Session
Technical Session IX: Advanced Technologies II
Abstract
It is an important technological challenge to ensure a LEO satellite ground terminal autonomy as well as to make it small, lightweight and power efficient along with the ability to predict the satellite visibility passes. Another important feature is to make it able to compensate for Doppler on the satellite link with an economical method. In this paper, an orbit and Doppler calculation methodology has been developed for a general orbital model. The algorithm that manages the ground terminal automatic operation ensures many advantages and is adapted to a microcontroller programming. Inputs to the algorithm are time, position and keplerian elements from NORAD. The NORAD elements are injected in the terminal memory via its serial port once before it is deployed on the operation field. Time is provided by a real time clock read and written by the terminal microcontroller. Terminal geographic position is provided by an internal integrated miniature GPS which makes the terminal free to move anywhere on the terrestrial globe and still be able to contact the satellite without any reprogramming. The orbit calculation methodology used expresses the satellite coordinates in the terminal relative topocentric (horizontal) coordinate system which easily yield the values of elevation and azimuth angles along with the slant range. This is achieved by means of satellite vector transformations through different coordinate systems. Doppler shift is obtained by deriving the slant range in time. A simple methodology for Doppler correction is also proposed in this paper and is adapted for low cost transceivers.
Orbit Calculation and Doppler Correction Algorithm in a LEO Satellite Small Ground Terminal
It is an important technological challenge to ensure a LEO satellite ground terminal autonomy as well as to make it small, lightweight and power efficient along with the ability to predict the satellite visibility passes. Another important feature is to make it able to compensate for Doppler on the satellite link with an economical method. In this paper, an orbit and Doppler calculation methodology has been developed for a general orbital model. The algorithm that manages the ground terminal automatic operation ensures many advantages and is adapted to a microcontroller programming. Inputs to the algorithm are time, position and keplerian elements from NORAD. The NORAD elements are injected in the terminal memory via its serial port once before it is deployed on the operation field. Time is provided by a real time clock read and written by the terminal microcontroller. Terminal geographic position is provided by an internal integrated miniature GPS which makes the terminal free to move anywhere on the terrestrial globe and still be able to contact the satellite without any reprogramming. The orbit calculation methodology used expresses the satellite coordinates in the terminal relative topocentric (horizontal) coordinate system which easily yield the values of elevation and azimuth angles along with the slant range. This is achieved by means of satellite vector transformations through different coordinate systems. Doppler shift is obtained by deriving the slant range in time. A simple methodology for Doppler correction is also proposed in this paper and is adapted for low cost transceivers.
