.. default-domain:: py .. highlight:: py .. currentmodule:: SpaceCenter Orbit ===== .. class:: Orbit Describes an orbit. For example, the orbit of a vessel, obtained by calling :attr:`Vessel.orbit`, or a celestial body, obtained by calling :attr:`CelestialBody.orbit`. .. staticmethod:: create_from_position_and_velocity(body, position, velocity, ut, [reference_frame = None]) Create the orbit that passes through a given position at a given velocity. The orbit coasts freely under the gravity of the body being orbited, so it describes where an object left to fall from that position and velocity would be at any later time. :param CelestialBody body: The celestial body being orbited. :param tuple position: The position, as a position vector. :param tuple velocity: The velocity, as a vector pointing in the direction of travel, whose magnitude is the speed in meters per second. :param float ut: The universal time, in seconds, at which the object is at *position* traveling at *velocity*. :param ReferenceFrame or None reference_frame: The reference frame that *position* and *velocity* are in. Defaults to :attr:`CelestialBody.non_rotating_reference_frame` of *body*. :rtype: :class:`Orbit` .. note:: The orbit is a single conic around *body*. It never changes sphere of influence, so :attr:`Orbit.next_orbit` is ``None``, and no atmosphere slows it. A vessel held on rails follows its own orbit exactly, while one inside the physics bubble is simulated and drifts from it a little. :attr:`Orbit.radius`, :attr:`Orbit.speed`, :meth:`Orbit.position`, :meth:`Orbit.velocity` and the like describe the orbit at *ut* and stay there. Use :meth:`Orbit.radius_at`, :meth:`Orbit.speed_at`, :meth:`Orbit.position_at`, :meth:`Orbit.velocity_at` and :meth:`Orbit.true_anomaly_at_ut` for another time, and :attr:`Orbit.reference_frame` and :attr:`Orbit.orbital_reference_frame` to follow the orbit as time passes. The orbit is held until :meth:`Orbit.remove` is called on it or the client that created it disconnects. Remove each one created by a script that creates them repeatedly, for example once per update. .. staticmethod:: create_from_orbital_elements(body, semi_major_axis, eccentricity, inclination, longitude_of_ascending_node, argument_of_periapsis, mean_anomaly_at_epoch, epoch) Create the orbit with the given `orbital elements `_ around a given body. The orbit coasts freely under the gravity of that body, so it describes where an object on it would be at any time. :param CelestialBody body: The celestial body being orbited. :param float semi_major_axis: The semi-major axis of the orbit, in meters. Positive for an ellipse and negative for a hyperbola. :param float eccentricity: The eccentricity of the orbit. Below one for an ellipse and above one for a hyperbola. :param float inclination: The inclination of the orbit, in radians. :param float longitude_of_ascending_node: The longitude of the ascending node, in radians. :param float argument_of_periapsis: The argument of periapsis, in radians. :param float mean_anomaly_at_epoch: The mean anomaly at *epoch*, in radians. :param float epoch: The universal time, in seconds, that *mean_anomaly_at_epoch* is measured at. :rtype: :class:`Orbit` .. note:: The orbit is a single conic around *body*. It never changes sphere of influence, so :attr:`Orbit.next_orbit` is ``None``, and no atmosphere slows it. The angles are measured against the reference plane and direction that :attr:`Orbit.inclination`, :attr:`Orbit.longitude_of_ascending_node` and :attr:`Orbit.argument_of_periapsis` report them against. :meth:`Orbit.reference_plane_normal` and :meth:`Orbit.reference_plane_direction` give these as vectors in a reference frame. :attr:`Orbit.radius`, :attr:`Orbit.speed`, :meth:`Orbit.position`, :meth:`Orbit.velocity` and the like describe the orbit at *epoch* and stay there. Use :meth:`Orbit.radius_at`, :meth:`Orbit.speed_at`, :meth:`Orbit.position_at`, :meth:`Orbit.velocity_at` and :meth:`Orbit.true_anomaly_at_ut` for another time, and :attr:`Orbit.reference_frame` and :attr:`Orbit.orbital_reference_frame` to follow the orbit as time passes. The orbit is held until :meth:`Orbit.remove` is called on it or the client that created it disconnects. Remove each one created by a script that creates them repeatedly, for example once per update. .. method:: remove() Remove the orbit, releasing the memory the server holds for it. .. note:: Only an orbit created by :meth:`Orbit.create_from_position_and_velocity` or :meth:`Orbit.create_from_orbital_elements` can be removed. Every other orbit