Développement d'une méthode de télémétrie de haute exactitude par chronométrie et interférométrie d'impulsions laser – ILIADE

The Iliade project aims at demonstrating a telemetry measurement method with very high accuracy, for application to formation flight space missions like earth gravimetry or synthetic aperture telescopes. The requirements for the Darwin mission are that the distance (a few hundred metres) between spacecrafts should be measured with an accuracy of 30µm and a resolution of 5nm. We plan to reach a sub-micron accuracy over distances of 100m to 100km by combining three measurements on short laser pulses at 20 or 40GHz repetition rate, using i) a time of flight measurement with an accuracy of about 1ps, ii) measurement of the phase difference between the return and reference modulations, iii) an interferometric phase measurement. An accuracy of ≤10^-4 is required for the modulation phase measurement (at 20GHz) in order to escape the ambiguity of the measurement (modulo 2pi) of the interferometric phase and provide a sub-micron accuracy distance measurement. The high repetition rate short pulses will be obtained from the shaping of the sinusoidal beatnote between two single-frequency lasers, in dispersive non-linear optical fibres. The two CW lasers will be phase locked, the master laser being locked on an absolute optical frequency reference, to provide the required stability to the interferometric measurement despite the large distance. The Iliade project combines the complementary expertise of three laboratories: ARTEMIS (high resolution interferometry, laser stabilisation), Gémini (laser time of flight telemetry) and Institut Carnot de Bourgogne (non-linear propagation of laser pulses in optical fibres)