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Magnetic controllers for maintaining and varying spacecraft's directivity using only magnetorquers are presented using dynamic attitude simulator environment (DASE), which includes a flight computer and the complete satellite communications architecture. Magnetorquers are environmental actuators that on the contrary to reaction wheels do not have any moving parts. For that reason using only magnetorquers for the tasks where precise attitude control is not required prolongs mission lifetime. Despite the inability to produce torque along the Earth's magnetic field vector magnetorquers can still provide the sufficient pointing accuracy for the on-board antennae with help of B-max and VBC controllers. The controllers are designed for RASAT, an Earth observation satellite, to be launched to a sun-synchronous low Earth orbit (LEO) orbit. The satellite ground communication is achieved via rigidly mounted X-band and S-band antennae with restricted radiation patterns. The controllers' purpose is to maximize the high speed communication duration by directing the satellite's side where the antennae are located towards the ground station during each pass. The results show that magnetic actuation provides sufficient pointing accuracy that surpasses the Nadir-pointing flight mode in terms of communication duration. Nomenclature e = error received by a controller SET v = set-point vector B = Earth' magnetic field vector as measured in satellite's body frame m = magnetic dipole moment vector expressed in satellite's body frame  τ = torque vector Z = satellite's +Z vector expressed in orbit frame P K = proportional gain of a controller D K = differential gain of a controller b o R = rotation matrix from orbit frame to body frame / b bi ω  = angular velocity vector of satellite body frame with respect to inertial frame, represented in satellite body frame. I = Inertia matrix of the satellite D T  = total disturbance torques MT T  = torques generated by the magnetorquers 1 Researcher, Electrical and Electronics Engineer, M.Sc.

RASAT is a 3-axis stabilized earth observation satellite to be launched to a sun-synchronous LEO (Low Earth Orbit ) orbit. The primary design of attitude determination and control system (ADCS) flight software is performed by utilizing combination of MATLAB® and C environments. MATLAB environment ensures an easy design and test platform for quick algorithm simulation. After MATLAB simulations are performed successfully, the same algorithms are coded in C language to obtain the source code for the flight software. In the further development stage, Dynamic Attitude Simulator Environment (DASE) is used for simulating the real data to run the flight code in onboard computer. DASE software simulates the attitude and the orbit dynamics of the satellite and generates the corresponding sensor and actuator signals by using the satellite data bus as if they were received from the real sensors and sent to real actuators. Thus, DASE provides a suitable environment necessary to test and verify controllers and estimators as it simulates the satellite dynamics well before the launch. In this work, various aspects of ADCS flight code testing are considered and presented, such as sensor processing issues and actuator limitations. The success in realizing RASAT's operational phases are demonstrated by comparing the DASE-results with the desired behavior of RASAT in space. Two fundamental operational scenarios are presented as the result of simulations: 1) satellite de-tumbling after launcher separation and 2) 3-axis nadir pointing control.

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Pointing error budget calculations are considered for RASAT satellite. RASAT is designed to point its payload, an optical camera, in a desired direction within specified limits and maintain this direction via attitude determination and control. These limits are decided by attitude performance requirements, which are dependent upon top-level pointing and mapping requirements. The budgeting process takes into account possible errors appropriately, so that their cumulative effect would not exceed the imposed requirements. In an effort to cover the desired area and achieving the mission objectives, the total error made in the pointing has to be minimized. The first step in this effort is to build a pointing error budget to identify and manipulate possible sources of errors. Fundamental concepts are defined in prescribing attitude performance for satellite pointing and mapping. Then, error budgeting is detailed and a tool developed for executing the pointing budget is presented.