High-Precision Orbit Propagator

satkit.propagate(*args, **kwargs)

High-precision orbit propagator

Propagate orbits with high-precision force modeling via adaptive Runge-Kutta methods (default is order 9/8).

Args:

• state (npt.ArrayLike[float], optional)

  6-element numpy array representing satellite GCRF position and velocity in meters and meters/second

• begin (satkit.time, optional)

  satkit.time object representing instant at which satellite is at “pos” & “vel”

• end (satkit.time, optional keyword)

  satkit.time object representing instant at which new position and velocity will be computed

• duration (satkit.duration, optional keyword)

  duration from “begin” at which new position & velocity will be computed.

• duration_secs (float, optional keyword)

  duration in seconds from “begin” for at which new position and velocity will be computed.

• duration_days (float, optional keyword)

  duration in days from “begin” at which new position and velocity will be computed.

• output_phi (bool, optional keyword)

  Output 6x6 state transition matrix between “begintime” and “endtime” (and at intervals, if specified)

• propsettings (propsettings, optional keyword)

  “propsettings” object with input settings for the propagation. if left out, default will be used.

• satproperties (satproperties_static, optional keyword)

  “sat_properties_static” object with drag and radiation pressure susceptibility of satellite.

Returns:

• (propresult)

  Propagation result object holding state outputs, statistics, and dense output if requested

Notes:

• Propagates satellite ephemeris (position, velocity in gcrs & time) to new time and output new position and velocity via Runge-Kutta integration.

• Inputs and outputs are all in the Geocentric Celestial Reference Frame (GCRF)

• Propagator uses advanced Runge-Kutta integrators and includes the following forces:

  • Earth gravity with higher-order zonal terms

  • Sun, Moon gravity

  • Radiation pressured

  • Atmospheric drag: NRL-MISE 2000 density model, with option to include space weather effects (which can be large)

• End time must be set by keyword argument, either explicitly or by duration

• Solid Earth tides are not (yet) included in the model

class satkit.propresult

Results of a satellite propagation

This class lets the user access results of the satellite propagation

Notes:

• If “enable_interp” is set to True in the propagation settings, the propresult object can be used to interpolate solutions at any time between the begin and end times of the propagation via the “interp” method

time

Time at which state is valid

Returns:

• satkit.time

  Time at which state is valid

time_end

Time at which state is valid

Notes:

• This is identical to “time” property

Returns:

• satkit.time

  Time at which state is valid

class satkit.propstats

Statistics of a satellite propagation

num_accept

Number of accepted steps in adaptive RK integrator

num_eval

Number of function evaluations

num_reject

Number of rejected steps in adaptive RK integrator

class satkit.propsettings(**kwargs)

This class contains settings used in the high-precision orbit propagator part of the “satkit” python toolbox

Notes:

• Default settings:

  • abs_error: 1e-8

  • rel_error: 1e-8

  • gravity_order: 4

  • use_spaceweather: True

  • use_jplephem: True

  • enable_interp: True

  • enable_interp enables high-precision interpolation of state between begin and end times via the returned function,

  it is enabled by default. There is a small increase in computational efficiency if set to false

propsettings.precompute_terms(begin, end)

Precompute terms for fast interpolation of state between begin and end times

This can be used, for example, to compute sun and moon positions only once if propagating many satellites over the same time period

Args:

• begin (satkit.time)

  Begin time of propagation

• end (satkit.time)

  End time of propagation

• step (satkit.duration, optional)

  Step size for interpolation. Default = 60 seconds