India’s first lunar mission Chandrayaan-1 initial phase orbit determination

India’s first Moon mission Chandrayaan-1 carrying eleven scientific instruments for the purpose of expanding scientific knowledge about the Moon was launched on 22 October 2008. The spacecraft was put into Moon’s polar, circular orbit of about (100×100) km on 12 November 2008 by carrying out a sequence of Earth bound and Lunar bound maneuvers. Precise orbit determinations are carried out during each phase of the mission using tracking data collected from network of tracking stations configured for the mission. The determined orbital solutions are used for spacecraft navigation, mission planning and science data processing. ISRO’s operational orbit determination program (ODP) used for low earth missions was suitably updated and validated before the launch of Chandrayaan-1. The purpose of this paper is to describe the methodology and the performance of Chandrayaan-1 orbit determination system during initial phase of the mission along with achieved orbit determination accuracy in the early normal phase.