ESA GNC Conference Papers Repository

ESA?s future mission LISA, Laser Interferometry Space Antenna, will detect and observe gravitational waves that are emitted during the most powerful events in the universe. LISA will consist of three spacecraft traveling in near-circular heliocentric orbits in a (near)equilateral triangular formation with arm length of 2.5 million of kilometres. Each spacecraft will contain two Moving Optical System Assemblies (MOSA), each one composed by a Telescope, an Optical Bench (OB) and a Gravitational Reference Sensor (GRS), the latter containing in turn a Test Mass (TM). A gravitational wave propagating through the LISA constellation produces a tiny modulation of the distance between the TMs which is detected by laser interferometers. Each LISA satellite can be described by a complex dynamic which accounts for 20 degrees-of-freedom (DoFs). In science, 18 of the aforementioned 20 DoFs have to be controlled by the DFACS (Drag-Free and Attitude Control System) in order point the inter-spacecraft laser interferometer at nano-radian level and maintain the TMs in ?free-fall? condition along the LISA interferometer arms. An high-fidelity simulation environment is therefore deemed necessary to design and verify the DFACS performance, which is fundamental for the mission success. In the frame of one ESA contracts ?LISA Phase-A System Study for a Gravitational Wave Observatory? of which Thales Alenia Space (TAS) is prime, a DFACS functional simulator has been set up exploiting the TAS simulation framework called NUMES (New Mission End-to-End Simulator) that enables to easily build-up specific End-to-End (E2E) software environments for different kind of missions. The TAS NUMES framework consists of validated collection of C/C++, Fortran source files and Matlab/Octave, Python macros running on different environments (e.g. Linux, Windows). Each new specific simulator is built starting from the available ?bricks? of the NUMES environment. They constitute a tool capable to numerically simulate, with the appropriate level of fidelity, the dynamics of one or more satellites subject to the external environment (solar radiation pressure, magnetic field, etc.) and to the action computed by the board controller for various mission phases and operational modes. This library includes models of the sensors and actuators entering in the control loop, which for several missions, as for LISA one, comprises also elements of the payloads (e.g. accelerometers feeding the drag-free control system). The following paper briefly describes the LISA scientific mission challenges and the TAS LISA simulator environment. It shows as well some preliminary results relevant to the LISA science phase.