Preliminary Optical Performance Analysis of the Space Interferometer Mission Using an Integrated Modeling Methodology

Abstract

Abstract The Space Interferometer Mission (SIM) scheduled for launch in 2008, is one of the premiere missions in the Origins Program, NASA’s endeavor to understand the origins of the galaxies, of planetary systems around distant stars, and perhaps the origins of life itself. The precise tolerance required by the SIM instrument facilitates the investigation of many design options, trades, and methods for minimizing interaction between the actively controlled optics and the structure. One of the activities that addresses these technological challenges is the integrated modeling methodology development and validation at Jet Propulsion Laboratory (JPL). The methodology integrates structural, optical, and control system modeling into a common computational environment and enables end-to-end performance evaluation of complex optomechanical systems. This paper provides an overview of the integrated modeling methodology and introduces the most recent SIM Reference Design model. The SIM integrated model is used in system requirement trade studies and performance analyses to support the overall system design and ongoing error budget efforts. Optical performance in interferometry is typically measured in terms of optical pathlength difference (OPD) and differential wavefront tilt (DWT). This paper focuses on the OPD performance metric and investigates the OPD jitter resulting from reaction wheel assembly (RWA) disturbances. The RWA is the largest anticipated disturbance source on the spacecraft. Therefore, assessing the impact of the wheel disturbance frequency content and magnitude levels on the optical performance is essential for the success of the mission. Broadband and discrete frequency models of a reaction wheel are used to perform the disturbance analysis. The overall system design can benefit from such analysis results by identifying the critical regions in the frequency domain and decoupling the dynamics of the optical and structural components from the disturbance spectrum and the control bandwidth. The preliminary performance results show that the current SIM Reference Design meets the mission requirements with respect to RWA induced disturbances. However, some of the modeling assumptions and component models must be validated by experimental studies before the subsystem requirements are finalized.