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To run simulations, D2S2 relies on models that specify the behaviour of each component. The basic components in every simulation are the Earth, Sun, Moon, one or more satellites, and geographic locations. This section of the documentation focuses the behaviour and representation of satellite models.
The SatelliteModel type object is available to represent a generic satellite with arbitrary size. Satellite models in D2S2 are constructed using a satellite container model object, plus several components. The container model object can be thought of as a structure or frame into which components are placed, or onto which components are mounted. Several generic container model objects are available for specific use. They are specified according to their form factor;
These satellite containers can be created by selecting Satellites in the model tree, then pressing the Create 
button.
Once a satellite container object is created, components can be added to it by selecting its components dependency from the model tree, then pressing the Create button again.
A drop-down list of components appears, which includes cover panels, solar panels, reaction wheels, a number of sensors and electrical components, etc.
These components will appear as children to the satellite container in the model view.
An example of a 6U structure without any components (i.e., only the container model object), as well as with covering panel and solar panel components are shown in Figure 1.
Figure 1: 3D visualisation of only a 6U satellite frame (top), and with cover panels and solar panels included (bottom).
Most components will render a visual element, which makes it convenient to interact with them from the simulation view. Figure 2 shows an example where an ACS was selected by interacting with the 3D model of the satellite.
Figure 2: The ACS selected by interacting with the 3D model of the satellite.
Furthermore, Each satellite component has its own local coordinate frame that defines its axis definition and origin of the 3D model and surface model areas. A component has two properties that control where a component is placed in the satellite, and its orientation. These are:
Each satellite has a surface model that is utilised to calculate the aerodynamic and solar radiation forces and torques on the satellite body. The rendered 3D elements are not necessarily the same as the surface model, as the latter is often simplified to allow efficient computation. Components that are added to the satellite contribute to the surface model. For example, the cover panel and solar panels contribute flat areas.
An option to subdivide each surface into a grid of smaller areas is available. The surface model evaluation includes shadowing or occlusion, and the size of surface grid elements influences the overall accuracy. It should be noted that a larger number of grid elements will increase computation time and memory usage.
The surface model can be overlaid on top of the satellite using the 'Satellite Overlay' selection button, which becomes visible after selecting the satellite in the 3D view. The table below indicates the button icon corresponding to each available overlay.
| Icon | Name | Description |
|---|---|---|
 |
No overlay | No surface model overlay is displayed. |
 |
Aerodynamic | Surface model is overlaid, and segments are coloured to reflect aerodynamic force. |
 |
Solar | Surface model is overlaid, and segments are coloured to reflect solar force. |
Depending on the overlay selection, surface segments are coloured either to reflect the magnitude of the aerodynamic force, or solar force. Figure 3 shows an example of the aerodynamic surface overlay for a 6U satellite with deployed panels. The shadowing effect from occlusion also evident in the example.
Figure 3: An example of an aerodynamic force overlay.
The satellite container model has properties to capture the mass and moment of inertia matrix of the structure, while any component that is added to the satellite can also contribute to the total mass and moment of inertia of the satellite.
It is often more convenient to set only the mass and moment of inertia properties for the satellite container model to the total mass and moment of inertia of the satellite. This is usually favourable if these values are already known from CAD models. In this case the mass and moment of inertia for components would be kept at their default values (zero).
If a component has a non-zero mass or moment of inertia value, the total satellite mass is calculated by summing the container mass and component masses. The centre-of-mass offset relative to the geometric centre is then found by weighted average of the component locations. Additionally, the total moment of inertia matrix is found by combining moments of inertia matrices using the parallel axis theorem.
The force and torque contribution of each component is transformed from the local component coordinate frame to the satellite body frame using the Orientation and Position properties of the component, from where it is used by the kinematic model to propagate orbit and attitude. In fact, each satellite component can potentially contribute to the force and torque that the satellite experiences. This depends greatly on the component model’s implementation. For example, solar panels can contribute a disturbing torque when sunlight falls on the solar panel surface because of the induced magnetic dipole due to current loops in the solar panel. In this case, the maximum magnetic dipole is a setting for the solar panel model object. Actuator model objects such as reaction wheels and thrusters will generate control forces and torques.
Satellite components that inherit from the 'SatelliteElectricalComponent' class report the amount of power they consume, in Watt units. Additionally, solar panel model objects report the amount of power they are generating in Watt units. This information (power consumed and power generated) is necessary to construct power budgets.