Dynamics and Operations of an Orbiting Satellite Simulation. Requirements Specification 13 May 2009

Transcription

1 Dynamics and Operations of an Orbiting Satellite Simulation Requirements Specification 13 May 2009 Christopher Douglas, Karl Nielsen, and Robert Still Sponsor / Faculty Advisor: Dr. Scott Trimboli ECE 4890 Senior Seminar Spring 2009 Semester

2 Table of Contents 1. Overview Statement of the Problem Operational Description Requirements Specification Stretch Goals Design Deliverables Preliminary System Acceptance Test Plan Implementation Considerations...6 List of Figures Figure 1 Satellite Simulator Conceptual Drawing (Notional)...2 Figure 2 High Level System Block Diagram (Notional)...3

3 1. Overview Space technology serves as an effective focus for many multidisciplinary research and education initiatives. Educational institutions focus on providing students with an understanding of satellite dynamics and command and control functions enabling students the opportunity to experience real-world conditions and conduct engineering experiments through use of a simulation environment. This project is designed to take the first step toward satellite research at UCCS through the design and development of a small-scale satellite simulator with functionality simulating movement dynamics, feedback control, Kalman filtering, satellite attitude determination and perform as a test-bed for research on feedback control algorithms, satellite pointing, and tracking. The satellite simulation project utilizes a system engineering approach to ensure successful simulation development. The system engineering encompasses requirements engineering, architectural design, component development and implementation, unit and integration testing, system verification and acceptance testing. Dr. Scott Trimboli, Director for the Center for Space Studies at UCCS, sponsors this project. The Air Force Office of Scientific Research (AFOSR) provides funding. 2. Statement of the Problem The satellite simulator models the hardware-in-the-loop operation and dynamics of an orbiting satellite within the constraints of the laboratory/classroom environment and surface gravitational field. The simulator calculates current position and repositions the satellite based upon the commands from the human-in-control ground station. The simulator, upon commands from the Ground Station: Calculates the satellite current position and orientation Executes the positioning thrust calculations to position the satellite to the commanded position and orientation Activates the attitude determination system and the attitude control system for satellite positioning Constantly measures and calculates the positioning and orientation until the new position is achieved Provides communication feedback on the satellite position to the Ground Station The following basic components are required for satellite simulation: Ground Station for wired or wireless human-in-control command and control Microprocessor for control of command messages and feedback Computer software for message processing and position and orientation calculations Power system Attitude determination system Attitude control system 1

4 The satellite simulator is not intended for actual space operations thus space-qualified hardware is not a requirement. A notional conceptual drawing of the small-scale satellite simulator is depicted in Figure 1 below. Figure 1 Satellite Simulator Conceptual Drawing (Notional) Currently, a commercially available satellite simulator called the EyasSat is available. However, this product does not support the adaptability desired for the classroom environment and research. 3. Operational Description The proposed satellite model will encompass two distinct use cases described as follows. Case 1: Educational Demonstration In the educational environment, the satellite model will easily interface with faculty and students to provide a demonstration of command and control capabilities through the wired or wireless downlink. A simple computer based GUI could provide students the ability to start up the device, observe current operational statistics such as current mode of operation and current attitude. This GUI would also allow users to command the device to perform specific actions or to change the current mode of operation or simply perform a preprogrammed demonstration of the model's core features. As the satellite model grows with future development, the new 2

5 features will also be demonstrated to the faculty and students during any classroom demonstration. Case 2: Research and Development The model's on-board microcontroller will be easily programmable to allow for future testing of improved control algorithms. This ease of programming will also facilitate the inclusion and testing of new modules provided by the extensible design of the model itself. The inclusion of new modules on board the satellite model will allow further expansion of the features provided by the model as well as providing a test bed for these features. With this test bed, future researchers will be able to refine their payloads for full inclusion onto the model, thus expanding it's educational value as well as providing yet another starting place for future modification and testing. In essence, the satellite model will be a foundation on which future students and researchers will be able to add their own building blocks. 4. Requirements Specification The requirements for the satellite simulator are outlined by the shall statements below. The high level notional system block diagram in Figure 2 outlines the components covered by the requirements. Figure 2 High Level System Block Diagram (Notional) 3

