.. default-domain:: cs
.. highlight:: csharp
.. namespace:: KRPC.Client.Services.SpaceCenter

Orbit
=====


.. class:: Orbit

   Describes an orbit. For example, the orbit of a vessel, obtained by calling
   :prop:`Vessel.Orbit`, or a celestial body, obtained by calling
   :prop:`CelestialBody.Orbit`.

   .. function:: static Orbit CreateFromPositionAndVelocity(IConnection connection, CelestialBody body, System.Tuple<double,double,double> position, System.Tuple<double,double,double> velocity, double ut, ReferenceFrame referenceFrame = null)

      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.

      :parameters:

       * **body** -- The celestial body being orbited.
       * **position** -- The position, as a position vector.
       * **velocity** -- The velocity, as a vector pointing in the direction of travel, whose magnitude is the speed in meters per second.
       * **ut** -- The universal time, in seconds, at which the object is at *position* traveling at *velocity*.
       * **referenceFrame** -- The reference frame that *position* and *velocity* are in. Defaults to :prop:`CelestialBody.NonRotatingReferenceFrame` of *body*.

      :Game Scenes: All


      .. note::

         The orbit is a single conic around *body*. It never changes
         sphere of influence, so :prop:`Orbit.NextOrbit` is ``null``, 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.

         :prop:`Orbit.Radius`, :prop:`Orbit.Speed`, :meth:`Orbit.Position`,
         :meth:`Orbit.Velocity` and the like describe the orbit at
         *ut* and stay there. Use :meth:`Orbit.RadiusAt`,
         :meth:`Orbit.SpeedAt`, :meth:`Orbit.PositionAt`, :meth:`Orbit.VelocityAt` and
         :meth:`Orbit.TrueAnomalyAtUT` for another time, and
         :prop:`Orbit.ReferenceFrame` and :prop:`Orbit.OrbitalReferenceFrame` 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.

   .. function:: static Orbit CreateFromOrbitalElements(IConnection connection, CelestialBody body, double semiMajorAxis, double eccentricity, double inclination, double longitudeOfAscendingNode, double argumentOfPeriapsis, double meanAnomalyAtEpoch, double epoch)

      Create the orbit with the given
      `orbital elements <https://en.wikipedia.org/wiki/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.

      :parameters:

       * **body** -- The celestial body being orbited.
       * **semiMajorAxis** -- The semi-major axis of the orbit, in meters. Positive for an ellipse and negative for a hyperbola.
       * **eccentricity** -- The eccentricity of the orbit. Below one for an ellipse and above one for a hyperbola.
       * **inclination** -- The inclination of the orbit, in radians.
       * **longitudeOfAscendingNode** -- The longitude of the ascending node, in radians.
       * **argumentOfPeriapsis** -- The argument of periapsis, in radians.
       * **meanAnomalyAtEpoch** -- The mean anomaly at *epoch*, in radians.
       * **epoch** -- The universal time, in seconds, that *meanAnomalyAtEpoch* is measured at.

      :Game Scenes: All


      .. note::

         The orbit is a single conic around *body*. It never changes
         sphere of influence, so :prop:`Orbit.NextOrbit` is ``null``, and no
         atmosphere slows it.

         The angles are measured against the reference plane and direction that
         :prop:`Orbit.Inclination`, :prop:`Orbit.LongitudeOfAscendingNode` and
         :prop:`Orbit.ArgumentOfPeriapsis` report them against.
         :meth:`Orbit.ReferencePlaneNormal` and :meth:`Orbit.ReferencePlaneDirection`
         give these as vectors in a reference frame.

         :prop:`Orbit.Radius`, :prop:`Orbit.Speed`, :meth:`Orbit.Position`,
         :meth:`Orbit.Velocity` and the like describe the orbit at
         *epoch* and stay there. Use :meth:`Orbit.RadiusAt`,
         :meth:`Orbit.SpeedAt`, :meth:`Orbit.PositionAt`, :meth:`Orbit.VelocityAt` and
         :meth:`Orbit.TrueAnomalyAtUT` for another time, and
         :prop:`Orbit.ReferenceFrame` and :prop:`Orbit.OrbitalReferenceFrame` 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.

   .. function:: void Remove()

      Remove the orbit, releasing the memory the server holds for it.


      :Game Scenes: All


      .. note::

         Only an orbit created by :meth:`Orbit.CreateFromPositionAndVelocity` or
         :meth:`Orbit.CreateFromOrbitalElements` 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.

