mechanic
Sajjad Ghazanfarinia; Ehsan Mousivand; Masoud Khoshsima; Yaser Saffar
Abstract
This research is going to present design of a LEO Constellation for Navigation service with minimum number of Satellites. The goal is to achieve Dilution Of Precision (DOP) less than 6. This Requirement is going to be achieved using predefined launch vehicles limitation on orbit which is 500 km in circular ...
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This research is going to present design of a LEO Constellation for Navigation service with minimum number of Satellites. The goal is to achieve Dilution Of Precision (DOP) less than 6. This Requirement is going to be achieved using predefined launch vehicles limitation on orbit which is 500 km in circular orbit altitude and 55 degrees for orbit inclination. Design has been done based on Analyses resulting in Optimization for least number of Satellites in this orbit, to satisfy all requirements for Navigation Performance and in conformance with the constraints related to launch and orbit. Multiple analyses have been done resulted in Constellation with 324 satellites, formed in 18 Orbits with 18 Satellites in each. This design shows the performance of 4.7 in DOP for a User located in Tehran, however, the distribution of DOP over the target area shows that the requirement has been passed through the whole region
control
Sayyed Mohammad Mousavi; Sayyed Majid Esmailifar; Mohammad Chiniforoushan
Abstract
In this research, the time-optimal 6 degrees of freedom (6DOF) orbital rendezvous maneuver problem for an inertially asymmetric rigid spacecraft with independent attitude and position control actuators has been investigated. It is also assumed that the spacecraft is equipped with the thruster actuators ...
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In this research, the time-optimal 6 degrees of freedom (6DOF) orbital rendezvous maneuver problem for an inertially asymmetric rigid spacecraft with independent attitude and position control actuators has been investigated. It is also assumed that the spacecraft is equipped with the thruster actuators and the control forces and torques are generated along the three principal axes of the spacecraft. In order to obtain the time-optimal 6DOF maneuver state and control trajectories, at first, the relative translational and rotational dynamics of the spacecraft are described. Then, the Gauss pseudospectral method is used to solve the time-optimal control problem in the presence of constraints on control forces and torques. Also, the costates are estimated to first-order optimality proof of the obtained solutions. The Numerical simulation results show that for the assumed time-optimal 6DOF maneuver problem, the control structure for all of the control forces and torques is ‘bang-bang’. Eventually, the optimality of the obtained solutions is verified by checking the fulfillment of Pontrygain’s minimum principle
