On-Board Computers (OBCs) for Small-satellite missions are typically required to be designed usin... more On-Board Computers (OBCs) for Small-satellite missions are typically required to be designed using industrial grade Commercial-of-the-shelf (COTS) components due to budget constraints and short mission duration. The OBC must provide a variety of interfaces due to the diverse nature of COTS subsystems having different interface definitions. Traditional OBC designs with standard microcontrollers have fixed interfaces that require modification of the motherboard circuit/layout when the external interfaces require changes. Thus, a possible solution is to have an FPGA in-addition to the micro-controller thereby providing a configurable interface capability. System-on-Chip (SoC) devices that integrate a microcontroller with FPGA fabric provide an ideal solution for reducing the development time. Additionally, the limited availability of power in small satellite missions makes it essential to use power-efficient devices. Furthermore, single event upsets (SEUs) and single event latch-up (SELs) are a major problem for OBCs designed for Low Earth Orbit (LEO) small-satellite missions. Flash memory-based FPGAs provide the benefit of low power consumption and they are more also fault-tolerant due to their intrinsic robustness against induced single event upsets compared to SRAM-based FPGAs. This article describes the OBC developed using the flash-based Microsemi SmartFusion2 SoC FPGA as its key component, for the INSPIRESat-1 and INSPIRESat-2 small-satellite missions. The OBC is designed in two form factors one with 13cm x 10cm dimensions for INSPIRESat-1 and the other with 10cm x 10cm dimensions for INSPIRESat-2. The OBC uses a COTS System-on-Module (SoM) developed by Emcraft containing the SmartFusion2 SoC, which is mounted on a custom-designed motherboard containing other peripherals including flash memory, SD Cards, and an external watchdog timer. The OBC has a total power consumption of approximately 1 W, in the final flight configuration. The article here describes the architecture of the OBC in detail, the key features of which include multiple on-board memories, a multi-level reset methodology, and reconfigurable input/output interfaces. The article concludes with the details of comprehensive performance tests conducted on the INSPIRESat-1 OBC, which has qualified TRL-8 (technology readiness level) status after completing required environmental tests such as the Thermal Vacuum Test (TVAC) and vibration test as a part of the integrated satellite. INSPIRESat-2 was launched in January 2021 and due to the successful working of the OBC in fight it has achieved TRL-9 status through this mission. The OBC developed for INSPIRESat-1 is planned to achieve TRL-9 status after its launch in the third quarter of 2021.
3D pendulum is a rigid body supported at a fixed pivot with three rotational degrees of freedom. ... more 3D pendulum is a rigid body supported at a fixed pivot with three rotational degrees of freedom. The objective is to maneuver the 3D pendulum from an initial attitude and angular rate to a desired attitude and angular rate in minimum time in presence of uniform gravity, subjected to constraints on the control input. We derive the necessary conditions for time optimality for a 3D pendulum by formulating a discrete-time optimal control problem using a Lie group variational integrator. The approach does not use local parameterizations (like Euler angles or quaternion) for attitude representation but necessary conditions for optimality are derived directly on the special orthogonal group. Further, discrete-time, time optimal attitude control satisfying the necessary conditions is computed using geometrically exact technique on special orthogonal group, such that it preserves the geometric properties of a rigid body.
We design a discrete-time linear controller for spacecraft attitude dynamics whose configuration ... more We design a discrete-time linear controller for spacecraft attitude dynamics whose configuration space is a Lie group, by linearizing the discrete non-linear model obtained by Lie group variational integrator (LGVI) technique. The advantage, in terms of sampling rate requirement, of the proposed technique over designing a discrete-time linear controller by discretizing the linearized continuous time system model using a classical transformation technique (zero order hold) is illustrated with the help of simulation results.
Control Moment Gyroscopes are widely used momentum exchange devices with spinning rotors and one ... more Control Moment Gyroscopes are widely used momentum exchange devices with spinning rotors and one or more actuated gimbals. The primary problem associated with a control moment gyroscope array is the existence of singularities. Singularities occur when the torque vector is constrained to a plane or a line and hence torque cannot be generated in IR3 space. In this paper, we study the singularity of the rooftop arrangement of a control moment gyroscope array using a recently developed model for control moment gyroscope dynamics. The effect of a non-zero offset between the gimbal and rotor center of masses on the singularity properties of a rooftop configuration is the focus of the study. This study was carried out by numerical simulation of the matrix relating the angular momentum contribution of the single gimbal control moment gyroscope array and the gimbal angle rates for a large number of permutation of the gimbal angles. Comparison with that of the classical model of a control mom...
