Page 2 of 3
Previous The Onboard Galileo Rubidium and Passive Maser, Status & Performance Figure 9. PHM EM frequency and time stabilities
The new design of the physics package has been also focussed on parts count reduction. Less than one half individual parts has been used in the new design compared to the EM model. For the electronics package and the whole instrument:
 Figure 10. PHM atomic signal measured in FM1  Figure 11. Technological models with/without cover Two technological models (Fig. 11), a Structural Model and an EQM were built for these objectives and to qualify the new upgraded design. In addition, four EQMs for life demonstration are being manufactured and will be submitted to prolonged testing. In the frame of GSTB-V2, which is presently being tested at P/L level, one PFM (Fig. 12) has completed the proto-qualification testing and has been delivered. One spare FM will be delivered by the end of 2005. Table II shows the achieved performance of PHM/PFM for GSTBV2. Significant improvement has been achieved by a better silver coating process and surface polishing of the magnetron cavity (Fig 13). Fig. 14 is showing the performances improvements of the physics package of FM1 model before its integration, obtained by the quality factor improvement.  Figure 12. Picture of PHM PFM TABLE II. PHM FOR GSTB-V2 PERFORMANCE ACHIEVED
 Figure 13. PHM magnetron cavity  Figure 14. PHM performance improvement PHM Lifetime The PHM is being sized to guarantee 12 years of orbit life plus 1 year of ground storage, as well as the complete AIT program. The operational life is mainly limited by capacities of the hydrogen container (for H2 supply), bulk getters (for H2 sorption), ion pump (for pumping ungetterable background gases) and the total dose of ionising radiation. The lifetime is assessed by analysis and tests of subassemblies. Fig. 15 shows the H2 consumption test made in June 2005, which indicates the consumption of 1.53 bar*l/year at nominal flux, by measuring the pressure decay in the known volume of the high pressure pipeline. Taking account of the margin from the real consumption and the retrievable H2 amount in the fixed pressure of the metal hydride, the H2 container with the capacity of 30 bar*l is sufficient for the operational life time. A novel custom built getter pump is developed for the PHM. The getter material provides high sorption capability and mechanical stability. The H2 sorption test on the getter cartridge was performed in Sep 2003. Fig. 16 shows several cycles of the H2 filling and pumping during the test. It has demonstrated that the getter pump is capable of sorbing the required amount of H2 of 20 bar*l without embrittlement and the base pressure after the sorption was in the low 10-7 mbar range with only the getter cartridge pumping. For the ion pump, the operating life at 5*10-6mbar is specified 8000 hours, corresponding to 400'000 hours (45 years) at the nominal high vacuum of 10-7 mbar. Moreover, accelerated lifetime tests of the pump in a gas composition as close to the PHM situation as possible will be performed to assure the pump life. The total dose of ionising radiation over the mission lifetime on board of the Galileo Spacecraft was analysed on the PHM physics package and electronics package, respectively by the approach of ‘sector’. The radiation test will be performed.  Figure 15. H2 consumption test  Figure 16. H2 sorption test In order to gain more field data on the reliability and lifetime of PP subassemblies four EQMs will be produced dedicated to the lifetime. The objective of the lifetime test is to monitor, during the scheduled two years, the critical parameters drift or degradation in order to predict the lifetime of the instrument and identify possible correction areas. III. CONCLUSIONS Table III summarizes the Galileo clocks status up to now. Both clocks are subjected to electrical (functional, thermal vacuum, EMC, etc.), as well as, mechanical tests (shock and vibrations). Nine flight models are being produced for GSTB-V2, which will provide the first flight opportunity for Galileo clocks qualification. With more than 10 years of efforts, two clock technologies for Galileo are qualified. Those clocks use reliable and mature technologies leaving room from further improvements in term of mass & performances. TABLE III. GALILEO CLOCKS STATUS
REFERENCES
Page 2 of 3
Previous |