belongs to something in the game, and the server holds one of each. Any further use of this object throws an exception, as does use of a reference frame defined against it. An orbit belongs to the client that created it, and is removed when that client disconnects. .. attribute:: body The celestial body (e.g. planet or moon) around which the object is orbiting. :Attribute: Read-only, cannot be set :rtype: :class:`CelestialBody` .. attribute:: reference_frame The reference frame that moves along the orbit, and is orientated in a fixed direction. * The origin is at the point the orbit has reached at the current time. * The axes do not rotate. They point in the same fixed directions as those of :attr:`CelestialBody.non_rotating_reference_frame` of :attr:`Orbit.body`. :Attribute: Read-only, cannot be set :rtype: :class:`ReferenceFrame` .. note:: For the orbit of a vessel, the origin is the point the vessel's orbit has reached rather than the vessel's own center of mass. The two are a few meters apart, as a vessel inside the physics bubble is simulated rather than being held on its orbit. .. attribute:: orbital_reference_frame The reference frame that moves along the orbit, and is orientated with its prograde/normal/radial directions. * The origin is at the point the orbit has reached at the current time. * The axes rotate with the orbital prograde/normal/radial directions. * The x-axis points in the orbital anti-radial direction. * The y-axis points in the orbital prograde direction. * The z-axis points in the orbital normal direction. :Attribute: Read-only, cannot be set :rtype: :class:`ReferenceFrame` .. note:: For the orbit of a vessel, the origin is the point the vessel's orbit has reached rather than the vessel's own center of mass, which is what :attr:`Vessel.orbital_reference_frame` is centered on. .. attribute:: apoapsis Gets the apoapsis of the orbit, in meters, from the center of mass of the body being orbited. :Attribute: Read-only, cannot be set :rtype: float .. note:: For the apoapsis altitude reported on the in-game map view, use :attr:`Orbit.apoapsis_altitude`. .. attribute:: periapsis The periapsis of the orbit, in meters, from the center of mass of the body being orbited. :Attribute: Read-only, cannot be set :rtype: float .. note:: For the periapsis altitude reported on the in-game map view, use :attr:`Orbit.periapsis_altitude`. .. attribute:: apoapsis_altitude The apoapsis of the orbit, in meters, above the sea level of the body being orbited. :Attribute: Read-only, cannot be set :rtype: float .. note:: This is equal to :attr:`Orbit.apoapsis` minus the equatorial radius of the body. .. attribute:: periapsis_altitude The periapsis of the orbit, in meters, above the sea level of the body being orbited. :Attribute: Read-only, cannot be set :rtype: float .. note:: This is equal to :attr:`Orbit.periapsis` minus the equatorial radius of the body. .. attribute:: semi_major_axis The semi-major axis of the orbit, in meters. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: semi_minor_axis The semi-minor axis of the orbit, in meters. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: semi_latus_rectum The semi-latus rectum of the orbit, in meters. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: radius The current radius of the orbit, in meters. This is the distance between the center of mass of the object in orbit, and the center of mass of the body around which it is orbiting. :Attribute: Read-only, cannot be set :rtype: float .. note:: This value will change over time if the orbit is elliptical. .. attribute:: altitude The current altitude of the object, in meters above the sea level of the body being orbited. :Attribute: Read-only, cannot be set :rtype: float .. note:: This is equal to :attr:`Orbit.radius` minus the equatorial radius of the body. .. method:: radius_at(ut) The orbital radius at the given time, in meters. :param float ut: The universal time to measure the radius at. :rtype: float .. method:: radius_at_true_anomaly(true_anomaly) The orbital radius at the point in the orbit given by the true anomaly. :param float true_anomaly: The true anomaly. :rtype: float .. method:: position([reference_frame = None]) The position the orbit has reached at the current time, in the given reference frame. :param ReferenceFrame or None reference_frame: The reference frame that the returned position vector is in. Defaults to :attr:`CelestialBody.non_rotating_reference_frame` of :attr:`Orbit.body`. :returns: The position as a vector. :rtype: