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On November 16, the Orion probe, which was launched on the American lunar exploration project ‘Artemis 1’ rocket, is returning to Earth after passing the moon. Korea’s first lunar orbiter, ‘Danuri’, which was launched on August 5, is currently heading toward the moon at a distance of about 440,000 km from the earth after about four months.
As the difference in flight duration between the two spacecraft launched toward the moon in the second half of this year reaches about 25 times, attention is also focused on the flight method of Danuri and Orion.
◆Orion gets out of DRO and starts maneuvering to return to Earth… Danuri, sailing 440,000 km from Earth
According to the scientific community on the 3rd, Orion completed a flight in the ‘Distance Retrograde Orbit (DRO)’ around the moon at 3:53 pm (US local time) on the 1st, after 16 days of flight, to return to Earth. started maneuvering.
Previously, Orion entered the moon’s sphere of influence on the 20th, four days after the start of the flight, and received the moon’s gravity in earnest. Afterwards, Orion took the DRO to the farthest point from Earth and began returning to Earth.
According to the Korea Aerospace Research Institute and others, the Danuri is currently sailing about 440,000 km away from Earth, about 120 days after launch. So far, Danuri has successfully carried out a total of three trajectory correction maneuvers to compensate for the error between Earth-Moon navigation. Initially, it was expected that Danuri would undergo a total of six maneuvers by the 2nd of last month, but the number of corrective maneuvers was reduced as there were no major problems with the route.
Danuri is scheduled to arrive in lunar orbit on the 17th. Before arriving in lunar orbit, additional trajectory correction maneuvers can be carried out again on the 7th to 9th, and after entering lunar orbit on the 17th, about 5 lunar mission orbit entry maneuvers, including deceleration, are planned.
◆Orion uses a fast ‘direct transfer orbit’ instead of high fuel consumption… The purpose of minimizing human damage during manned exploration
The time it took for Orion and Danuri to enter the lunar gravitational field is about 4 days and about 4 months. They are definitely going to the same destination, but why is there such a difference?
According to Anti-Coincidence, the path from the earth to the moon is generally classified into four types: ▲ direct transition trajectory ▲ phase transition trajectory ▲ WSB (BLT) trajectory and ▲ spiral transition trajectory. A direct transition trajectory can go to the moon the fastest, and a spiral transition trajectory takes the longest. In addition, the fastest method consumes more fuel.
The reason why Orion started returning to Earth so quickly is because it chose the ‘direct transition trajectory’ method. Direct transition trajectory, as the name suggests, is a method of adopting the shortest distance from the Earth to the Moon.
The direct transition trajectory has clear disadvantages as it can quickly go to the moon. Because the speed of the spacecraft is the fastest, a large amount of fuel is required for deceleration maneuvers after entering lunar orbit, resulting in high costs, and the greater the fuel consumption, the shorter the mission period. As such, there is no room for consuming fuel for trajectory adjustment. Since the moon has to choose the day closest to the earth, the launch window is also limited.
The reason why Orion chose the direct transition trajectory is that the purpose of this Orion launch is to test the impact it will have on the spacecraft and crew prior to future manned lunar exploration. It focuses on returning quickly because exposure to the deep space environment for a long time can have adverse effects on the human body. The ‘Apollo Project’, which was a manned lunar exploration mission 50 years ago, has also been to the moon using a direct transfer trajectory.
◆Danuri, ‘BLT trajectory’ that is slow but reduces fuel consumption… Using celestial gravity, securing fuel for a year-long mission
On the other hand, Danuri is heading to the moon using the BLT trajectory, which will inevitably take some time. The BLT trajectory is a method of launching a spacecraft toward the sun, not toward the moon. There is a point called ‘Lagrange Point L1’ between the earth and the sun where gravity balances, and at this point, even a weak force can greatly change the trajectory. At this point, the sun’s gravity can be used to significantly change its trajectory, allowing it to decelerate more effectively when it arrives at the moon.
In fact, on September 27th, Danuri also flew 1,548,272km away from the earth, flying ‘the farthest distance since leaving the earth’. Although the BLT trajectory travels such a long distance, it has the advantage of reducing fuel consumption in that it actively utilizes the gravity of the celestial body.
Initially, the Korea Aerospace Research Institute planned to send Danuri to the moon using a phase transition trajectory method that required a flight period of 1 to 2 months. done.
The reason why Danuri focuses on fuel efficiency rather than speed is that, unlike Orion, which returns immediately after orbiting the moon, it must perform an exploration mission 100 km above the moon for one year after entering lunar orbit.
As the Danuri’s weight increased, it became necessary to reduce the fuel consumption during the voyage in order to carry out the mission for a year. Moreover, since Danuri is an unmanned lunar orbiter, there is no reason to consider the adverse effects of the space environment on the human body like Orion.
An official from Korea Aerospace Research Institute said, “During the process of preparing Danuri, we chose a longer and more difficult BLT trajectory due to weight problems.” The most important maneuver is performed. At this time, if there is a problem such as not decelerating properly, the fuel consumption is high and I have to aim for another opportunity, so I will concentrate until the end and do my best.”