2. 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

3. 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

4. Colorado Space Grant Consortium
Magnetometer
Honeywell HMC2003
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

5. 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

6. 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

7. 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

8. 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

9. 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

10. Torque Rod Optimization
Colorado Space Grant Consortium

11. Torque Rod Optimization
Too Long
Colorado Space Grant Consortium

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

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

14. 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