The Korea Aerospace Research Institute (KARI) is preparing to launch its Korea Pathfinder Lunar Orbiter (KPLO), recently named Danuri. Danuri is South Korea’s first of many planned lunar missions in the coming future. This mission is developed and operated by KARI with contributions from NASA. A SpaceX Falcon 9 will launch Danuri on August 2, 2022.
Danuri is the first step in KARI’s lunar exploration program. KARI was established in 1989 and became an independent organization in 1996. The institute launched its first sounding rocket in June 1993 with the single-stage Korea Sounding Rocket (KSR-I). Five years later, it launched its two-stage sounding rocket named KSR-II.
In December 1999, KARI’s Korea Multi-Purpose Satellites (KOMPSAT-1) reached orbit, becoming South Korea’s first satellite. 10 years later, KARI completed its first orbital launch attempt with the Korea Satellite Launch Vehicle (KSLV)-1, also known as the Naro-1. South Korea became the 11th country to reach orbit in 2013 with the third and final launch of the Naro-1.
With South Korea learning how to operate in space, KARI began the Korean Lunar Exploration Program (KLEP) to explore farther. KARI started a long-term plan for space development in 2013. In 2014, KARI and NASA began talks to cooperate on a lunar spacecraft. Negotiations continued until December 2016 when they signed the Cooperation Implementation Agreement for the Danuri spacecraft.
As a part of the agreement, NASA would provide an instrument while supporting the mission design, communications, tracking, and navigation using NASA’s deep-space ground stations. Both will form a joint science team to conduct scientific research using the data from the mission. In 2021, NASA assigned nine scientists with an associated instrument to help with science.
KARI would provide the spacecraft five instruments and be the primary lead of the Danuri mission. Danuri will become KARI’s first mission to travel beyond Earth orbit.
The Danuri spacecraft is a 678 kg spacecraft bus with the aforementioned six instruments. Danuri is a cubic-shaped spacecraft with two solar arrays and communications antennae. For propulsion, it uses four Orbit Maneuver Thrusters (OMT), each having ~30 N of thrust with a specific impulse of 227 seconds. Eight Attitude Control Thrusters (ACT) will also be used with ~five N of thrust and 218 seconds of specific impulse.
The OMT will be used for large trajectory correction maneuvers (TCM) with 10 m/s or more Delta-V required. For burns needing 10 m/s or less, the ACT will be used instead. It will also be used to allow small orbital corrections and propellant settling. Monopropellant will be used to fuel the thrusters.
The twin solar arrays will provide 760 watts of energy to power the spacecraft. On the spacecraft, two bands of communication will be used: a low-gain S-band antenna will be used for both uplink and downlink communications, and a high-gain X-band antenna will be used for high-speed downlink communications.
Danuri’s six instruments all cover a wide range of tasks to complete its mission objectives. Three instruments are camera-based to image the lunar surface, with two of the imagers provided by KARI.
The first imager is called the Lunar Terrain Imager (LUTI). LUTI’s goal is to capture high-resolution images of a future landing site on the lunar surface. This imager will have a high spatial resolution of five meters with a swath of eight km. Its mass will be less than 15 kg.
The second KARI-provided imager is the Wide-Angle Polarimetric Camera (PolCam). PolCam will be used to capture polarimetric images for the entire surface except for the polar regions. These polarimetric images will have medium spatial resolution with wider angles for photos. Using these images, PolCam will be used to investigate the detailed characteristics of lunar regolith. Two nadir-facing cameras make up the three kg instrument.
Danuri’s final imager is NASA’s provided ShadowCam. ShadowCam is based on the Lunar Reconnaissance Orbiter Camera (LROC) Narrow-Angle Camera (NAC) imager. The LROC NAC is currently being used on the still operating LRO spacecraft which was launched in 2009. For Danuri, ShadowCam is modified to be 200 times more sensitive than the LRO original imager.
When in orbit, ShadowCam will map the reflectance of permanently shadowed regions (PSR) to find evidence of frost or ice deposits. ShadowCam will observe the PSR monthly to detect the seasonal changes to measure the terrain inside craters, including boulders. The <15 kg imager will have a resolution of 1.7-meters. It was delivered to KARI in August 2021 and was installed onto the spacecraft in October.
