Space worthy electronics package for the 35 kg space active hydrogen maser on ACES

The 35 kg active space hydrogen maser (SHM-35) developed at the Observatory of Neuchatel is one core element of the ACES experiment (atomic clock ensemble in space). ACES is an European experiment on the International Space Station (ISS) comprising the SHM-35 and the cold atom caesium clock PHARAO locked to each other. The resulting ultra- stable clock provides an optimised time scale and allows for fundamental physics tests. SHM-35 consists of the physical package (PP) and of the electronics package (EP). The operation outside the ISS and thus in space environment together with the demanding performance needs of the SHM-35 puts challenging requirements on the EP design. The development of the EP is on-going at Contraves Space with the flight design underway together with the build and test of an elegant breadboard model (EBB) of this EP. The EP EBB incorporates the same architecture, design and functionality as the flight hardware but using commercial EEE parts. With this approach the performance of the EP and SHM can be verified at an early stage in the flight development programme. This paper presents the architecture of the space worthy electronics for SHM-35 with emphasis on the radio frequency part. The control part and special problems arising from the operation in the space environment will also be discussed. The required performance is compared with measurement results at the EBB EP. Furthermore first results of the integrated SHM consisting of the EBB EP and a ground Maser physical package will be reported.