Session
Session V: Advanced Technologies & Subsystems, Components & Sensors I
Abstract
This paper describes the design and performance verification of a magnetically controlled smallsat being built by students and staff at the Naval Postgraduate School. The spacecraft (NPSAT1) will carry a number of experiments, including two sponsored by the Naval Research Lab and a commercial, off-the-shelf digital camera. Since NPSAT1 will be a secondary payload, it must be designed for a large mission box at minimum cost. Attitude control pointing requirements are less than 10° and an active magnetic control system is planned. NPSAT1 is manifested on the Department of Defense Space Test Program (STP) MLV-05, Delta IV mission, due to launch in January 2006. Many spacecraft have employed magnetic sensing and actuation for attitude control. However, in most instances, the systems are designed with long gravity gradient booms for pitch and roll stabilization. The systems usually employ an extended Kalman filter when active damping is required. The NPSAT1 design employs a magnetic control system based on favorable moments of inertia realized by optimum equipment placement and ballast. The control system uses a standard quaternion control law for attitude control with a linear reduced order estimator for rate information. Attitude capture from initial orbit injection rates and steady state attitude errors less than 2° are demonstrated by simulation. The simulation is based on an 8th order magnetic field model and includes onboard computer sampling, torque rod command quantization, lag and saturation. Sensing and torque events are separated in time to prevent contamination of magnetometer data. Air bearing tests are planned for final performance verification. The control system hardware and software represent a minimum cost approach to spacecraft attitude control.
NPSAT1 Magnetic Attitude Control System
This paper describes the design and performance verification of a magnetically controlled smallsat being built by students and staff at the Naval Postgraduate School. The spacecraft (NPSAT1) will carry a number of experiments, including two sponsored by the Naval Research Lab and a commercial, off-the-shelf digital camera. Since NPSAT1 will be a secondary payload, it must be designed for a large mission box at minimum cost. Attitude control pointing requirements are less than 10° and an active magnetic control system is planned. NPSAT1 is manifested on the Department of Defense Space Test Program (STP) MLV-05, Delta IV mission, due to launch in January 2006. Many spacecraft have employed magnetic sensing and actuation for attitude control. However, in most instances, the systems are designed with long gravity gradient booms for pitch and roll stabilization. The systems usually employ an extended Kalman filter when active damping is required. The NPSAT1 design employs a magnetic control system based on favorable moments of inertia realized by optimum equipment placement and ballast. The control system uses a standard quaternion control law for attitude control with a linear reduced order estimator for rate information. Attitude capture from initial orbit injection rates and steady state attitude errors less than 2° are demonstrated by simulation. The simulation is based on an 8th order magnetic field model and includes onboard computer sampling, torque rod command quantization, lag and saturation. Sensing and torque events are separated in time to prevent contamination of magnetometer data. Air bearing tests are planned for final performance verification. The control system hardware and software represent a minimum cost approach to spacecraft attitude control.
