Katake, Anup Bharat (2006-08). Modeling, image processing and attitude estimation of high speed star sensors. Doctoral Dissertation. Thesis uri icon

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.
  • 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.

publication date

  • August 2006