HYPER stands for Hyper-precision cold atom interferometry in space. HYPER is a potential Future Flexi-mission of the European Space Agency, ESA, in the fundamental physics domain. Following a preliminary feasibility study (Ref 1) conducted in the Concurrent Design Facility of the European Space Technology Center, ESTEC, which was supported by Professor W. Ertmer of the "Institut fuer Quantenoptik, Hanover" and his team of scientists, ESA awarded Astrium Germany and its industrial team with a "follow-on" Feasibility Study Contract. As part of this team, Galileo Avionica was responsible for the design and performance requirements simulation of the optical bench and precision star tracker, two of the components at the heart of the HYPER payload. This paper provides first of all an essential but quick introduction to cold atom-wave interferometry which is at the core of the high-performance HYPER pay-load and provides the capability of measuring accelerations and rotations with extremely high accuracy. A summary of the scientific mission objectives, which entail the repeated measurement of extremely small rotations and accelerations over at least one-year period with respect to an inertial reference frame, is described. Thereafter, a short resume of the main mission requirements is given. Among these requirements are two "critical" requirements, which dominate the overall spacecraft design: 1. The superior thermo-mechanical stability between the HYPER instruments and a Precision Star Tracker, PST, which provides the inertial attitude reference in science mode (Spectral Density=2.75x10~(10) rad/Hz~(-0.5), in the frequency range between 3.2x10~(-5) Hz and 0.15 Hz); 2. The PST Absolute Measurement Accuracy (Spectral Density=1.75x10~(-9) rad/Hz~(-0.5), in the frequency range between 3.2x10~(-5) Hz and 5 Hz). Finally, this paper highlights the challenges the Industrial Team faced in meeting those requirements and describes the optical design of this extremely accurate Precision Star Tracker. The preliminary results of the performance requirements simulation are also presented.
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