Graphite-epoxy Composite Gravity -gradient Boom for a Small Satellite

Passive stabilization methods for satellites have undergone extensive research and development. Recently the number of small satellites (satellites less than I 00 kg.) has increased dramatically. This has lead to increased use of passive stabilization methods, such as gravity-gradient The core of a gravity-gradient stabilization system is a deployable boom with a damping mechanism. Traditionally, this boom is consuucted from metal alloys. Uneven heating and cooling occurs when these alloys are exposed to varying solar radiation conditions. This can induce thennal vibrations which can lead to undesired satellite attitude inversions. Graphite-epoxy composites can be fabricated to minimize thermal expansion. This will be beneficial when applied to gravity-gradient booms. The goal of this project is to demonstrate the use of graphite-epoxy composites in gravity-gradient booms. This project encompasses: the use of a satellite attitude simulation program for boom sizing and determination of gravity-gradient boom loading, development of joint-locking mechanisms for boom deployment, and selection and testing of appropriate fabrication methods. Gravity-Gradient Stability The Earth's gravitational field provides a ready source of stability for satellites in low Earth orbit. The inverse square nature of the Earth's gravitational field causes a torque to act on a spacecraft in orbit. This torque causes the spacecraft's principal axis of minimum moment of inertia to align itself with the local vertica1.! 2 Student, Aerospace Engineering Member AIAA Student, Aerospace Engineering Member AIAA 4 The magnitude of the torque is a function of the distance from the center of the earth (orbital radius) and the ratios of the mass moments of inertia A cartesian coordinate system is introduced with the origin at the spacecraft center of mass, with the x-axis along the orbital velocity vector, y-axis perpendicular to the orbital plane, and the z-axis nadir pointing and completing a right-handed system. Figure 1. Spacecraft Axis System Professor, Aerospace Engineering Member AIAA Associate Professor, Aerospace Engineering