   .. property:: CelestialBody Body { get; }

      The celestial body (e.g. planet or moon) around which the object is orbiting.

      :Game Scenes: All

   .. property:: ReferenceFrame ReferenceFrame { get; }

      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
        :prop:`CelestialBody.NonRotatingReferenceFrame` of
        :prop:`Orbit.Body`.

      :Game Scenes: All


      .. 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.

   .. property:: ReferenceFrame OrbitalReferenceFrame { get; }

      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.

      :Game Scenes: All


      .. 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
         :prop:`Vessel.OrbitalReferenceFrame` is centered on.

   .. property:: double Apoapsis { get; }

      Gets the apoapsis of the orbit, in meters, from the center of mass
      of the body being orbited.

      :Game Scenes: All


      .. note::

         For the apoapsis altitude reported on the in-game map view,
         use :prop:`Orbit.ApoapsisAltitude`.

   .. property:: double Periapsis { get; }

      The periapsis of the orbit, in meters, from the center of mass
      of the body being orbited.

      :Game Scenes: All


      .. note::

         For the periapsis altitude reported on the in-game map view,
         use :prop:`Orbit.PeriapsisAltitude`.

   .. property:: double ApoapsisAltitude { get; }

      The apoapsis of the orbit, in meters, above the sea level of the body being orbited.

      :Game Scenes: All


      .. note::

         This is equal to :prop:`Orbit.Apoapsis` minus the equatorial radius of the body.

   .. property:: double PeriapsisAltitude { get; }

      The periapsis of the orbit, in meters, above the sea level of the body being orbited.

      :Game Scenes: All


      .. note::

         This is equal to :prop:`Orbit.Periapsis` minus the equatorial radius of the body.

   .. property:: double SemiMajorAxis { get; }

      The semi-major axis of the orbit, in meters.

      :Game Scenes: All

   .. property:: double SemiMinorAxis { get; }

      The semi-minor axis of the orbit, in meters.

      :Game Scenes: All

   .. property:: double SemiLatusRectum { get; }

      The semi-latus rectum of the orbit, in meters.

      :Game Scenes: All

   .. property:: double Radius { get; }

      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.

      :Game Scenes: All


      .. note::

         This value will change over time if the orbit is elliptical.

   .. property:: double Altitude { get; }

      The current altitude of the object, in meters above the sea level of the body
      being orbited.

      :Game Scenes: All


      .. note::

         This is equal to :prop:`Orbit.Radius` minus the equatorial radius of the body.

   .. function:: double RadiusAt(double ut)

      The orbital radius at the given time, in meters.

      :parameters:

       * **ut** -- The universal time to measure the radius at.

      :Game Scenes: All

   .. function:: double RadiusAtTrueAnomaly(double trueAnomaly)

      The orbital radius at the point in the orbit given by the true anomaly.

      :parameters:

       * **trueAnomaly** -- The true anomaly.

      :Game Scenes: All

   .. function:: System.Tuple<double,double,double> Position(ReferenceFrame referenceFrame = null)

      The position the orbit has reached at the current time, in the given reference
      frame.

      :parameters:

       * **referenceFrame** -- The reference frame that the returned position vector is in. Defaults to :prop:`CelestialBody.NonRotatingReferenceFrame` of :prop:`Orbit.Body`.

      :returns: The position as a vector.
      :Game Scenes: All

   .. function:: System.Tuple<double,double,double> PositionAt(double ut, ReferenceFrame referenceFrame = null)

      The position at a given time, in the specified reference frame.

      :parameters:

       * **ut** -- The universal time to measure the position at.
       * **referenceFrame** -- The reference frame that the returned position vector is in. Defaults to :prop:`CelestialBody.NonRotatingReferenceFrame` of :prop:`Orbit.Body`.

      :returns: The position as a vector.
      :Game Scenes: All

   .. function:: System.Tuple<double,double,double> PositionAtTrueAnomaly(double trueAnomaly, ReferenceFrame referenceFrame = null)

      The position at the point in the orbit given by the true anomaly, in the specified
      reference frame.

      :parameters:

       * **trueAnomaly** -- The true anomaly.
       * **referenceFrame** -- The reference frame that the returned position vector is in. Defaults to :prop:`CelestialBody.NonRotatingReferenceFrame` of :prop:`Orbit.Body`.

      :returns: The position as a vector.
      :Game Scenes: All

   .. function:: System.Tuple<double,double,double> Velocity(ReferenceFrame referenceFrame = null)

      The velocity the orbit has reached at the current time, in the given reference
      frame.

