ETS-VIII Precise Orbit and Clock Estimation Experiments

R. Nakamura, T. Inoue, S. Nakamura, S. Katagiri, S. Noppanakeepong, Y. Feng

Abstract:	Japan Aerospace Exploration Agency (JAXA) has carried out High Accuracy Clock (HAC) Experiment, one of the main experiments of Engineering Test Satellite-VIII (ETS-VIII), for verification of global navigation satellite technologies. The experiment consists of management of onboard atomic clocks, satellites’ precise orbit and clock estimation and satellite positioning with Global Positioning System (GPS) satellites and ETS-VIII. ETS-VIII carries a cesium clock and can transmit navigation signals similar to GPS signals in L band and S band. The ETS-VIII’s navigation signals are received by four Satellite Monitor Stations (SMSs). Navigation observations collected by the SMSs are sent to the Master Control Station (MCS) in JAXA Tsukuba space center in real time, processed and used for orbit and clock estimation of ETS-VIII. There are some difficulties of orbit and clock estimation caused by strong correlation between radial direction errors of the orbit and clock offset and between alongtrack direction errors of the orbit and inter-system biases of pseudorange. In order to overcome these difficulties, another means of precise ranging such as Satellite Laser Ranging (SLR) is quite usable. ETS-VIII carries a laser retro reflector array. SLR measurements are also used for evaluation of orbits estimated by ETS-VIII signals. Precise orbit and clock estimation experiments are performed for several times. The orbit estimation periods for each experiment are about 24 hours in which ETSVIII is in a free flight. The orbits of ETS-VIII estimated by navigation observations coincided with ones estimated by SLR measurements within the accuracy of 20m in any cases. The ETS-VIII’s clock offsets are successfully estimated within the accuracy of 10 nanoseconds, evaluated by dispersions of estimated clock offsets except the first order drift. User positioning experiments are also performed, in which a point positioning by ETS-VIII signals combined with GPS signals are carried out. ETSVIII’s navigation message is created using the result of the precise orbit and clock estimation. The result is that the accuracy of the point positioning is improved by adding ETS-VIII as a GNSS satellite, especially in the north-south direction.
Published in:	Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010) September 21 - 24, 2010 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	1572 - 1579
Cite this article:	Nakamura, R., Inoue, T., Nakamura, S., Katagiri, S., Noppanakeepong, S., Feng, Y., "ETS-VIII Precise Orbit and Clock Estimation Experiments," Proceedings of the 23rd International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2010), Portland, OR, September 2010, pp. 1572-1579.
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