Title of Paper:  STellar Absorption and Refraction Sensor (STARS)


Principal Author:  Dr. Jeng-Hwa Yee


Abstract:  The Stellar Absorption and Refraction Sensor (STARS) is a compact, large-aperture instrument that combines a UV-IR imaging spectrograph with a co-aligned visible-light imager to make simultaneous absorptive and refractive stellar occultation measure-ments. The absorption measurements provided by the spectrograph allow the determi-nation of vertical profiles of atmospheric constituents (i.e. ozone, water vapor). The coincident refraction obser-vations made by the imager yield high-precision measurements of atmospheric density, pressure, and temperature and provide independent knowledge of both the refracted light path and Rayleigh extinction, which are critical in reducing the uncertainty in the retrieved constituent profiles in the lower atmosphere. STARS employs a two-axis gimbaled telescope to acquire and track the star and a two-axis, high-precision vernier mirror to correct for spacecraft jitter and maintain the star within the spectrograph field of view. The relative star position measured by the imager provides position feedback to the active tracking loop of the vernier mirror. With funding from NASA’s Instrument Incubator Program, a laboratory facility has been set up to demonstrate the overall instrument performance and, in particular, its capability to acquire and track a setting, refracting, and scintillating star, to compensate for various degrees of platform jitter, and to provide the pointing knowledge required for accurate determination of the at-mospheric quantities. The combination of built-in image tracking and motion compen-sation capabilities, small size, and limited spacecraft resource requirements makes STARS and its tracking mechanism suitable for deployment on existing and future spacecraft platforms for applications that require high-precision pointing. We will present details of the instrument design and its expected performance based on our laboratory tests.