P078 00005

Acceleration disturbances due to gravity gradients in ASTROD I : 

Acceleration disturbances due to gravity gradients in ASTROD I Sachie Shiomi National Tsing-Hua University, Hsinchu, Taiwan 30013, ROC The Astrodynamical Space Test of Relativity using Optical Devices (ASTROD) mission consists of three spacecraft in separate solar orbits to carry out laser interferometric ranging. ASTROD aims at testing relativistic gravity, measuring the solar system and detecting gravitational waves. Because of the larger arm length, the sensitivity of ASTROD to gravitational waves is estimated to be about 30 times better than LISA in the frequency range lower than about 0.1 mHz. ASTROD I is a simple version of ASTROD, employing one spacecraft in a solar orbit. It is the first step of ASTROD with several scientific goals and simultaneously serves as a technology demonstration mission for ASTROD. The required acceleration noise level of ASTROD I is 10−13 ms−2 at the frequency of 0.1 mHz. In this paper we give an overview of the sources and magnitudes of acceleration disturbances to the ASTROD I proof mass. We focus on local gravity gradient noise that could be one of the largest acceleration disturbances in the ASTROD I experiment. We discuss possible sources of local gravity gradients and present the results of gravitational analyses using simplified models for the current configuration of ASTROD I. 6th Edoardo Amaldi Conference on gravitational waves, June 20-24, 2005 Bankoku Shinryoukan Kise Nago, Okinawa ASTROD I concept References: W.-T. Ni et al. 2002 I.J.M.P.D 11 1035-1048 X. Xu and W.-T. Ni et al. 2003 Adv.Space.Rev. 32 1443-1446 W.-T. Ni, S.Shiomi and A.C.Liao 2004 Class. Quantum Grav. 21 S641-S646 S. Shiomi and W.-T. Ni 2005 arXiv:gr-qc/0506012 v1 2 Jun 2005 S. Shiomi et al. 2001 Class. Quantum Grav. 18 2533-25415 D’Urso and Adelberger 1997 Phys. Rev. D 55 7970-7972 Acceleration disturbances: estimated assuming the control-loop. Local gravity gradients Monte Carlo simulation Positional fluctuations of ~1 mm in the x-y plane are insignificant for a model of homogeneous spacecraft (density 35.6 kgm-3, mass 350 kg) with a rectangular housing at its centre (2mm gap from the rectangular test mass, 5050 35 mm3). More realistic models of the spacecraft are under study. S. Shiomi and W.-T. Ni 2005 W.-T. Ni, S.Shiomi and A.C.Liao 2004 Two-Way Interferometric and Pulse Laser Ranging between Spacecraft and Ground Laser Station Positional fluctuations of the test mass produce dominant terms q1m, which are proportional to q00(fluctuation). These terms couple to Q2m’ and produce unwanted acceleration (see above equations). Therefore, the magnitude of the unwanted acceleration is independent of the shapes of the test mass to the first order, but is dependent of the mass distribution of the spacecraft (Q2m’). These analyses agree with results given by Xu and Ni.