ELISA: An ultra-stable oscillator for esa deep space antennas

Deep space tracking requires frequency references exhibiting excellent frequency stability. The frequency standards currently implemented in the European Space Agency (ESA) ground stations are based on an ultra-stable X-tal oscillator stabilized at long term on an hydrogen maser. The short term frequency stability of this system is typically of 1 x 1CP13 for integration times r < 100s resulting from the performance of the state-of-the-art X-tal oscillator. For longer integration time the frequency stability is improved by the locking on the hydrogen maser. In order to validate new experiments in the field of radiosciences or space navigation, the short term performance of the ground station frequency reference must be improved. ESA has founded a project called ELISA with the objective to get a short term frequency stability of 3 x 10~15 over time intervals between 1 s and 1000 s. The project is realized in collaboration between the FEMTO-ST Institut (prime), the National Physical Laboratory (NPL) and Timetek GmBh.