Orbit#

class Orbit#

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

static Orbit create_from_position_and_velocity(Client &connection, CelestialBody body, std::tuple<double, double, double> position, std::tuple<double, double, double> velocity, double ut, std::optional<ReferenceFrame> reference_frame = std::optional<ReferenceFrame>())#

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.

  • reference_frame – The reference frame that position and velocity are in. Defaults to CelestialBody::non_rotating_reference_frame() of body.

Note

The orbit is a single conic around body. It never changes sphere of influence, so Orbit::next_orbit() 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.

Orbit::radius(), Orbit::speed(), Orbit::position(), Orbit::velocity() and the like describe the orbit at ut and stay there. Use Orbit::radius_at(), Orbit::speed_at(), Orbit::position_at(), Orbit::velocity_at() and Orbit::true_anomaly_at_ut() for another time, and Orbit::reference_frame() and Orbit::orbital_reference_frame() to follow the orbit as time passes.

The orbit is held until 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.

static Orbit create_from_orbital_elements(Client &connection, CelestialBody body, double semi_major_axis, double eccentricity, double inclination, double longitude_of_ascending_node, double argument_of_periapsis, double mean_anomaly_at_epoch, double 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.

Parameters:

  • body – The celestial body being orbited.

  • semi_major_axis – 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.

  • longitude_of_ascending_node – The longitude of the ascending node, in radians.

  • argument_of_periapsis – The argument of periapsis, in radians.

  • mean_anomaly_at_epoch – The mean anomaly at epoch, in radians.

  • epoch – The universal time, in seconds, that mean_anomaly_at_epoch is measured at.

Note

The orbit is a single conic around body. It never changes sphere of influence, so Orbit::next_orbit() is NULL, and no atmosphere slows it.

The angles are measured against the reference plane and direction that Orbit::inclination(), Orbit::longitude_of_ascending_node() and Orbit::argument_of_periapsis() report them against. Orbit::reference_plane_normal() and Orbit::reference_plane_direction() give these as vectors in a reference frame.

Orbit::radius(), Orbit::speed(), Orbit::position(), Orbit::velocity() and the like describe the orbit at epoch and stay there. Use Orbit::radius_at(), Orbit::speed_at(), Orbit::position_at(), Orbit::velocity_at() and Orbit::true_anomaly_at_ut() for another time, and Orbit::reference_frame() and Orbit::orbital_reference_frame() to follow the orbit as time passes.

The orbit is held until 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.

void remove()#

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

Note

Only an orbit created by Orbit::create_from_position_and_velocity() or 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.

CelestialBody body()#

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

ReferenceFrame reference_frame()#

The reference frame that moves along the orbit, and is orientated in a fixed direction.

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.

ReferenceFrame 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.

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 Vessel::orbital_reference_frame() is centered on.

double apoapsis()#

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

Note

For the apoapsis altitude reported on the in-game map view, use Orbit::apoapsis_altitude().

double periapsis()#

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

Note

For the periapsis altitude reported on the in-game map view, use Orbit::periapsis_altitude().

double apoapsis_altitude()#

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

Note

This is equal to Orbit::apoapsis() minus the equatorial radius of the body.

double periapsis_altitude()#

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

Note

This is equal to Orbit::periapsis() minus the equatorial radius of the body.

double semi_major_axis()#

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

double semi_minor_axis()#

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

double semi_latus_rectum()#

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

double 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.

Note

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

double altitude()#

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

Note

This is equal to Orbit::radius() minus the equatorial radius of the body.

double radius_at(double ut)#

The orbital radius at the given time, in meters.

Parameters:

  • ut – The universal time to measure the radius at.

double radius_at_true_anomaly(double true_anomaly)#

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

Parameters:

  • true_anomaly – The true anomaly.

std::tuple<double, double, double> position(std::optional<ReferenceFrame> reference_frame = std::optional<ReferenceFrame>())#

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

Parameters:
Returns:

The position as a vector.

std::tuple<double, double, double> position_at(double ut, std::optional<ReferenceFrame> reference_frame = std::optional<ReferenceFrame>())#

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

Parameters:
Returns:

The position as a vector.

std::tuple<double, double, double> position_at_true_anomaly(double true_anomaly, std::optional<ReferenceFrame> reference_frame = std::optional<ReferenceFrame>())#

