Why the Moon Exploration Vehicle Is an 'Orbiter' Not a 'Satellite' [Reading Science]

Korean Lunar Exploration Orbiter Q&A

[Asia Economy Reporter Kim Bong-su] President Moon Jae-in revealed the plan to launch Korea's first lunar exploration orbiter on the 25th of last month, drawing public attention. If the launch succeeds in August next year, Korea will stand shoulder to shoulder with space powers such as the United States, China, Russia, Japan, and the European Union (EU). Here is a summary of the public's frequently asked questions about the lunar exploration orbiter.

Q. Why is it called a "ship" (선) and not a satellite?

△ The official name of the lunar exploration orbiter scheduled for launch next year is the "Korean Pathfinder Lunar Orbit (KPLO)." It differs from a typical "satellite" in terms of mission, performance, and system. Satellites usually have small propulsion modules and carry a limited amount of fuel. The lunar exploration orbiter must travel from Earth to the Moon and carries a propulsion module with strong thrust and a large amount of fuel for orbital insertion. Dr. Kim Eun-hyuk of the Korea Aerospace Research Institute's Lunar Exploration Project Team explained, "Objects orbiting Earth are called satellites, but since the lunar exploration orbiter departs from Earth to the Moon, its purpose and performance are different."

Q. How does it enter lunar orbit?

△ KPLO adopts the "WBS (Weak Stability Boundary)" method for lunar orbit insertion. The orbiter, launched from Earth toward the Sun, travels straight, then turns and approaches the Moon orbiting Earth at a speed similar to the Moon's orbital velocity. Initially, it orbits elliptically and gradually transitions to a circular orbit, allowing extreme fuel savings.

However, the orbiter must travel about 1.5 million km, nearly four times the Earth-Moon distance (approximately 380,000 km), taking about four months. The increased distance from Earth raises the risk of communication blackout and requires precise design.

This method was first successfully used by NASA in 2011 for launching two lunar orbiters. Korean researchers faced a crisis when the orbiter's weight exceeded the plan by 128 kg, reaching 678 kg, risking fuel shortage and inability to maintain the planned operation period (one year) and orbit. After consultations with NASA, this method was adopted early last year. Dr. Kim said, "The WBS method has not been widely used because it takes a long time. Space exploration can fail anytime, but success or failure does not depend on whether the WBS method or another method is used; it depends on the mission and environment."

Q. What are the main missions?

△ The lunar exploration orbiter will be the world's first to capture detailed images of the lunar surface using a wide-field polarization camera and create a titanium map. It will study magnetic anomaly regions on the lunar surface by measuring subtle magnetic fields with a magnetometer and explore helium-3, water, oxygen, and construction resources using a gamma-ray spectrometer. It will verify space internet communication technology between Earth and the lunar orbiter using a space internet verifier. Notably, it will photograph the lunar polar regions with the ShadowCam, developed by NASA, serving as a scout for humanity's second lunar landing project (Artemis) scheduled for 2024.