FFSim:

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   Formation flying simulation. 

 *** Notes on Usage ***

   The input data for this function can be created automatically for  
   different test cases, using the "FFMaintenanceTests" function.

   Once this function has run and the outputs have been created, use the
   "FFSimPlotter" function to plot the data.

 *** Inputs ***
   Supply the initial state of the reference (el0) and the initial relative 
   state (dEl0), define the desired relative motion (goals), how many 
   orbits to simulate (nOrbits), the number of simulation points per orbit 
   (nSPO), the disturbance options (distOpt), the cross-sectional area, mass.

 *** Estimated Absolute and Relative States (ECI) ***
   The estimated absolute and relative ECI position and velocity are provided 
   by adding noise to the true state. This emulates the data provided by a 
   relative navigation unit.

 *** Estimated Relative State (Hills) ***
   The estimated relative position and velocity in the Hill's frame is 
   computed via a transformation from the estimated absolute and relative 
   ECI position and velocity. This computation is performed in the 
   "AbsRelECI2Hills" function.

 *** Estimated Orbital Elements ***
   The estimated mean orbital elements and mean orbital element differences
   are computed from the estimated absolute and relative ECI position and
   velocity. This computation is performed in the "ECI2MeanElements" function.

 *** Desired Orbital Elements ***
   At each step in the simulation, the initial goals are used along with the 
   current estimate of the mean orbital elements to compute the desired 
   orbital element differences. 

 *** Desired Relative State (Hills) ***
   The desired element differences are transformed to the Hill's frame, 
   defining the desired relative position and velocity.

 *** Relative State Error (Hills) ***
   The relative position errors and relative velocity errors are computed by
   comparing the desired and estimated states.
 
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   Usage:
   simData = FFSim( simOptions );
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   ------
   Inputs
   ------
   simOptions    (.)   Data structure with the following fields:
     - el0            (1,6)  Initial reference orbital elements  (Alfriend format) [a,theta,i,q1,q2,W]
     - dEl0           (1,6)  Initial orbital element differences (Alfriend format)
     - goals           (.)   Goals data structure defining desired relative motion
     - nOrbits         (1)   Number of orbits to simulate
     - nSPO            (1)   Number of simulation points per orbit
     - distOpt        (1,3)  Disturbance options (flags)
                          (1) solar:  whether to simulate with solar pressure or not
                          (2) drag:   whether to simulate with drag or not
                          (3) J2:     whether to simulate with J2 or not
     - mass           (1,2)  Mass of reference and relative [kg]
     - aera           (1,2)  Cross-sectional area of reference and relative [m^2]

   -------
   Outputs
   -------
   simData       (.)   Simulation output data structure with the following fields
     - time          (1,:)   Time vector [orbits] 
     - rE            (3,:)   True ECI position of reference
     - vE            (3,:)   True ECI velocity of reference
     - rE_est        (3,:)   Estimated ECI position of reference
     - vE_est        (3,:)   Estimated ECI velocity of reference
     - rH            (3,:)   True Hills-frame relative position
     - vH            (3,:)   True Hills-frame relative velocity
     - rH_est        (3,:)   Estimated Hills-frame relative position
     - vH_est        (3,:)   Estimated Hills-frame relative velocity
     - rH_des        (3,:)   Desired Hills-frame relative position
     - vH_des        (3,:)   Desired Hills-frame relative velocity
     - dElMean       (6,:)   True mean element differences
     - dElMean_est   (6,:)   Estimated mean element differences
     - dElMean_des   (6,:)   Desired mean element differences
     - elRefMean_est (6,:)   Estimated mean elements of reference
     - fDiffDragH    (3,:)   Hills-frame differential drag force
     - fDiffDragE    (3,:)   ECI-frame differential drag force
     - fDiffSolarH   (3,:)   Hills-frame differential solar force
     - fDiffSolarE   (3,:)   ECI-frame differential solar force
     - fDiffJ2H      (3,:)   Hills-frame differential J2 force (apparent)
     - fDiffJ2E      (3,:)   ECI-frame differential J2 force (apparent)

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Children:

Common: Coord/Altitude
Common: Coord/QForm
Common: Coord/QHills
Common: Coord/QTForm
Common: Coord/RPhiTheta2Cart
Common: Database/Constant
Common: Math/Mag
Common: Math/RK4
Common: Math/RK4TI
Common: Math/Unit
Common: Time/JD2000
Common: Time/JD2T
CubeSat: RelativeOrbit/FFSimPlotter
FormationFlying: Analysis/FFMaintenanceTests
FormationFlying: Coord/IsCircGeom
FormationFlying: Coord/OrbElemDiff
FormationFlying: Transformation/AbsRelECI2Hills
FormationFlying: Transformation/ECI2Hills
FormationFlying: Transformation/ECI2MeanElements
FormationFlying: Transformation/FFEccGoals2Hills
FormationFlying: Transformation/FFEccHills2DeltaElem
FormationFlying: Transformation/Goals2Hills
FormationFlying: Transformation/Hills2DeltaElem
Orbit: GravityModels/LoadGravityModel
Orbit: OrbitCoord/Alfriend2El
Orbit: OrbitMechanics/AGravity
Orbit: OrbitMechanics/OrbRate
SC: Attitude/SolarF
SC: BasicOrbit/El2RV
SC: BasicOrbit/M2Nu
SC: BasicOrbit/RV2El
SC: Environs/AtmDens2
SC: Ephem/EarthRot
SC: Ephem/Eclipse
SC: Ephem/SunV1