In this paper, we study the design of energy based controller to control the magnetic needle at d... more In this paper, we study the design of energy based controller to control the magnetic needle at desired location. The magnetic needle is allowed rotate about one axis, in the external magnetic field by pivoting its center. Due to attraction and repulsive forces between the magnetic needle and external magnetic field, the magnetic needle will have two equilibrium points, one is stable and the other is an unstable equilibrium point. The magnetic needle dynamics are derived by considering uniform and non-uniform external magnetic field. The controller is designed to control the magnetic needle at the desired location. Different control strategies are derived based on the Lyapunov's function. Different control strategies steady state and transient performance are compared based on the simulation results.
This article describes the design and development of INSPIRE-0, a payload on the spent stage of t... more This article describes the design and development of INSPIRE-0, a payload on the spent stage of the ISROs PSLV. Recently, the Indian Space Research Organisation (ISRO) released an announcement of opportunity inviting proposals to develop payloads that can be tested on the PS4-Orbital Platform (PS4-OP). This platform is a novel idea formulated by ISRO to use the spent fourth/final stage of the Polar Satellite Launch Vehicle (PSLV), called the PS4, to conduct in-orbit scientific experiments and technology demonstration of small-satellite subsystems. INSPIRE-0 is a PS4-OP payload, jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, the Indian Institute of Space Science and Technology (IIST), and the Nanyang Technological University (NTU) in Singapore. This payload has two main objectives. Firstly, the scientific objective is to characterize the solar spectrum using a novel sensor, developed by NTU, that has a wide frequenc...
In this paper, we study the detailed modeling of the magnetic needle in a nonuniform external mag... more In this paper, we study the detailed modeling of the magnetic needle in a nonuniform external magnetic field. Center of the magnetic needle is pivoted so that it is allowed to rotate about one axis. A magnetic needle placed in an external magnetic field has two equilibrium points, one is stable and the other is unstable. A passivity based non-linear controller is designed for nonuniform external magnetic field system, and its tracking performance is studied at the unstable equilibrium point. The transient and steady state performance are compared between different control strategies in terms of settling time, peak overshoot, the steady state amplitude of oscillations. Further, the control strategies designed for uniform external magnetic field system are applied to the nonuniform external magnetic field system, to study the change in performance when compared to the designed controller for nonuniform external magnetic field system. The conclusions are made based on the simulation re...
2019 IEEE 16th India Council International Conference (INDICON)
CubeSats are a class of nano-satellites primarily built using commercial off-the-shelf components... more CubeSats are a class of nano-satellites primarily built using commercial off-the-shelf components for electronics and structure, aimed at space and atmospheric research. The Electrical Power System (EPS) of the CubeSat is responsible for extracting power from solar panels to provide regulated power to all the satellite subsystems and using the surplus power to charge the satellite’s batteries in order to sustain the satellite’s operations during eclipses. The battery charger integrated circuit, with the photovoltaic (PV) input, should be able to charge the batteries of the satellite while extracting maximum power from the solar panels. Since there are multiple solar panels for a given satellite, the chosen charging scheme should be able to operate in parallel from different PV inputs and common battery output terminals. This manuscript describes parallel operation of a PV battery charger, which is capable of interfacing PV panels of different incident solar radiation with a common battery. Experimental results are presented to validate the circuit operation.
In recent years, there has been a desire to develop space-based optical telescopes with large pri... more In recent years, there has been a desire to develop space-based optical telescopes with large primary apertures. Current monolithic large telescopes, as exemplified by 6.5m aperture James Webb Space Telescope, are limited by the diameter of the launch vehicle – despite their ability to unfold and deploy mirror elements. One method to overcome this obstacle is to autonomously assemble small independent spacecraft, each with their own mirror, while in orbit. In doing so, a telescope with a large, segmented primary mirror can be constructed. Furthermore, if each of these mirrors is manufactured to have an identical initial shape and then adjusted upon assembly, a substantial reduction in manufacturing costs can be realized. In order to prove the feasibility of such a concept, a collaborative effort between the California Institute of Technology, the University of Surrey, and the Indian Institute of Space Science and Technology has been formed to produce and fly the "Autonomous Ass...
