2014.B.3.3 Implementation of three axis magnetic control mode for PISAT

Author(s)

Shashank Nagesh Bhat (1)
Arjun Haritsa Krishnamurthy (1)
Rao A Divya (1)
Nayak M Mahendra (1)
Vinod Kumar Agrawal (1)

PES Institute of Technology, India

Session

B.3

Keywords

ADCS; OBC; Software cycle; IMU; major cycle; minor cycle

Abstract

Orientation of a satellite is important so as to carry out payload operation. To maintain the satellite’s orientation Attitude Determination and Control System (ADCS) is the essential subsystem of the satellite. PISAT, a nano class satellite of 5.3Kg is equipped with an imaging payload to capture the images of Earth. The images are captured during normal mode of operation of ADCS, i.e., three axis magnetic control mode. This paper explains a simple and effective implementation of three axis magnetic control mode. . The PISAT software cycle is designed for 64 msec major cycle and divided by 4 minor cycles (each 16 msec) in which all the said functionalities are executed. The three axis magnetic control mode is divided into different software modules so as to fit into time slices in software cycle designed for 64 msec. The software modules are implemented on an AVR32-AT32UC3A0512 microcontroller. This Paper details implementation of three axis magnetic control mode modules, the optimization performed to ensure faster results and proper placement of individual modules in software cycle The aim of the paper is to provide information quantifying the execution time of three axis magnetic control mode of ADCS. The paper is intended to deliver the onboard software requirements and implementation of three axis magnetic control mode on OBC of PISAT. The execution time of the three axis magnetic control mode modules were measured with a core system clock of 12 MHz using test system. Also, the difference of execution times for single precision, and double precision, floating point operations were measured. Finally, to verify the estimated times, all the modules were executed using single and double precision variables in hardware for which the real execution time was measured. Knowing the execution time, the three axis magnetic control mode modules were placed in appropriate minor cycles of the OBC software cycle.