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![Figure 1. 1U CubeSat Source [2]: J. Puig-Suari, "The CubeSat: The...](profile/Halis-Polat/publication/335243556/figure/fig1/AS:793688510824448@1566241495597/1U-CubeSat-Source-2-J-Puig-Suari-The-CubeSat-The-picosatellite-standard-for_Q320.jpg)
![Figure 6. NanoSail-D On-Orbit Deployed Configuration Source [27]:...](profile/Halis-Polat/publication/335243556/figure/fig3/AS:793688510840834@1566241495651/NanoSail-D-On-Orbit-Deployed-Configuration-Source-27-NanoSail-D-2010-NASA_Q320.jpg)
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In order to accomplish complex and sophisticated missions, small satellites, particularly CubeSat, need a robust and accurate attitude control system. Due to the mass- and volume-constrained design environment of CubeSat, conventional methods are sometimes inadequate to provide needed performance at low altitudes where environmental disturbances ar...
Citations
... Finally, for attitude control of the Solar Sail, novel methods such as using the aerodynamic force [30] and/or gravity gradient to orient the satellite along with the classical tip vane, modulation of the reflectivity and SRP force use with the offset between center of pressure and center of mass will be investigated. These means of control methods will be complementary to the high torque Momentum Exchange Device(s) (MED) to be used in the pitch axis. ...
Solar Sail applications utilizing the advantages of propellant-free and theoretically infinite specific impulse are widely investigated, especially for interplanetary/interstellar and near-Earth asteroid missions and non-Keplerian orbit designs. However, applications regarding to the Low Earth Orbit (LEO), specifically below 700 km, are rarely studied as aerodynamic drag is dominant. This study is aimed to harvest the LEO mission advantages by proposing an elliptical orbit design and control via continuous low thrust. Two-tier mode based control algorithm is employed and maximum energy gain or loss thrust vector control is implemented depending on the phase of the mission, i.e. raising or decreasing. It is shown that the proposed mission orbit and successive low thrust maneuvers are applicable. The results depending on the initial orbit and satellite parameters are also investigated.
... All the components, subsystems and shifting masses, are COTS to ensure their commercial availability. More detailed information on this design can be found in Polat (2016). ...
At very low orbital altitudes (≲450 km) the aerodynamic forces can become major attitude disturbances. Certain missions that would benefit from a very low operational altitude require stable attitudes. The use of internal shifting masses, actively shifting the location of the spacecraft center-of-mass, thus modulating, in direction and magnitude, the aerodynamic torques, is here proposed as a method to reject these aerodynamic disturbances. A reduced one degree-of-freedom model is first used to evaluate the disturbance rejection capabilities of the method with respect to multiple system parameters (shifting mass, shifting range, vehicle size, and altitude). This analysis shows that small shifting masses and limited shifting ranges suffice if the nominal center-of-mass is relatively close to the estimated center-of-pressure. These results are confirmed when the analysis is extended to a full three rotational degrees-of-freedom model. The use of a quaternion feedback controller to detumble a spacecraft operating at very low altitudes is also explored. The analysis and numerical simulations are conducted using a nonlinear dynamic model that includes the full effects of the shifting masses, a realistic atmospheric model, and uncertain spacecraft aerodynamic properties. Finally, a practical implementation on a 3U CubeSat using commercial-off-the-shelf components is briefly presented, demonstrating the implementation feasibility of the proposed method.
