Most effective method of detumbling cubeSat

Most effective method of detumbling cubeSat

1. Project Description

The aim of this project is to determine the most effective method of detumbling a CubeSat following deployment into a low orbit. A CubeSat is the name given to a low cost, miniature satellite developed through a joint venture by the California Polytechnic State University and Sanford University; all CubeSats are required to adhere to a number of set standards specified in the CubeSat design specification1. The University of Strathclyde is currently working with a number of partners such as Clydespace to develop the capability for production and deployment of such CubeSats. The standard three unit CubeSat being studied for the purposes of this project measures approximately 300 x 100 x 100 mm and weighs up to 4kg.

CubeSats are taken into orbit mounted to a launch vehicle and are deployed at their specified altitude using a common deployment system known as a Poly Picosatellite Orbital Deployer. The majority of current generation CubeSats have limited means of stabilization and are left to tumble; this significantly reduces their performance and research capabilities as they are unable to point instruments or solar panels with any degree of accuracy or control.

Analysis is performed on the attitude of the satellite over the initial 60 seconds of orbit following deployment, with the aim of finding a range of angular rates from which detumbling will be necessary. This analysis will be performed using a simulation created through MATLAB and Simulink, The University of Strathclyde's Department of Mechanical Engineering is home to StrathLab; a library of Simulink blocks modelling various spacecraft components. The use of these blocks will greatly reduce the time taken to create a full simulation of a CubeSat.

2. Background Information

2.1 CubeSats

A CubeSat is a miniature satellite adhering to the standards outlined by California Polytechnic University in the CubeSat design specification. The CubeSat project originated as a joint venture between California Polytechnic State University and Sanford University in 1999 and is now a collaboration of over 100 universities, high schools and private firms developing picosatellites allowing them to take part in space science and exploration, this is made possible due to the CubeSat's relative low cost and ease of construction.

A standard one unit CubeSat, as shown in figure 1, has a cross sectional area of 100mm by 100mm and a height of 113.5mm with a mass of up to 1.33kg while a three unit CubeSat has a height of 340.5mm and a mass of up to 4kg. CubeSats are able to carry small scientific instruments as part of their payload allowing research and experimentation to take place.

All CubeSat are launched using a standardized deployment system known as the Poly-Picosatellite Orbital Deployer, as shown in figure 2, capable of carrying three one unit CubeSats or one three unit CubeSat. The P-POD is a rectangular box made of anodized aluminium, when actuated torsion springs push the door open the CubeSat is deployed by gliding on its rails and the P-POD's rails.

2.2 MATLAB / Simulink

MATLAB, short for Matrix Laboratory, is an application developed by The MathWorks which integrates data computation, visualisation and programming within a single environment. The library contains a large number of algorithms used to solve mathematical problems particularly those containing matrix and vector manipulation. The application also contains facilities for plotting vectors and matrices as well as the annotation and printing of these graphs. Functionality is also available for the creation of three dimensional visualisation and animation and the building of graphical user interfaces for MATLAB applications.

Simulink is an extension of MATLAB for the simulation and analysis of dynamic systems, the application provides a graphical user interface which allows models to be viewed as block diagrams. Simulink contains a large built in library of sinks, sources, components and connectors as well as the functionality for user defined blocks.

2.3 StrathLab

StrathLab is a library of Simulink blocks modelling various elements of a spacecraft simulation allowing for organisation and easier access to these models. StrathLab provides a graphical interface, as shown in figure3, separating the Simulink models into categories such as dynamics, actuators and guidance with all blocks conforming to the colour standards specified by the European Space Agency for Simulink models.

Also contained in StrathLab is a documentation block which creates an html file containing the documentation for each of the models contained within the library Information provided by the documentation includes a overview of model, its parameters, inputs and outputs as shown in figure 4.

The addition of further models into the StrathLab library is simple requiring the addition of the model into the appropriate sub directory within the StrathLab folder. The model is then automatically integrated into the library interface the next time that the MATLAB script is run.

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