The ESA-developed NIRSpec performance simulator

The James Webb Space Telescope (JWST) Observatory is the successor mission to the Hubble Space Telescope and will lead to great scientific advancements in near- and mid-infrared astronomy. One of the four science instruments on board the spacecraft is NIRSpec, which is being developed by the European Space Agency (ESA) with EADS Astrium Germany GmbH as the prime contractor. This multi-object spectrograph will be able to measure the spectra of at least 100 objects simultaneously in the near infrared wavelength range from 0.6µm to 5.0µm and at various spectral resolutions. In order to assess the performance of the instrument, a simulator has been developed to calculate key characteristics of the optical design and the final instrument output. It uses Fourier Optics with wavefront error maps to predict the point spread function on the Micro Shutter Assembly (MSA) and the detector and can include real, as measured, spectral data of filters and dispersive elements. With the implementation of parameterized image distortion and detector features, it is possible to obtain full realistic detector frames for any optical input. Still the computation time is comparably short. The program will be of great use to predict and verify response of NIRSpec during the test and calibration campaigns.