Abstract
Star Trackers are often the most accurate instrument in an Attitude Determination and Control Systems, but often present a slow update rate, requiring additional sensor and sensor fusion algorithms to provide a smoother and faster output. However, the available rate gyros are either noisy, or expensive and heavy. The proposed work investigates the feasibility of high-speed star trackers with modern optics, sensors, and computing systems. Firstly, we investigate the sensitivity of an optoelectrical acquisition system stimulated by dim stars, secondly, we propose and evaluate an algorithm designed to operate at high speed and to be compatible with an Field-Programmable Gate Array implementation, before evaluating the performance of the implementation on FPGA. Finally, we debate the usability of such a system, both in terms of compatibility with a mission and CubeSat ecosystems, and in terms of performance. As a result, aside from removing the need for a rate gyro, Attitude Determination and Control Systems overall pointing performances can be increased. The proposed attitude determination system achieved a 0.001° accuracy, with a 99.1% sky coverage and an ability to reject false-positive while performing a single-frame lost-in-space star identification at a 50 Hz update rate with a total delay of 19 ms, including 13 ms.
Highlights
With the development of the satellite industry, the requirement of commercial-off-the-shelf (COTS)subsystems is rapidly increasing
The induced delay by the star tracker is of maximum of 158,581 clock cycles (1.59 ms at 100 MHz) for a database containing 2176 elements
Total estimated power usage by Vivado is of 1.372 W, of which 1.262 W is attributed to the processor, and 0.110 W are attributed to the Field Programmable Gate Array (FPGA) design, including the testing elements
Summary
With the development of the satellite industry, the requirement of commercial-off-the-shelf (COTS). As star trackers are intended to be the most accurate Attitude Determination sensor, these are required to use a relatively long exposure time to gather more light and, increase the number of detected stars and better estimate their position This low update rate has been traditionally compensated through the use of a rate gyro in most satellites, ranging from Hubble Space. A recent breakthrough being StarGyro100 [9] which proposes a novel approach implementing a 100 Hz image-based gyroscope, combined with a 100 ms lost-in-space search to provide a 100 Hz update-rate This approach has the added benefits to demonstrate the possibility to perform multiple measurements from a single image sensor, which is suitable on FPGA platforms where the video stream could be duplicated and fed to multiple instrumentations Intellectual Properties blocks (IP blocks).
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