Inter-satellite ranging in the Low Earth Orbit

Abstract

Many satellite systems require knowledge about inter-satellite distances. Inter-satellite links provide direct connectivity between satellites and may be used for ranging, while they remove the need of dedicated hardware. This paper addresses inter-satellite ranging at the Low Earth Orbit (LEO) using S-Band signals. We take the requirements from recent missions and future applications into account and analyze the factors that limit ranging. We show how these factors affect the quality of distance estimation in terms of the Cramér-Rao Lower Bound for ranging. Two-way-ranging (TWR) provides the best accuracy and sustains the low-cost objective of small satellites. We further propose an enhanced TWR message exchange that enables on-the-fly delay calibration and sub-sample corrections. We implemented the transceiver modules on a Software-Defined Radio (SDR) platform and evaluated them with real-world data. The results show that the proposed ranging algorithm achieves an accuracy of few centimeters

Architectures and Synchronization Techniques for Distributed Satellite Systems: A Survey

“…In this way, there is no need VOLUME 4, 2016 to synchronize both satellites' clocks [99]. The evaluation of the algorithm on a SDR platform is reported in [99], showing an accuracy of a few centimeters.…”

“…Articles such as [96], published in 1985, already proposed a design to measure satellite-to-satellite range-rate with a precision smaller than 1 µm/s in distances between 100 km and 300 km. However, further analyses included the frequency instability of the oscillators [97], the channel noise conditions [98], and the requirements of low-cost small satellites [99] among other specifications. Distances can be determined from either the signal's modulation (PRN codes) or the carrier phase.…”

“…On the other hand, the TWR method does not have this drawback. In TWR, introduced in [99], one satellite sends the ranging signal and activates a counter to calculate the elapsed time until the reception of the other satellite replies. In this way, there is no need VOLUME 4, 2016 to synchronize both satellites' clocks [99].…”

“…In TWR, introduced in [99], one satellite sends the ranging signal and activates a counter to calculate the elapsed time until the reception of the other satellite replies. In this way, there is no need VOLUME 4, 2016 to synchronize both satellites' clocks [99]. The evaluation of the algorithm on a SDR platform is reported in [99], showing an accuracy of a few centimeters.…”

Architectures and Synchronization Techniques for Distributed Satellite Systems: A Survey

“…Articles such as [97], published in 1985, already proposed a design to measure satellite-to-satellite range-rate with a precision smaller than 1 µm/s in distances between 100 km and 300 km. However, further analyses included the frequency instability of the oscillators [98], the channel noise conditions [99], and the requirements of low-cost small satellites [100] among other specifications. Distances can be determined from either the signal's modulation (PRN codes) or the carrier phase.…”