      :parameters:

       * **referenceFrame** -- The reference frame that the returned velocity vector is in. Defaults to :prop:`CelestialBody.NonRotatingReferenceFrame` of :prop:`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.
      :Game Scenes: All

   .. function:: System.Tuple<double,double,double> VelocityAt(double ut, ReferenceFrame referenceFrame = null)

      The velocity at a given time, in the specified reference frame.

      :parameters:

       * **ut** -- The universal time to measure the velocity at.
       * **referenceFrame** -- The reference frame that the returned velocity vector is in. Defaults to :prop:`CelestialBody.NonRotatingReferenceFrame` of :prop:`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.
      :Game Scenes: All

   .. function:: System.Tuple<double,double,double> VelocityAtTrueAnomaly(double trueAnomaly, ReferenceFrame referenceFrame = null)

      The velocity at the point in the orbit given by the true anomaly, in the specified
      reference frame.

      :parameters:

       * **trueAnomaly** -- The true anomaly.
       * **referenceFrame** -- The reference frame that the returned velocity vector is in. Defaults to :prop:`CelestialBody.NonRotatingReferenceFrame` of :prop:`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.
      :Game Scenes: All

   .. property:: double Speed { get; }

      The current orbital speed of the object in meters per second.

      :Game Scenes: All


      .. note::

         This value will change over time if the orbit is elliptical.

   .. function:: double SpeedAt(double ut)

      The orbital speed at the given time, in meters per second.

      :parameters:

       * **ut** -- The universal time to measure the speed at.

      :Game Scenes: All

   .. function:: double SpeedAtRadius(double radius)

      The orbital speed at the given orbital radius, in meters per second.

      :parameters:

       * **radius** -- The orbital radius in meters.

      :Game Scenes: All


      .. 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.

   .. function:: double SpeedAtTrueAnomaly(double trueAnomaly)

      The orbital speed at the point in the orbit given by the true anomaly, in meters
      per second.

      :parameters:

       * **trueAnomaly** -- The true anomaly.

      :Game Scenes: All

   .. property:: double SpecificEnergy { get; }

      The specific orbital energy, in Joules per kilogram (equivalently,
      meters squared per second squared).

      :Game Scenes: All


      .. note::

         This is the sum of the orbit's specific kinetic and potential energy, and
         is negative for a bound (elliptical) orbit.

   .. property:: double SpecificAngularMomentum { get; }

      The specific relative angular momentum, in meters squared per second.

      :Game Scenes: All

   .. property:: double Period { get; }

      The orbital period, in seconds.

      :Game Scenes: All

   .. property:: double MeanMotion { get; }

      The mean motion, in radians per second.

      :Game Scenes: All

   .. property:: double TimeToApoapsis { get; }

      The time until the object reaches apoapsis, in seconds.

      :Game Scenes: All

   .. property:: double TimeToPeriapsis { get; }

      The time until the object reaches periapsis, in seconds.

      :Game Scenes: All

   .. property:: double Eccentricity { get; }

      The `eccentricity <https://en.wikipedia.org/wiki/Orbital_eccentricity>`_
      of the orbit.

      :Game Scenes: All

   .. property:: double Inclination { get; }

      The `inclination <https://en.wikipedia.org/wiki/Orbital_inclination>`_
      of the orbit,
      in radians.

      :Game Scenes: All

   .. property:: double LongitudeOfAscendingNode { get; }

      The `longitude of the ascending node <https://en.wikipedia.org/wiki/Longitude_of_the_ascending_node>`_, in radians.

      :Game Scenes: All


      .. note::

         For a near-equatorial orbit, the ascending node is ill-defined and
         this value may vary erratically over time.

   .. property:: double ArgumentOfPeriapsis { get; }

      The `argument of periapsis <https://en.wikipedia.org/wiki/Argument_of_periapsis>`_, in radians.

      :Game Scenes: All


      .. note::

         For a near-circular orbit, the periapsis is ill-defined and
         this value may vary erratically over time.

   .. property:: double MeanAnomalyAtEpoch { get; }

      The `mean anomaly at epoch <https://en.wikipedia.org/wiki/Mean_anomaly>`_.

      :Game Scenes: All

   .. property:: double Epoch { get; }

      The universal time, in seconds, at which the
      `mean anomaly at epoch <https://en.wikipedia.org/wiki/Mean_anomaly>`_
      is measured.

