EarthGuidance:

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 Guidance law for planet-centered missions.
 The sail front normal is assumed to be +X in the body frame.
 Can be called in batch.
 The available profiles are:
    1. Sun-pointing (sun)
    2. Constant force component along velocity vector (v)
    3. Constant rotation with respect to LVLH frame (lvlh)
    4. Edge-on (no solar pressure force, 'off')
    5. Optimal orbit energy, see PlanetOptimalTraj (sma)
    6. Inclination (inc)
    7. Fixed, pass in d.cone and d.clock and see ConeClockToU (fixed)
 Pass in a method of -5 to get orbit lowering.

   Since version 9.
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   Form:
   [q,cone,clock,u] = EarthGuidance( t, x, d, env )
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   Inputs
   ------  
   t         (1,1)      Time, unused
   x         (6,n)      ECI state [r;v]
   d          (:)       Data structure
                         .method  (1,1)   Control method
   env        (:)       Environment struct
                         .uSun  (3,1)  Vector to sun

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   Outputs
   -------
   q        (4,n)       Inertial to body quaterion
   cone     (1,n)       Cone angle (rad)
   clock    (1,n)       Clock angle (rad)
   u        (3,n)       Sail normal vector in inertial frame

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Children:

AeroUtils: Coord/QLVLH
Common: Quaternion/QMult
Common: Quaternion/QTForm
Common: Quaternion/U2Q
Common: Transform/Eul2Q
Math: Linear/Cross
Math: Linear/Dot
Math: Linear/Unit
Sail: Coordinates/ConeClockToU
Sail: Coordinates/UToConeClock
Sail: Guidance/PlanetOptimalTraj