Ze-Bing+Zhou

ASTROD I is the first step of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices), which measures the relativistic parameters and detects gravitational waves at the lower frequencies compared with LISA. The inertial sensor design is similar to one developed for LISA. The requirements of the inertial sensor for ASTROD I are listed as (1) limit of spurious accelerations applied on the inertial sensor is 10-13 m s-2 Hz-1/2 at 0.1 mHz, and (2) limit of the relative displacement between each sensor proof-mass and the spacecraft to 3 ´ 10-7 m Hz-1/2 at 0.1 mHz [1-2].
 * Torsion Pendulum to test performance of Inertial Sensor for ASTROD-1 **
 * Z B Zhou, ** S B Qu, H B Tu, Y Z Bai, S C Wu, Q Y Wan, J Luo
 * Huazhong **** University of Science and Technology, Wuhan **

The inertial sensor consists of a test mass and a set of electrodes that are used to read out the position and orientation with respective to the spacecraft. The inertial sensor is free along its sensitive axis as an end reference mass of optical measurement, while other axes should be controlled by electrostatic actuators [3-4].

The torsion pendulum, as a high sensitive probe in laboratory, is used to investigate the effects to the inertial sensor of the environmental parameters on ground, such as temperature, pressure, parasitical stiffness of capacitance transducer and so on [3]. In addition, the coupling between the sensitive and electrostatically servo axes should be controlled within the requirement.

To test performance of an inertial sensor for ASTROD I, a torsion pendulum facility is constructed, and the twist motion of the torsion pendulum is used to simulate the state of inertial sensor in space due to its very soft linkage. A torsion pendulum facility has been constructed in our laboratory [5]. Here the test mass is a cubic aluminum block with 50 mm on each side and a mass of 330 g. A tungsten fiber with a diameter of 50 micrometer and a length of about 1.1 m is used to suspend the test mass to act a torsion pendulum. The twist motion of the pendulum has been electrostatic-servo locked-in, and preliminary experiment shows that its torque noise level comes to 9 ´ 10-12 N m Hz-1/2 from 1 mHz to 0.1 Hz. The residual disturbances acting on the test mass are being analyzed and measured by the modulating experiments. References [1] Ni W. T., //Int. J. Mod. Phys. D//, **11**, 947, 2002. [2] Ni W. T. et al, //Class. Quantum Grav.//, **21**, S641, 2004. [3] Carbone L. et al, //Phys. Rev. Lett.// **91**, 151101, 2003. [4] Touboul P. et al., Aerospace Sci. Technol., **8**, 431, 2004. [5] Zhou Z. B. et al, // Class. Quantum Grav. //, **22**, S537, 2005.