Temporal Variations in KGRS Gamma-Ray Data over the KPLO/DANURI Mission

South Korea’s first lunar probe, the Korea Pathfinder Lunar Orbiter (KPLO, DANURI), was launched in August 2022 and successfully entered lunar orbit in December of the same year. KPLO is currently conducting a mission with the KPLO Gamma-Ray Spectrometer (KGRS), developed by the Korea Institute of Geoscience and Mineral Resources (KIGAM). KGRS detects gamma-ray energies from 30 keV to 12 MeV and consists of a LaBr3 gamma-ray spectrometer and a Boron-Loaded Plastic Scintillator (BLPS) containing 5 % boron for background rejection. The primary scientific objective of KGRS is to collect gamma-ray spectral data from the lunar surface and to produce elemental abundance maps, which provide critical constraints on the bulk composition of the lunar surface and subsurface. Such elemental maps are directly relevant to the planning of future in situ robotic and human exploration missions, including site selection for resource utilization and ground-truth validation of orbital datasets.

KGRS data are processed through multiple steps, including positional data integration and exclusion of unusable data, in order to make them suitable for scientific analysis. KGRS data are currently available to the public through the KARI Planetary Data System (KPDS) website in Raw, PP, and CAL formats. All KGRS data transmitted to KIGAM are monitored daily, tracking both engineering parameters (e.g., instrument temperature) and science data, enabling the detection of transient events such as solar flares and gamma-ray bursts.

Since 2023, KGRS has accumulated more than three years of continuous gamma-ray spectral data from the lunar surface. The total gamma-ray count decreased by approximately 15% between 2023 and 2025. The decreasing trend is consistent with enhanced heliospheric modulation during the approach to solar maximum, which suppress the galactic cosmic-ray (GCR) flux responsible for inducing lunar gamma-ray emissions.

The orbit of KPLO was modified twice in 2025. Following initial operations in a near-circular orbit at approximately 100 km altitude, the orbit was lowered to approximately 60 km in February 2025. In late September 2025, KPLO transitioned into a frozen orbit with altitudes ranging from approximately 60 to 200 km.

This presentation reports on how KGRS spectral data vary as a function of time and changing mission environments, including orbital altitude modifications, over the course of the KPLO mission, and discusses the scientific implications of long-term lunar gamma-ray datasets in support of future lunar landing-site selection and exploration planning.