Importing orbits and space environments
Simcenter 3D Space Systems Thermal provides several entities for defining orbits and space environments:
- Orbit modeling object,
- Orbital Heating simulation object,
- Solar Heating Space simulation object,
- Free Molecular Heating simulation object.
In Thermal Desktop you use the External Heating Environment boundary condition for defining orbits and space environment for your spacecraft.
Thermal Model Exchanger does not support Solar Heating Space and Free Molecular Heating simulation objects.
Orbital Heating
The Simcenter 3D Orbit modeling object specifies the planet, orbit type and parameters, and the spacecraft attitude that are used by the Orbital Heating simulation object to compute the heat transfer between the spacecraft and the space environment. This simulation object specifies the parts of the model that are affected by the orbit, and the calculation method used to compute the radiation with the environment.
Thermal Model Exchanger only supports the Illuminate All Elements type of Orbital Heating simulation object. During the import process, the application creates a Thermal Desktop analysis group that contains all the elements of the Simcenter 3D model.
Thermal Model Exchanger does not support the Illuminate Selected Elements type of Orbital Heating simulation object. During the import process, the application import the orbit but it does not create a Thermal Desktop analysis group with the selected elements.
In Thermal Desktop, all the orbit characteristics and parameters are defined within the Orbit dialog box with several tabs. Note that the first tab changes with the type of orbit you select.
Supported orbit characteristics
Planets and orbit types
Thermal Model Exchanger supports all the planets available in the Simcenter 3D Orbit modeling object. For the orbit types, Simcenter 3D offers a larger list of orbits than Thermal Desktop. For each Simcenter 3D orbit type that Thermal Model Exchanger converts, the following table lists the corresponding Thermal Desktop External Heating Environment type.
| Simcenter 3D Orbits | Thermal Desktop External Heating Environments |
| Beta-Angle | Basic Orbit |
| Geostationary | Keplerian Orbit |
| Classical | Keplerian Orbit |
| Sun-synchronous | Keplerian Orbit |
| Shuttle | Keplerian Orbit |
| Molniya | Keplerian Orbit |
| Sun Planet Vectors | Orbital Sun/Planet/Radius Vector List |
Spacecraft Attitude
When you define the spacecraft attitude or orientation in Thermal Desktop, you can only select a predefined axis while in Simcenter 3D you can specify any vector. Thermal Model Exchanger reproduces the spacecraft attitude specified in Simcenter 3D calculating additional rotations needed to align the +Z axis in Thermal Desktop with the Aim at vector specified in Simcenter 3D.
Thermal Model Exchanger supports all the Simcenter 3D alignment options except the Orbit Normal, South and North options for the Aim at and Align with vectors, which you specify on the Spacecraft Attitude page in the Simcenter 3D Orbit dialog box. These alignment options are not supported in Thermal Desktop. If you import a Simcenter 3D orbit that uses one of these alignment options, Thermal Model Exchanger keeps the default values of the Orientation tab and displays a warning in the import summary.
Sun Planet Characteristics
Thermal Model Exchanger uses the information specified on the Sun Planet Characteristics page in the Simcenter 3D Orbit modeling object to fill the options on the Planetary Data, Solar, Albedo and IR Planetshine tabs in the Thermal Desktop Orbit dialog box.
Orbit Parameters
Because the Simcenter 3D Beta-Angle orbit and the Thermal Desktop Basic Orbit are equivalent, Thermal Model Exchanger does not apply specific operations during the import process.
Because the Simcenter 3D Geostationary, Classical, Sun-synchronous, Shuttle and Molniya orbit types are all special cases of the Keplerian Thermal Desktop orbit type, the application converts the parameters specified in Simcenter 3D into the equivalent parameters specified in Thermal Desktop.
For the Simcenter 3D Sun Planet Vectors orbit type, Thermal Model Exchanger imports the table field used to specify time, coordinates of the sun and planet vectors and the spacecraft altitude to the Vector Input tab in the Thermal Desktop Orbital Sun/Planet/Radius Vector List orbit type. The application converts the spacecraft altitude into the ratio of distance from Earth's center to Earth's radius required by Thermal Desktop.
Calculation Positions
Thermal Model Exchanger supports full and partial Simcenter 3D orbits.
For orbits that use the Number of Intervals angular interval method, Thermal Model Exchanger enables the Use Equal Increments option on the Positions tab in the Thermal Desktop Orbit dialog box.
For orbits that use the Angular Positions angular interval method, Thermal Model Exchanger enables the Use Positions option on the Positions tab in the Thermal Desktop Orbit dialog box.