Santosh Ratan - Academia.edu (original) (raw)
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Papers by Santosh Ratan
14th Biennial Conference on Mechanical Vibration and Noise: Nonlinear Vibrations, 1993
A method for performing transient dynamic analysis of multi-shaft rotor system is proposed. The p... more A method for performing transient dynamic analysis of multi-shaft rotor system is proposed. The proposed methodology uses the reported Successive Merge and Condensation (SMAC) method [12] and a decoupling technique to decouple the shafts. Multi-shaft rotor systems are treated as systems of many independent single shaft rotor systems with external unknown coupling forces acting at the points of couplings. For each time step, first, the SMAC method is used to get the transient response in terms of the unknown coupling forces. This is followed by the application of the coupling constraints to calculate the coupling forces and, in turn, the response at the end of that time step. The proposed method preserves the efficiency advantages of the SMAC algorithm for single-shaft rotor system. Numerical examples to validate and illustrate the applicability of the method are given. The method is shown to be applicable to linear and non-linear coupling problems.
SpaceOps 2008 Conference, 2008
This paper presents a method to slew a spinning satellite in the inertial frame using reaction wh... more This paper presents a method to slew a spinning satellite in the inertial frame using reaction wheels. Presently, the slew is performed using chemical thrusters because they produce high actuation torques. The use of reaction wheels saves fuel and thus extends the mission life of the satellite. Angular momentum is loaded on the reaction wheels so that the total momentum of the satellite including the reaction wheels is zero. Then a slew torque profile is followed to achieve the slew in minimum time without stopping the spin of the satellite.
On fait fonctionner un micropropulseur de modification de vitesse (ΔV) sur un vaisseau spatial, c... more On fait fonctionner un micropropulseur de modification de vitesse (ΔV) sur un vaisseau spatial, ce qui entraine immanquablement une erreur d'attitude. Une roue a reaction (RWA) corrige l'attitude. Au debut de la manoeuvre du micropropulseur, on determine la force d'impulsion de commande d'attitude total requise pour au moins corriger les erreurs d'attitude induites par le micropropulseur ΔV pendant la duree de la manoeuvre complete, et on doit aussi determiner la force d'impulsion de la roue RWA. On fait fonctionner des micropropulseurs de commande d'attitude (REA). On fait fonctionner ces micropropulseurs REA pour corriger au moins l'erreur d'attitude nette induite par le micropropulseur ΔV et, de preference, pour remettre la roue RWA a son niveau de force d'impulsion nominale. Cette manoeuvre peut etre une manoeuvre de maintien a poste.
22nd AIAA International Communications Satellite Systems Conference & Exhibit 2004 (ICSSC), 2004
To reduce stationkeeping propellant and extend orbital maneuver life, a predictive momentum adjus... more To reduce stationkeeping propellant and extend orbital maneuver life, a predictive momentum adjust system has been developed for the Lockheed Martin A2100 spacecraft. This system is designed for maneuvers where high-efficiency Arcjets (AJTs) fire continuously for Delta-V, Reaction Wheel Assemblies (RWAs) are used for attitude control, and hydrazine Rocket Engine Assemblies (REAs) are pulsed for momentum control. The predictive momentum control strategy improves fuel efficiency by optimizing the use of the REAs, which have a much lower specific impulse than the AJTs. To reduce the REA firing impulse, sequences of contiguous REA pulses, or pulse bursts, are executed to drive the RWA momentum error at the end of the maneuver to zero. The final maneuver momentum error is calculated based on an estimate of the AJT disturbance impulse as well as the commanded and measured RWA momentum. By using prediction, the system eliminates REA firing in response to that portion of the momentum error that would naturally be corrected by the AJT disturbance torque alone. Innovative control logic maximizes the REA duty cycles to reduce the total number of pulses and increase the specific impulse of the firings. The system executes pulse bursts interspersed with intervals of quiescent RWA control in a way that adjusts the RWA momentum and simultaneously maintains the RWA speeds within their allowable limits. The recursive implementation provides feedback to ensure the target momentum is achieved in the presence of REA torque uncertainties and the time-varying AJT disturbance torque. The paper provides an overview of the control system logic, and includes numerical simulation results and in-orbit A2100 spacecraft flight data that illustrate the benefits of the new approach.
AIAA Guidance, Navigation, and Control Conference and Exhibit, 2002
This paper presents three techniques for managing spacecraft momentum so as to maximize time betw... more This paper presents three techniques for managing spacecraft momentum so as to maximize time between momentum adjust maneuvers. The techniques apply to spinning spacecraft using thrusters and reaction wheels for 3-axis control in the presence of an inertially fixed disturbance. By switching from wheel control to thruster control and back with the correct timing, momentum growth in the body frame can be redirected so that wheel speeds will gradually diminish in the course of normal control operations before again increasing to the point where another momentum adjust maneuver is required. Techniques of varying operational complexity are presented, with flight data showing their effectiveness.