tuple(float, float, float) .. method:: position_at(ut, [reference_frame = None]) The position at a given time, in the specified reference frame. :param float ut: The universal time to measure the position at. :param ReferenceFrame or None reference_frame: The reference frame that the returned position vector is in. Defaults to :attr:`CelestialBody.non_rotating_reference_frame` of :attr:`Orbit.body`. :returns: The position as a vector. :rtype: tuple(float, float, float) .. method:: position_at_true_anomaly(true_anomaly, [reference_frame = None]) The position at the point in the orbit given by the true anomaly, in the specified reference frame. :param float true_anomaly: The true anomaly. :param ReferenceFrame or None reference_frame: The reference frame that the returned position vector is in. Defaults to :attr:`CelestialBody.non_rotating_reference_frame` of :attr:`Orbit.body`. :returns: The position as a vector. :rtype: tuple(float, float, float) .. method:: velocity([reference_frame = None]) The velocity the orbit has reached at the current time, in the given reference frame. :param ReferenceFrame or None reference_frame: The reference frame that the returned velocity vector is in. Defaults to :attr:`CelestialBody.non_rotating_reference_frame` of :attr:`Orbit.body`. :returns: The velocity as a vector. The vector points in the direction of travel, and its magnitude is the speed in meters per second. :rtype: tuple(float, float, float) .. method:: velocity_at(ut, [reference_frame = None]) The velocity at a given time, in the specified reference frame. :param float ut: The universal time to measure the velocity at. :param ReferenceFrame or None reference_frame: The reference frame that the returned velocity vector is in. Defaults to :attr:`CelestialBody.non_rotating_reference_frame` of :attr:`Orbit.body`. :returns: The velocity as a vector. The vector points in the direction of travel, and its magnitude is the speed in meters per second. :rtype: tuple(float, float, float) .. method:: velocity_at_true_anomaly(true_anomaly, [reference_frame = None]) The velocity at the point in the orbit given by the true anomaly, in the specified reference frame. :param float true_anomaly: The true anomaly. :param ReferenceFrame or None reference_frame: The reference frame that the returned velocity vector is in. Defaults to :attr:`CelestialBody.non_rotating_reference_frame` of :attr:`Orbit.body`. :returns: The velocity as a vector. The vector points in the direction of travel, and its magnitude is the speed in meters per second. :rtype: tuple(float, float, float) .. attribute:: speed The current orbital speed of the object in meters per second. :Attribute: Read-only, cannot be set :rtype: float .. note:: This value will change over time if the orbit is elliptical. .. method:: speed_at(ut) The orbital speed at the given time, in meters per second. :param float ut: The universal time to measure the speed at. :rtype: float .. method:: speed_at_radius(radius) The orbital speed at the given orbital radius, in meters per second. :param float radius: The orbital radius in meters. :rtype: float .. note:: This is the vis-viva speed. A radius the orbit never reaches is accepted. On an ellipse the speed is ``NaN`` above twice the semi-major axis. .. method:: speed_at_true_anomaly(true_anomaly) The orbital speed at the point in the orbit given by the true anomaly, in meters per second. :param float true_anomaly: The true anomaly. :rtype: float .. attribute:: specific_energy The specific orbital energy, in Joules per kilogram (equivalently, meters squared per second squared). :Attribute: Read-only, cannot be set :rtype: float .. note:: This is the sum of the orbit's specific kinetic and potential energy, and is negative for a bound (elliptical) orbit. .. attribute:: specific_angular_momentum The specific relative angular momentum, in meters squared per second. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: period The orbital period, in seconds. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: mean_motion The mean motion, in radians per second. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: time_to_apoapsis The time until the object reaches apoapsis, in seconds. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: time_to_periapsis The time until the object reaches periapsis, in seconds. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: eccentricity The `eccentricity `_ of the orbit. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: inclination The `inclination `_ of the orbit, in radians. