Description
The CelestialObject makes it possible to model custom physical objects (ie, a planet, moon, asteroid, or comet). A CelestialObject's movement can be specified using SPICE Files. Any CelestialObject can be used as a force and be applied to any Spacecraft. See Celestial Objects for more information.
Inheritance Hierarchy: Object->CelestialObject
Available In Editions:
Engineer
Mission
Timing Precision Mode
This page describes functionality in nanosecond timing precision mode.
Click here to see the documentation for this object in millisecond timing precision mode.
Name
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Description
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Attributes
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AttitudeModel
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The object that contains the attitude advancer for the CelestialObject.
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Type: Propagator
Access: Read-Only
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BodyID
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Numerical representation of a celestial body. Allows for the tracking of the celestial body in question by using numbers rather than strings.
The following body ID's are assigned to the default Solar System objects: Mercury = 1; Venus = 2; Earth = 3; Mars = 4; Jupiter = 5; Saturn = 6; Uranus = 7; Neptune = 8; Pluto = 9; Moon = 10; Sun = 11. Custom CelestialObjects will have body ID's that change with each run of a Mission Plan.
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Type: Variable
Access: Read-Only
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CentralBody
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Gets or sets the name of the CelestialObject that defines the origin of this CelestialObject's position and velocity. The central body can be a built-in solar system body (i.e. Earth, Moon, etc.) or a custom CelestialObject created within the Mission Plan.
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Type: String
Access: Read/Write
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CentralBodyObject
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The CelestialObject that defines the origin of this CelestialObject's position and velocity. Use the CelestialObject.CentralBody property to change the central body.
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Type: CelestialObject
Access: Read-Only
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DeclaredName
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The name of the object as declared.
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Type: String
Access: Read-Only
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DisplayName
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The name displayed for this object in output windows such as views, plots, and reports.
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Type: String
Access: Read/Write
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Epoch
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Current date for the CelestialObject measured in International Atomic Time (TAI) in the Modified Julian Date format. The returned value has units of days, measured from January 5, 1941 at 12:00:00.000 TAI. When retrieving information about the state of a Celestial Object, the CelestialObject GetPositionAtEpoch, GetVelocityAtEpoch, or GetPosVelAtEpoch methods should be used instead of attempting to access this property.
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Type: TimeSpan
Access: Read/Write
Units: day
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Flattening
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Physical property defined by the difference of the equatorial radius and polar radius divided by the equatorial radius of the CelestialObject body.
This value is used in calculating properties such as Spacecraft.Height. When a Spacecraft is propagated using a gravitational potential field file, the Reciprocal Flattening specified in the file is used for propagation of that Spacecraft.
This value is also used with the VisibilityCalculator and VisibilitySegment objects if the VisibilitySegment.CelestialObjectTargetModel and/or VisibilitySegment.CelestialObjectOccultationModel properties are set to "ellipsoid".
The Flattening, RadiusPolar, and RadiusEquatorial properties of a CelestialObject are all linked. Setting the Flattening value will update the RadiusPolar value automatically, while setting the RadiusPolar value will automatically update the Flattening value.
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Type: Variable
Access: Read/Write
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Globe
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Options for controlling celestial object rendering in a ViewWindow.
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Type: GlobeOptions
Access: Read/Write
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J2
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The J2 gravitational coefficient of the CelestialObject. This value is used for propagation of a Spacecraft with a point mass gravitational model using a J2Mean propagator. It is also used for the Brouwer-Lyddane and J2 Brouwer-Lyddane Mean element-set conversions.
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Type: Variable
Access: Read/Write
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J3
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The J3 gravitational coefficient of the CelestialObject. This property is used to perform Brouwer-Lyddane Mean element set conversions for Earth orbits.
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Type: Variable
Access: Read/Write
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J4
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The J4 gravitational coefficient of the CelestialObject. This property is used to perform Brouwer-Lyddane Mean element set conversions for Earth orbits.
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Type: Variable
Access: Read/Write
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J5
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The J5 gravitational coefficient of the CelestialObject. This property is used to perform Brouwer-Lyddane Mean element set conversions for Earth orbits.
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Type: Variable
Access: Read/Write
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Mass
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The mass of the CelestialObject.
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Type: Variable
Access: Read/Write
Units: kg
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Mu
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The gravity constant of the CelestialObject. This value is used for propagation of a Spacecraft with a point mass gravitational model. When a Spacecraft is propagated using a gravitational potential field file, the Mu (Gravity Constant) specified in the file is used for propagation of that Spacecraft.
Mu = GM (in km^3/s^2), where: G = 6.67259x10^-20 km^3/(kg*sec^2), M = mass (kg).
For custom CelestialObjects, the default Mu value is that of Earth from the DE440 file. For built-in CelestialObjects, the default value is retriefed from the DE file specified by the FF_SolarSystem.DefaultDEXXXFile property.
