Pure Geometrical Precise Orbit Determination of a LEO Based on GNSS Carrier Phase Observations

Abstract

The interest in a precise orbit determination of Low Earth Orbiters (LEOs) especially in pure geometrical mode using Global Navigation Satellite System (GNSS) observations has been rapidly grown. Conventional GNSS-based strategies rely on the GNSS observations from a terrestrial network of ground receivers (IGS network) as well as the GNSS receiver on-board LEO in double difference (DD) or in triple difference (TD) data processing modes. With the advent of precise orbit and clock products at centimeter level accuracy provided by the IGS centers, the two errors associated with broadcast orbits and clocks can be significantly reduced. Therefore, higher positioning accuracy can be expected even when only a single GNSS receiver is used in a zero difference (ZD) procedure. Along with improvements in the International GNSS Services (IGS) products in terms of Global Position System (GPS) satellite orbits and clock offsets, the Precise Point Positioning (PPP) technique based on zero (un-) differenced carrier phase observations has been developed in recent years. In this paper, the zero difference procedure has been applied to the CHAllenging Minisatellite Payload (CHAMP) high–low GPS Satellite to Satellite Tracking (hl-SST) observations, then the solution has been denoted as Geometrical Precise Orbit Determination (GPOD). The estimated GPOD CHAMP results are comparable with results of other groups e.g. Švehla at TUM (Švehla D, Rothacher M (Švehla and Rothacher 2002) and Bock at Bern (Bock 2003) but because of different outliers detection and data processing strategies, the GPOD results presented here are more or less different than the other groups’ results. The estimated geometrical orbit of CHAMP is point-wise and its accuracy relies on the geometrical status of the GNSS satellites and on the number of the tracked GNSS satellites as well as on the GNSS measurement accuracy in the data processing. The position accuracy of 2–5 cm of CHAMP based on high–low GPS carrier phase observations with zero difference procedure has been achieved. These point-wise absolute positions can be used to estimate kinematical orbit of the LEOs.