Modeling the Planet
The planet accounts for two source of heat, the diffusely emitted infrared (IR) flux due to the nonzero temperature of the planet, and the diffusely reflected IR, or albedo, from the Sun.
The planet is approximated via a set of radiation sources on a spherical cap representing the part of the planet that can be seen from the spacecraft. The viewable planet can reasonably be tesselated into patches where the flux from each patch is reduced to a single point emitter, placed at the center of that patch. The magnitude of the source heat rate from that point emitter is the equivalent area of the patch, times the known flux and multiplied by a factor to account for the included angle of the patch.
The discretization of planet into patches is designed such that each source has an equal view factor to the spacecraft.
Since the total view factor from the relatively small spacecraft to the visible section of the planet is known, we know what the view factor should be for every point in the tesselation. This starts with one point immediately below the spacecraft, and the other points arranged in concentric rings, as illustrated in
Figure 4-25
. The number of ring and points per ring can be modified in the
Planet Properties
feature.
Figure 4-25:
As viewed along the nadir direction, the arrangement of the radiation sources on the spherical cap representing the planet with 2 rings and 4 points per ring.