Transactions of the Institute of Measurement and Control
In this paper, we propose a novel problem in control systems area involving the control of a magn... more In this paper, we propose a novel problem in control systems area involving the control of a magnetic needle in the presence of an external magnetic field. A magnetic needle when restricted to rotate about a single axis in an external magnetic field, by pivoting its center will produce a stable and unstable equilibrium. Here, we present the detailed mathematical modeling of the 1-D inverted magnetic needle system and its control in the unstable equilibrium point. We use sliding mode controller (SMC) to achieve the control objectives. The simulation results are validated with the experimental results. For achieving a close match, we consider sensor and actuator nonlinearities. Further, its robust performance is compared with proportional-derivative (PD), proportional-integral-derivative (PID) controllers in the presence of system parameter uncertainty, disturbance, and sensor delay. We also study the effect of change in SMC parameters, proportional and derivative gains on the system ...
49Th Ieee Conference on Decision and Control, 2010
A dielectrophoretic (DEP) force is a result of the interaction between a nonuniform electric fiel... more A dielectrophoretic (DEP) force is a result of the interaction between a nonuniform electric field and a polarizable particle. As the electric field is dominant at the micro/nano scale, this force can be effectively used to manipulate and control particles on this scale. We consider the motion of a particle on an invariant line with the suspending medium being a fluid with a low Reynolds number. This DEP system has two states and two parameters: the two states are indicative of the particle's position and the induced dipole moment and the two parameters are α and c which depend upon the electric properties of the particle and the medium. The system is described by a set of ordinary differential equations with a quadratic term in the control variable (control being the applied voltage on the electrodes which induces the electric field) making the system non-affine in control. In the existing literature, the controllability studies of the DEP system have been restricted to reachability issues in the context of the time-optimal control problem. Here we present a comprehensive study of reachability, accessibility and controllability.
The Dielectrophoretic (DEP) force arises as a result of the interaction between a nonuniform elec... more The Dielectrophoretic (DEP) force arises as a result of the interaction between a nonuniform electric field and a neutrally charged particle. As the effect of the electric field is more dominant than other forces at the micro/nano scale, this force can be effectively used to manipulate and control particles on this scale. We consider the motion of a particle on an invariant line with the suspending medium being a fluid with low Reynolds number. The system is described by a set of ordinary differential equations with a quadratic term in the control variable (control being the applied voltage on the electrodes which induces the electric field) making the system non-affine. For this system, we address certain aspects of existence and uniqueness of the time-optimal trajectories.
On-Board Computers (OBCs) for Small-satellite missions are typically required to be designed usin... more On-Board Computers (OBCs) for Small-satellite missions are typically required to be designed using industrial grade Commercial-of-the-shelf (COTS) components due to budget constraints and short mission duration. The OBC must provide a variety of interfaces due to the diverse nature of COTS subsystems having different interface definitions. Traditional OBC designs with standard microcontrollers have fixed interfaces that require modification of the motherboard circuit/layout when the external interfaces require changes. Thus, a possible solution is to have an FPGA in-addition to the micro-controller thereby providing a configurable interface capability. System-on-Chip (SoC) devices that integrate a microcontroller with FPGA fabric provide an ideal solution for reducing the development time. Additionally, the limited availability of power in small satellite missions makes it essential to use power-efficient devices. Furthermore, single event upsets (SEUs) and single event latch-up (SELs) are a major problem for OBCs designed for Low Earth Orbit (LEO) small-satellite missions. Flash memory-based FPGAs provide the benefit of low power consumption and they are more also fault-tolerant due to their intrinsic robustness against induced single event upsets compared to SRAM-based FPGAs. This article describes the OBC developed using the flash-based Microsemi SmartFusion2 SoC FPGA as its key component, for the INSPIRESat-1 and INSPIRESat-2 small-satellite missions. The OBC is designed in two form factors one with 13cm x 10cm dimensions for INSPIRESat-1 and the other with 10cm x 10cm dimensions for INSPIRESat-2. The OBC uses a COTS System-on-Module (SoM) developed by Emcraft containing the SmartFusion2 SoC, which is mounted on a custom-designed motherboard containing other peripherals including flash memory, SD Cards, and an external watchdog timer. The OBC has a total power consumption of approximately 1 W, in the final flight configuration. The article here describes the architecture of the OBC in detail, the key features of which include multiple on-board memories, a multi-level reset methodology, and reconfigurable input/output interfaces. The article concludes with the details of comprehensive performance tests conducted on the INSPIRESat-1 OBC, which has qualified TRL-8 (technology readiness level) status after completing required environmental tests such as the Thermal Vacuum Test (TVAC) and vibration test as a part of the integrated satellite. INSPIRESat-2 was launched in January 2021 and due to the successful working of the OBC in fight it has achieved TRL-9 status through this mission. The OBC developed for INSPIRESat-1 is planned to achieve TRL-9 status after its launch in the third quarter of 2021.
