Written by Kenneth Chang
South Korea set off for the moon on Thursday. But it doesn’t want to stop there.
“We are also considering using the moon as an outpost for space exploration,” Kwon Hyun-joon, director general of space and nuclear energy at South Korea’s Ministry of Science, said in a written response to questions. “Although we hope to explore the moon itself, we also recognize its potential to act as a base for further deep space exploration such as Mars and beyond.”
South Korea’s lunar spacecraft, named Danuri, was launched on a SpaceX Falcon 9 rocket from Florida, setting out on a roundabout but fuel-efficient path that will have it arriving at the moon in mid-December. There, it will begin an orbit at an altitude of 62 miles above the moon’s surface. The main mission is scheduled to last for one year.
Originally known as the Korea Pathfinder Lunar Orbiter, the mission was given the name Danuri after it became the winning entry in a naming contest. It is a portmanteau of the Korean words for “moon” and “enjoy.”
Danuri will join spacecraft from NASA, India and China that are currently exploring Earth’s companion. Much like the United Arab Emirates, which launched toward Mars on a Japanese rocket in 2020, South Korea is the latest country with a small but ambitious space program to set out on a beyond low-Earth orbit. And also like the UAE’s Hope orbiter, the Danuri mission is intended to make meaningful scientific contributions to global efforts to explore and understand the solar system.
Kwon said the main goal of the Danuri mission was to develop basic technologies like the design of orbital trajectories, deep space navigation, a high-thrust propulsion system and a 35-meter antenna to communicate with distant spacecraft.
But the spacecraft’s scientific payload is sophisticated and will aid scientists in South Korea and globally in studying the moon’s magnetic field, measuring its quantities of elements and molecules like uranium, water and helium-3 and photographing the dark craters at the lunar poles, where the sun never shines. In addition to providing one of the instruments, called ShadowCam, NASA chose nine scientists to participate on Danuri.
One of its most important scientific instruments is a magnetometer. The moon’s interior no longer generates a magnetic field, but it once did, and that primordial field is preserved in lava flows that hardened during this era.
Ian Garrick-Bethell, a professor of planetary science at the University of California, Santa Cruz and a participating scientist on the Danuri mission, said that the early magnetic field appears to have been surprisingly strong — potentially even as much as double the strength of Earth’s current magnetic field.
Garrick-Bethell said it was puzzling that “such a small little iron core could have generated such a strong magnetic field.”
He is hoping that after the spacecraft’s primary mission of one year is complete, South Korea could choose to move Danuri much closer to the moon’s surface, within 12 miles or less, where the magnetometer could get a much better look at the magnetized rocks.
“Even a few passes at those low altitudes could help constrain how strongly magnetized those rocks are,” he said.
Garrick-Bethell is also looking to use the magnetometer to study magnetic fields generated within the moon as it is buffeted by the solar wind, a stream of charged particles emanating from the sun.
The rise and fall in the strength of the magnetic field in the solar wind induces electric currents in the moon, and those electric currents in turn generate magnetic fields that will be measured by Danuri. The characteristics of the magnetic field will give hints of the structure and composition of the moon’s interior.
This work also requires combining measurements with those made by two NASA spacecraft, THEMIS-ARTEMIS P1 and P2, which travel around the moon on highly elliptical orbits, so they can measure the changes in the solar wind while Danuri measures the induced magnetic fields closer to the surface.
“What we would learn from that is kind of a global map of the interior temperature and potentially composition and maybe even water content of the deep parts of the moon,” Garrick-Bethel said.
Scientists will use another of Danuri’s instruments, a gamma-ray spectrometer, to measure quantities of different elements on the moon’s surface. Danuri’s device can pick up a wider spectrum of lower energy gamma rays than similar instruments on earlier lunar missions, “and this range is full of new information to detect elements on the moon,” said Naoyuki Yamashita, a New Mexico-based scientist who works for the Planetary Science Institute in Arizona. He is also a participating scientist on Danuri.
Yamashita is interested in radon, which forms from the decay of uranium. Because radon is a gas, it could travel from the moon’s interior to its surface. (This is the same process that sometimes causes the buildup of radon, which is also radioactive, in the basements of houses.)
The amounts of the radioactive elements could provide a history explaining when various parts of the moon’s surface cooled and hardened, Yamashita said, helping scientists to work out which of the moon’s lava flows are older or younger.
The Korean Aerospace Research Institute, South Korea’s equivalent of NASA, will use Danuri’s high-resolution camera to scout the lunar surface for potential sites for a robotic lander mission in 2031, Kwon said.
A second camera will measure polarized sunlight bouncing off the lunar surface, revealing details about the size of particles that make up the lunar soil. Because constant bombardment by solar wind, radiation and micrometeorites breaks the soil apart, the size of grains found in a crater could give an estimate of its age. (Smaller grains would suggest an older crater.)
The polarized light data will also be used to map abundances of titanium on the moon, which could one day be mined for use on Earth.
NASA supplied one of the cameras, a ShadowCam, which is sensitive enough to pick up the few photons that bounce off the terrain into the moon’s dark, permanently shadowed craters.
These craters, located at the moon’s poles, remain forever cold, below minus 300 degrees Fahrenheit, and contain water ice that has accumulated over the eons.
The ice could provide a frozen history of the 4.5 billion-year-old solar system. It could also be a bounty of resources for future visiting astronauts. Machinery on the moon could extract and melt the ice to provide water. That water could then be broken apart into oxygen and hydrogen, which would provide both air to breathe for astronauts and rocket propellants for travelers seeking to travel from the moon to other destinations.
One of the main purposes of ShadowCam is to find the ice. But even with Danuri’s sophisticated instruments, that could be challenging. Shuai Li, a researcher at the University of Hawaii and a Danuri participating scientist, thinks the concentrations might be so low that they will not be obviously brighter than areas not containing ice.
“If you don’t look at it carefully, you might not be able to see it,” Li said.
Jean-Pierre Williams, a planetary scientist at the University of California, Los Angeles, and another participating scientist in the Danuri mission, is hoping to produce detailed temperature maps of the craters by combining the ShadowCam images with data gathered by NASA’s Lunar Reconnaissance Orbiter.
NASA’s orbiter, which has been studying the moon since 2009, carries an instrument that records temperatures of the lunar surface. But those measurements are blurred over a fairly large area, about 900 feet across. The resolution of a ShadowCam is about 5 feet per pixel. Thus, the ShadowCam images used together with computer models might make it possible to tease out temperature variations on the surface.
“With this data we can map out local and seasonal temperatures,” Williams said. That, in turn, can help scientists understand the stability of water and carbon dioxide ices in the crater.
Researchers will have to wait several months for the science to begin. The spacecraft is taking a long, energy-efficient route to the moon. It first heads toward the sun, then loops back around to be captured in lunar orbit on Dec. 16. This “ballistic trajectory” takes longer but does not require a large engine firing to slow the spacecraft when it gets to the moon.
South Korea has an extensive military missile program and has placed several communications and earth observation satellites in low-Earth orbit since launching its first in 1992. And it has been expanding its domestic rocket launching capabilities so that future missions may not need to rely on SpaceX, or on other countries, to get to space. In June, the Korean Aerospace Research Institute successfully placed several satellites in orbit with the second flight of Nuri, its homegrown rocket.
“We will take on challenging projects such as lunar landers and asteroid exploration,” Kwon said.