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.
This paper details techniques for the absolute calibration of receiver chains as used in timing reference stations. The delays experienced by the GNSS signals in all elements of the receiving chain (antenna, receiver and cable) are each measured individually and with careful consideration regarding the uncertainty level assigned to them. Two different receiving chains based on different equipment units, were absolutely calibrated for GPS and Galileo signals.The calibration process and the uncertainty evaluation were then validated through the relative comparison in common clock setup in different real environments. The validation results show that some additional uncertainty has to be considered when the absolute calibration results are transferred to real signals, due to the real environment and to the difference between the chip shapes of the simulated signals and of the true signals coming from the satellites. The final 1 − σ uncertainties are below 1.1 ns for all the GPS and Galileo signals, except 1.8 ns for GPS C/A. The satellite group delays are also determined from the calibrated stations. An agreement at the ns level is found between the so-determined satellite group delays and the values provided by the system operators.
We summarise the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with the European Space Agency (ESA) and national space and research funding agencies.
Galileo navigation program is in progress under the technical supervision of the European Space Agency (ESA). The preliminary activities related to GSTBV2 experimental satellite provide the first results and the implementation of the In Orbit Validation (IOV) phase are in progress. Atomic clocks represent critical equipment for the satellite navigation system and clocks development has been continuously supported by ESA. The Rubidium Atomic Frequency Standard (RAFS) and the Passive Hydrogen Maser (PHM) are at present the baseline clock technologies for the Galileo navigation payload. For the PHM, initial ground technological project related to lifetime possible limitation of the clock was initiated in parallel to satellite experimentation (GIOVE-B). Long duration frequency stability performance tests were recorded on ground demonstrating 2*10 -15 clock stability at one day (including the drift). This article gives an overview on the ground lifetime data and performance of the PHM. Extrapolation for the 12 years Galileo mission duration is discussed.
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