3D pendulum is a rigid body supported at a fixed pivot with three rotational degrees of freedom. ... more 3D pendulum is a rigid body supported at a fixed pivot with three rotational degrees of freedom. The objective is to maneuver the 3D pendulum from an initial attitude and angular rate to a desired attitude and angular rate in minimum time in presence of uniform gravity, subjected to constraints on the control input. We derive the necessary conditions for time optimality for a 3D pendulum by formulating a discrete-time optimal control problem using a Lie group variational integrator. The approach does not use local parameterizations (like Euler angles or quaternion) for attitude representation but necessary conditions for optimality are derived directly on the special orthogonal group. Further, discrete-time, time optimal attitude control satisfying the necessary conditions is computed using geometrically exact technique on special orthogonal group, such that it preserves the geometric properties of a rigid body.
We design a discrete-time linear controller for spacecraft attitude dynamics whose configuration ... more We design a discrete-time linear controller for spacecraft attitude dynamics whose configuration space is a Lie group, by linearizing the discrete non-linear model obtained by Lie group variational integrator (LGVI) technique. The advantage, in terms of sampling rate requirement, of the proposed technique over designing a discrete-time linear controller by discretizing the linearized continuous time system model using a classical transformation technique (zero order hold) is illustrated with the help of simulation results.
Control Moment Gyroscopes are widely used momentum exchange devices with spinning rotors and one ... more Control Moment Gyroscopes are widely used momentum exchange devices with spinning rotors and one or more actuated gimbals. The primary problem associated with a control moment gyroscope array is the existence of singularities. Singularities occur when the torque vector is constrained to a plane or a line and hence torque cannot be generated in IR3 space. In this paper, we study the singularity of the rooftop arrangement of a control moment gyroscope array using a recently developed model for control moment gyroscope dynamics. The effect of a non-zero offset between the gimbal and rotor center of masses on the singularity properties of a rooftop configuration is the focus of the study. This study was carried out by numerical simulation of the matrix relating the angular momentum contribution of the single gimbal control moment gyroscope array and the gimbal angle rates for a large number of permutation of the gimbal angles. Comparison with that of the classical model of a control mom...
In this paper, we study the design of energy based controller to control the magnetic needle at d... more In this paper, we study the design of energy based controller to control the magnetic needle at desired location. The magnetic needle is allowed rotate about one axis, in the external magnetic field by pivoting its center. Due to attraction and repulsive forces between the magnetic needle and external magnetic field, the magnetic needle will have two equilibrium points, one is stable and the other is an unstable equilibrium point. The magnetic needle dynamics are derived by considering uniform and non-uniform external magnetic field. The controller is designed to control the magnetic needle at the desired location. Different control strategies are derived based on the Lyapunov's function. Different control strategies steady state and transient performance are compared based on the simulation results.
This article describes the design and development of INSPIRE-0, a payload on the spent stage of t... more This article describes the design and development of INSPIRE-0, a payload on the spent stage of the ISROs PSLV. Recently, the Indian Space Research Organisation (ISRO) released an announcement of opportunity inviting proposals to develop payloads that can be tested on the PS4-Orbital Platform (PS4-OP). This platform is a novel idea formulated by ISRO to use the spent fourth/final stage of the Polar Satellite Launch Vehicle (PSLV), called the PS4, to conduct in-orbit scientific experiments and technology demonstration of small-satellite subsystems. INSPIRE-0 is a PS4-OP payload, jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, the Indian Institute of Space Science and Technology (IIST), and the Nanyang Technological University (NTU) in Singapore. This payload has two main objectives. Firstly, the scientific objective is to characterize the solar spectrum using a novel sensor, developed by NTU, that has a wide frequenc...
In this paper, we study the detailed modeling of the magnetic needle in a nonuniform external mag... more In this paper, we study the detailed modeling of the magnetic needle in a nonuniform external magnetic field. Center of the magnetic needle is pivoted so that it is allowed to rotate about one axis. A magnetic needle placed in an external magnetic field has two equilibrium points, one is stable and the other is unstable. A passivity based non-linear controller is designed for nonuniform external magnetic field system, and its tracking performance is studied at the unstable equilibrium point. The transient and steady state performance are compared between different control strategies in terms of settling time, peak overshoot, the steady state amplitude of oscillations. Further, the control strategies designed for uniform external magnetic field system are applied to the nonuniform external magnetic field system, to study the change in performance when compared to the designed controller for nonuniform external magnetic field system. The conclusions are made based on the simulation re...