      :Game Scenes: All

   .. property:: double MeanAnomaly { get; }

      The `mean anomaly <https://en.wikipedia.org/wiki/Mean_anomaly>`_.

      :Game Scenes: All

   .. function:: double MeanAnomalyAtUT(double ut)

      The mean anomaly at the given time.

      :parameters:

       * **ut** -- The universal time in seconds.

      :Game Scenes: All

   .. property:: double EccentricAnomaly { get; }

      The `eccentric anomaly <https://en.wikipedia.org/wiki/Eccentric_anomaly>`_.

      :Game Scenes: All

   .. function:: double EccentricAnomalyAtUT(double ut)

      The eccentric anomaly at the given universal time.

      :parameters:

       * **ut** -- The universal time, in seconds.

      :Game Scenes: All

   .. property:: double TrueAnomaly { get; }

      The `true anomaly <https://en.wikipedia.org/wiki/True_anomaly>`_.

      :Game Scenes: All

   .. function:: double TrueAnomalyAtUT(double ut)

      The true anomaly at the given time.

      :parameters:

       * **ut** -- The universal time in seconds.

      :Game Scenes: All

   .. function:: double TrueAnomalyAtRadius(double radius)

      The true anomaly at the given orbital radius.

      :parameters:

       * **radius** -- The orbital radius in meters.

      :Game Scenes: All

   .. function:: double UTAtTrueAnomaly(double trueAnomaly)

      The universal time, in seconds, corresponding to the given true anomaly.

      :parameters:

       * **trueAnomaly** -- True anomaly.

      :Game Scenes: All

   .. function:: double TrueAnomalyAtAN(Orbit target)

      The true anomaly of the ascending node with the given target orbit.

      :parameters:

       * **target** -- Target orbit.

      :Game Scenes: All

   .. function:: double TrueAnomalyAtDN(Orbit target)

      The true anomaly of the descending node with the given target orbit.

      :parameters:

       * **target** -- Target orbit.

      :Game Scenes: All

   .. property:: double OrbitalSpeed { get; }

      .. warning:: Deprecated. Use :prop:`Orbit.Speed` instead.

      The current orbital speed in meters per second.

      :Game Scenes: All

   .. function:: double OrbitalSpeedAt(double ut)

      .. warning:: Deprecated. Use :meth:`Orbit.SpeedAt` instead.

      The orbital speed at the given time, in meters per second.

      :parameters:

       * **ut** -- The universal time to measure the speed at.

      :Game Scenes: All

   .. property:: double OrbitalEnergy { get; }

      .. warning:: Deprecated. Use :prop:`Orbit.SpecificEnergy` instead.

      The specific orbital energy of the orbit, in Joules per kilogram.

      :Game Scenes: All

   .. function:: static System.Tuple<double,double,double> ReferencePlaneNormal(IConnection connection, ReferenceFrame referenceFrame)

      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.

      :parameters:

       * **referenceFrame** -- The reference frame that the returned direction is in.

      :returns: The direction as a unit vector.
      :Game Scenes: All

   .. function:: static System.Tuple<double,double,double> ReferencePlaneDirection(IConnection connection, ReferenceFrame referenceFrame)

      The direction from which the orbits longitude of ascending node is measured,
      in the given reference frame.

      :parameters:

       * **referenceFrame** -- The reference frame that the returned direction is in.

      :returns: The direction as a unit vector.
      :Game Scenes: All

   .. function:: double RelativeInclination(Orbit target)

      Relative inclination of this orbit and the target orbit, in radians.

      :parameters:

       * **target** -- Target orbit.

      :Game Scenes: All

   .. property:: double TimeToSOIChange { get; }

      The time until the object changes sphere of influence, in seconds. Returns ``NaN``
      if the object is not going to change sphere of influence.

      :Game Scenes: All

   .. property:: Orbit NextOrbit { get; }

      If the object is going to change sphere of influence in the future, returns the new
      orbit after the change. Otherwise returns ``null``.

      :Game Scenes: All

   .. function:: ClosestApproach NextClosestApproach(Orbit target)

      The next closest approach to a target orbit.

      :parameters:

       * **target** -- Target orbit.

      :Game Scenes: All

   .. function:: System.Collections.Generic.IList<ClosestApproach> ClosestApproaches(Orbit target, int orbits)

      A list of the closest approaches to a target orbit, one for each of the next
      *orbits* orbital periods.

      :parameters:

       * **target** -- Target orbit.
       * **orbits** -- The number of future orbits to search.

      :Game Scenes: All