"To BTS on the Moon"... D-1, Korea's First Lunar Probe 'Danuri' 12 Questions and Answers [Reading Science]

Preview of Launch Process, How to Go to the Moon?
Scientific Mission to Unveil Moon Mysteries
If Water Confirmed, a New Era of Human Moon Exploration

[Asia Economy Reporter Kim Bong-su] South Korea's first lunar probe, 'Danuri (KPLO)', will be launched tomorrow morning (Korean time) on the 5th. It plays the pioneering role in Korean space exploration as well as the important role of guiding humanity's second lunar landing project. Especially, if the presence of water is confirmed, it is expected to mark a new milestone for humanity's lunar advancement. Oxygen supply becomes possible and it can be used as energy, enabling the construction of long-term habitation bases. Let's resolve curiosities through 12 questions and answers about Danuri.

1. Why go to the Moon?

Danuri is South Korea's first planetary exploration mission. Space development consists of three major fields: satellites, launch vehicles, and exploration. South Korea has been a strong nation in the satellite field, and after successfully developing the launch vehicle (Nuri) on June 21, it is expanding into exploration with Danuri. Globally, South Korea joins the ranks of lunar exploration countries as the seventh, following the United States, China, Russia, Japan, India, and Europe. For the first time since its founding, South Korea is stepping into all three major areas of space development, solidifying its status as the world's seventh major space power. Following Danuri's remote exploration, South Korea plans to conduct a lunar landing exploration by 2030.

The Moon lost humanity's attention for a while after the US Apollo project in the 1960s and 70s. However, since the 2000s, with advances in science and technology reducing space launch costs and increasing interest in lunar resource extraction and Mars colonization, deep space exploration has become a focus again worldwide. Particularly, India confirmed the presence of water in the Moon's permanently shadowed regions in October 2008, reigniting lunar exploration. China further fueled interest by landing Chang'e 3 in 2013 and Chang'e 4 in 2018 on the far side of the Moon, and successfully returning samples with Chang'e 5 in December 2019.

The US is promoting the Artemis program, aiming to build a lunar base through international cooperation and establish the 'Lunar Gateway,' a second international space station. According to the Korea Aerospace Research Institute (KARI), there are 18 major lunar exploration plans scheduled after this year, including South Korea's lunar lander launch planned for 2030. This 'return to the Moon' by humanity is driven primarily by 'curiosity.' Experts say that without curiosity, humanity would not have discovered the American continent, and space exploration is essential for a sustainable and challenging future. Moreover, the Moon can serve as an intermediate base as deep space exploration of Mars and beyond becomes active. It reduces the burden on launch vehicles overcoming Earth's gravity, significantly lowering space exploration costs. In the future, resource extraction such as helium-3, known to be abundant on the Moon, and energy production like space solar power plants may become feasible. Long-term, the construction of colonies with large populations on the Moon is anticipated.

South Korea's lunar probe Danuri at Space Force Launch Complex 40 in Cape Canaveral, Florida, USA. Photo by Ministry of Science and ICT press corps joint coverage.

2. Can't it go on Nuriho?

Danuri separates about 40 minutes after launch at an altitude of 1,650 km in Earth orbit and enters the lunar transfer orbit. The problem is that Nuriho cannot carry Danuri to that altitude. Nuriho can only place 1.5 tons of cargo into an orbit of 600?800 km. Moreover, although Nuriho has just succeeded in development, its performance, safety, and reliability have not yet been fully verified. During its first launch in October last year, the third-stage engine shut down early, failing to place the satellite mock-up into orbit and thus failing the mission. It was only during the second launch on June 21 that it performed perfectly. The government plans to launch it four more times to increase reliability. At one point, the government considered launching Danuri using the Korean launch vehicle, but due to schedule conflicts, it early decided to use a foreign launch vehicle. Meanwhile, Danuri's total weight was increased somewhat comfortably from 550 kg to 678 kg. The government plans to develop an upgraded version of Nuriho with significantly enhanced performance through the next-generation launch vehicle development project, to be used for the lunar exploration planned in 2030.

