Pierre Waller

Analysis of helical slow-wave structures for space TWTs using 3-D electromagnetic simulators

This paper presents a detailed analysis of traveling wave tube (TWT) helical slow-wave structures (SWSs) using three-dimensional (3-D) electromagnetic simulators. The main advantages of this approach are its capability to take into account the real 3-D geometry of this complex structure, and consequently to eliminate the approximations used in the analytical approach. In addition, it provides higher accuracy than experimental results. Two different methods have been applied (finite elements and finite integration) to predict the cold parameters (phase velocity, coupling impedance, and attenuation) at a level of accuracy higher than the usual practice. An extended analysis has been performed to guarantee the stability and accuracy of the results, as well as to study the sensitivity of the results to the discretization. This paper has shown that both methods, as implemented in two commercially available simulators, are perfectly suitable for the accurate modeling of such complex geometries.

The In-Orbit performances of GIOVE clocks

The Galileo In-Orbit Validation Element (GIOVE) is an experiment led by the European Space Agency (ESA) aimed at supporting the on-going implementation of Galileo, the European global navigation satellite system (GNSS). Among the objectives of the GIOVE Mission are the validation and characterization of the on-board clock technologies. The current baseline technologies for on-board clocks are the rubidium atomic frequency standard (RAFS) and the passive hydrogen maser (PHM). Both technologies have been validated and qualified on ground and are now being further validated in a representative in-orbit environment aboard 2 spacecrafts, GIOVE-A and GIOVE-B. This paper presents the results obtained in the frame of the GIOVE experimentation. The behavior and performances of the clock technologies on board both spacecrafts has been investigated and analyzed in terms of operation, frequency stability, and clock prediction error after more than 3 years of operation for GIOVE-A and almost one year for GIOVE-B. In addition, relativistic frequency shifts of GIOVE spacecrafts have been investigated.

Update on the In-Orbit performances of GIOVE clocks

The Galileo In-Orbit Validation Element (GIOVE) is an experiment led by the European Space Agency (ESA) aimed at supporting the on-going implementation of Galileo, the European Global Navigation Satellite System (GNSS). Among others, the objectives of the GIOVE Mission are the validation and characterization of the on-board clock technologies. The today baseline technologies for on-board clocks are the Rubidium Atomic Frequency Standard (RAFS) and the Passive Hydrogen Maser (PHM). Both technologies have been validated and qualified on ground and are now being further validated in a representative in-orbit environment on-board two spacecrafts, GIOVE-A and GIOVE-B. This paper presents the results obtained on both spacecrafts, after more than three years (GIOVE-A) and almost one year (GIOVE-B) of operation.