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.