Abstract
This paper proposes high-accuracy and reliable attitude measurement methods exclusive for CubeSat with restrictions of low cost, limited space, and low power consumption. The attitude measurement unit is equipped with Commercial Off-The-Shelf (COTS) components including Micro-Electro-Mechanical System (MEMS) gyro and two simultaneously operating star trackers (STR) to enhance the measurement accuracy. The Multiplicative Extended Kalman Filter (MEKF) is used to estimate the attitude of CubeSat, and four kinds of attitude estimation layouts are put forward according to the idea of weighted average of two quaternions from two STR and different architectures of information fusion. Using the proposed methods, the attitude measurement unit can continuously provide accurate and reliable attitude knowledge for attitude control unit when the CubeSat is running in orbit. Numerical simulation is performed to verify the effectiveness of the proposed methods, and it offers a reference for CubeSat developers from the perspective of engineering application.
Highlights
CubeSat has become an interesting innovation in the space frontier due to advantages such as low cost, good flexibility, short development period, and high functional density [1,2,3]
The small satellite Flying Laptop adopts one star trackers (STR) and four fiber-optic gyros (FOG) to accomplish inertial attitude measurement when the satellite is working in earth observation mode [5]; a novel STR named NSTT with high-accuracy attitude measurement capacity (3°/s) is utilized in Super Low Altitude Test Satellite (SLATS) as a technology demonstration payload [6]; the nanosatellite TechnoSat uses one FOG to integrate angular rate to generate attitude knowledge when the satellite is working in attitude maneuver mode [7]; there are two STR vertical to each other in the small satellite Bispectral InfraRed Optical System (BIROS), one of them works as cold backup [8]
Ref. [11] proposes Moving Horizon Filter (MHF) to estimate the attitude and gyro calibration parameters by jointly using one STR and one gyro and draws a conclusion that the proposed method results in an increased accuracy on nonlinear systems with respect to Extended Kalman Filter (EKF); in Ref. [12], attitude fusion data obtained by Complementary Filter (CF) according to different noise frequency characteristics of one gyro and one STR is introduced as the observed values of the Unscented Kalman Filter
Summary
CubeSat has become an interesting innovation in the space frontier due to advantages such as low cost, good flexibility, short development period, and high functional density [1,2,3]. [18] reviews a kind of gyroless attitude measurement method which utilizes the TRIAD algorithm to estimate the attitude angles of satellite based on stellar vectors from two simultaneously operating STR calculates the angular rate of a satellite by a first-order difference; Federated Extended Kalman Filter (FEKF) and Federated Unscented Kalman Filter (FUKF) are, respectively, proposed in Ref. SVD, QUEST, and TRIAD belong to single-frame methods; they do not deal with measurement errors of attitude sensors and use any knowledge about kinematics and dynamics of satellites compared with Kalman filter-based methods such as EKF, UKF, and CKF; the Kalman filter-based methods generally provide more accurate estimates than the single-frame methods [21, 22].
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