GUIDANCE the right direction ORBIT GNC(FUNCTIONS) 1. Orbit

GUIDANCENAVIGATION AND CONTROL·        TheGNC functions includes guidence algorithms ,navigation filters, controllers,and possibly actuator managment functions.·        Threemain functions on board a spacecraft1.      Navigation/where am i: determiningthe vehicle’s position and velocity or orbital elements as a function of time(attitude, angular velocity, orientation).

2.      Guidence/ where to go:defining theoptimal state vectors of the vehicle as a function of time.3.      Control /how to get there:the processof deriving the commands to match the current and optimal vehicle statevectors.·        Mainly2 subsystems 1.      Attitude GNC2.      Orbit GNCATTITUDEGNC(functions)1.      Payload pointing2.

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      Antennae pointing3.      Thermal control by changingorientation4.      Thrusting in the right direction                      ORBIT GNC(FUNCTIONS)1.     Orbit maintanace2.

     Station keeping3.     Relative motion controlAttitude GNC, sensors and navigation·        Sun sensors, magnetometers,gyroscopes:1.      deterministic three-axis attitudedetermination(TRIAD, QUEST ,q-method)2.      low pass filter applied to the sensoroutputs·        Star tracker(uses on board catalogue of stars)1.      Filter merge sensor measurements withon board dynamics model2.

      High accurate and autonomous3.      Do not require measurement of allstates ATTITUDE GNC –GUIDANCE·        Way points (desired pointing directions)·        Trajectory generation(desires attitude profile) ATTITUDE GNC-ATTITUDE CONTROL AND ACTUATORS1)    Spin stabilizationi)       Quaternioncontrolii)      Yaw steering in sun-syncnchronousorbit2)    Gravity gradient stabilization3)    Magnetic  stabilization (magnetorquer)4)    Zero momentum three axis controli)       control moment gyrosii)     reaction wheelsiii)   thrusters ORBIT –GNC  SENSORS AND NAVIGATION·        Groundbased orbit determination(lamberts problem)·        GPSreceiversORBIT GNC – GUIDANCE·       Desiredway points·       Desiredrelative trajectory ORBIT GNC-CONTROL ANDACTUATORS·       Impulsivemaneuvers to instantaneously modify the velocity i.       Ionthrusters ii.      Chemical thrusters·       continousthrust to track a trajectory through electrical propulsion

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