Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21344910l&link_type=abstract
American Astronomical Society, AAS Meeting #213, #449.10; Bulletin of the American Astronomical Society, Vol. 41, p.342
Astronomy and Astrophysics
Astrophysics
Scientific paper
Solar wind and residual atmospheric drag can produce disturbances that are unacceptable for high precision scientific experiments. The drag free concept is to shield a proof mass from these disturbances, and sense the proof mass position to fly the spacecraft around the proof mass. LISA and a large array of astrophysical missions must fly drag-free to achieve their desired scientific goals. In the modular gravitational reference sensor (MGRS), the proof mass is kept a large distance away from housing to minimize the disturbances, and will be suitable for advanced drag-free missions.
We have proposed and demonstrated differential optical shadow sensing scheme, to generate the primary signal for spacecraft drag-free control. In this scheme, a pair of detectors spaced at the diameter of a spherical proof mass is used measure the proof mass movement. By differencing their outputs, the laser intensity noise is cancelled, while the proof mass displacement signal is doubled.
We have designed and constructed an optical shadow sensing test platform comprised of a step motor driven actuator for large movement and a piezo driven flexture structure for fine adjustment. We investigated signal formation and methods of signal to noise ratio enhancement. We reduced the noise effects of electronics, electromagnetic interference, air flow and temperature. Currently we have achieved a sensitivity of 2 nm/Hz1/2 at 2 Hz, limited by lab air currents. The dynamic range is 1 mm, limited by the detector diameter. We applied the differential optical sensing technique to mass center determination measurement and improved the mass center precision to 200 nm. Further, we are designing and constructing a new platform that will have spinning spherical proof mass and multiple optical shadow sensors, to demonstrate full 3-d optical shadow sensing.
Buchman Sasha
Byer Robert
Conklin John
Goebel John
Leidecker Nick
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