2019 IEEE 16th India Council International Conference (INDICON)
CubeSats are a class of nano-satellites primarily built using commercial off-the-shelf components... more CubeSats are a class of nano-satellites primarily built using commercial off-the-shelf components for electronics and structure, aimed at space and atmospheric research. The Electrical Power System (EPS) of the CubeSat is responsible for extracting power from solar panels to provide regulated power to all the satellite subsystems and using the surplus power to charge the satellite’s batteries in order to sustain the satellite’s operations during eclipses. The battery charger integrated circuit, with the photovoltaic (PV) input, should be able to charge the batteries of the satellite while extracting maximum power from the solar panels. Since there are multiple solar panels for a given satellite, the chosen charging scheme should be able to operate in parallel from different PV inputs and common battery output terminals. This manuscript describes parallel operation of a PV battery charger, which is capable of interfacing PV panels of different incident solar radiation with a common battery. Experimental results are presented to validate the circuit operation.
In recent years, there has been a desire to develop space-based optical telescopes with large pri... more In recent years, there has been a desire to develop space-based optical telescopes with large primary apertures. Current monolithic large telescopes, as exemplified by 6.5m aperture James Webb Space Telescope, are limited by the diameter of the launch vehicle – despite their ability to unfold and deploy mirror elements. One method to overcome this obstacle is to autonomously assemble small independent spacecraft, each with their own mirror, while in orbit. In doing so, a telescope with a large, segmented primary mirror can be constructed. Furthermore, if each of these mirrors is manufactured to have an identical initial shape and then adjusted upon assembly, a substantial reduction in manufacturing costs can be realized. In order to prove the feasibility of such a concept, a collaborative effort between the California Institute of Technology, the University of Surrey, and the Indian Institute of Space Science and Technology has been formed to produce and fly the "Autonomous Ass...
Transactions of the Institute of Measurement and Control
In this paper, we propose a novel problem in control systems area involving the control of a magn... more In this paper, we propose a novel problem in control systems area involving the control of a magnetic needle in the presence of an external magnetic field. A magnetic needle when restricted to rotate about a single axis in an external magnetic field, by pivoting its center will produce a stable and unstable equilibrium. Here, we present the detailed mathematical modeling of the 1-D inverted magnetic needle system and its control in the unstable equilibrium point. We use sliding mode controller (SMC) to achieve the control objectives. The simulation results are validated with the experimental results. For achieving a close match, we consider sensor and actuator nonlinearities. Further, its robust performance is compared with proportional-derivative (PD), proportional-integral-derivative (PID) controllers in the presence of system parameter uncertainty, disturbance, and sensor delay. We also study the effect of change in SMC parameters, proportional and derivative gains on the system ...
49Th Ieee Conference on Decision and Control, 2010
A dielectrophoretic (DEP) force is a result of the interaction between a nonuniform electric fiel... more A dielectrophoretic (DEP) force is a result of the interaction between a nonuniform electric field and a polarizable particle. As the electric field is dominant at the micro/nano scale, this force can be effectively used to manipulate and control particles on this scale. We consider the motion of a particle on an invariant line with the suspending medium being a fluid with a low Reynolds number. This DEP system has two states and two parameters: the two states are indicative of the particle's position and the induced dipole moment and the two parameters are α and c which depend upon the electric properties of the particle and the medium. The system is described by a set of ordinary differential equations with a quadratic term in the control variable (control being the applied voltage on the electrodes which induces the electric field) making the system non-affine in control. In the existing literature, the controllability studies of the DEP system have been restricted to reachability issues in the context of the time-optimal control problem. Here we present a comprehensive study of reachability, accessibility and controllability.
The Dielectrophoretic (DEP) force arises as a result of the interaction between a nonuniform elec... more The Dielectrophoretic (DEP) force arises as a result of the interaction between a nonuniform electric field and a neutrally charged particle. As the effect of the electric field is more dominant than other forces at the micro/nano scale, this force can be effectively used to manipulate and control particles on this scale. We consider the motion of a particle on an invariant line with the suspending medium being a fluid with low Reynolds number. The system is described by a set of ordinary differential equations with a quadratic term in the control variable (control being the applied voltage on the electrodes which induces the electric field) making the system non-affine. For this system, we address certain aspects of existence and uniqueness of the time-optimal trajectories.
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Papers by Harsha Simha