The engineering model of the space passive hydrogen maser for the European global navigation satellite system Galileo

In the frame of the new European global navigation satellite system Galileo, the Observatory of Neuchatel, Switzerland has developed the Engineering model of the main clock on board, the space passive hydrogen maser. It weighs 15 kg, and it is 521 mm long, 355 mm wide and 251 mm high. Its steady state power consumption is 45 W in the middle of the environment temperature range (-5°C). After the initial performance tests, the frequency stability is 8.8×10^-13@1 s, but the white frequency noise follows a 5×10^-13 τ^{- 1}2 / dependence from 20 s up to 1 hour. A Flicker floor of 7×10^-15 is reached after 10´000 s. At 50´000 s the Allan standard deviation is 1.2×10^-14, mainly driven by the excessive residual frequency drift (2×10^-14/day). The frequency sensitivity to magnetic field variation is 1.3×10^-14/G, it is 2×10^-15/V to power supply variation and 5×10^-14/K to temperature variation due to non optimal temperature regulation of the microwave cavity.