14th Biennial Conference on Mechanical Vibration and Noise: Nonlinear Vibrations, 1993
A method for performing transient dynamic analysis of multi-shaft rotor system is proposed. The p... more A method for performing transient dynamic analysis of multi-shaft rotor system is proposed. The proposed methodology uses the reported Successive Merge and Condensation (SMAC) method [12] and a decoupling technique to decouple the shafts. Multi-shaft rotor systems are treated as systems of many independent single shaft rotor systems with external unknown coupling forces acting at the points of couplings. For each time step, first, the SMAC method is used to get the transient response in terms of the unknown coupling forces. This is followed by the application of the coupling constraints to calculate the coupling forces and, in turn, the response at the end of that time step. The proposed method preserves the efficiency advantages of the SMAC algorithm for single-shaft rotor system. Numerical examples to validate and illustrate the applicability of the method are given. The method is shown to be applicable to linear and non-linear coupling problems.
SpaceOps 2008 Conference, 2008
This paper presents a method to slew a spinning satellite in the inertial frame using reaction wh... more This paper presents a method to slew a spinning satellite in the inertial frame using reaction wheels. Presently, the slew is performed using chemical thrusters because they produce high actuation torques. The use of reaction wheels saves fuel and thus extends the mission life of the satellite. Angular momentum is loaded on the reaction wheels so that the total momentum of the satellite including the reaction wheels is zero. Then a slew torque profile is followed to achieve the slew in minimum time without stopping the spin of the satellite.
On fait fonctionner un micropropulseur de modification de vitesse (ΔV) sur un vaisseau spatial, c... more On fait fonctionner un micropropulseur de modification de vitesse (ΔV) sur un vaisseau spatial, ce qui entraine immanquablement une erreur d'attitude. Une roue a reaction (RWA) corrige l'attitude. Au debut de la manoeuvre du micropropulseur, on determine la force d'impulsion de commande d'attitude total requise pour au moins corriger les erreurs d'attitude induites par le micropropulseur ΔV pendant la duree de la manoeuvre complete, et on doit aussi determiner la force d'impulsion de la roue RWA. On fait fonctionner des micropropulseurs de commande d'attitude (REA). On fait fonctionner ces micropropulseurs REA pour corriger au moins l'erreur d'attitude nette induite par le micropropulseur ΔV et, de preference, pour remettre la roue RWA a son niveau de force d'impulsion nominale. Cette manoeuvre peut etre une manoeuvre de maintien a poste.
22nd AIAA International Communications Satellite Systems Conference & Exhibit 2004 (ICSSC), 2004
To reduce stationkeeping propellant and extend orbital maneuver life, a predictive momentum adjus... more To reduce stationkeeping propellant and extend orbital maneuver life, a predictive momentum adjust system has been developed for the Lockheed Martin A2100 spacecraft. This system is designed for maneuvers where high-efficiency Arcjets (AJTs) fire continuously for Delta-V, Reaction Wheel Assemblies (RWAs) are used for attitude control, and hydrazine Rocket Engine Assemblies (REAs) are pulsed for momentum control. The predictive momentum control strategy improves fuel efficiency by optimizing the use of the REAs, which have a much lower specific impulse than the AJTs. To reduce the REA firing impulse, sequences of contiguous REA pulses, or pulse bursts, are executed to drive the RWA momentum error at the end of the maneuver to zero. The final maneuver momentum error is calculated based on an estimate of the AJT disturbance impulse as well as the commanded and measured RWA momentum. By using prediction, the system eliminates REA firing in response to that portion of the momentum error that would naturally be corrected by the AJT disturbance torque alone. Innovative control logic maximizes the REA duty cycles to reduce the total number of pulses and increase the specific impulse of the firings. The system executes pulse bursts interspersed with intervals of quiescent RWA control in a way that adjusts the RWA momentum and simultaneously maintains the RWA speeds within their allowable limits. The recursive implementation provides feedback to ensure the target momentum is achieved in the presence of REA torque uncertainties and the time-varying AJT disturbance torque. The paper provides an overview of the control system logic, and includes numerical simulation results and in-orbit A2100 spacecraft flight data that illustrate the benefits of the new approach.
AIAA Guidance, Navigation, and Control Conference and Exhibit, 2002
This paper presents three techniques for managing spacecraft momentum so as to maximize time betw... more This paper presents three techniques for managing spacecraft momentum so as to maximize time between momentum adjust maneuvers. The techniques apply to spinning spacecraft using thrusters and reaction wheels for 3-axis control in the presence of an inertially fixed disturbance. By switching from wheel control to thruster control and back with the correct timing, momentum growth in the body frame can be redirected so that wheel speeds will gradually diminish in the course of normal control operations before again increasing to the point where another momentum adjust maneuver is required. Techniques of varying operational complexity are presented, with flight data showing their effectiveness.