Panchromatic, multispectral, and hyperspectral image sensors spanning the visible to longwave IR (LWIR) regions of the electromagnetic spectrum are finding increased application in advanced DOD, civil, scientific, and commercial space- based programs. Research and development advancing the state-of-the-art in visible to LWIR focal plane technology requires a careful understanding of system level requirements and a methodology for the translation of these requirements to focal pane specifications. At the focal plane level, signal-to-noise based performance is generally defined in terms of wavelength dependent noise equivalent irradiance and dynamic range specifications under conditions dictated by the system application. In this paper we illustrate a process that starts with system level performance requirements and results in focal plane performance requirements. The input spectral radiances were determined with the MODTRAN atmospheric code coupled with simple sensor and focal pane signal and noise models. The process is illustrated with two different space-based sensor examples, resulting in very different focal plane designs, configurations, and physical operating conditions. Finally, these characteristics were translated to focal pane electro- optical, thermal and electronic design parameters such as: spectral quantum efficiency, integration capacitance values and areas, and likely pixel unit-cell circuit selections.