lunar probe 'Danuriho' was successfully launched on the 5th. It is expected to fly for four and a half months and enter a circular orbit 100 km above the moon on December 31. Although the distance to the moon is far, is it necessary to fly for such a long time?

To understand this, we need to know about the three methods of sending a probe to the moon. The first is the 'direct transfer' method. It pushes the probe out of Earth's gravity directly into lunar orbit in one go, which can take just a few days. However, it requires a lot of fuel and limits the amount of observational equipment that can be carried.

Therefore, the commonly used method is the 'phasing transfer.' The launched probe orbits Earth repeatedly, gradually using fuel to raise its altitude. When the altitude becomes high enough to overlap with the lunar orbit, the rocket is fired at that moment to jump into lunar orbit. Then, the altitude is lowered again to reach the desired height. This method uses relatively less fuel and takes a few weeks.

Danuriho, having been equipped with more scientific exploration equipment than expected during development, chose the last method called 'low-energy transfer.' The method is as follows. After leaving Earth, Danuriho is pulled by the sun's gravity and first moves in the opposite direction of the moon. It proceeds to the Lagrange point (where Earth's and the sun's gravity cancel each other out), then changes direction there and uses a small amount of fuel to fly back toward Earth. This is to gain propulsion by using Earth's gravity. Returning Danuriho then jumps into lunar orbit and begins orbiting the moon. Although it takes a long time, it can save about 25% of fuel.

Fuel is life for space probes and satellites. Without fuel to adjust orbit when necessary, they may crash onto the lunar surface or become space debris drifting away.

Jeon Seung-min, Science and Technology Writer

This content was produced with the assistance of AI translation services.