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Type: Variable
Access: Read/Write
Units: km^3/s^2
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ObjectId
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The unique identifier for the object.
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Type: Variable
Access: Read-Only
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ObjectType
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The type of the object.
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Type: String
Access: Read-Only
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Propagator
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The object that contains the orbit advancer for the CelestialObject.
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Type: Propagator
Access: Read-Only
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RadiusEquatorial
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The equatorial radius of the celestial body. This value is used in calculating properties such as Spacecraft.Height or evaluating drag perturbations.
The RadiusEquatorial, RadiusPolar, and Flattening properties of a CelestialObject are all linked. Setting the RadiusEquatorial value will update the RadiusPolar value automatically.
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Type: Variable
Access: Read/Write
Units: km
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RadiusPolar
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The polar radius of the celestial body.
The RadiusPolar, Flattening, and RadiusEquatorial properties of a CelestialObject are all linked. Setting the RadiusPolar value will update the Flattening value automatically, while setting the Flattening value will automatically update the RadiusPolar value.
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Type: Variable
Access: Read/Write
Units: km
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ReferenceFrameIDs
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The various Reference Frame IDs for this CelestialObject.
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Type: ReferenceFrameIDs
Access: Read/Write
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TailLength
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The number of historical position points to save and draw in visualizations deriving from the View command. If the View command is "Global" a new point will be added each time the Spacecraft is stepped. Otherwise a new point will be added each time the View command is called. If you use the ViewWindow the tail length set there will override this tail length.
Use caution in setting tail lengths longer than 10,000 - 30,000 points. Tail lengths exceeding this range can cause memory problems due to the large amount of relative position data that must be maintained. The maximum tail length that can be used safely depends on the amount of memory in the system and the number of objects managed by the Mission View. The tail length can be overridden for an individual view using ViewWindow.SetObjectTailLength() method.
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Type: Variable
Access: Read/Write
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Name
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Description
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ClearSavedStates
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Clears previous saved states for this object.
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FixedPositionOfObject
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Returns an Array containing the position of the target object, expressed in the body-fixed coordinate system of the prefix object.
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FixedVectorToObject
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Returns an Array containing the components of the vector originating at the location of the prefix object and terminating at the location of the argument object, in the body fixed coordinate frame of the prefix object.
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FixedVelocityOfObject
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Returns an Array containing the velocity of the target object relative to the prefix object, expressed in the body-fixed coordinate system of the prefix object.
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GetAngularVelocityAtEpoch
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Returns the angular velocity vector referenced to the ICRF.
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GetBodyRotationAngle
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Returns the angular difference between the true rotation axis reference frame X axis and the pseudo-body fixed reference frame X axis in the true rotation axis reference frame XY plane.
When the CelestialObject is Earth, this value is equivalent to Earth Rotation Angle (ERA).
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GetBodyRotationAngleInertial
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Returns the angular difference between the ICRF X axis and the body fixed reference frame X axis in the ICRF XY plane.
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GetCartesianStateAtEpoch
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Returns the X, Y, Z, VX, VY and VZ components of the state of the CelestialObject at the specified epoch, referenced from the CentralBody.
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GetFromFile
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Load the object state from the specified FreeFlyer object file.
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GetFromString
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Load the object state from the specified string.
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GetKeplerianStateAtEpoch
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Returns the A, E, I, RAAN, W, TA components of the state of the CelestialObject at the specified epoch, referenced from the CentralBody.
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GetOrientationAtEpoch
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Returns the attitude quaternion of the CelestialObject, referenced to the ICRF.
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GetPositionAtEpoch
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Returns the X, Y, Z components of the state of the CelestialObject in the ICRF, referenced from the CentralBody.
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GetPosVelAtEpoch
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Returns the X, Y, Z, VX, VY, VZ components of the state of the CelestialObject, referenced from the CentralBody.
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GetPrimeMeridianApparentSiderealTime
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Returns the angular difference between the true equinox of date and the body fixed reference frame X axis in the true rotation axis reference frame XY plane.
When the CelestialObject is Earth, this value is equivalent to Greenwich Apparent Sidereal Time (GAST) and also to the Greenwich Hour Angle (GHA) of the true equinox of date.
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GetSpinRateAtEpoch
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Returns the instantaneous spin rate about the angular velocity vector. Note that a positive spin rate indicates a counter-clockwise rotation as viewed from the z-axis of the ICRF; a negative spin rate indicates a clockwise rotation as viewed from the z-axis of the ICRF, eg. for Venus.
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GetVelocityAtEpoch
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Returns the VX, VY, VZ components of the state of the CelestialObject, referenced from the CentralBody.
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PutToFile
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Convert the object state to FreeFlyer object xml and write to a file.
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PutToString
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Convert the object state to FreeFlyer object xml and return as a string.
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Range
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Returns the distance between the calling CelestialObject and the specified target object.
