| dc.description.abstract | Attitude estimation and angular velocity estimation are the most critical components
of a spacecraft's guidance, navigation and control. Usually, an array of tightlycoupled
sensors (star trackers, gyroscopes, sun sensors, magnetometers) is used to
estimate these quantities. The cost (financial, mass, power, time, human resources)
for the integration of these separate sub-systems is a major deterrent towards realizing
the goal of smaller, cheaper and faster to launch spacecrafts/satellites. In this
work, we present a novel stellar imaging system that is capable of estimating attitude
and angular velocities at true update rates of greater than 100Hz, thereby eliminating
the need for a separate star tracker and gyroscope sub-systems.
High image acquisition rates necessitate short integration times and large optical
apertures, thereby adding mass and volume to the sensor. The proposed high
speed sensor overcomes these difficulties by employing light amplification technologies
coupled with fiber optics. To better understand the performance of the sensor, an
electro-optical model of the sensor system is developed which is then used to design
a high-fidelity night sky image simulator. Novel star position estimation algorithms
based on a two-dimensional Gaussian fitting to the star pixel intensity profiles are
then presented. These algorithms are non-iterative, perform local background estimation
in the vicinity of the star and lead to significant improvements in the star
centroid determination. Further, a new attitude determination algorithm is developed that uses the inter-star angles of the identified stars as constraints to recompute
the body measured vectors and provide a higher accuracy estimate of the attitude
as compared to existing methods. The spectral response of the sensor is then used
to develop a star catalog generation method that results in a compact on-board star
catalog. Finally, the use of a fiber optic faceplate is proposed as an additional means
of stray light mitigation for the system. This dissertation serves to validate the conceptual
design of the high update rate star sensor through analysis, hardware design,
algorithm development and experimental testing. | en |
