Attitude Determination Overview Obtain expected B field vector from model in orbit frame. Orbit data update Propagate orbit Compare the s/c frame to the orbit frame Obtain B field and rates in s/c frame Euler Angles and Rates The Euler angles and rates will provide and attitude error to the control algorithm. Colorado Space Grant Consortium

Colorado Space Grant Consortium Attitude Knowledge Onboard magnetometer data and rotational rate information. Software-based orbit propagation and magnetic field model. Partial error analyses has been completed. Sensitivity of the magnetometer provides negligible attitude knowledge errors on the order of 0.01°. Tracking data must be uploaded periodically to correct propagation errors. Sun sensors may be used if suitable vendor is found. These are not needed for accurate attitude knowledge within requirements. Bdot data derivations could also be used for comparison between s/c and orbital attitude frames. Colorado Space Grant Consortium

Colorado Space Grant Consortium Magnetometer Honeywell HMC2003 20mA @ 12V mass < 100g -40 to 85 C operating temp. 40 μGauss Resolution $200 3 Analog Outputs (Bx, By, Bz) Set/Reset Capabilities Colorado Space Grant Consortium

Colorado Space Grant Consortium Rate Gyros Analog Devices ADXRS150 Single axis rate gyros provide the rotational rate of the s/c about the output axis Microchip operating at 5V and 6mA. Single analog output -40 to 85°C operating temp $33 each Colorado Space Grant Consortium

Colorado Space Grant Consortium Attitude Control The s/c magnetic dipole moment interacts with the Earth’s magnetic field to provide a torque on the s/c. → The s/c magnetic dipole moment can be controlled by passing specified currents through magnetic torque rods. → M = INA Torque rods can provide three-axis stabilization for detumbling at less weight, power, and cost than reaction wheels. Control algorithm will determine how much current to provide to each torque rod to produce the desired dipole moment for the necessary torque. Colorado Space Grant Consortium

Colorado Space Grant Consortium Gravity Gradient Gravity gradient provides a restoring torque when a disturbance torque causes a movement from local vertical. The torque produced is dependent upon the s/c moments of inertia. This shall be a design concern for placement of s/c components. Maximum disturbance torque is Aerodynamic Drag Daytime during Solar max τDrag = 5.56 x 10-5 Nm Solar Radiation Pressure 4.37 x 10-6 Nm Magnetic disturbance torques are not considered as disturbances because active magnetic control will be utilized. Colorado Space Grant Consortium

Colorado Space Grant Consortium Magnetic Torque Rods Ferrite Material wound with wire Produces a dipole moment that interacts with Earth’s magnetic field. Will be designed in-house (unless donated) Colorado Space Grant Consortium

Colorado Space Grant Consortium Torque Rod Sizing Var Description Want How m Magnetic Moment Big N # wrappings More wire, Longer Coil A Area of each wrapping Wider, Longer Coil I Current in wire More power μr Relative Permeability Better material Nd Demagnetization Factor Small Big (l/r) factor Colorado Space Grant Consortium

Torque Rod Optimization Colorado Space Grant Consortium

Torque Rod Optimization Too Long Colorado Space Grant Consortium

Torque Rod Optimization Too Massive! Too Long Colorado Space Grant Consortium

Torque Rod Optimization Too Massive! Too Long Colorado Space Grant Consortium

Colorado Space Grant Consortium Zoom-in Optimization Design Common ferrite material 33 with μ=800 24 Gauge Wire 3-10 Wrappings 7”-10” long 1/2” - 3/4” diameter 0.2 – 0.4 kg each Max Power: 1.5 W each (300 mA) 0.75 W Dissipation each Complete manufacture under $100 each After detumbling normal use should not exceed 150mA The bigger the better Colorado Space Grant Consortium