In-Orbit Tuning of PI Omega Control of LAPAN-A3 Satellite's Wheel HCP

A necessity to perform in-orbit tuning of the spare pitch wheel connected to horizon control processor (HCP), namely wheel HCP, arose after the failure of primary pitch wheel during satellite operation. The PI omega control loop is used to control the angular rate of LAPAN-A3 satellite and is essential for maintaining the nadir pointing operation by giving the angular velocity command to the pitch wheel at a nadir rate value. Hence, in-orbit tuning of PI omega control of wheel HCP was performed in order to obtain controller parameters that provide an acceptable output response with the lowest error. The trial-and-error approach was selected as the tuning method because of the unavailability of wheel HCP measurement data at a high sampling rate. The only data available are sporadic telemetry data with large measurement gaps. This study shows that the trial-and-error tuning method is reliable for obtaining an acceptable output response for a fast response system such as a reaction wheel, despite the large gaps of up to tens of seconds in measurement data. The steady-state error at the nadir rate value is 5% for PI parameters at
$K_{p}$
25000 and
$K_{i}$
7, which is good enough to have pitch drift in satellite attitude of 0.2° per hour. The simulation of PI omega control of wheel HCP based on a priori knowledge of the physical model is useful to provide insight into the system stability and the settling time of system response which has initial angular rate of satellite near zero.