A celestial body model
The CelestialBody resource is a model of a celestial body containing settings for the physical properties, as well as the model for the orbital motion and orientation. GMAT contains built-in models for the Sun, the 8 planets, Earth's moon, and Pluto. You can create a custom CelestialBody resource to model a planet, asteroid, comet, or moon.
See Also: SolarSystem, Barycenter, LibrationPoint, CoordinateSystem.
See the User Interface Spec spreadsheet for reference information for fields. This section is usually empty other than the hyperlink.
The CelestialBody GUI has three tabs that allow you to set the physical properties, orbital properties, and the orientation model. CelestialBody resources can be used in ForceModels, CoordinateSystem, LibrationPoints, Barycenters among others. For a built-in CelestialBody, the Orbit and Orientation tabs are largely inactive and the behavior is discussed further below. To create create a custom asteroid - as an example of how to create a custom CelestialBody- perform the following steps.
- Expand the SolarSystem folder
- Right-click the desired central body (here we choose the Sun)
- Select Add -> Planet
The CelestialBody Properties tab is shown above. GMAT models all bodies as a spherical ellipsoid and you can set the Equatorial Radius, Flattening, and gravitation parameter (Mu) on this dialog, as well as the texture map used in graphical displays.
The CelestialBody Orbit tab, for a custom CelestialBody, is shown above. For a built-in CelestialBody, the fields on this panel are inactive and are inherited from the settings on the SolarSystem Resource. For a custom CelestialBody, the CentralBody field is automatically populated depending upon the central body used when creating the
|For Developer and GUI Tester: If we add DE421 as Lunar RotatationDataSource, then we will need to make that field active in the panel above.|
Overview of Celestial Body Orientation Model
Let’s look more closely at the data provided by the IAU. Figure 2.5 contains an illustration of the three variables, αo, δo, and W, that are used to define a body’s spin axis and prime meridian location w/r/t MJ2000Eq. αo and δo are used to define a body’s spin axis direction. W is the body’s sidereal time. The equations for αo, δo, and W for the nine planets and the Earth’s moon are found in Tables 2.1 and 2.2. From
You can define the orientation of a celestial body
GMAT asdf.OrientationEpoch = 21545;
GMAT asdf.SpinAxisRAConstant = 0;
GMAT asdf.SpinAxisRARate = -0.641;
GMAT asdf.SpinAxisDECConstant = 90;
GMAT asdf.SpinAxisDECRate = -0.5570000000000001;
GMAT asdf.RotationConstant = 190.147;
GMAT asdf.RotationRate = 360.9856235;
Configuring Physical Properties
GMAT asdf.Flattening = 0.0033527;
GMAT asdf.EquatorialRadius = 6378.1363;
GMAT asdf.Mu = 398600.4415;
Configuring Orbit Ephemerides
GMAT asdf.NAIFId = -123456789;
GMAT Earth.SourceFilename = '../data/planetary_ephem/de/leDE1941.405';
Unique fields Earth and Moon
GMAT Earth.RotationDataSource = 'FK5IAU1980';
GMAT Earth.NutationUpdateInterval = 60;
Use Custom Texture Map
GMAT Earth.TextureMapFileName = '../data/graphics/texture/ModifiedBlueMarble.jpg';
Resolve: Are these obsolete
GMAT asdf.PosVelSource = 'SPICE';
GMAT asdf.RotationDataSource = 'IAUSimplified';
Configure a CelestialBody to model the asteroid RQ236.
Configure a CelestialBody to model the Mars’ moon Phobos.