3. Then who will carry it?

Danuri will be launched to the Moon aboard SpaceX's Falcon 9 launch vehicle. It will be launched at 8:08 AM Korean time on the 5th from Launch Pad 40 at the US Space Force Base in Cape Canaveral, Florida. This will be the sixth reuse of the Falcon 9, carrying only Danuri for a solo launch. The total length is 70 meters, external diameter 3.7 meters, and it is a 1st and 2nd stage liquid-propellant rocket capable of placing 22.8 tons into low Earth orbit. The launch pad is located at 28.29 degrees north latitude and 80.34 degrees west longitude. It is closest to Earth's equator in the US, allowing the use of Earth's rotational speed to minimize fuel consumption. Danuri, weighing 678 kg, was flown from Incheon Airport in South Korea on the 6th of last month and arrived at Cape Canaveral two days later. It underwent system checks, communication tests, and leak tests. The launch was originally scheduled for the morning of the 3rd but was delayed two days due to issues with the Falcon 9 launch vehicle.

4. Why does it take 4.5 months to travel a 3-day distance?

There are three ways to travel to the Moon. The first is the direct transfer used during the US Apollo missions, heading straight from Earth to the Moon. To escape Earth's gravity and adjust the orbit en route to the Moon requires an enormous amount of fuel. It can reach the Moon within 5 days, suitable for manned missions vulnerable to space environments. The second is the phase transfer method, which involves orbiting Earth several times in a very elongated elliptical orbit before gently entering the lunar orbit. This takes about a month. It consumes less fuel than direct transfer but requires a significant amount to enter lunar orbit. South Korea uses neither of these two but employs the Ballistic Lunar Transfer (BLT) method.

Danuri separates about 40 minutes after launch at an altitude of 1,650 km and uses its own propulsion to head toward the Lagrange point where Earth's and Sun's gravity balance. At this point, the distance from Earth reaches up to 1.56 million km. Then it changes direction, using Earth's gravity to return and enter the Moon's Earth orbit. This requires traveling a long distance over about 4.5 months. It involves the challenging task of remote control while communicating with the spacecraft over a long distance. Among the three lunar orbit insertion methods, this takes the longest time but consumes the least fuel. Japan in 1990 and the US in 2011 each tried and succeeded with this method. South Korea chose the BLT method considering Danuri's limited weight of 678 kg, the mission duration of one year, optimized fuel tank size, payload, and expected consumption period. This reduces fuel by over 20%, extending the probe's mission duration. However, the downside is the increased difficulty in communication and control as it travels over 1.5 million km away from Earth and back.

5. How will the mission be carried out?

Danuri has attracted worldwide attention, being named this year's most notable lunar exploration plan in the international journal 'Nature' last May. This is because it can observe the Moon most closely and precisely since the Apollo project, which directly landed on the Moon. Danuri will operate in a circular orbit 100 km above the lunar surface, passing over the lunar poles. It will orbit the Moon 12 times a day, conducting lunar observation and scientific and technological missions, and transmit observation data to Earth via antenna. The mission duration is one year.

Danuri's first mission is to find candidate landing sites for South Korea's lunar landing exploration planned after 2030. It also has scientific goals such as measuring the Moon's magnetic field and radiation and verifying space internet technology. To this end, it carries five scientific instruments developed by domestic research institutes and universities, and NASA's Shadowcam for permanently shadowed regions, totaling six scientific instruments.

6. What lunar mysteries will Danuri reveal?

Among these, the Wide-field Polarization Camera (PolCam) developed by the Korea Astronomy and Space Science Institute will conduct precise observations of the lunar surface. The international scientific community expects it to solve long-standing questions such as the nature of the Moon's peculiar terrain called the 'Fairy castles.' The 'Fairy castles' were discovered in photos taken from 160 km altitude during the Apollo missions. They are small, tall, twisted tower-like structures resembling twisted doughnuts. NASA's Shadowcam is also expected to confirm the presence of water on the Moon. While indirect evidence has been found through impact experiments by India's Chandrayaan satellite and others, direct confirmation of water has not yet been made. If water is confirmed, South Korea is expected to be recorded as a nation that opened a new chapter in lunar development. The magnetic field camera developed by the Korea Institute of Geoscience and Mineral Resources is also expected to solve another lunar mystery. The Moon's core is a cold, small metal body, making it impossible to generate a magnetic field by core rotation like Earth. However, strong magnetic fields have been observed in various parts of the lunar surface. Scientists believe that analyzing Danuri's magnetic field measurement data to understand the overall magnetic field distribution on the Moon will help solve this mystery. Additionally, the space internet equipment developed by the Electronics and Telecommunications Research Institute plans to conduct an experiment streaming BTS's music video, attracting global K-pop fans' attention.

