Session
Session XII: Advanced Technologies II
Location
Utah State University, Logan, UT
Abstract
Small satellites have become capable platforms for a wide range of commercial, scientific and defense missions. Improved onboard clocks would make small satellites a viable option for even more missions, enabling radio aperture interferometry, improved radio occultation measurements, high altitude GPS navigation, and GPS augmentation missions, among others.
Previous research by the authors investigated methods for creating a high stability reference clock for small satellites by combining a heterogeneous group of oscillators including multiple CSACs, a GPS receiver and an EMXO. This work predicted that time error standard deviations of ~500 ps were possible with GPS timing errors modeled as AWGN.
This paper builds on previous work by developing a high-fidelity model for the GPS receiver timing error onboard a LEO spacecraft. Signal-In-Space Ranging Errors (SISRE) are modeled using post-fit GPS orbit and clock data, and ionospheric delays are approximated using IONEX maps and ionosphere models.
GPS point solutions are then calculated over several days of LEO orbits to generate realistic receiver timing errors, which were then used in simulations of the high-stability heterogeneous clock ensemble. Simulations show degraded clock system performance compared to the prior model, with standard deviations of time errors increasing to 1.3 ns 1-σ. The results provide insight into the nature of GPS receiver clock errors for LEOs, as well as practical limitations that should be expected when implementing advanced clock systems on small satellites.
Simulation of a High Stability Reference Clock for Small Satellites with Modeled GPS Timing Errors
Utah State University, Logan, UT
Small satellites have become capable platforms for a wide range of commercial, scientific and defense missions. Improved onboard clocks would make small satellites a viable option for even more missions, enabling radio aperture interferometry, improved radio occultation measurements, high altitude GPS navigation, and GPS augmentation missions, among others.
Previous research by the authors investigated methods for creating a high stability reference clock for small satellites by combining a heterogeneous group of oscillators including multiple CSACs, a GPS receiver and an EMXO. This work predicted that time error standard deviations of ~500 ps were possible with GPS timing errors modeled as AWGN.
This paper builds on previous work by developing a high-fidelity model for the GPS receiver timing error onboard a LEO spacecraft. Signal-In-Space Ranging Errors (SISRE) are modeled using post-fit GPS orbit and clock data, and ionospheric delays are approximated using IONEX maps and ionosphere models.
GPS point solutions are then calculated over several days of LEO orbits to generate realistic receiver timing errors, which were then used in simulations of the high-stability heterogeneous clock ensemble. Simulations show degraded clock system performance compared to the prior model, with standard deviations of time errors increasing to 1.3 ns 1-σ. The results provide insight into the nature of GPS receiver clock errors for LEOs, as well as practical limitations that should be expected when implementing advanced clock systems on small satellites.
