Precise Orbit Determination of LEO Satellites Based on Undifferenced GNSS Observations

Abstract

Precise orbit determination (POD) is the procedure for determining the orbit of a satellite with high accuracy. Compared with global navigation satellite systems (GNSS), the low Earth orbit (LEO) satellites have some different features in space, mainly due to perturbations caused by dynamic forces related to their altitudes. Methods for POD of LEO satellites have been developed over the last decades. Nowadays, postprocessed precise orbits are used in different space applications such as radio occultation, satellite altimetry, and interferometric syntheticaperture radar missions. The advancements in technology decrease the size of LEO satellites and developments in theory increase their orbital accuracy. In recent years, onboard POD has become a hot topic in the navigation and positioning field, which is crucial for, e.g., formation flying of small satellites and GNSS-aided LEO megaconstellations for positioning purposes. This contribution reviews LEO POD methods based on undifferenced GNSS observations in both postmission and real-time data processing. It comprises the quality control step, the models used and their limitations, processing algorithms, and different validation methods. To have a clear insight into the current and the future state of the LEO POD, the most recent developments and important achievements are also discussed.

Precise Orbit Determination of CubeSats Using Proposed Observations Weighting Model

“…The reduced-dynamic POD (RD-POD) is considered the main method in this study. It is based on exploiting available dynamic models as well as GNSS observations to estimate the CubeSat's state vector, which includes position and velocity, clock offsets, float ambiguities, and some piece-wise constant stochastic accelerations to compensate for deficiencies in dynamic models (Allahvirdi-Zadeh et al 2022a). The type of data used, processing information, and models in the RD-POD processing are provided in Table 1.…”

“…Precise Orbit Determination (POD) of CubeSats is essential for some missions such as radio-occultation, Interferometric Synthetic Aperture Radar (InSAR), satellite altimetry, gravity field recovery, and future mega-constellations as an augmentation system for positioning and navigation (Allahvirdi-Zadeh and El-Mowafy 2022). POD of CubeSats using the observations of Global Navigation Satellite Systems (GNSS) can be performed using the reduced-dynamic and the kinematic methods in post-mission or real-time (Allahvirdi-Zadeh et al 2022a). In this study, we analyze the POD of CubeSats from the Spire CubeSat Constellation (Spire Global, Inc.), comparing elevation angle-dependent and Signal-to-Noise ratio (SNR) based weighting models.…”

GPS-SBAS-Based Orbit Determination for Low Earth Orbiting Satellites

“…Hauschild et al [6] studied the application of orbit and clock corrections from GEO satellite to LEO satellites. Allahvirdi-Zadeh et al [7,8] studied on the application of QZSS MADOCA orbit and clock corrections from QZSS satellite to LEO satellites. These LEO-PPP experiments applied precise orbit and clock data to phase measurements for PPP applications.…”

A Concise Method for Calibrating the Offset of GPS Precise Satellite Orbit

“…Among them, the reduced dynamic method has gradually replaced the dynamic-only method and is used as the main method for determining the orbits of various LEO missions [21] due to its ability to produce more accurate and smooth orbits by incorporating process noise to absorb force model errors. In contrast, the kinematic methodology utilizes only GNSS observations and lacks a priori information on the gravity field and dynamical parameters, making it more appropriate for LEO satellites performing gravity field recovery missions [22,23]. The major of LEO satellite orbits are derived from various GNSS precise orbit and clock products.…”