[Reading Science] 'China Succeeds at Once, Japan Fails'... Was Moon Landing That Difficult?

Experts Point Out "Experience of Failure in Advanced Technology Is Essential"

"Space development is a representative field where failure leads to success."

Japan, boasting over 20 Nobel laureates in science and a high level of scientific technology, failed in its first attempt at a lunar landing in the early hours of the 26th (Korean time). Compared to China's one-time success, this is a 'humiliation.' However, so far, only three countries? the United States, Russia (former Soviet Union), and China?have succeeded in landing on the moon. Why is lunar landing so difficult?

The lunar lander Hakuto-R M1 developed by the Japanese private company ispace.

The international academic journal Nature reported on the 27th (local time) the answers from scientists to this question. First, entering lunar orbit itself is quite tricky. NASA's Luna Flashlight, launched in December last year, is a representative case. This small spacecraft, originally tasked with exploring ice at the lunar poles, failed to enter its mission orbit due to a propulsion system malfunction after launch. South Korea's first lunar orbiter, Danuri (KPLO), after about four months of navigation following its launch in September last year, safely entered lunar orbit in December, much to the relief of those involved.

The difficulty in entering lunar orbit lies in the difference in 'speed.' The moon orbits at about 1 km/s, similar to a bullet. Spacecraft attempting to enter lunar orbit generally travel much faster. Danuri, for example, was flying at 2.08 km/s. Even a tiny error beyond the ninth decimal place in orbital calculations could cause the spacecraft to miss lunar gravity capture and become a 'space orphan.' Precise technology is required to reduce the spacecraft's speed appropriately while consuming minimal fuel. Fortunately, the Korea Aerospace Research Institute (KARI) succeeded in joining lunar orbit with only three propulsion maneuvers instead of the initially expected five. This moment extended Danuri's lifespan by at least one to two years.

Regarding this, there are three methods to enter lunar orbit about 384,000 km from Earth: direct transfer, which goes straight like a cannonball or bullet; phasing transfer, which first enters Earth's orbit and gradually expands the orbit radius to join the moon's Earth orbit before ascending; and ballistic lunar transfer (BLT), which first heads toward the sun and then returns to lunar orbit. All methods require reducing the spacecraft's speed during lunar orbit insertion while consuming a lot of fuel for attitude control, direction changes, and altitude adjustments, which must be minimized to extend lifespan.

Even after arriving in lunar orbit, landing is another challenge. Landing on the surface without satellite navigation systems (GPS) or atmospheric lift, as on Earth, is extremely difficult. The critical moment is especially when approaching the lunar surface. The lander's sensors can be disturbed by large amounts of dust or rock fragments caused by gas ejected from thrusters. The failures of India and Israel in 2019 were analyzed to have been caused by software and sensor errors occurring at the final landing moments. The recent failure of ispace is also presumed to have been caused by dust interfering with altitude calculation, leading to fuel depletion just before landing.

[Image source=Yonhap News]

Steven Indyk, a space systems expert at the American space development company Honeybee Robotics, explained, "The reason lunar landing is difficult is because there are so many factors to consider," adding, "The moon has less gravity than Earth, a much thinner atmosphere, and more dust." Lunar gravity is only one-sixth of Earth's, and there is almost no atmosphere. Instead, the surface is covered with rocks and dust. Indyk said, "To succeed in lunar landing, you must anticipate how this environment affects the lander and spend money testing how things can go wrong. The lander must be repeatedly tested to adapt to as many scenarios as possible, but even then, nothing is guaranteed."

The lack of experience among private space companies is also a major issue. The lunar landing attempt by the Japanese private space company ispace this time is not actually the first in the private sector. Israel's private company SpaceIL already recorded a failure in 2019. Government agencies have accumulated know-how through numerous failures. The United States and the former Soviet Union, which attempted lunar landings in the 1960s, also experienced multiple failures. Based on lessons learned from these failures, the former Soviet Union successfully soft-landed Luna 9 in January 1966, and the United States followed with Surveyor 1 in April of the same year. China's success in the Chang'e-3 mission, its first lunar landing attempt in 2013, was rather an exception. China subsequently succeeded in landing Chang'e-4 on the far side of the moon for the first time and achieved sample collection and return with Chang'e-5. However, India also failed in its first lunar landing attempt in 2019 and plans to retry in the second half of this year.

What lesson does this history of lunar landings offer to South Korea? Perhaps it is that 'smart failure'?not fearing failure, learning what can be learned, and encouraging progress?is necessary. South Korea has been involved in space development for over 20 years, starting from indifference. Its history and technological level are still limited. After about a decade of failures and development, it succeeded in launching its first indigenous launch vehicle, Nuri, in June last year. The third launch is scheduled after the 24th of next month. South Korea is also developing a next-generation launch vehicle to follow Nuri by 2031 and aims to challenge independent lunar landing exploration. Various projects, including the establishment of the Korean Positioning System (KPS), are underway. Any failure that may occur should not be seen as a setback but as part of 'progress.'