LISA system design overview

An overview of the LISA measurement chain is given and the design of the spacecraft with the main focus on the LISA payload is described. The main highlights of the current payload design baseline are the introduction of the strap-down system in connection with a dedicated actuator for the point-ahead angle compensation, and the laser frequency swap. The strap-down system separates the problems of the 5 mio. km interferometry from the proof-mass metrology. This gives more design freedom in the mechanical configuration, a clear separation of the different subsystems, and it also improves the testability on ground. The laser frequency swap significantly reduces the problems of straylight and also yields a clear separation between the incoming and outgoing laser beam which introduces the possibility of an optimal adjustment of the local oscillator independently from the outgoing beam. Both design changes are presented and their impacts on the overall system design and the measurement performance is discussed. Compared to the last study in 2000, the mechanical design has changed in an effort of reducing the overall system mass while keeping a reliable and technologically feasible design. The design baseline is supported by the corresponding structural, thermal, drag-free and attitude control, vacuum, and optical analyses such that the revised error budgets are now supported by results from more detailed models instead of rough estimates. Finally, an overview of the latest performance estimates is given and the derived requirements on the main subsystems are discussed. The paper presents the current status of the LISA system design as it is established in the framework of the European Space Agency's Mission Formulation Study at EADS Astrium.