THE SHM HYDROGEN ATOMIC CLOCK FOR SPACE APPLICATIONS DEVELOPMENT AND TEST OF THE PEM PHYSICS PACKAGE

A campact Space-borne active Hydrogen Maser (SHM) frequency standard is being developed By the Observatory of Neuchhtel under the Swiss PRODEX program of ESA. The SHM instrument will be jl'own on the Radioastron (RA) mission in 2000 to be used as the reference clock for orbital Very Long Baseline Inte$erometry (VLBI) and for the red-ship experiment CRONOS. The SHM design is based on a miniature sapphire loaded microwave cavity which makes possible an active hydro- gen maser with a 1.7 liter storage volume for atomic hydrogen within a 50 kg space qualified instrument. A preliminary measurement of the SHM inslrument frequency stability using breadboard electronics has yielded an Allan deviation of ~,(~OIJO~)= 3x10-l~ which is already close to the ~.(~OCICI~) < 15 x ~o-~sinstrument specifwation. An extensive program for the design verification by test & analysis of the PEM-PP was pevormed in 1997 and is now near completion. Potential space applications of a compact active hydrogen maser instrument include scientific experiments related to relativity, precise ranging and navigation, time dissemination and synchronization. Present plans are to push miniaturization even further with the development of a 35 kg active hydrogen MAser for Navigation (MAN) for GNSS applications.