August 8, 2016

Space Hydrogen Maser (SHM)

Space Hydrogen Maser
Space Hydrogen Maser

The Space Hydrogen Maser, designed in Switzerland, is developed by Spectra Time.
Hydrogen maser performances do not depend on the micro-gravity environment. However, because of their simplicity and predicted reliability, H-maser are expected to be key instruments in future satellite positioning systems and other science missions such as ultra-high resolution space-space VLBI (Very Long Baseline Interferometry) experiments.
H-masers are based on the hyperfine transition of atomic hydrogen at 1.420405751 GHz. H2 molecules are dissociated by a plasma discharge and the resulting beam of H atoms is selected and sent to storage bulb. The bulb is made of a sapphire which loads a microwave cavity that, tuned on the resonance frequency, supports the maser action.

The ACES mission will be a test-bed for the space qualification of the active hydrogen maser. The on board frequency comparison between the SHM and PHARAO will be a key element for the evaluation of the accuracy and the short/medium-term stability of the caesium clock. Furthermore, it will allow to identify the optimal operating conditions for PHARAO and to select a good trade-off between frequency accuracy and stability.