Propagators

Compute the state derivative.

Arguments:

• epc::Epoch: Current epoch
• x::Array{<:Real, 1}: Satellite state vector
• mass::Real: Satellite mass [kg]
• area_drag: Velocity-facing area affected by drag. [m^2]
• coef_drag: Coefficient of drag [dimensionless]
• area_srp: Velocity-facing area affected by drag. [m^2]
• coef_srp: Coefficient of reflectivity [dimensionless]
• n_grav::Integer: Gravity model degree (Default: 20)
• m_grav::Integer: Gravity model order (Default: 20)
• drag::Bool: Include cannonball atomospheric drag in force model (Default: true)
• srp::Bool: Include flat-plate solar radiation pressure in force model (Default: true)
• moon::Bool: Include thridbody lunar gravity in force model (Default: true)
• sun::Bool: Include thirdbody solar in force model (Default: true)
• relativity::Bool: Include relativistic effects in force model (Default: true)

Returns:

• dx::Array{<:Float64, 1}: Satellite state derivative, velocity and accelerations [m; m/s]

Satellite orbit state vector using an Earth inertial state representation and dynamics model.

If an initial state transition matrix is provided it will be used for propagation if there is no state transition matrix then only the state will be propagated.

Attributes:

• rk4::RK4 Internal numerical integrator used for state propagation
• dt::Real Default propagation time step. All steps will be this size unless

the state vector is requested to propagate to a time smaller than this step size, which it will do.

• epc::Epoch Epoch of state
• x::Array{Float64, 1} State vector. Earth-centered inertial Cartesian state.
• phi::Union{Nothing, Array{Float64, 2}} State transition matrix, or the matrix

of partial derivatives of the state at the current time with respect to the start of propagation.

The following force model parametters can be set as keyword arguments

Parameters:

• mass::Real: Satellite mass [kg]
• area_drag: Velocity-facing area affected by drag. [m^2]
• coef_drag: Coefficient of drag [dimensionless]
• area_srp: Velocity-facing area affected by drag. [m^2]
• coef_srp: Coefficient of reflectivity [dimensionless]
• n_grav::Integer: Gravity model degree (Default: 20)
• m_grav::Integer: Gravity model order (Default: 20)
• drag::Bool: Include cannonball atomospheric drag in force model (Default: true)
• srp::Bool: Include flat-plate solar radiation pressure in force model (Default: true)
• moon::Bool: Include thridbody lunar gravity in force model (Default: true)
• sun::Bool: Include thirdbody solar in force model (Default: true)
• relativity::Bool: Include relativistic effects in force model (Default: true)

Step dynamics state the specified time.

Arguments:

• state::EarthInertialState State vector to propagate
• dt::Real Step size. If no value is provided will use default state stepsize

Step dynamics state to the specified time. Will take as many internal steps as required to advance the propagator to the correct time. No internal step will exceed the size specified in the state propagator.

Arguments:

• state::EarthInertialState State vector to propagate
• time::Union{Real, Epoch} Time to propagate internal state too. Can be either

a real number to advance the state by or the Epoch

Simulate the sttate dynamics to the specified time. Takes same inputs as stepto! but instead of just updating the state vector to the specified time, this function also returns the timesteps, state values, and state transition matrices for each time step.

Arguments:

• state::EarthInertialState State vector to propagate
• time::Union{Real, Epoch} Time to propagate internal state too. Can be either

a real number to advance the state by or the Epoch

Returns:

• t::Array{Float64, 1} Elapsed time as a scalar from the initial simulation epoch
• epc::Array{Epoch, 1} Epoch at each timestep
• x::Array{Float64, 2} State vectors at each time step. Time is along second axis
• Phi::Array{Float64, 2} Stacked array of state transition matrices

Reinitialize State transition matrix to identity at the current time step.

Used to reinitialize the state transition matrix value to identity