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    Launch vehicle simulation for an SSTO vertical launch.

    The goal is to get the vehicle moving horizontally at orbital velocity.

    Uses LaunchVehicle2D which has a 'flat' earth. The simulation can handle
    any number of stages which are set by the arrays d.mStage, d.thruster, d.uE
    and d.cDA each of which have one element for each stage.

    You vary gammaPitchover to get different trajectories. The number in
    the script gives the vehicle a horizontal trajectory (that begins to
    drop due to drag) at 68 km. The trajectory is very sensitive to
    gammaPitchover.

    LaunchVehicle2D uses an exponential atmosphere.

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