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On November 16, the Orion probe, which was launched on the rocket of the American lunar exploration project “Artemis 1”, is returning to Earth after passing the moon. Korea’s first lunar orbiter, “Danuri”, launched on August 5, is currently heading towards the moon at a distance of about 440,000 km from the earth after about four months.
Since the difference in flight duration between the two spacecraft launched to the moon in the second half of this year reaches about 25 times, attention is also focused on the method of flight of Danuri and Orion.
◆Orion exits the DRO and begins maneuvering back 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 15:53 (US local time) on the 1st, after 16 flight days, to return to Earth began to maneuver.
Earlier, on the 20th, four days after the start of the flight, Orion had entered the moon’s sphere of influence and received the moon’s gravity seriously, and the next day it had crossed the sky, about 128 km (80 miles ) away from the moon. surface and approached the nearest moon. Afterwards, Orion took the DRO to its furthest point from Earth and began returning to Earth.
According to the Korea Aerospace Research Institute and others, the Danuri is currently cruising about 440,000 km from Earth, about 120 days after launch. So far, Danuri has successfully performed a total of three trajectory correction maneuvers to compensate for the error between Earth-Moon navigation. Initially, Danuri was due to undergo a total of six maneuvers by the 2nd of last month, but the number of corrective maneuvers has been reduced as there have been no major problems with the course.
Danuri is expected to arrive in lunar orbit on the 17th. Before arriving in lunar orbit, further trajectory correction maneuvers can be performed once again from the 7th to the 9th, and after entering lunar orbit on the 17th, approximately 5 entry maneuvers are expected in orbit of the lunar mission, including deceleration.
◆Orion uses a fast “direct transfer orbit” instead of high fuel consumption… Intended to minimize human damage during manned exploration
The time it takes 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 faster, and a spiral transition trajectory takes longer. Also, the faster method consumes more fuel.
The reason why Orion started returning to Earth so quickly is because he chose the “direct transition trajectory” method. The 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 in that it can quickly go to the moon. Since the speed of the spacecraft is the highest, a large amount of fuel is required for deceleration maneuvers after entering lunar orbit, resulting in high costs, and the higher the fuel consumption, the shorter the mission period . Thus, there is no room to consume fuel for trajectory adjustment. Since the moon has to pick the day closest to the earth, the launch window is also limited.
The reason Orion chose the direct transition trajectory is that the purpose of this Orion launch is to test the impact it will have on spacecraft and crew ahead of future manned lunar exploration. It focuses on quick return because exposure to the deep space environment for a long time can have adverse effects on the human body. Even “Project Apollo,” which was a manned lunar exploration mission 50 years ago, has been to the moon using a direct transfer trajectory.
◆Danuri, ‘BLT trajectory’ which is slow but reduces fuel consumption… Using celestial gravity, securing fuel for year-long mission
On the other hand, Danuri is making its way to the moon using the BLT trajectory, which will inevitably take some time. The BLT trajectory is a method for launching a spacecraft towards the sun, not the moon. Between the Earth and the Sun there is a point called “Lagrange point L1” where the gravitational force is balanced and, at this point, the trajectory can be greatly changed even with a weak force. At this point, the sun’s gravity can be used to significantly change its trajectory, allowing it to decelerate more effectively as it arrives at the moon.
Indeed, on September 27, Danuri also flew 1,548,272 km from earth, covering the “longest distance since leaving earth”. Although the BLT trajectory travels such a long distance, it has the advantage of reducing fuel consumption as it actively uses the celestial body’s gravity.
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.
The reason Danuri focuses on fuel efficiency rather than speed is that, unlike Orion, which returns immediately after orbiting the moon, it has to perform an exploratory mission 100 km above the moon for a year after being entered lunar orbit.
As the weight of the Danuri increased, it became necessary to reduce fuel consumption during the voyage to complete the mission for one year. Also, since Danuri is an uncrewed lunar orbiter, there is no reason to consider the negative effects of the space environment on the human body like Orion.
A Korea Aerospace Research Institute official said, “In the process of preparing Danuri, we chose a longer and more difficult BLT trajectory due to weight issues.” I’ll do the most important maneuver. Right now, if there’s a problem like not decelerating well, I’ll concentrate until the end and do my best, as fuel consumption is high and I have to aim for another opportunity.”
