The Korea Pathfinder Lunar Orbiter (KPLO), also known as Danuri, successfully survived total lunar eclipses in Mar. and Sep. 2025 during its second Extended Mission (EM) phase. Unlike previous lunar orbiters, KPLO faced significantly more severe operational constraints. To survive the eclipse, KPLO intentionally entered a Safe-Hold (SH) mode, shutting down not only science payloads and attitude control systems but also critical components such as the thruster's catalyst bed heater and Valve Driving Electronics (VDE). This operational strategy represented a particularly challenging approach, even compared to typical SH mode operations. To manage this high-risk scenario, the mission team carefully developed and validated a three-step eclipse survival strategy comprising a Phase Adjustment Maneuver (PAM) to optimize solar exposure, a Power Saving Mode (PSM) to minimize energy consumption, and a Pre-Heating Mode (PHM) for thermal conditioning. In addition, detailed spacecraft bus operational procedures were established based on KPLO's health status. KPLO executed two PAMs to maximize solar exposure prior to the first eclipse on Mar. 2025, and two on-orbit rehearsals were conducted to validate the established PSM and PHM strategies. Deficiencies identified during these rehearsals were addressed to refine operational procedures. Asa result, KPLO successfully survived the first encountered total lunar eclipse without any anomalies. For the second total lunar eclipse on Sep. 2025, the verified operational strategy was successfully applied, and KPLO also endured the event without any issues. This paper provides details of the total eclipse survival process, starting from the establishment of the survival strategy, telemetry-based analysis results from the on-orbit rehearsals, and the actual eclipse operation. The flight-proven results presentedin the current work offer practical insights into the lunar exploration community facing extreme system constraints and limited design margins, especially under conditions similar to those encountered during a total lunar eclipse. (c) 2026 COSPAR. Published by Elsevier B.V. All rights are reserved, including those for text and data mining, AI training, and similar technologies.

The Korea Pathfinder Lunar Orbiter (KPLO), also known as Danuri, has been successfully operating in lunar orbit for over two years. During this period, KPLO itself executed four Collision Avoidance Maneuvers (CAMs) to mitigate conjunction risks with other spacecraft in lunar orbit. This paper presents an in-depth analysis of KPLO's CAM operations, from risk assessment to execution, emphasizing the critical role of international collaboration in ensuring lunar orbital safety. The conjunction risk analysis leveraged state-of-the-art tools, including the National Aeronautics and Space Administration’s (NASA) Multi-Mission Automated Deep-space Conjunction Assessment Process (MADCAP) and Conjunction Assessment of Risk in Deep Space (CARDS), to identify potential collision threats. Decision-making processes were conducted in coordination with international stakeholders, ensuring timely and effective CAM execution. The operational results of the four CAMs done by KPLO are thoroughly discussed, highlighting the detailed timeline of work process, challenges faced, and efforts made during each event. Furthermore, this study outlines key lessons learned from KPLO's CAM experience, offering practical recommendations to address the growing risks of orbital collisions in the increasingly crowded lunar environment. The findings emphasize the necessity of international collaboration and standardized protocols for sustainable future missions to or at the Moon.

