THE LASER INTERFEROMETER SPACE ANTENNA (LISA) AIMS TO OBSERVE GRAVITATIONAL WAVES FROM A CORNUCOPIA OF LOW-FREQUENCY ASTROPHYSICAL SOURCES INCLUDING EXTRAGALACTIC BLACK HOLES WITH MASSES RANGING FROM 10S TO 10S OF MILLIONS OF SOLAR MASSES THOUSANDS OF BINARY STAR SYSTEMS IN OUR OWN MILKY WAY GALAXY AND COSMOLOGICAL STOCHASTIC BACKGROUND SOURCES AND EXOTIC PHYSICS IN THE EARLY UNIVERSE. TO ACHIEVE THIS AIM LISA WILL EMPLOY A PM-PRECISION INTERFEROMETRIC MEASUREMENT OF SIX TEST MASSES IN THREE SPACECRAFT DISTURBED BY ACCELERATIONS OF ORDER FM/S^2 AND SEPARATED BY 2.5 MILLION KM. UNLIKE ALMOST ANY ASTROPHYSICS MISSION THAT HAS PRECEDED IT THE LISA INSTRUMENT AND SPACECRAFT ARE INEXTRICABLY LINKED IN DETERMINING THE QUALITY OF THE FINAL SCIENTIFIC PRODUCT. THE SCIENTIFIC PERFORMANCE OF THE MISSION DEPENDS ON THE INTERPLAY BETWEEN ALMOST EVERY ELEMENT OF THE PAYLOAD AND PLATFORM. FOR EXAMPLE THE OPTICAL METROLOGY SYSTEM (OMS) IS USED NOT ONLY AS THE PRIMARY DISTANCE MEASUREMENT BETWEEN TEST MASSES BUT ALSO FOR SPACECRAFT ATTITUDE CONTROL. THE NEED TO MAINTAIN THE INTERFEROMETRIC REFERENCE TEST MASSES IN PURE FREE FALL DRIVES THE SPACECRAFT DYNAMICS THROUGH THE ON-BOARD MICRO-PROPULSION SYSTEM AND THE QUALITY OF FREE-FALL DEPENDS CRITICALLY ON THE STABILITY OF THE PLATFORM. STUDYING THE PERFORMANCE OF THE INSTRUMENT AND GENERATING REALISTIC SYNTHETIC DATA WITH WHICH TO TRAIN DATA PROCESSING ALGORITHMS WILL REQUIRE DETAILED SIMULATIONS CAPABLE OF REPRODUCING THE FULL COMPLEXITY OF THE LISA INSTRUMENT. THE WORK DESCRIBED IN THIS PROPOSAL WILL CONTRIBUTE TO THIS EFFORT IN THREE AREAS: SIMULATING THE DRAG-FREE AND ATTITUDE CONTROL SYSTEM (DFACS) OF LISA THAT GOVERNS THE DYNAMICS OF THE TEST MASSES AND SPACECRAFT; SIMULATING THE RELEVANT LIGHT PATH FOR THE ENTIRE OPTICAL CHAIN OF EACH LASER LINK INCLUDING MODELING THE INTERFEROMETRIC LENGTH AND ALIGNMENT SENSING; AND DEVELOPING TOOLS TO PREDICT LASER HETERODYNE FREQUENCIES BASED ON ORBIT DATA AND PLAN NECESSARY SWITCHES OR TUNINGS OF THE OFFSET-FREQUENCIES IN THE PHASE-LOCKED LOOPS. WE PROPOSE TO DEVELOP SIMULATION TOOLS DESCRIBING THE LISA DFACS INCORPORATING NON-TRIVIAL TEST MASS ACCELERATION AND READ-OUT NOISE THE MOTION OF THE MOVING OPTICAL SUB-ASSEMBLIES (MOSAS) AND THE INTERACTION OF SPACECRAFT AND TEST MASS DYNAMICS THROUGH THE CONTROL LAWS AND ACTUATORS. WE WILL DEVELOP A SIMULATION OF THE LISA OPTICAL METROLOGY SYSTEM BASED ON A HERMITE-GAUSS MODE EXPANSION AND SCATTER MATRICES CAPABLE OF MODELING TILT-TO-LENGTH COUPLING AS WELL AS THE EFFECTS OF OTHER IMPERFECTIONS IN THE OPTICAL PATH SUCH AS TELESCOPE WAVEFRONT ERRORS MODE MISMATCHES BETWEEN INTERFERED BEAMS AND BEAM SPOT MIS-CENTERING ON QUADRANT PHOTODETECTORS. WE PROPOSE TO DEVELOP A TOOL THAT WILL RAPIDLY DEVISE SUITABLE FREQUENCY PLANS TO KEEP THE HETERODYNE BEAT SIGNALS WITHIN A WORKABLE RANGE BASED ON INPUTS OF ORBITAL DATA. THE INTEGRATION OF THIS TOOL WITH THE OMS AND DFACS SIMULATION TOOLS WILL ALLOW US TO TRANSITION FROM A SOLELY FREQUENCY-LIMIT-BASED FIGURE OF MERIT TO ONE THAT IS DRIVEN BY THE ACTUAL IMPACT OF THE HETERODYNE FREQUENCY ON THE ENDTO- END NOISE. TO PROVIDE MAXIMUM BENEFIT TO THE LISA MISSION THE PRODUCTS FROM EACH OF THESE TASKS WILL BE BUILT FOR COMPATIBILITY WITH AN END-TOEND PERFORMANCE SIMULATOR ARCHITECTURE. THE LISANODE INFRASTRUCTURE IS BEING DEVELOPED WITHIN THE LISA CONSORTIUM TO FACILITATE THE IMPLEMENTATION OF AND COMMUNICATION BETWEEN DISTINCT BUT NOT ISOLATED SIMULATIONS OF THE LISA SUBSYSTEMS. THE DISTINCT SIMULATIONS WILL BE DEVELOPED AS MODULES CALLED NODES WITHIN THE SIMULATION ENVIRONMENT.