The last three instruments are provided by KARI. A 3.5 kg magnetometer instrument will be used to measure the magnetic strength of the lunar environment. Known as KPLO Magnetometer (KMAG), it is comprised of three fluxgate magnetometers placed on different parts of the spacecraft. One is placed inside the spacecraft body, while two are mounted on the 1.55-meter-long boom. Using these sensors, KMAG will measure the magnetic strength up to ~100 km from the lunar surface.
Danuri’s final science instrument is the KPLO Gamma-Ray Spectrometer (KGRS). The KGRS will measure the gamma-rays that are emanating from the lunar surface. Using the gamma-rays detected, it will investigate the characteristics of the resources of the Moon and map the spatial distributions of the elements. This instrument will mass five kg.
Danuri’s final payload is a technology demonstrator for KARI. The Disruption Tolerant Network experiment payload (DTNPL) will test space communications based on a disruption tolerant network technology. As another test, Danuri will attempt to implement a wireless internet environment to connect satellites or exploration spacecraft. Using this wireless environment, Danuri will stream the song Dynamite by the South Korean band BTS.
Danuri’s goal is to test new lunar exploration technologies while demonstrating space internet and conducting scientific investigations. KARI has built new ground support equipment to help with Danuri and future lunar missions. In 2021, KARI completed a new deep-space antenna to talk with Danuri during its mission. NASA has also started testing with Danuri using its Deep Space Network to support the mission.
To name the spacecraft, KARI conducted a nationwide competition to have the honor of naming KPLO. In May 2022, Danuri was selected to be the name of KPLO. Danuri is a mix of the work Dal — meaning Moon — and Nuri — meaning enjoy.
The spacecraft has already been assembled and has completed environment testing ahead of its delivery and launch.
In late 2017, KARI selected SpaceX to launch Danuri from Cape Canaveral, Florida. SpaceX will use a Falcon 9 rocket to take the spacecraft on a path to the Moon. Falcon 9 will initially take the spacecraft to a low-Earth parking orbit, where it will then enter an elliptical transfer orbit. Danuri will be using a Weak Stability Boundary/Ballistic Lunar Transfer (BLT) method to reach the Moon.
The transfer orbit will place the spacecraft in an apogee near Lagrange Point 1 (L1). When it approaches L1, its gravitational pull will help boost the spacecraft on a path toward the Moon. Using its onboard propulsion, it will then maneuver itself to enter lunar orbit.
Once it reaches the Moon, Danuri will complete multiple burns to reach its 100 (+- 30) km circular orbit at 90 degrees inclination, set to be reached on December 31. The 100 km orbit is where Danuri’s year-long primary mission will take place. If Danuri reaches orbit, South Korea will be the seventh country to reach lunar orbit.
If a mission extension is granted, it will lower its orbit to ~70 km to conduct more science.
In May 2021, South Korea signed the Artemis Accords to support NASA to return humans to the Moon. South Korea wants to establish a long-term presence on the Moon, and the accords aligned with that goal. Using the lessons learned for Danuri, KARI will then move on to phase two of their lunar exploration program.
By 2030, KARI wants to attempt to land on the Moon as a part of phase two. Phase two will consist of a lunar orbiter, a lander, and a rover. While no vehicle has been selected to launch this mission, an indigenous vehicle will likely be used to support this mission.
KARI will have a busy few months in 2022 as they are currently getting ready for the return to flight of the KSLV-II or the Nuri rocket. Nuri took its first flight on October 21, 2021. While the rocket did not reach orbit, the test flight was able to successfully test the first and second stages. During the flight, the payload fairing and payload simulator was successfully separated. It failed to reach orbit due to an anchor for a third-stage helium tank failing which caused a premature engine shutdown.
Nuri is currently set to take its second test flight no earlier than June 15, 2022. This time, it will carry four CubeSats with a single large performance verification satellite.
(Lead image: rendering of Danuri in lunar orbit. Credit: KARI)