South Korea's first lunar orbiter, Danuri, was successfully launched on August 4, 2022, and entered its designated lunar mission orbit at the end of 2022. This paper presents the operational results of Danuri during the trans-lunar phase, with a focus on its flight dynamics and trajectory control. Danuri employed a Ballistic Lunar Transfer (BLT) trajectory to minimize fuel consumption, a method requiring precise maneuver planning and execution due to the trajectory's high sensitivity. Originally, nine Trajectory Correction Maneuvers (TCMs) were planned for its journey to the Moon. Following its launch from Cape Canaveral Space Force Station, Florida, four TCMs, TCM1, TCM3, TCM5, and TCM6, were conducted during the mission to correct navigation and burn errors and satisfy the stringent lunar arrival conditions. As a result, Danuri successfully entered lunar orbit on December 16, 2022, completing three Lunar Orbit Insertion (LOI) maneuvers to achieve a stable polar orbit at an altitude of 100 +/- 20 km. This study provides a comprehensive analysis of the Orbit Determination (OD) and Maneuver Planning (MP) results for each TCM, supported by data from the actual flight operation. It also evaluates TCM performance through post-OD analysis and maneuver reconstruction results, offering valuable insights into burn accuracy and error mitigation strategies. Additionally, this paper presents the wheel-off loading (WOL) maneuver used in conjunction with TCMs to satisfy lunar arrival conditions. The findings of this study contribute significantly to the understanding of flight dynamics and operational strategies for mission employing BLT trajectories. By demonstrating the adaptability required for real-time decision-making and the successful management of navigation and operational challenges, the Danuri mission sets a precedent for future space exploration endeavors, particularly those utilizing fuel-efficient transfer trajectories. Danuri's success has provided practical insights and operational experiences that are instrumental for advancing the field of space exploration. (c) 2025 Published by Elsevier B.V. on behalf of COSPAR.

This work proposes improving the Flight Dynamics (FD) operational system for future planetary missions using insights gained from the real-flight experience of the Korea Pathfinder Lunar Orbiter (KPLO) mission. The KPLO, also known as Danuri, is South Korea’s first lunar explorer launched on August 4, 2022 UTC, and is currently successfully conducting its mission around the Moon. The KPLO FD specialists (FDSp) worked extensively on designing, developing, verifying, validating, and operating the FD-related ground system, currently in nominal condition without major issues. After a year of real-flight experience, FDSp identified areas in architecture and functionality that require further improvement, specifically focusing operational reliability and efficiency. This work first provides an overview of KPLO’s bus and ground system, subsequently presenting the design architecture and corresponding functionalities of the FD-related ground systems. Following that, suggestions for improving the design and functionality of FD-related ground systems are made, with in-depth discussions to enhance operational reliability and efficiency for future planetary missions. The results from this work can serve as valuable guidelines for the design and operation of FD ground systems in planetary exploration missions, facilitating more efficient and reliable FD operations.

The Korea Pathfinder Lunar Orbiter (KPLO), also known as Danuri, has completed its primary mission and is now in the first phase of its extended mission. Given the current overall programmatic status, particularly the spacecraft’s health and remaining fuel, executing the second phase of the extended mission appears viable. This study presents the design and evaluation of the second phase of the Extended Mission Orbit (EMO) for KPLO, focusing on the practical considerations and rationale behind designing the additional extended mission. The process began with a preference survey conducted among the science Principal Investigators (PIs) of the onboard payloads to maximize scientific output and solidify the extended mission. Following this, real-world operational constraints were considered to refine and finalize the candidate EMOs. The study introduces two viable candidates for the second phase of EMO scenarios for KPLO, along with details of associated operational timelines, maneuvers, and orbital characteristics. The feasibility of both candidate orbits has been confirmed from the perspective of flight dynamics. However, the final decision on which EMO scenario to implement remains undecided. The ultimate selection will greatly depend on the operational results up to 2025. Regardless of which EMO option is ultimately chosen, ongoing analyses based on real-time flight data will allow for adjustments and refinements to the EMO plans, ensuring compliance with planetary protection requirements and optimizing the mission’s success. This study comprehensively addresses all critical aspects of EMO design by combining real-world operational constraints with scientific objectives, providing practical insights for future lunar exploration missions.

