South Korea's probe is on its way to the Earth's Moon

SpaceX rocket launched KPLO into lunar orbit

South Korea joined the lunar explorers club on Thursday, August 4, 2022, with the launch of a lunar orbiter that will explore future landing spots. The KPLO or Danuri spacecraft, launched by SpaceX from Space Launch Complex 40 at Cape Canaveral Space Force Station in Florida, is already traveling an indirect Earth-Moon trajectory to save propellant and will reach its target in December. The Falcon 9 Rocketv1.2 FT Block 5 number B1052.6 took off at 19:08 ET (23:08 UTC). If successful, the spacecraft will join those of the US and India already operating around the Moon and a Chinese rover exploring the far side of Earth's natural satellite. India, Russia, and Japan have new lunar missions slated for later this year or next, as do a number of private companies in the US and elsewhere. The first stage 'core' Booster landed 640 km from the launch site on the Just Read The Instructions drone ship. The rocket's head fairing shells were recovered by the SpaceX vessel "Bob" 730 km away from Florida.

The second stage of the rocket fired several times to place the probe on an initial apogee and perigee trajectory of 250 km, inclined at 28.5 degrees. Afterward, the trajectory will change to a perigee of 1,687,814 km and an apogee of 1,687,813.9 km.

Danuri – Korean for “Moon Explorer,” or KPLO – Korean Pathfinder Lunar Orbiter – is carrying six science instruments, including a NASA camera. It was designed to study ice-filled, permanently shadowed craters at the lunar poles. NASA favors the lunar South Pole for future astronaut outposts due to evidence of frozen water and natural resources. South Korea plans to land its own spacecraft on the Moon – a robotic probe – by 2030 or later.

KPLO is the first lunar mission developed and managed by the Korean Aerospace Research Institute, and will be a joint mission with NASA. The cube-shaped orbiter will circle the Moon for about a year. During this period, it will carry out six experiments: five from Korean universities and research institutes and one from the US, the South Korean space agency said.

The onboard experiments are:

  • Measurement of gamma rays coming from the lunar surface.

  • Spatial Internet: Demonstrating an interruption-tolerant network, or "spatial internet".

  • Measurement of the lunar magnetic field.

  • Lunar Terrain Imager: A high resolution camera that will take pictures of potential landing sites for future lunar exploration missions.

  • Wide-Angle Polarimetric Camera: This experiment will study the composition of the Moon's surface, except for the polar regions and volcanic deposits.

  • ShadowCam: NASA-funded experiment using an ultra-sensitive camera to take pictures of permanently shadowed areas of the Moon to study terrain and look for evidence of frost and ice deposits.

The $180 million mission — the country's first step in lunar exploration — features a square, solar-powered satellite designed to orbit 100 kilometers above the lunar surface. Scientists hope to collect geological and other data for at least a year from this low polar orbit.

In June, South Korea successfully launched a package of satellites into orbit around the Earth for the first time using its own rocket. The first attempt failed last fall, with the test satellite failing to reach orbit. In May, the country joined an American-led coalition to explore the moon with astronauts for years and decades to come, which NASA is targeting later this month for the first launch, in its Artemis program. The goal is to send an unmanned capsule around the Moon and back to test the systems before a crew comes aboard in two years. “…Danuri is just the beginning,” said Sang-Ryool Lee, president of the Korea Aerospace Research Institute, at the SpaceX launch webcast.

The life of the mission provides for one year of operation in a circular orbit 100 km above the lunar surface, with a tilt angle of 90 degrees. KPLO's total launch mass is approximately 678 kg, including the six payloads. The spacecraft is cubic in shape (dimensions are 1.82 m x 2.14 m x 2.29 m) with two solar panels and a high-gain satellite dish mounted on a lance. Communications are via S-band (telemetry and command) and X-band (payload data downlink). Power (760 W at 28 V) is provided through solar panels and rechargeable batteries. The original initial transfer method for reaching the Moon was to use a 3.5-phase "loop" orbit around the Earth; however, the WSB/BLT (Weak Stability Boundary/Ballistic Lunar Transfer) method was selected later to save delta V, which ends up guaranteeing more fuel. It is known that an average of around 160 m/s delta V savings can be achieved by selecting the WSB/BLT method compared to the conventional transfer method, and KPLO will actually save around 165 m/s delta V .

