| Abstract
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1969 |
| Title |
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Gravitational Reference Mass Center Determination by Velocity Modulation |
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Metrology: Instrumentation, Design & Testing |
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| Organization |
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| Content |
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Future space-born gravitational observatories such as the Laser Interferometer Space Antenna (LISA) and the Space Test of the Equivalence Principal (STEP) require test masses whose center of mass (CM) location is known to 0.1 µm or better. LISA will observe gravitational waves by measuring distance variations between test masses housed inside three free flying spacecraft to an accuracy of 40 pm. STEP will advance testing of the Equivalence Principle to 1 part in 1018 by measuring the differential acceleration of four pairs of test masses. Each of the four STEP accelerometers consist of two concentric belted cylinders, while the LISA test masses may be faceted (cubic) or spherical.
A new technique for determining the center of mass relative to the center of geometry (CG) of a spherical test mass to 0.1 µm has been developed. Previous methods involve the pendulous technique, which is typically limited to CM offsets greater than 1 µm due to the increase in 1/f noise as the CM and CG come closer together and the pendulous frequency approaches zero. The new technique avoids the 1/f noise boundary by rolling the sphere down a set of parallel rails so that the CM offset modulates the sphere’s velocity at the rolling rate frequency. This technique uses a novel optical detection sensor to measure the sphere's trajectory and a Monte Carlo parameter search to recover the phase and magnitude CM offset. Initial validation of the technique will occur using spherical proof masses. Later, the apparatus may be modified to accommodate cylindrical STEP test masses, and possibly faceted test masses for LISA. The measurement apparatus and optical detection system are discussed, and preliminary results are presented. |
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