Korea Pathfinder Lunar Orbiter (KPLO) is South Korea’s first space exploration mission, developed by the Korea Aerospace Research Institute. It aims to develop technologies for lunar exploration, explore lunar science, and test new technologies. KPLO was launched on August 5, 2022, by a Falcon-9 launch vehicle from cape canaveral space force station (CCSFS) in the United States and placed on a ballistic lunar transfer (BLT) trajectory. A total of four trajectory correction maneuvers were performed during the approximately 4.5-month trans-lunar cruise phase to reach the Moon. Starting with the first lunar orbit insertion (LOI) maneuver on December 16, the spacecraft performed a total of three maneuvers before arriving at the lunar mission orbit, at an altitude of 100 kilometers, on December 27, 2022. After entering lunar orbit, the commissioning phase validated the operation of the mission mode, in which the payload is oriented toward the center of the Moon. After completing about one month of commissioning, normal mission operations began, and each payload successfully performed its planned mission. All of the spacecraft operations that KPLO performs from launch to normal operations were designed through the system operations design process. This includes operations that are automatically initiated post-separation from the launch vehicle, as well as those in lunar transfer orbit and lunar mission orbit. Key operational procedures such as the spacecraft’s initial checkout, trajectory correction maneuvers, LOI, and commissioning were developed during the early operation preparation phase. These procedures were executed effectively during both the early and normal operation phases. The successful execution of these operations confirms the robust verification of the system operation.

This paper outlines the collaborative efforts between the Korea Aerospace Research Institute (KARI) and the National Aeronautics and Space Administration (NASA) Johnson Space Center (JSC) for the Flight Dynamics (FD) operation of the Korea Pathfinder Lunar Orbiter (KPLO). From the outset of the KPLO program, the joint KARI KPLO FD team and NASA JSC Flight Operations Directorate (FOD) have devoted significant time and effort towards ensuring the mission’s success. This paper begins by introducing the aims and scope of the collaborative work, followed by a detailed description of the efforts made between the KPLO FD team and JSC FOD. This includes the top-level concept, interface architecture, test results, established operation procedures/timeline, and the summary of the joint rehearsal conducted. Finally, the paper discusses the challenges and lessons learned from this journey, particularly from the practical FD operational perspectives. Thanks to the joint team’s collaborative efforts, KPLO has successfully entered lunar orbit and is performing its mission exceptionally well. The joint experience has fostered mutual trust between KARI and NASA JSC, serving as a foundation for further cooperation and collaboration. The efforts and outcomes described in this work will provide valuable insights to experts worldwide who are willing to foster similar international collaborations in the future.

On Aug. 4, 2022, at 23:08:48 (UTC), the Korea Pathfinder Lunar Orbiter (KPLO), also known as Danuri, was launched using a SpaceX Falcon 9 launch vehicle. Currently, KPLO is successfully conducting its science mission around the Moon. The National Aeronautics and Space Administration (NASA)’s Deep Space Network (DSN) was utilized for the successful flight operation of KPLO. A great deal of joint effort was made between the Korea Aerospace Research Institute (KARI) and NASA DSN team since the beginning of KPLO ground system design for the success of the mission. The efficient utilization and management of NASA DSN in deep space exploration are critical not only for the spacecraft’s telemetry and command but also for tracking the flight dynamics (FD) operation. In this work, the top-level DSN interface architecture, detailed workflows, DSN support levels, and practical lessons learned from the joint team’s efforts are presented for KPLO’s successful FD operation. Due to the significant joint team’s efforts, KPLO is currently performing its mission smoothly in the lunar mission orbit. Through KPLO cooperative operation experience with DSN, a more reliable and efficient partnership is expected not only for Korea’s own deep space exploration mission but also for the KARI-NASA DSN joint support on other deep space missions in the future.

