Galileo Orbit Selection

R. Zandbergen, S. Dinwiddy, J. Hahn, E. Breeuwer and D. Blonski

Abstract:	The Galileo Constellation will consist of 30 satellites in three orbit planes, with 27 operational spacecraft and three in-orbit spares. The nine operational spacecraft in each orbit plane will be equally spaced along the orbit, forming a 27/3/1 Walker constellation. During Phase B of the Galileo project, two different orbit altitudes have been used in system studies, leading to a three-day ground track repeat orbit on the one hand and a ten day repeat orbit on the other. In the C0 phase, which is now nearing completion, the final orbit parameters had to be defined. Availability analyses had already led to the selection of the mean orbit inclination of 56 degrees. This paper presents the final choice for the semi-major axis of the Galileo orbits. Several different criteria play a role in this choice. A short repeat period is advantageous for In-Orbit Validation (IOV) and commissioning, as each satellite returns more frequently to the same position over the Earth’s surface, but leads to undesirable orbit perturbations due to resonance phenomena, which will require correction by means of maintenance manoeuvres. There is a strong desire to minimise the number of these manoeuvres, which require the satellite to be taken out of service while the orbit is adjusted. It is important to use identical orbit parameters in IOV and the Full Operational Configuration (FOC), as IOV satellites will continue in service through to FOC and would otherwise need to be moved. The paper also analyses two alternative types of orbits, and concludes by presenting the best alternative available, the orbit finally selected for the Galileo constellation, by joint decision of the European Space Agency and the Galileo industrial consortium. It has a 10-day repeat cycle, with 17 revolutions in close to ten sidereal days, and a mean semi-major axis of about 29600 km. The paper finally briefly addresses the requirements on orbit injection accuracy and long-term orbit prediction accuracy, which are pre-requisites for a long-term operation of the constellation without the need for frequent maintenance manoeuvres.
Published in:	Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004) September 21 - 24, 2004 Long Beach Convention Center Long Beach, CA
Pages:	616 - 623
Cite this article:	Zandbergen, R., Dinwiddy, S., Hahn, J., Breeuwer, E., Blonski, D., "Galileo Orbit Selection," Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), Long Beach, CA, September 2004, pp. 616-623.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In