6 1. The satellite shall fall under the nanosat range (1-10kg) for portability. 2. A permanent power source shall initially supply power to operate the simulator, such as an AC outlet. 3. The system shall contain one form of actuation along a single spin axis. One method would be using a reaction wheel. A trade study will be necessary to determine the appropriate method of actuation. 4. Attitude determination shall be characterized by factors such as 2.5 degrees from a reference point specified by the user. A trade study will be needed to compare other attitude determination factors to the commercially available EyasSat and what will be necessary in the classroom and research environments. 5. A microcontroller shall process commands and send and receive data between the modules The microcontroller shall send and receive commands between Command and Control and the satellite simulator The microcontroller shall send and receive commands between attitude control and attitude determination The microcontroller shall send and receive commands between attitude control and actuation. 6. Attitude control shall be programmable through a digital control card such as a PD controller so gains can be changed in software Attitude control shall send back position and error data through the microcontroller to Command and Control Attitude control shall send movement commands to the actuation system to move the satellite along its single axis of rotation. 7. A Command and Control system shall be used for communication between the satellite simulator and ground station The ground station shall consist of a computer with a graphical user interface (GUI) a user can use to communicate with the satellite The communication link between the ground station and the satellite shall be a two-way communication system able to send data to the satellite and download data from the satellite The communication link shall be wired or wireless, but if wired shall not interfere with the dynamics simulating a true orbiting satellite. 4

7 4.1 Stretch Goals The following shall statements outline the stretch goals of the project. 1. As a stretch goal, power shall be supplied from the sun by incident solar energy. 2. An on-board battery shall supply sufficient power to the on-board components. 3. A sun tracker or star tracker shall be used for the satellite to autonomously obtain a position and move to the location. 5. Design Deliverables The design deliverables consist of the following: Operations Manual Working modular satellite model prototype that performs core features outlined by the requirements. Software interface for controlling the satellite model. 6. Preliminary System Acceptance Test Plan The acceptance test plan consists of the following: Weight and size must be measured to comply with the nanosat range. The satellite model must be operated to test the attitude actuation, determination, and programmability. In order to do this several test must be completed. o Attitude actuation and programmability: The satellite model must correctly rotate on its single axis to a user specified coordinate. This will be tested with the following steps: The user will calibrate the satellite model with a reference location. The user will give the satellite a coordinate The user will verify that the satellite rotates to the specified coordinate Repeat the process with different coordinates across the 360-degree axis. o Attitude stability: The satellite model must sustain a user specified coordinate with minimal error. This will be tested with the following steps: The user will calibrate the satellite model with a reference location. With the satellite at the reference location, the user will then manually rotate the satellite on its 360-degree axis. The user will then observe to see if the satellite will automatically correct itself back to the reference location. 5

8 o Attitude determination: The satellite must know its coordinates based on a reference location and relay them to a graphical user interface for the user. This will be verified with the following steps: The user will calibrate the satellite model with a reference location. The user will manually rotate the satellite to another known location. The user will then verify the new known location is displayed on the graphical user interface. Repeat the steps for several known locations. 7. Implementation Considerations The implementation of the satellite model will require several design considerations, which will be discussed below. Portability Since the satellite model will be used for educational demonstrations in different classrooms, it will have to be a portable device. The design of the model to fit into the nanosat category of satellite will enable the device to be easily transported due to weight and size considerations. Usability One of the main uses for the satellite model will be the demonstration of its features in an educational setting, making the interaction between the user and the system of utmost importance. The GUI enabling commands and data to be exchanged between the satellite and the user must be as user friendly and easy to use as possible. The other main use of the satellite model will be for research and development, and so the microcontroller should be easy to interface with and program. Extensibility The satellite model will be used in the future as a foundation to build upon for further research and demonstration of functionality. To facilitate this, the design of the model must be modular, thus allowing future payloads to be easily incorporated into the design. The microcontroller programming must also be easily extensible, allowing for easy interfacing of new components with existing on board systems. Any design allowing for this level of expandability will greatly facilitate future demonstration and research potentials. 6