The Korea Pathfinder Lunar Orbiter (KPLO), officially named as Danuri, is the Republic of Korea's first spacecraft to orbit the Moon. The goal of KPLO is to secure core deep space technology for future space exploration in Korea and contribute to lunar science by gathering data from the lunar orbit for one year. This paper presents the results of KPLO's Lunar Orbit Acquisition (LOA) phase in detail, with a particular focus on the operational results of Flight Dynamics (FD). During the LOA phase, the KPLO FD team experienced many expected and unexpected issues. These issues were mitigated by making real-time updates to the LOA phase Design Reference Mission (DRM). The paper also presents the results of the Orbit Determination (OD) and performance of each Lunar Orbit Insertion (LOI) maneuver conducted during the actual flight operation. The importance of considering operational constraints when designing the DRM is emphasized by presenting lessons learned based on actual flight experiences. Unlike the original KPLO LOA phase DRM, KPLO successfully achieved the final mission orbit using only three LOI burns, instead of the planned five LOI burns and an Orbit Trim Maneuver (OTM). Despite the extensive revisions made to the DRM, all mission requirements were still fulfilled during the final lunar orbit insertion, taking into account the significant operational constraints.

This paper presents an analysis of the trans-lunar trajectory insertion performance of the Korea Pathfinder Lunar Orbiter (KPLO), the first lunar exploration spacecraft of the Republic of Korea. The successful launch conducted on August 4, 2022 (UTC), utilized the SpaceX Falcon 9 rocket from Cape Canaveral Space Force Station. The trans-lunar trajectory insertion performance plays a crucial role in ensuring the overall mission success by directly influencing the spacecraft's onboard fuel consumption. Following separation from the launch vehicle (LV), a comprehensive analysis of the trajectory insertion performance was performed by the KPLO flight dynamics (FD) team. Both orbit parameter message (OPM) and orbit determination (OD) solutions were employed using deep space network (DSN) tracking measurements. As a result, the KPLO was accurately inserted into the ballistic lunar transfer (BLT) trajectory, satisfying all separation requirements at the target interface point (TIP), including launch injection energy per unit mass (C3), right ascension of the injection orbit apoapsis vector (RAV), and declination of the injection orbit apoapsis vector (DAV). The precise BLT trajectory insertion facilitated the smoother operation of the KPLO's remainder mission phase and enabled the utilization of reserved fuel, consequently significantly enhancing the possibilities of an extended mission.

The Korea Pathfinder Lunar Orbiter (KPLO), also known as Danuri, successfully entered its mission orbit on December 27, 2022 (UTC), and is currently performing its mission smoothly. To mitigate potential contingencies during the flight and to navigate the spacecraft into the desired lunar orbit, the KPLO flight dynamics (FD) team analyzed major trajectory-related contingencies that could lead to the violation of mission requirements and prepared operational procedures from the perspective of trajectory and FD. This paper presents the process of preparing contingency trajectory operations for the KPLO, including the identification of trajectory contingencies, prioritization results, and the development of recovery plans and operational procedures. The prepared plans were successfully applied to address minor contingencies encountered during actual operations. The results of this study will provide valuable insights to FD engineers preparing for space exploration mission operations.

Korea Pathfinder Lunar Orbiter (KPLO), also known as Danuri, was successfully launched on 4 Aug. from Cape Canaveral Space Force Station using a Space-X Falcon-9 rocket. Flight dynamics (FD) operational readiness was one of the critical parts to be checked before the flight. To demonstrate FD software’s readiness and enhance the operator’s contingency response capabilities, KPLO FD specialists planned, organized, and conducted four simulations and two rehearsals before the KPLO launch. For the efficiency and integrity of FD simulation and rehearsal, different sets of blind test data were prepared, including the simulated tracking measurements that incorporated dynamical model errors, maneuver execution errors, and other errors associated with a tracking system. This paper presents the simulation and rehearsal results with lessons learned for the KPLO FD operational readiness checkout. As a result, every functionality of FD operation systems is firmly secured based on the operation procedure with an enhancement of contingency operational response capability. After conducting several simulations and rehearsals, KPLO FD specialists were much more confident in the flight teams’ ability to overcome the challenges in a realistic flight and FD software’s reliability in flying the KPLO. Moreover, the results of this work will provide numerous insights to the FD experts willing to prepare deep space flight operations.