With an investment of 237 billion won (South Korean currency and equivalent to US$180 million) and developed over six years, KPLO brings enthusiasm to researchers and scientists as the probe aims to reveal crucial aspects of the Moon. , including ancient magnetism and dust scattered across its surface. The researchers hope the spacecraft will shed light on hidden water sources along with ice near the poles, especially in areas that remain permanently cold and dark.

Going to the Moon with BLT/WSB method

With the WSB/BLT method, the baseline release period for KPLO was approximately 40 days (late July to early September 2022). After several months of transfer, the spacecraft will reach the Moon in mid-December 2022 and begin the Lunar Orbit Acquisition (LOA) phase. During the LOA phase, which is expected to last approximately 15 days, KPLO will perform a total of five Lunar Orbit Insertion (LOI) burns to reach its final target orbit. Immediately following the LOA phase, the commissioning phase will begin for a period of approximately one month. During the commissioning phase, not only the KPLO chassis, but also all onboard instruments will be calibrated and validated to conduct the next nominal one-year mission around the Moon.

To be placed in lunar orbit (lunar orbit acquisition, LOA), the spacecraft was designed with four orbital maneuver engines, the Orbit Maneuver Thruster (OMT), with approximately 31.8 Newtons of thrust with 227 s of Isp (specific impulse) for executing large burns, and eight attitude control engines, the Attitude Control Thruster (ACT) with approximately 3.48 N with 218 s of Isp for executing small burns. All these engines will be grouped together for recording runs. Four OMT engines will be grouped together to be used for the main thruster set for large burns during the transfer and LOA phase, i.e. lunar orbit insertionor LOIs, as well as large Trajectory Correction Maneuvers (TCMs) that require more than 10 m/s deltaVs. For small burns, such as TCMs below 10 m/s, thrust dump and orbit maintenance during the nominal mission phase, eight individual ACT engines will be grouped into sets of two ACTs.

Scientific Ambitions

South Korean space scientists hope the country's inaugural lunar mission will facilitate more ambitious projects in the future. Kyeong-ja Kim, the principal investigator of an instrument at Danuri, the gamma-ray spectrometer and planetary geoscientist at the Korean Institute of Geoscience and Mineral Resources in Daejeon, expressed his hopes about the mission saying, “Success for Danuri will ensure the future planetary exploration. Everyone is very happy and excited.”

Eunhyeuk Kim, the project scientist for the KARI mission in Daejeon, said: "The spacecraft is ready to launch." Expressing the team's cautions, Kim said, "Until the time of launch, we will be checking all systems repeatedly." Rachel Klima, a planetary geologist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, and part of the mission's science team, commented: "It's so interesting to see more and more countries sending their orbiters and increasing global understanding of what's happening. on the moon." Danuri will have five science instruments, including the PolCam, which will be the first camera to scan the lunar surface using polarized light and record how light reflects off the lunar surface.

"This can help researchers study unusual objects, such as small, porous dust towers called fairy castle structures," Klima said. Another highly sensitive camera provided by NASA, the ShadowCam, will capture images of permanently shadowed regions. These regions never receive sunlight.

“Since shortly after the formation of the Moon, volatile materials, such as water from comets, have bounced off its surface and become trapped in these very cold regions. We have billions of years of Solar System history trapped in the layers of these cold traps . By giving researchers a view of the terrain in these regions and identifying brighter regions that could be ice deposits, ShadowCam will be able to inform future landing missions to study this history,” commented Klima.

Danuri also has a magnetometer along with the optical instruments, and scientists believe it could help reveal crucial aspects of the Moon's magnetism. The Moon's surface demonstrates highly magnetic regions, suggesting that the lunar core generated a magnetic field as strong as Earth's through a process known as a dynamo. Scientists remain intrigued by the lunar magnetic phenomenon. The Moon's core is much smaller and proportionately farther from the surface compared to Earth. So how the core could have maintained such a strong dynamo remains elusive. The South Korean mission may reveal something about this, experts believe.

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