facility (telescope NEP), and from the natural zodiacal light and galactic dust emission background (background -limited NEP, sometimes called BLIP, for

SIRTF is a high-sensitivity, cooled astronomical telescope operating from 2 to 1000pm. The techniques used in analyzing the sensitivity of the SIRTF system performance to several technical issues are presented. Lowering the telescope temperature to near 4K is found to produce margin in several areas. A refined observing requirements model relieves the hard­ ware performance requirements, and identifies extended source size/observing strategy as an important system specification. Other major conclusions are presented. The Phase A hardware concept has been defined5 as an 85 cm Ritchey-Cretien telescope cooled to 10 K by supercritical helium, with an articulated secondary mirror to provide spatial chopping and image motion compensation, and with 2 to 6 user-provided instruments at the focal plane. It is assumed to be mounted on the Shuttle with the Instrument Pointing System (IPS), and to be flown for multiple sortie missions. Later thinking has included the possibility of a long-life mission as a free-flyer. The system performance goals include diffraction-limited image quality over a 2 arc-min field at 2pm, image stability of 0.1 arc sec, and radiometric sensitivity limited only by the external natural radiation background between 2 and 200pm. Ball Aerospace Systems Division (BASD) recently completed one of three parallel SIRTF Technology System Studies for NASA-ARC as part of the preparation for Phase B design studies. Papers » discussing the other two studies are presented elsewhere in these pro­ ceedings. The objectives of this study were to: Assess the impact on system performance of several areas of technical concern iden­ tified by NASA-ARC or by BASD, Assess the system impact of improving the system performance in the areas of image quality, radiometric sensitivity, and pointing and control, and Identify and quantify the major driving technical issues. In this paper we will describe the methods used to analyze the system, and present the principal study results. Further details are to be found in the study report.8 Methodology