China
Africa
Explore chapters and articles related to this topic
Spacecraft and Missions
Published in Julio Sanchez, Maria P. Canton, William Perrizo, Space Image Processing, 2018
Julio Sanchez, Maria P. Canton
The term nominal orientation refers to the sun angle that optimizes the position of the solar array and that meets power and thermal constraints. For each observation the Hubble’s nominal orientation depends on the date and astronomical location of the target. In general, observations made at different times require different nominal orientation. The term roll is used to define the angle about the VI axis between a given orientation and the nominal orientation. The allowed roll depends on the sun angle. When the sun angle is between 50 and 90°, the roll cannot exceed 5°. When the sun angle is between 90 and 178°, the allowed roll is up to 30°. The roll is unlimited when the sun angle is between 178 to 180° degrees. The slew rate is approximately 6 degrees per minute. Therefore, it takes approximately one hour for a full circle of pitch, yaw, or roll. Once the telescope arrives at a new target position, it takes an additional nine minutes for the guidance system to acquire a new pair of guide stars.
Robust attitude tracking control for a rigid spacecraft under input delays and actuator errors
Published in International Journal of Control, 2019
Alireza Safa, Mehdi Baradarannia, Hamed Kharrati, Sohrab Khanmohammadi
Broadly speaking, the spacecraft maneuvers can be categorised into two classes: (1) rest-to-rest slew and (2) spin maneuver. The former is the subject of this paper where its objective is to bring a spacecraft to the desired rest attitude from another rest attitude. This means that the initial angular velocity is considered to be zero and the desired attitude is a constant vector.
An effective approach to identify the mass properties of a satellite attitude dynamics simulator
Published in Australian Journal of Mechanical Engineering, 2020
Ghasem Sharifi, Ehsan Zabihian
The momentum technique to estimate spacecraft inertia using robotic arm to change the velocity of the spacecraft has been applied in (Ma, Dang, and Pham 2008). By consideration of dynamic equation as a constraint condition, the identification issue was changed into a nonlinear optimal problem, and a particle swarm optimisation algorithm was employed to estimate centre of mass and inertia parameters (Wenfu et al. 2010). It is suggested in (Wang and Cao 2006) to estimate inertia terms through recursive least squares algorithms, only based on gyro signals and thruster torques. This approach addressed the issue by dividing the problem into two sub-problems. The measurement system was designed according to the principles of three-point measures and constant torque. Norman (Norman, Peck, and O’Shaughnessy 2011) presented a bunch of schemes based on measurement algorithms to calculate the mass characteristics of spacecraft. The validity of the algorithms was proved via comparing simulation and on orbit data. Lee (Lee and Wertz 2002) suggested and validated a methodology to identify the inertia of the Cassini spacecraft. The method estimated the moments and products of inertia of a spacecraft using the data associated with the slew manoeuvre by the reaction wheels. Bois, Lieven and Adhikari (2009) proposed a series formula to calculate the moment of inertia using a trifler suspension system and the errors were determined via a particular experiment. In (Dong et al. 2010) the BLS and EKF methods combined with each other in order to eliminate the influence of measurement noise on the results. Chashmi and Malaek (2016) proposed a fast formulation to identify the moment of inertia of a spacecraft. The formulation has a larger scope of application than previous ones in the space industry. There is a simple and popular methods to calculate the moment of inertia: period of oscillation and torque as pendulums methods (Tang and Shangguan 2011). It has numerous drawbacks and cant estimate complex system properly.