ELISA : an Ultra-Stable Frequency Reference for Space Mission Ground Segment
GIORDANO, V.¹; GROP, S.¹; BOURGEOIS, P.Y.¹; BAZIN, N.¹; KERSALE, Y.¹; OXBORROW, M.²; Marra, G.²; Langham, C.²; SCHAFER, W.³; SICCARDI, M.³; RUBIOLA, E.¹; DeVICENTE, J.^4
1Femto-ST Institute - CNRS; ²National Physical Laboratory; ³TimeTech GmbH; ⁴ESA

Femto-ST Institute in collaboration with the National Physical Laboratory (NPL UK) and TimeTech GmbH are currently developping under an ESA contract a new Cryogenic Sapphire Oscillator (CSO) for space mission ground segment with the main objective to achieve a short term frequency stability of 3x10^-15 . Indeed the ever increasing need for better tracking data in deep space missions calls for the development of new frequency references of improved stability. Sapphire oscillators offer unbeatble stability performances in timescales ranging from milliseconds to a few hundred of seconds, and therefore extremely low phase noise close to the carrier. Compared to current performance available from state of the art quartz oscillators, the CSO would provide the means to improve the orbit determination and would open the field to new radio science experiments.

The design phase of this CSO is now achieved. The CSO is based on a sapphire resonator cooled down to 6K in a cryocooler. The resonator has been designed to present a high-Q mode at 10GHz. (Q=10⁹). The sustaining loop placed at room temperature is completed with real time controls to correct any phase or power fluctuations along the loop. Eventually a low noise frequency synthesis delivers the usefull frequencies from the CSO signal.

In this paper the main technological choices will be presented emphasizing on the resonator and oscillator loop microwave design and on the associated frequency synthesis. Moreover preliminary results obtained with similar sapphire resonators will be presented.