1. Divya Rao A., P. Natarajan, Rahil Ahmed S., and V. K. Agrawal, “Onboard Attitude Estimation using MEMS based Tri Axial Vector Magnetometers for Magnetically controlled Nano-Satellites,” ICIUS-2013-283.
For magnetically controlled satellites tri axial magnetometer data is used to derive the three axis attitude onboard. MEMS based tri axial Inertial Measurement Unit (IMU) is normally used in nano/pico satellites for attitude determination and control. The main aim of this paper is to estimate the attitude in terms of quaternions using tri axial magnetometer measurements. The paper deals with the construction of attitude profile matrix using the equally spaced normalized measurement and reference magnetic field vectors. The estimation of optimal quaternion in terms of Gibbs vectors and implementation of attitude estimation by computation of maximum Eigen value solution. This paper demonstrates the onboard implementation of the attitude estimation for the nano satellite PISAT.
2. Divya Rao A., P. Natarajan, Rahil Ahmed S. and V. K. Agrawal, “Onboard estimation and correction of magnetometer bias in MEMS based Tri axial Inertial Measurement Unit,” ICIUS-2013-274.
MEMS based tri axial Inertial Measurement Unit (IMU) are used in nano/pico satellites for attitude determination and control. For magnetically controlled satellites triaxial magnetometer data of Inertial Measurement Unit (IMU), is used to derive the three axis attitude onboard. But the accuracy of the magnetometer may be compromised by large systematic magnetic disturbances on the satellite. Even the magnetic fields due to onboard electronics leads to residual magnetic fields which adds as bias in the measured magnetic field data. This paper describes the onboard estimation and correction of magnetometer bias using state estimator. The attitude independent state estimator is derived to ensure bias estimation even at high attitude errors. The algorithm has been implemented onboard for a nano satellite with active magnetic control system named PISAT
3. Shashank Nagesh Bhat, Arjun Haritsa Krishnamurthy, Rao A. Divya, Nayak M Mahendra, and Vinod Kumar Agrawal, “Implementation of three axis magnetic control mode for PISAT,” 4th Interplanetary CubeSat Workshop, South Kensington, London, UK, 26-27 May 2015, 2014.B.3.3.
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.
4. Ketan Kulkarni, Rohith, Pramath H., Karunakar Praveen, Divya Rao, and Dr. V.K Agrawal, “Sustainable Passive Solar Daylighting with Open Loop Dual Axis Sun Tracking System,” Indian sustainability congress – 2014, 4-5 march 2014, The Atria hotel, Palace Road, Bangalore – 560001.
The idea here is to provide illumination inside spaces which are beyond the reach of natural sunlight – like basements, garages, hallways – by channeling sunlight through end glowing optical fiber cables. Solar rays are concentrated over an area where a bundle of end glowing optical fibers are placed to receive the focused light from the optical collector system. The collected visible spectrum of sunlight is then channeled through the fibers till the targeted location where a diverging device such as a concave lens is placed to spread out the light. Because of the sun’s daily and seasonal motion, a sun-tracking mechanism is incorporated to make sure that the sunlight is focused onto the optical collector system throughout the day. An open loop system will determine the position of the sun using algorithms that have been developed based on solar geometry. This algorithm uses the astronomical data to determine the position of sun for any given time and date by using the microcontroller. A dual axis tracker has been developed for tracking the sun throughout the day, over a long period of time. This tracking mechanism considers both daily and seasonal changes by variation in hour angle and declination angle respectively. Daily changes are taken into account by moving the collector system at a rate of 0.24 degree per minute which enhances the performance. We have designed a system to light up an area of around 78m 2 with an illumination of 500 Lux. The paper describes in detail about the selection procedure of components, design, development and implementation of Sustainable Passive Solar Daylighting System with Open Loop Dual Axis Sun Tracking System.
5. Inchara Lakshminarayan and Divya Rao A, “Kalman Filter based estimation of constant angular rate bias for MEMS Gyroscope,” Proceedings of IEEE TechSym 2014 Satellite Conference, VIT University, 7th-8th March, 2014.
The reduction in size of sensor elements gives rise to challenges in attaining good measurement performance and high resolution. The presence of constant bias and varying noise contributes to a significant performance degradation of Micro Electro Mechanical Systems (MEMS) Gyroscopes. Here we propose a method to estimate the constant bias in noisy measurements using the recursive Kalman filter. The filter was tested for gyroscope readings from ADIS16405 tri axial inertial sensor. By estimating and eliminating the constant bias from gyroscope measurements, a significant reduction in error was observed.