Abstract
This paper is the second part of a series of studies discussing a novel attitude determination method for nano-satellites. Our approach is based on the utilization of thermal imaging sensors to determine the direction of the Sun and the nadir with respect to the satellite with sub-degree accuracy. The proposed method is planned to be applied during the Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT) mission aimed at detecting and localizing gamma-ray bursts with an efficiency and accuracy comparable to large gamma-ray space observatories. In our previous work we determined the spherical projection function of the MLX90640 infrasensors planned to be used for this purpose. We showed that with the known projection function the direction of the Sun can be located with an overall accuracy of sim 40^prime. In this paper we introduce a simulation model aimed at testing the applicability of our attitude determination approach. Its first part simulates the orbit and rotation of a satellite with arbitrary initial conditions while its second part applies our attitude determination algorithm which is based on a multiplicative extended Kalman filter. The simulated satellite is assumed to be equipped with a GPS system, MEMS gyroscopes and the infrasensors. These instruments provide the required data input for the Kalman filter. We demonstrate the applicability of our attitude determination algorithm by simulating the motion of a nano-satellite on Low Earth Orbit. Our results show that the attitude determination may have a 1sigma error of sim 30' even with a large gyroscope drift during the orbital periods when the infrasensors provide both the direction of the Sun and the Earth (the nadir). This accuracy is an improvement on the point source detection accuracy of the infrasensors. However, the attitude determination error can get as high as 25^{circ } during periods when the Sun is occulted by the Earth. We show that following an occultation period the attitude information is immediately recovered by the Kalman filter once the Sun is observed again.
Highlights
Owing to the enormous funding requirements, satellite missions were only conducted by the economically most powerful countries of the world in the first few decades of the space era
As a consequence of the explosive technological development, small satellite missions with substantially lower funding requirement – for instance, nano-satellites including as CubeSats – became a viable alternative for traditional largesize and high-cost satellites, which made space an achievable goal for countries/ organizations with less financial resources
In our recent paper [7] we proposed a new, cost-efficient approach to this problem which is based on the utilization of thermal imaging infrasensors
Summary
Owing to the enormous funding requirements, satellite missions were only conducted by the economically most powerful countries of the world in the first few decades of the space era. In our recent paper [7] we proposed a new, cost-efficient approach to this problem which is based on the utilization of thermal imaging infrasensors For this purpose we chose the MLX90640 infrasensor of [10], which is a small-size, low-cost sensor having 32× 24 pixels and a relatively large, 110× 75 degree field of view. This coverage by a single sensor implies that six of these sensors, placed on the six sides of a cube, could cover the full sphere, see Fig. 4 of [7]. A detailed description of the equations used for the Kalman filter can be found in Appendix 1
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