7. How is it different from a satellite?

Danuri's appearance is not much different from a typical satellite. It is a box-shaped body with wing-like solar panels attached. However, it is not a satellite but a 'probe.' Satellites are placed in a fixed orbit and orbit Earth using gravity with little variation, performing missions such as Earth observation. Being a probe means Danuri has autonomous navigation capabilities unlike satellites. It is a 'spacecraft' that travels over 1.5 million km from Earth to the Lagrange point using its independently developed propulsion system, then changes direction to join lunar orbit. Danuri carries several tens of kilograms of fuel, enabling about nine directional maneuvers, with three maneuvers expected to be consumed during the round trip between Earth and the Lagrange point.

8. How are navigation and communication handled?

Because Danuri is a probe navigating in deep space up to 1.5 million km from Earth, KARI has devoted great effort to establishing a communication network with Danuri. With a total project cost of 28.4 billion KRW, KARI built South Korea's first deep space ground communication system in Yeoju, Gyeonggi Province, including a 40-meter diameter giant antenna. It also collaborates with NASA, utilizing a network of deep space antennas located in Canberra, Australia; Goldstone, Los Angeles, USA; and Madrid, Spain. The mission operation control room located at KARI's headquarters in Daejeon sends various commands to Danuri and receives status information. It is also responsible for mission planning, orbit determination, maneuver planning, and receiving and distributing payload data.

Researchers at the Korea Aerospace Research Institute in Yuseong-gu, Daejeon, are inspecting South Korea's lunar orbiter, Danuri. Danuri will be loaded into a specially made container and transported to the U.S. Space Force Base at Cape Canaveral, Florida, on July 5, and is scheduled to be launched into space at 8:20 a.m. on August 3.
/Daejeon=Photo by Kang Jin-hyeong aymsdream@

9. Why is Danuri black?

In deep space beyond geostationary orbit (about 36,000 km), electrostatic charging and discharging phenomena occur due to space radiation. That is, static electricity causes charges to accumulate on the spacecraft surface, which must be discharged externally. KARI researchers coated the outermost layer of a multilayer thin-film insulation with an electrically conductive material to more effectively move charges. This material is a polyimide called Black Kapton, which can withstand extreme cold and heat. KARI researchers attached this multilayer insulation to the spacecraft surface to protect it from rapid thermal changes in space. This multilayer insulation causes Danuri to appear black.

10. What happens after the mission ends?

Danuri will operate in the target orbit for one year, and if fuel remains, the operation period may be extended. This decision will be made in July next year, six months before the planned end of normal operation. At that time, the post-mission handling method for Danuri will also be decided. One option is to crash it onto the lunar surface while capturing video until just before impact. Another is to move it to a lunar frozen orbit, which maintains altitude without energy consumption, allowing it to continue orbiting the Moon. For reference, NASA's Lunar Reconnaissance Orbiter (LRO), launched in 2009, completed its three-year mission but still remains in a frozen orbit and operates.

11. What domestically developed technologies are used?

A large-capacity, high-thrust propulsion system is required for lunar orbit insertion. KARI independently developed a system capable of producing 30 Newtons (1 Newton = force to accelerate 1 kg at 1 m/s²) of thrust. It is a single-propellant propulsion system with adjustable pressure to change orbit. The main body maximizes the use of the next-generation medium satellite platform, and the structure system, thermal control system, power system, onboard software, onboard computer, and attitude control system were also developed domestically. KARI independently assembled and tested the spacecraft based on existing satellite development facilities and technologies. Although NASA provided advice and review, the lunar transfer trajectory and mission orbit design were completed using domestic technology.

12. What is the origin of the name Danuri?

It is a pure Korean word combining 'dal' (Moon) and 'nuri-da' (to enjoy or spread). It was selected through a national public contest held in January and February. The winning entry was submitted by Ha Tae-hyun, a doctoral student in the Department of Materials Science and Engineering at KAIST. The name expresses the hope that the Moon will be fully enjoyed and that the first lunar exploration will be successful. It is unrelated to Nuriho. The 'Nuri' in Nuriho means 'world' or 'universe' in pure Korean and was also selected through a national contest. According to KARI officials, the official Korean name omits 'ho' (meaning 'ship'), so it is correct to simply call it 'Danuri.' There is no special reason for omitting 'ho.' The official English name is Korea Pathfinder Lunar Orbiter, abbreviated as KPLO.