ODTK supports motion models for the following:
- Orbiter - satellite only
- Lander - satellite only
- SurfaceVehicle - surface vehicle only
You can select Orbiter or Lander from the Motion Type section of the satellite Properties window. You can also generate a state transition from one model to another. Surface vehicles must use the SurfaceVehicle motion type.
Orbiter motion type
When you select the Orbiter motion model, you can give the initial conditions for the spacecraft in terms of orbital elements or Cartesian position and velocity. This section of the Properties page has settings describing the force model environment and numerical integration method. From these you can specify how ODTK will propagate the orbital trajectory. You need to provide the initial uncertainty in the spacecraft position and velocity. ODTK provides error and uncertainty representations in output in trajectory-based reference frames such as Radial/In-track/Cross-track and Normal/Tangential/Cross-track.
Lander motion type
When you select the Lander motion model, you can give the initial conditions for the spacecraft in terms of geodetic (planetodetic) coordinates or Cartesian position. ODTK assumes a lander to be stationary on the surface of a central body; therefore, you do not need to choose settings describing the force model environment and numerical integration method. However, you do need to provide the initial uncertainty in the spacecraft location. ODTK provides error and uncertainty representations in output in topocentric reference frame South-East-Zenith coordinates. Output reporting and graphing styles specifically intended for use with landed spacecraft begin with “Lander”.
Surface vehicle motion type
For surface vehicles, you provide the initial conditions: epoch, position (choose a coordinate system), heading, and speed. ODTK assumes that the motion of a surface vehicle will remain near the surface of a central body and will not be predictable based on environmental forces. Therefore, you do not need to choose settings describing the force model environment and numerical integration method. However, you do need to provide the initial uncertainty in the vehicle location and velocity and specify motion model segments that describe the motion of the surface vehicle over discrete periods of time. ODTK provides error and uncertainty representations in output in topocentric reference frame South-East-Zenith coordinates. Output reporting and graphing styles specifically intended for use with surface vehicles begin with “Surf Veh”.
Transitioning between motion types
ODTK provides an HTML tool, ChangeMotionModelTool, that uses the ChangeMotionModels functional attribute on the Filter object as a mechanism for transitioning a state estimate between satellite motion types within a Filter restart record. You can access the ChangeMotionModelTool from Help > ODTK LaunchPad, in the installed utilities list.