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

Parameters:
Returns:

The position as a vector.

std::tuple<double, double, double> velocity(std::optional<ReferenceFrame> reference_frame = std::optional<ReferenceFrame>())#

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

Parameters:
Returns:

The velocity as a vector. The vector points in the direction of travel, and its magnitude is the speed in meters per second.

std::tuple<double, double, double> velocity_at(double ut, std::optional<ReferenceFrame> reference_frame = std::optional<ReferenceFrame>())#

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

Parameters:
Returns:

The velocity as a vector. The vector points in the direction of travel, and its magnitude is the speed in meters per second.

std::tuple<double, double, double> velocity_at_true_anomaly(double true_anomaly, std::optional<ReferenceFrame> reference_frame = std::optional<ReferenceFrame>())#

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

Parameters:
Returns:

The velocity as a vector. The vector points in the direction of travel, and its magnitude is the speed in meters per second.

double speed()#

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

Note

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

double speed_at(double ut)#

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

Parameters:

  • ut – The universal time to measure the speed at.

double speed_at_radius(double radius)#

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

Parameters:

  • radius – The orbital radius in meters.

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.

double speed_at_true_anomaly(double true_anomaly)#

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

Parameters:

  • true_anomaly – The true anomaly.

double specific_energy()#

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

Note

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

double specific_angular_momentum()#

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

double period()#

The orbital period, in seconds.

double mean_motion()#

The mean motion, in radians per second.

double time_to_apoapsis()#

The time until the object reaches apoapsis, in seconds.

double time_to_periapsis()#

The time until the object reaches periapsis, in seconds.

double eccentricity()#

The eccentricity of the orbit.

double inclination()#

The inclination of the orbit, in radians.

double longitude_of_ascending_node()#

The longitude of the ascending node, in radians.

Note

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

double argument_of_periapsis()#

The argument of periapsis, in radians.

Note

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

double mean_anomaly_at_epoch()#

The mean anomaly at epoch.

double epoch()#

The universal time, in seconds, at which the mean anomaly at epoch is measured.

double mean_anomaly()#

The mean anomaly.

double mean_anomaly_at_ut(double ut)#

The mean anomaly at the given time.

Parameters:

  • ut – The universal time in seconds.

double eccentric_anomaly()#

The eccentric anomaly.

double eccentric_anomaly_at_ut(double ut)#

The eccentric anomaly at the given universal time.

Parameters:

  • ut – The universal time, in seconds.

double true_anomaly()#

The true anomaly.

double true_anomaly_at_ut(double ut)#

The true anomaly at the given time.

Parameters:

  • ut – The universal time in seconds.

double true_anomaly_at_radius(double radius)#

The true anomaly at the given orbital radius.

Parameters:

  • radius – The orbital radius in meters.

double ut_at_true_anomaly(double true_anomaly)#

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

Parameters:

  • true_anomaly – True anomaly.

double true_anomaly_at_an(Orbit target)#

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

Parameters:

  • target – Target orbit.

double true_anomaly_at_dn(Orbit target)#

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

Parameters:

  • target – Target orbit.

double orbital_speed()#

Warning

Deprecated. Use Orbit::speed() instead.

The current orbital speed in meters per second.

double orbital_speed_at(double ut)#

Warning

Deprecated. Use Orbit::speed_at() instead.

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

Parameters:

  • ut – The universal time to measure the speed at.

double orbital_energy()#

Warning

Deprecated. Use Orbit::specific_energy() instead.

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

static std::tuple<double, double, double> reference_plane_normal(Client &connection, ReferenceFrame 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.

Parameters:

  • reference_frame – The reference frame that the returned direction is in.

Returns:

The direction as a unit vector.

static std::tuple<double, double, double> reference_plane_direction(Client &connection, ReferenceFrame reference_frame)#

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

Parameters:

  • reference_frame – The reference frame that the returned direction is in.

Returns:

The direction as a unit vector.

double relative_inclination(Orbit target)#

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

Parameters:

  • target – Target orbit.

double 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.

std::optional<Orbit> next_orbit()#

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

ClosestApproach next_closest_approach(Orbit target)#

The next closest approach to a target orbit.

Parameters:

  • target – Target orbit.

std::vector<ClosestApproach> closest_approaches(Orbit target, int32_t 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.