Clock synchronization on the RAX spacecraft

The Radio Aurora Explorer (RAX) is a CubeSat that was developed to study space weather in Earth׳s ionosphere. The scientific payload is a bistatic radar system in which an onboard receiver works in cooperation with a ground-based transmitter. Accuracy of the onboard clock is critical for processing...

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Bibliographic Details
Published in:Acta astronautica 2014-05, Vol.98, p.111-119
Main Authors: Springmann, John C., Kempke, Benjamin P., Cutler, James W., Bahcivan, Hasan
Format: Article
Language:English
Subjects:
Algorithms
Clock correction
Clock drift
Clocks
CubeSat
Onboard
Radar measurement
Range delay
Satellite design
Space weather
Spacecraft
Time
Time measurements
Transmitters
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Summary:The Radio Aurora Explorer (RAX) is a CubeSat that was developed to study space weather in Earth׳s ionosphere. The scientific payload is a bistatic radar system in which an onboard receiver works in cooperation with a ground-based transmitter. Accuracy of the onboard clock is critical for processing the radar measurements. The RAX timing system utilizes commercial off-the-shelf components integrated into custom subsystems. GPS is used to maintain absolute timing accuracy better than 1μs, but the subsystem is not always available due to power constraints, so a method has been developed to correct the onboard clock error without the use of GPS. The clock correction utilizes range measurements extracted from the pulses emitted by the transmitter, and resulting absolute clock accuracies of better than 0.20s with drift of less than 21ns/s have been demonstrated. The RAX timing system and the clock correction algorithm are presented as a reference for other spacecraft designers and are critical for those analyzing RAX data.
ISSN:0094-5765
1879-2030
DOI:10.1016/j.actaastro.2014.01.021