Stray Light Performance of the Long Range Reconnaissance Imager (LORRI) on the New Horizons Mission

The LOng-Range Reconnaissance Imager (LORRI) is the high resolution imager for the New Horizons mission to the Pluto system and the Kuiper Belt, which is the vast region of icy bodies extending roughly from 30 to 50 astronomical units (AU). LORRI is a monolithic SiC, Ritchey-Chretien telescope with a 20.8 cm diameter primary mirror and with an 0.29 degrees field of view. The detector is a thinned, backside-illuminated charge-coupled device (CCD) operated in frame transfer mode to obtain 1024 x 1024 pixel, panchromatic images over a bandpass of approximately 350 nm to 850 nm with 4.96 mu rad pixels. LORRI operated successfully at the New Horizons Jupiter encounter in Feb-Mar 2007 and made challenging observations of faint sources, such as the Jovian rings within a few degrees of sunlit Jupiter and the nightside of Io illuminated by Jupiter shine. Ambitious observations are planned at Pluto encounter including some with LORRI pointed within 15 degrees of the Sun. A unique program of inflight calibrations has measured LORRI's stray light rejection using Jupiter and the Sun. The measured point source transmittance (PST) function for LORRI decreases from 145 on axis to 4x10(-10) at 75 degrees off-axis.