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ReferenceEquals
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Returns 1 if the argument refers to the calling object and 0 otherwise.
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ResetToDefaultPropagator
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Resets the CelestialObject's Propagator to the default. For built-in CelestialObjects, this will restore the DE State Advancer. Custom CelestialObjects will have their propagator restored to a TwoBody propagator.
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Restore
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Restore an object's state from a previously saved state.
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Save
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Save the object's state so that it can be restored later.
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SetCartesianState
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Sets the Cartesian state of the CelestialObject, referenced from the CentralBody. This requires that the CelestialObject uses a TwoBody propagator, and will error if other propagators are used.
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SetKeplerianState
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Sets the Keplerian state of the CelestialObject, referenced from the CentralBody. This requires that the CelestialObject uses a TwoBody propagator, and will error if other propagators are used.
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SetOrientation
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Sets the orientation of the CelestialObject's body fixed frame referenced from the ICRF.
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SetPropagatorType
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Sets the propagator type to use to advance the orbit state in time. The existing Propagator is overridden with a new object of the specified type. Valid Propagator Types are TwoBody and SpiceEphemeris. Note that when setting the Propagator Type to be that of TwoBody, the CelestialObject must be given an initial state and epoch.
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SetState
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Sets the position / velocity the state of the CelestialObject in the ICRF, referenced from the CentralBody.
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VectorToObject
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Returns an Array containing the components of the vector originating at the location of the prefix object and terminating at the location of the argument object, in the ICRF.
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Name
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Description
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Attributes
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AngularVelocity
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The angular velocity vector associated with the quaternion attitude system.
This property has been Deprecated. Please use the CelestialObject.GetAngularVelocityAtEpoch, GetOrientationAtEpoch or SetOrientation method instead.
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Type: Array
Access: Read/Write
Units: deg/s
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Position
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Returns the CelestialObject's X, Y, Z position referenced to the ICRF.
This property has been Deprecated. Please use the CelestialObject.GetPositionAtEpoch or SetState method instead.
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Type: Array
Access: Read/Write
Units: km
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Quaternion
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The attitude quaternion. The quaternion represents the rotation between the CelestialObject's body coordinates and the ICRF.
This property has been Deprecated. Please use the CelestialObject.GetOrientationAtEpoch or SetOrientation method instead.
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Type: Array
Access: Read/Write
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Radius
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The equatorial radius of the celestial body. This value is used in calculating properties such as Spacecraft.Height or evaluating drag perturbations.
This property has been Deprecated. Please use CelestialObject.RadiusEquatorial instead.
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Type: Variable
Access: Read/Write
Units: km
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SpinAxisDeclination
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The declination of the pole of the CelestialObject measured from the ICRF. The pole of the CelestialObject falls on the North side of the mean equator and the vector from the origin of the CelestialObject to pole defines the instantaneous spin axis.
This property has been Deprecated. Please use the CelestialObject.GetOrientationAtEpoch or SetOrientation method instead.
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Type: Variable
Access: Read-Only
Units: deg
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SpinAxisRightAscension
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The Right ascension of the pole of the CelestialObject measured from the ICRF. The pole of the CelestialObject falls on the North side of the mean equator and the vector from the origin of the CelestialObject to pole defines the instantaneous spin axis.
This property has been Deprecated. Please use the CelestialObject.GetOrientationAtEpoch or SetOrientation method instead.
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Type: Variable
Access: Read-Only
Units: deg
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SpinPhase
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The phase angle of the x-axis of the CelestialObject with respect to the projection of the x-axis of the geocentric inertial frame into the equatorial plane of the CelestialObject.
This property has been Deprecated. Please use the CelestialObject.GetOrientationAtEpoch or SetOrientation method instead.
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Type: Variable
Access: Read-Only
Units: deg
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SpinRate
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The angular rotation rate of the CelestialObject about its spin axis.
This property has been Deprecated. Please use the CelestialObject.GetSpinRateAtEpoch method instead.
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Type: Variable
Access: Read/Write
Units: deg/s
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TextureFileName
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An image file to apply to the surface of the CelestialObject. The image may be in jpeg, png, tiff, gif, or bmp format. This property should be set before the first ViewWindow update. It has no effect for any built-in global CelestialObject, and the texture used for these objects should be set in User Preferences. The texture can be overridden for an individual view using the ViewWindow.SetCelestialObjectDaytimeImage() method.
This property has been Deprecated. Please use CelestialObject.Globe.SurfaceLayer.DaytimeImageFilename instead.
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Type: String
Access: Read/Write
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Velocity
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Returns the instantaneous CelestialObject velocity vector in Cartesian components (VX, VY, VZ) referenced to the ICRF.
This property has been Deprecated. Please use the CelestialObject.GetVelocityAtEpoch or SetState method instead.
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Type: Array
Access: Read/Write
Units: km/s
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See also
CelestialObjects Guide
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