Attitude Determination/Control System (ADCS)

Subsystem Top Level Requirements
--
The system shall control the spin rate and attitude of the spacecraft to ensure a communications link
-- The system shall determine the attitude and spin rate of the spacecraft
-- The attitude shall be determined in post-processing on the ground

Subsystem Functional Requirements
--
The system shall not exceed a mass of 50 grams and a volume of 100 cm^3
-- The system shall not exceed 0.1 Watts of power

Passive Attitude Control
The HERMES CubeSat is attitude controlled through the use of two Aluminum-Nickel-Cobalt (AlNiCo) permanent magnets. These magnets will align lengthwise with Earth's magnetic field, providing two-axes of stabilization. The third axis is not stabilized and the satellite will spin freely about the longitudinal axis of the magnets. A magnetic hysteresis material, either in the form of rods or plates will be used for magnetic damping to prevent oscillation about the spin axis. Above Boulder, Colorado, where the primary ground station is located, the magnetic field vector is at an angle of 66 degrees. The figure below shows the inclination angle of the magnetic field across the globe.

Magnetometer
The other component of the ADCS system is a Honeywell HMC2003 three-axis magnetometer,
designed to measure low-strength magnetic fields. Although this sensor is not used for any active attitude control, it will provide verification data for the accuracy with which the magnets align with the magnetic field. For this reason, the sensor is included within the ADCS subsystem, rather than the CDH subsystem.

Attitude Determination
The magnetometer data will be down linked to the ground station and analyzed to determine the orientation and spin of the satellite. This algorithm will also factor in data from current sensors on each solar panel which act as crude current sensors.

 

Links & Downloads

Magnetic Field Inclination

Magnetic Field Declination

Vertical Magnetic Field Intensity

Horizontal Magnetic Field Intensity

Total Magnetic Field Intensity

HMC2003
Magnetometer Datasheet