Influence of the Choice of Lunar Gravity Model on Orbit Determination for Lunar Orbiters

Abstract

We examine the influence of the lunar gravity model on the orbit determination (OD) of a lunar orbiter operating in a 100 km high, lunar polar orbit. Doppler and sequential range measurements by three Deep Space Network antennas and one Korea Deep Space Antenna were used. For measurement simulation and OD analysis, STK11 and ODTK6 were utilized. GLGM2, LP100K, LP150Q, GRAIL420A, and GRAIL660B were used for investigation of lunar gravity model selection effect. OD results were assessed by position and velocity uncertainties with error covariance and an external orbit comparison using simulated true orbit. The effect of the lunar gravity models on the long-term OD, degree and order level, measurement-acquisition condition, and lunar altitude was investigated. For efficiency verification, computational times for the five lunar gravity models were compared. Results showed that significant improvements to OD accuracy are observed by applying a GRAIL-based model; however, applying a full order and degree gravity modeling is not always the best strategy, owing to the computational burden. Consequently, we consider that OD using GRAIL660B with 70 × 70 degree and order is the most efficient strategy for mission preanalysis. This study provides useful guideline for KPLO OD analysis during nominal mission operation.

Ground Tracking Support Condition Effect on Orbit Determination for Korea Pathfinder Lunar Orbiter (KPLO) in Lunar Orbit

“…It means that twelve passes per day exist. In previous analyses, KPLO OD for the lunar mission phase was attempted using ideal tracking support (tracking for every orbit), which has eight passes per day for two DSN antennas and four passes per day for KDSA (Kim et al 2018;). In the real situation of the mission, each station's daily tracking frequency can be adjusted by ground supporting resource conditions.…”

“…The KPLO will be launched in the middle of 2022 and delivered at 100 km altitude lunar polar orbit. The details and recent progress of the KPLO mission were found in several pieces of literature (Ju et al 2013;Choi et al 2018;Davis et al 2018;Song et al 2018;Bae et al 2020;Hong et al 2020;Kim et al 2020;Lee et al 2020;Park et al 2020;Song et al 2020). For the successful mission operation and payload data acquisition of KPLO, the ground system has an important role.…”

“…For the lunar mission orbit, KPLO OD performance can be mainly affected by ground supporting conditions. The effect of the selection of lunar gravity models and supporting the number of stations was investigated for the KPLO OD in mission orbit (Kim et al 2018b). Most of the KPLO OD studies in the lunar mission orbit assumed ideal tracking support, which tracks every lunar orbit pass by three stations.…”

Observational Arc-Length Effect on Orbit Determination for KPLO Using a Sequential Estimation Technique

“…Detailed descriptions of the dynamic models e summarized in Table 1. The GL0660B lunar gravity model with a degree and order 100 by 100 d. For sequential orbit estimation of a 100-km-altitude lunar orbiter, it was shown that degree and y 70 provides balanced performance (Kim et al 2018a). However, it was recommended to employ an 100 by 100 degree and order to maintain similar accuracy of orbit propagation (Song et al or the third-body effect, the Sun and Earth were selected to calculate perturbation.…”

“…The GL0660B lunar gravity model with a degree and order 100 by 100 was applied. For sequential orbit estimation of a 100-km-altitude lunar orbiter, it was shown that degree and order 70 by 70 provides balanced performance (Kim et al 2018a). However, it was recommended to employ greater than 100 by 100 degree and order to maintain similar accuracy of orbit propagation (Song et al 2017b).…”