Korea's first lunar mission, the Korea Pathfinder Lunar Orbiter (KPLO), aims to launch in mid-2022 via the Space-X Falcon-9 launch vehicle. For the successful flight operation of KPLO, the Korea Aerospace Research Institute (KARI) has designed and developed the Flight Dynamics Subsystem (FDS). FDS is one of the subsystems in the KPLO Deep-Space Ground System (KDGS), which is responsible for the overall flight dynamics-related operation. FDS is currently successfully implemented and meets all of the requirements derived from the critical design phases. The current work addresses the design and implementation results for the KPLO FDS. Starting from overviews on KPLO payloads, bus systems, and mission trajectory characteristics, a review on KDGS is also treated briefly. Details on the design philosophy, unique characteristics, and functionalities of all six different modules nested inside the FDS with its Graphical User Interface (GUI) design are discussed. Moreover, efforts currently devoted to the flight operation preparation of the KPLO are summarized, including many collaborative works between KARI and the National Aeronautics and Space Administration (NASA) teams.

This technical paper deals the practical transformation algorithms between several lunar reference frames which will be used for Korea pathfinder lunar orbiter (KPLO) flight operation. Despite of various lunar reference frame definitions already exist, use of a common transformation algorithm while establishing lunar reference frame is very important for all members related to KPLO mission. This is because use of slight different parameters during frame transformation may result significant misleading while reprocessing data based on KPLO flight dynamics. Therefore, details of practical transformation algorithms for the KPLO mission specific lunar reference frames is presented with step by step implementation procedures. Examples of transformation results are also presented to support KPLO flight dynamics data user community which is expected to give practical guidelines while post processing the data as their needs. With this technical paper, common understandings of reference frames that will be used throughout not only the KPLO flight operation but also science data reprocessing can be established. It is expected to eliminate, or at least minimize, unnecessary confusion among all of the KPLO mission members including: Korea Aerospace Research Institute (KARI), National Aeronautics and Space Administration (NASA) as well as other organizations participating in KPLO payload development and operation, or further lunar science community world-wide who are interested in KPLO science data post processing.

The ground tracking support is a critical factor for the navigation performance of spacecraft orbiting around the Moon. Because of the tracking limit of antennas, only a small number of facilities can support lunar missions. Therefore, case studies for various ground tracking support conditions are needed for lunar missions on the stage of preliminary mission analysis. This study analyzes the ground supporting condition effect on orbit determination (OD) of Korea Pathfinder Lunar Orbiter (KPLO) in the lunar orbit. For the assumption of ground support conditions, daily tracking frequency, cut-off angle for low elevation, tracking measurement accuracy, and tracking failure situations were considered. Two antennas of deep space network (DSN) and Korea Deep Space Antenna (KDSA) are utilized for various tracking conditions configuration. For the investigation of the daily tracking frequency effect, three cases (full support, DSN 4 pass/day and KDSA 4 pass/day, and DSN 2 pass/day and KDSA 2 pass/day) are prepared. For the elevation cut-off angle effect, two situations, which are 5 deg and 10 deg, are assumed. Three cases (0%, 30%, and 50% of degradation) were considered for the tracking measurement accuracy effect. Three cases such as no missing, 1-day KDSA missing, and 2-day KDSA missing are assumed for tracking failure effect. For OD, a sequential estimation algorithm was used, and for the OD performance evaluation, position uncertainty, position differences between true and estimated orbits, and orbit overlap precision according to various ground supporting conditions were investigated. Orbit prediction accuracy variations due to ground tracking conditions were also demonstrated. This study provides a guideline for selecting ground tracking support levels and preparing a backup plan for the KPLO lunar mission phase.