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: longitude_of_ascending_node The `longitude of the ascending node `_, in radians. :Attribute: Read-only, cannot be set :rtype: float .. note:: For a near-equatorial orbit, the ascending node is ill-defined and this value may vary erratically over time. .. attribute:: argument_of_periapsis The `argument of periapsis `_, in radians. :Attribute: Read-only, cannot be set :rtype: float .. note:: For a near-circular orbit, the periapsis is ill-defined and this value may vary erratically over time. .. attribute:: mean_anomaly_at_epoch The `mean anomaly at epoch `_. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: epoch The universal time, in seconds, at which the `mean anomaly at epoch `_ is measured. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: mean_anomaly The `mean anomaly `_. :Attribute: Read-only, cannot be set :rtype: float .. method:: mean_anomaly_at_ut(ut) The mean anomaly at the given time. :param float ut: The universal time in seconds. :rtype: float .. attribute:: eccentric_anomaly The `eccentric anomaly `_. :Attribute: Read-only, cannot be set :rtype: float .. method:: eccentric_anomaly_at_ut(ut) The eccentric anomaly at the given universal time. :param float ut: The universal time, in seconds. :rtype: float .. attribute:: true_anomaly The `true anomaly `_. :Attribute: Read-only, cannot be set :rtype: float .. method:: true_anomaly_at_ut(ut) The true anomaly at the given time. :param float ut: The universal time in seconds. :rtype: float .. method:: true_anomaly_at_radius(radius) The true anomaly at the given orbital radius. :param float radius: The orbital radius in meters. :rtype: float .. method:: ut_at_true_anomaly(true_anomaly) The universal time, in seconds, corresponding to the given true anomaly. :param float true_anomaly: True anomaly. :rtype: float .. method:: true_anomaly_at_an(target) The true anomaly of the ascending node with the given target orbit. :param Orbit target: Target orbit. :rtype: float .. method:: true_anomaly_at_dn(target) The true anomaly of the descending node with the given target orbit. :param Orbit target: Target orbit. :rtype: float .. attribute:: orbital_speed .. warning:: Deprecated. Use :attr:`Orbit.speed` instead. The current orbital speed in meters per second. :Attribute: Read-only, cannot be set :rtype: float .. method:: orbital_speed_at(ut) .. warning:: Deprecated. Use :meth:`Orbit.speed_at` instead. The orbital speed at the given time, in meters per second. :param float ut: The universal time to measure the speed at. :rtype: float .. attribute:: orbital_energy .. warning:: Deprecated. Use :attr:`Orbit.specific_energy` instead. The specific orbital energy of the orbit, in Joules per kilogram. :Attribute: Read-only, cannot be set :rtype: float .. staticmethod:: reference_plane_normal(reference_frame) The direction that is normal to the orbits reference plane, in the given reference frame. The reference plane is the plane from which the orbits inclination is measured. :param ReferenceFrame reference_frame: The reference frame that the returned direction is in. :returns: The direction as a unit vector. :rtype: tuple(float, float, float) .. staticmethod:: reference_plane_direction(reference_frame) The direction from which the orbits longitude of ascending node is measured, in the given reference frame. :param ReferenceFrame reference_frame: The reference frame that the returned direction is in. :returns: The direction as a unit vector. :rtype: tuple(float, float, float) .. method:: relative_inclination(target) Relative inclination of this orbit and the target orbit, in radians. :param Orbit target: Target orbit. :rtype: float .. attribute:: time_to_soi_change The time until the object changes sphere of influence, in seconds. Returns ``NaN`` if the object is not going to change sphere of influence. :Attribute: Read-only, cannot be set :rtype: float .. attribute:: next_orbit If the object is going to change sphere of influence in the future, returns the new orbit after the change. Otherwise returns ``None``. :Attribute: Read-only, cannot be set :rtype: :class:`Orbit` or None .. method:: next_closest_approach(target) The next closest approach to a target orbit. :param Orbit target: Target orbit. :rtype: :class:`ClosestApproach` .. method:: closest_approaches(target, orbits) A list of the closest approaches to a target orbit, one for each of the next *orbits* orbital periods. :param Orbit target: Target orbit. :param int orbits: The number of future orbits to search. :rtype: list(:class:`ClosestApproach`)