Drag-free Spacecraft Technologies: criticalities in the initialization of geodesic motion

Abstract

Present and future space missions rely on systems of increasingly demanding performance for being successful. Drag-free technology is one of the technologies that is fundamental for LISA-Pathfinder, an ESA mission whose launch is planned for the end of September 2015. A purely drag-free object is defined by the absence of all external forces other than gravity. This is not a natural condition and thus requires a proper design of a spacecraft, whose core is an object in free-fall, called test mass (TM). The purity of the drag-free orbit depends on the spacecraft capability of protecting the TM from disturbances, which indeed has limitations. According to a NASA study, such a concept provides substantial economies for LEO satellites. At the same time, a drag-free motion is required in many missions of fundamental physics. eLISA is an ESA concept mission aimed at opening a new window to the universe, black holes, and massive binary systems by means of gravitational waves. LISA-Pathfinder is in charge of proving the eLISA concept. In this frame, the system holding the TM during launch and releasing it in free-fall before the science phase represents a single point of failure for the whole mission. This thesis describes the phenomena, operations, issues, tests, activities, and simulations linked to the release following a system engineering approach. Experimental studies have been carried out to investigate this phenomenon in conditions representative of the LISA-Pathfinder flight environment. The last part of the thesis is dedicated to the preliminary design of the housing of the TM in the frame of a low-cost mission conceived at Stanford (USA). The ambition of this work is increasing the maturity of the technology needed in drag-free projects and therefore provide a starting point for future fascinating and challenging missions of this kind.