RESUMEN Se presenta el diseño, fabricación y caracterización de los actuadores de un subsistema para la determinación y control de orientación de un nanosatélite tipo CubeSat 3U, que tiene una misión de percepción remota de captura de imágenes en el espectro visible con resolución de 30m en órbita polar (600km). El arreglo consta de tres ruedas inerciales y tres bobinas de torque magnético, colocadas de manera colineal a los ejes (x,y,z) del satélite. Para el diseño se utiliza una planta de simulación basada en las ecuaciones de movimiento del satélite, sus propiedades inerciales, las perturbaciones provocadas por el ambiente espacial en la órbita definida por la misión y los requerimientos de precisión y estabilidad del módulo de percepción remota del satélite SENSAT. Los actuadores fueron fabricados para ser colocados en tarjetas de factor de forma PC/104, junto con el circuito electrónico para su comando. Se realizó una caracterización dando como resultado un error máximo de 15% con respecto a lo esperado del diseño teórico, suficiente para la realizar las acciones de control y estabilización, ya que los diseños cuentan con tolerancia. El subsistema de determinación y control de orientación es fundamental en misiones satelitales que requieren de apuntamiento, ya que sin éste, el satélite podría entrar en un estado de giro sin control tan pronto sea expulsado del lanzador, reduciendo sus capacidades en órbita, entre las cuales están: la captura de imágenes, un uso eficiente de la energía solar y la utilización de antenas direccionales. Un satélite en órbita, está sujeto a numerosas fuerzas, las cuales producen pares perturbadores, mismos que desvían el apuntamiento del satélite; la compensación de estos pares es tarea del sistema de determinación y control de orientación. Estas perturbaciones, son consecuencia del ambiente espacial: arrastre aerodinámico, gradiente gravitacional, viento solar, etc. O por pares internos propios del funcionamiento del satélite: despliegue de antenas, paneles solares, desplazamiento de cubiertas de cámaras, corriente eléctrica circulando por un conductor [1] [2]. Actualmente, los componentes que conforman al subsistema: sensores, actuadores, procesadores de datos, etc… se encuentran en un alto nivel de TRL (nueve), en el caso de micro, medianos y grandes satélites [3]. Caso contrario a los pico y nanosatélites, los cuales se encuentran en una etapa joven de desarrollo (TRL 6), Se espera que alcancen la madurez en los próximos años, por lo que la innovación en este tipo de
Utilization of the propellant-free thrust capability of Solar Sail Spacecraft (SSS) is addressed. For this purpose, an elliptical orbit with a very low perigee altitude and an apogee altitude high enough to have solar sail acceleration is proposed for Earth observation mission. In the mission part, regional observation tasks are carried out that take place in very Low Earth Orbit region. The orbit maintenance and control are handled in the high altitude regions. The baseline SSS design is accomplished and presented. Orbital maintenance for station keeping and orbital maneuvers for carrying out specific missions are analyzed, and capabilities of SSS for changing orbital parameters are investigated. A constellation of observation satellites is also proposed addressing the weaknesses in rapid response of SSS to mission needs. Attitude control for smooth attitude maneuvers is also addressed. It is found that the novel quaternion-based attitude tracking control approach with time dependent attitude trajectory offers smooth, jerk-free and accurate attitude tracking.
This paper investigates an attitude control method for the CubeSat using a moving mass actuator to solve the problem of the strong aerodynamic disturbance in low Earth orbit. The rotational and translational equations are derived for the CubeSat with three moving masses, and their dynamic effects are analyzed. A magnetorquer is used to prevent the underactuation of the attitude control system. The movement of moving masses is slowed down by using a discrete double-loop Proportion Integral Differential control method, thereby reducing the fast time-varying additional disturbance. A nonlinear observer is used for the precise estimation of the slow time-varying disturbance. Notably, the ideal attitude control torque is allocated to two actuators by using the proposed control allocation algorithm. Numerical simulation indicates that the attitude convergence accuracy is up to ±0.1° despite the uncertain dynamics, unknown disturbances, and dynamic effects. The results verify the feasibility of the proposed control method.
This paper investigates an attitude control technique for a low Earth orbit nanosatellite with moving masses based on the active use of aerodynamic forces. A speed-adaptive dynamic surface control scheme is designed to comprehensively solve the practical problems of aerodynamic model error, the dynamic effect of movement, stroke limitation, and slow convergence. Multiple constraints are imposed on the inputs to reduce the fast-varying dynamic effect of the masses to be negligible. Other slow-varying disturbances are precisely estimated by a nonlinear observer. In particular, to resolve the contradiction between the overshoot and the attitude convergence speed, a novel adaptive law is designed based on the smooth hyperbolic tangent function to adjust the convergence parameter within the given boundary. Moreover, considering the actual physical limitation, hard constraints are imposed on two actuators. Finally, by using the Lyapunov approach, it is proven that, despite uncertain dynamics, unknown disturbances and input constraints, the attitude error can be adjusted to be arbitrarily small by choosing the proper parameters. A semi-physical simulation platform is built to verify the feasibility of the moving mass actuator and the effectiveness and robustness of the proposed control scheme.
