Attitude Determination and Control System (ADCS) Andrew Tudor SWARM 2 29 November 2010

Approximation of Space Craft Geometry Ares V payload bay dimensions and resulting individual spacecraft approximation, m=300 kg

Attitude Determination Control the craft WRT some reference frame SensorTypical PerformanceWeight Range (kg)Power (W) Inertial Measurement (Accelerometers and Gyros) Gyro drift rate = – 1 deg/hour Linearity = 1-5 e-6 g/g 2 over g 1 – Sun SensorsAccuracy = to 3 degrees 0.1 – 20 – 3 Star Sensors (Scanners and Mappers) Attitude Accuracy = – 3 degrees 2 – 55 – 20 Horizon Sensors 1) Scanner / Pipper 2) Fixed Static Head Attitude Accuracy = 1) 0.1 – 1 degree (LEO) 2) < degree 1) 1 – 4 2) 0.5 to 3.5 1) 5 – 10 2) 0.3 – 5 MagnetometerAttitude Accuracy = 0.5 – 3 degrees 0.3 – 1.2< 1

Attitude Determination High TRL and simplicity is preferred Combination of sensors for initialization and redundancy – GPS to initialize star sensors – Star sensors are very common and have a high TRL – 2 attitude determination sensors Information is shared among other systems

Attitude Control Quantify disturbance environment Size actuators – Reaction Wheels – Thrusters Disturbance TypeDisturbance Quantification (Nm) Gravity Gradient0 Solar Radiation6.41e-5 Magnetic Field4.05e-5 Aerodynamic4.78e-5 Total Disturbance (T d )1.524e-4

Guidance, Navigation and Control System (GN&C) Andrew Tudor SWARM 2 29 November 2010

Guidance Guidance = Orbit Control Autonomous on-station control – Constellation maintenance – Fast control in debris field – Maneuvers while out of contact Ground based “special case maneuvers” – Debris deorbiting – Orbital transfers – End of life maneuvers Semi-Autonomous Control System

Navigation Navigation = Orbit Determination Global Positioning System – Position and velocity information – Real time data – Possible inertial navigation outside LEO Orbits can be propagated using E.O.M.