Experimental Plan of Remote Synchronization System of Onboard Crystal Oscillators Using Quasi-Zenith Satellites
- Paper number
IAC-07-D1.I.06
- Author
Dr. Toshiaki Iwata, National Institute of Advanced Industrial Science and Technology, Japan
- Coauthor
Mr. Michito Imae, National Institute of Advanced Industrial Science and Technology, Japan
- Coauthor
Dr. Tomonari Suzuyama, National Institute of Advanced Industrial Science and Technology, Japan
- Coauthor
Dr. Akira Iwasaki, University of Tokyo, Japan
- Coauthor
Yasuhiro Takahashi, Japan
- Year
2007
- Abstract
The Japanese Quasi-Zenith Satellite System (QZSS) will be launched in 2009 or 2010, and after the launching and verification, a three-year experimental study is planned. The experiments of the synchronization system of the onboard crystal oscillator (RESSOX) with a standard time system using QZS are planned during this period. The purpose of RESSOX is the cost reduction and the extension of the lifetime of future missions as a result of eliminating the need for onboard atomic clocks, although the initial QZSS will be equipped with two rubidium atomic clocks. There are two categories of experiments: experiments in which the onboard crystal oscillator is and is not controlled. In the case of experiments without control of the crystal oscillator, the modeling of signal delay, such as ionospheric delay, tropospheric delay and orbit estimation error, will be evaluated. In the case of experiments with control of the crystal oscillator, the algorithm of feedback control at the ground station will be evaluated. Each category includes two methods: a method that uplinks time information, which is called the RESSOX control signal, and that which uplinks the control voltage command. The control algorithm using the RESSOX control signal has been confirmed by ground experiments. The algorithm for uplinking the control voltage command has been confirmed, however, the timing of command transmission and time lag are critical problems. Since the system will operate at 1.5 s intervals, the voltage command should be given exactly every 1.5 s. Twenty seconds are required to calculate the control voltage, prepare it as a command, and transmit it to QZS. The synchronization time system is also an issue; various time systems, such as coordinated universal time (UTC), GPS-time, space vehicle (SV)-clock and QZS-time, are being considered to determine the optimal one. The effect of the time system choice on positioning will be investigated. Furthermore, we also plan experiments on relaying the RESSOX control signal or voltage command from different ground stations in order to operate RESSOX continuously even if one ground station does not communicate with QZS for 24 hours. The experiments on the control of the onboard crystal oscillator will be conducted four times a year. The time schedule and contents of the experiments are discussed.
- Abstract document
- Manuscript document
IAC-07-D1.I.06.pdf (🔒 authorized access only).
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