Physics – Geophysics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.u51b0038n&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #U51B-0038
Physics
Geophysics
[0935] Exploration Geophysics / Seismic Methods, [0994] Exploration Geophysics / Instruments And Techniques, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
The Moon will be explored during the next decade by a series of missions, especially from Japan, China, India and USA. We present here the status of the development of space qualified Very Broad Band seismometer in Europe. This instrument, completed by Japanese Short Period Seismometers, is called Lunar Broad Band Seismometer (LBBS). It is considered for the Japanese project SELENE-2 and US project LUNETTE. The main scientific goals are to determine the internal structure of the whole Moon and more specifically the composition and size of the lunar core. The LBBS instrument is the result of an international consortium: A 3 axis short period (SP) seismometer (ISAS/JAXA) A 3 axis very broad band (VBB) seismometer (IPGP) A deployment system (DPL) (MPS) A data acquisition system (SEIS-AC) (ETHZ) Both SP and VBB development rely on technical heritage of cancelled space missions (LUNAR-A for the SP, Netlander & Humboldt/ExoMars for the VBB). This technical development lead VBB to reach a Technical Readiness Level (TRL) above 5 (ESA ExoMars PDR), and we aim at TRL 6 within the next few months. The adaptation of the VBB from Mars to Moon conditions and environment is challenging. The resolution has to be improved by a factor of ten and should be inferior to 2.10-11m/s^2/sqrt(Hz) @ 0.1 Hz while the Instrument are supporting very large temperature variations (several 10s of degrees) compared to those of typical VBB seismometers. Using Netlander & ExoMars heritage, It appeared that a trade-off between resolution and VBB thermal sensibility was possible. A passive thermal compensation device was designed and tested at IPGP reducing VBB thermal sensitivity by a factor of 12, and we aim at a factor of 20. It will be possible to improve the resolution consequently if thermal sensitivity is reduced. For Moon missions VBB developments, efforts have been made both on mechanical design and Displacement Capacitive Sensor (DCS). The mechanical part of VBB is an inverted pendulum; the theoretical study we made shows that the mechanical gain can be improved by a factor of 3 to 5. The DCS geometry has been modified : By improving the size and reducing the gap of the electrodes, the Signal to Noise Ratio will be improved; we also designed a DCS prototype with selectable active or passive electronics on the sensor head. The aim is to enlighten the role of power dissipation on the long-term global VBB noise. All these technical modifications have been realized on two VBB breadboards. The tests are undergoing this autumn in the urban seismic vault of the IPGP observatory in Saint Maur. Then all LBBS subsystems will be assembled and a field measurement campaign in low noise seismic site is foreseen, probably in BFO (Black Forest Observatory). Once the whole LBBS breadboard has been tested in relevant environment, the TRL will be close to 6.
Banerdt B.
Bierwirth M.
Christensen Ulrich R.
de Raucourt S.
Escande N.
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