Attitude Analysis of Small Satellites Using Model-Based Simulation

Samir A Rawashdeh

doi:10.1155/2019/3020581

Abstract

CubeSats, and small satellites in general, being small and relatively light, are sensitive to disturbance torques in the orbital environment. We developed a simulation tool that includes models of the major environmental torques and small satellite experiences in low Earth orbit, which allows users to study the attitude response for a given spacecraft and assist in the design of attitude control systems, such as selecting the magnet strength when using passive magnetic stabilization or designing the shape of the spacecraft when using aerodynamic attitude stabilization. The simulation tool named the Smart Nanosatellite Attitude Propagator (SNAP) has been public in precompiled form and widely used since 2010; this paper accompanies the release of SNAP’s source code with the inclusion of new models for aerodynamic torque and other new features. Details on internal models are described, including the models for orbit propagation, Earth’s magnetic field, gravity gradient torque, spacecraft shape modelling and aerodynamic torque, permanent magnetic dipole torque, and magnetic hysteresis. A discussion is presented on the significance of aerodynamic torque and magnetic hysteresis on a magnetically stabilized 3-unit CubeSat in the orbit of the International Space Station, from which many small satellites are deployed.

Highlights

Small satellites have demonstrated significant utility in recent years at a significantly lower cost and risk tolerance than larger single spacecraft missions
In orbits between 300 km and 650 km, in which many of CubeSat and small satellites are deployed, aerodynamic and gravity gradient torques can be expected to be significant and comparable in magnitude. (iii) With an increasing number of missions for small satellites venturing beyond low Earth orbit [1], solar pressure and gravitational torques can dominate attitude dynamics
Passive satellite stabilization techniques are popular in the small-satellite community when only coarse pointing is required, because they require no power and no active control system while being fairly simple to implement in small satellites

Summary

Introduction

Small satellites have demonstrated significant utility in recent years at a significantly lower cost and risk tolerance than larger single spacecraft missions. (ii) Because of the larger number of small satellites deployed, space debris concerns favour deployment into low orbits, where orbit lifetime can be limited At these altitudes, environmental disturbance torques such as gravity gradient and aerodynamic torques are more significant. Since rotation around the magnet axis in magnetic stabilization is uncontrolled, as well as roll in aerodynamic stability and rotations about the gravity gradient boom axis, it is difficult to predict the behaviour about these uncontrolled axes analytically This motivates the development of a high-fidelity simulation to propagate the attitude in six degrees of freedom (DOF). One of these environmental effects can be intentionally utilized for the satellite design to be greater than the other environmental torques This concept is the essence of most passive attitude stabilization techniques, in which case the remaining torques act as disturbances and are the main cause of the pointing error. Beyond LEO, solar radiation pressure can become significant, causing forces that can be used for orbit manoeuvres [6] and torques that affect attitude [7]

Smart Nanosatellite Attitude Propagator

Effect of Aerodynamic Torques on Passive Magnetic Stabilization

Conclusions