CC BY
16Малые космические аппараты: производство, эксплуатация и управление
УДК 669.713.7
T. Inamori, H. Ohsaki University of Tokyo, Japan, Tokyo
COMPENSATION OF A MAGNETIC DISTURBANCE TORQUE INCLUDING THE EFFECT OF FERROMAGNETIC MATERIALS FOR A PRECISE ATTITUDE CONTROL IN SMALL SATELLITES
This research analyses a magnetic disturbance torque caused by the interaction between the geomagnetic field and ferromagnetic materials in a satellite. This research also proposes a new method to compensate the magnetic disturbance torque including the effect of ferromagnetic materials for a precise attitude control in small satellite missions.
Small satellites attract interest as an easily achievable space application because of their relatively cheaper development cost and shorter development period. These small satellites are used in various mission applications such as remote sensing and astronomical observation that require precise attitude control. To achieve the precise attitude control, effects of attitude disturbances should be cancelled during the missions. Small-satellites in LEO suffer from various attitude disturbances such as magnetic disturbance, air pressure disturbance, solar disturbance, and gravity gradient disturbance. In standard-sized satellites, the effect of magnetic disturbance is insignificant and therefore not considered in previous researches. However, in small satellites, magnetic disturbance is the dominant attitude disturbance.
This is because the magnetic moment has a relatively strong effect on such satellites owing to their small moment of inertia [1]. To satisfy the strict attitude requirements for small-satellites in LEO, the effect of magnetic disturbance should be mitigated to achieve precise attitude control. Fig. 1, a shows the effect of magnetic disturbance in previous satellite missions. The horizontal and vertical axes show the satellite moment of inertia and the angular acceleration due to a magnetic field produced by magnetic disturbance, respectively. Fig. 1, a shows that magnetic disturbance has a larger effect in smaller satellites. Therefore, this effect should be compensated in small satellites.
Magnetic disturbance is caused by the interaction of the geomagnetic field and the residual magnetic moment of a satellite. If a satellite estimates the residual magnetic moment and compensates for it using the steady output of a magnetic torquer (MTQ), it can compensate for the effect of magnetic disturbance. Fig. 1, b shows an overview of the compensation of magnetic disturbance. To compensate for the magnetic disturbance precisely, a satellite must estimate the residual magnetic moment accurately and must have an accurate actuator to generate a magnetic moment.
The satellite can estimate the magnetic moment using an extended Kalman filter with magnetometers and gyro sensors. This method is examined using a small remote sensing satellite PRISM and a small astronomy satellite "Nano-JAMSINE" developed by the University of Tokyo.
Fig. 2 shows the result of magnetic compensation. Fig. 2, a shows the attitude rate of PRISM without magnetic compensation: the satellite attitude rate changes relatively rapidly because of the magnetic disturbance effect.
In Fig. 2, b, with magnetic compensation, the satellite can stabilize the attitude precisely because of the relatively small magnetic disturbance torque.
This research also considered a disturbance torque caused by ferromagnetic materials in a satellite. In previous works, the effect of the ferromagnetic materials causing a disturbance torque in the geomagnetic field is not considered for the precise attitude control.
a b
Fig. 1. Relationship between satellite mass and residual magnetic moment of a satellite (a) and Overview of the magnetic compensation (b) [1]
Решетневскце чтения
0008 З1 0.006 го 0.004
-0008
500
1000 1500 time (s)
2000
2500
500
1000 1500 time (s)
b
2000 2500
Fig. 2. Results of in-orbit experiments for magnetic compensation using remote sensing nano-satellite PRISM [1]: angular rate of PRISM: a - without magnetic compensation; b - with magnetic compensation
The ferromagnetic materials such as iron cores of MTQs and a magnetic hysteresis damper for a passive attitude control system are used in various small satellite missions. These materials cause a disturbance torque which is almost the same magnitude of the dipole magnetic disturbance in the worst cases. This research proposes an estimation and compensation method including the effect of the ferromagnetic materials using the extended Kalman filter. The research concludes that
the proposed method is useful for precise attitude control for small satellite missions from simulation results.
References
1. Inamori T, Sako N., Nakasuka S. Magnetic dipole moment estimation and compensation for an accurate attitude control in nano-satellite missions // Acta Astronautica. Elsevier. 2011. Vol. 68, Iss. 11-12. P. 2038-2046.
Т. Инамори, X Осаки Токийский университет, Япония, Токио
ВРАЩАЮЩИЙ МОМЕНТ МАГНИТНОГО ВОЗМУЩЕНИЯ, ВКЛЮЧАЯ ВЛИЯНИЕ ФЕРРИМАГНИТНЫХ МАТЕРИАЛОВ НА ТОЧНОСТЬ УПРАВЛЕНИЯ ПОЛОЖЕНИЕМ В ПРОСТРАНСТВЕ МАЛЫМИ КОСМИЧЕСКИМИ АППАРАТАМИ
Предлагается анализ вращающего момента магнитного возмущения, вызванного взаимодействием геомагнитного поля и ферримагнитных материалов в спутнике. Предлагается новый метод компенсации вращающего момента магнитного возмущения, включая влияние ферримагнитных материалов на точность управления положением в пространстве малым космическим аппаратом.
© 1патоп Т., Ohsaki Н., 2012
УДК 531.3
А. А. Давыдов
Государственный космический научно-производственный центр имени М. В. Хруничева, Россия, Москва
ИССЛЕДОВАНИЕ ВРАЩАТЕЛЬНОГО ДВИЖЕНИЯ КОСМИЧЕСКОГО АППАРАТА В РЕЖИМЕ ГАШЕНИЯ УГЛОВЫХ СКОРОСТЕЙ ПРИ НЕПОЛНЫХ ИЗМЕРЕНИЯХ
Исследована математическая модель управляемого движения космического аппарата (КА) в режиме гашения его угловых скоростей при отсутствии измерений угловой скорости вокруг одной из связанных осей КА. Рассмотрена задача определения фактического вращательного движения КА по телеметрической информации об угловых скоростях КА и кинетических моментах двигателей-маховиков.
В математической модели космический аппарат (КА) считается гиростатом. Он представляет собой твердое тело с расположенными на нем тремя двигателями-маховиками (симметричными роторами). Система координат ххх3 образована главными централь-
ными осями инерции КА. В этой системе тензор инерции КА задан матрицей diag(/1, 12, /3). Абсолютная угловая скорость главного тела определяется проекциями ю1, <в2, ю3 на оси системы х1х2х3. Оси вращения маховиков параллельны осям хи так что каждая
a
