  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.