The Korea Pathfinder Lunar Orbiter (KPLO) is Korea's first lunar exploration program developed by the Korea Aerospace Research Institute and will be launched in late 2020. The KPLO will employ a 3.5 phasing loop and 100 km altitude lunar polar orbit for lunar transfer and mission phases, respectively. In this study, we introduced orbit determination (OD) strategy of KPLO flight dynamics system and demonstrated OD simulation results using sequential estimation technique. The lunar transfer trajectory and mission orbit of KPLO were simulated by STK and KPLO tracking measurements were generated by ODTK using simulated trajectory and ground station configuration including two Deep Space Networks and Korea Deep Space Antenna. For the trans-lunar phase, the orbit prediction (OP) results at the time of perigee maneuvers were presented for stable maneuver execution. For the lunar mission phase, OD and OP results were investigated for payload data processing and mission operation and planning. For OD accuracy assessments, the position uncertainty and orbit overlap precision were utilized. The uncertainties of Keplerian elements and the differences between estimated and true orbits were analyzed for evaluation of OP performance in trans-lunar and mission phases, respectively. Finally, we confirmed that the simulated OD and OP performance addresses the orbit requirements of KPLO. This study provides a useful guideline for the operation of KPLO for trans-lunar and lunar mission phases.

In this study, the observational arc-length effect on orbit determination (OD) for the Korea Pathfinder Lunar Orbiter (KPLO) in the Earth-Moon Transfer phase was investigated. For the OD, we employed a sequential estimation using the extended Kalman filter and a fixed-point smoother. The mission periods, comprised between the perigee maneuvers (PM) and the lunar orbit insertion (LOI) maneuver in a 3.5 phasing loop of the KPLO, was the primary target. The total period was divided into three phases: launch–PM1, PM1–PM3, and PM3–LOI. The Doppler and range data obtained from three tracking stations [included in the deep space network (DSN) and Korea Deep Space Antenna (KDSA)] were utilized for the OD. Six arc-length cases (24 hrs, 48 hrs, 60 hrs, 3 days, 4 days, and 5 days) were considered for the arc-length effect investigation. In order to evaluate the OD accuracy, we analyzed the position uncertainties, the precision of orbit overlaps, and the position differences between true and estimated trajectories. The maximum performance of 3-day OD approach was observed in the case of stable flight dynamics operations and robust navigation capability. This study provides a guideline for the flight dynamics operations of the KPLO in the trans-lunar phase.

The preliminary error analysis is performed to design the midcourse correction (MCC) maneuver of the lunar orbiter. During the trans-lunar trajectory, the lunar orbiter will perform several MCC maneuvers using the on-board propulsion system. The objectives of these maneuvers are to remove the deviation from the nominal trajectory by the injection error of the launch vehicle and to achieve the high accuracy for the lunar orbit insertion (LOI). To design the MCC maneuver, it is required to analyze the dispersion of the trans-lunar injection (TLI) error from the launch vehicle. In addition, the MCC maneuver epoch is also considered to design the MCC maneuver, which is an essential factor to analyze the MCC maneuver. To investigate the effects of the TLI uncertainty and the MCC maneuver epoch on the MCC maneuver, the Monte Carlo simulation is performed for the statistical analysis. The numerical simulation results and analysis provide a guideline to design the trans-lunar trajectory using the MCC maneuver in the presence of various error sources in the preliminary design phase.

In spite of a short history of only 30 years in space development, Korea has achieved outstanding space development capabilities, and became the 11th member of the “Space Club” in 2013 by launching its own satellites with its own launch vehicle from a local space center. With the successful development and operation of more than 10 earth-orbiting satellites since 1999, Korea is now rapidly expanding its own aspirations to outer space exploration. Unlike earth-orbiting missions, planetary missions are more demanding of well-rounded technological capabilities, specifically trajectory design, analysis, and navigation. Because of the importance of relevant technologies, the Korean astronautical society devoted significant efforts to secure these basic technologies from the early 2000s. This paper revisits the numerous efforts conducted to date, specifically regarding flight dynamics and navigation technology, to prepare for future upcoming planetary missions in Korea. However, sustained efforts are still required to realize such challenging planetary missions, and efforts to date will significantly advance the relevant Korean technological capabilities.