The Aerospace COrporation has developed a general purpose simulation tool for modeling visible and infrared surveillance and imaging systems. VISTAS (visible and infrared sensor trades, analysis and simulations) has been used to model both scanning and staring systems, and to compare their performance against identical scenarios. The simulations begin with a high resolution background scene, which may be either real data or a synthetic construct. If desired, targets may be embedded in the scene. The next steps in the simulation include degrading and reformatting the scene according to the specifics of the sensor system transfer function, which includes the optical point-spread-function, detector aperture, temporal aperture and filter response. The process continues with the addition of noise and the scene is resampled to the sensor resolution, including the effects of multiple samples per dwell and cross-scan oversampling. FOr time-dependent simulations, jitter and platform drift are included to produce a sequence of output images which represent the sensor response. In this paper we will show how the modeling of systems can be used to provide feedback to the design stage through tradeoff analyses. For example, scanning systems can improve their performance by oversampling, but pay a penalty in higher data rates and potentially noisier output if the integration time must be lowered. Staring systems that utilize a frame different algorithm to detect moving targets can benefit by reducing jitter, but the increased costs associated with providing low jitter must be weighted against the potential benefits. Showing the system designer the results of tradeoff analyses has proven to be a substantial aid in the design of a sensor for a given mission.