The Sun Properties feature defines the Sun position and the solar flux.

Select any of the predefined option for the Sun direction (Winter solstice, Summer solstice, Spring equinox, or Fall equinox) to define the Sun vector and solar flux. In this case the Sun vector in ECS field is not editable and show the vector definition for the selected value.

When the Solar flux is set to Automatic a Plank’s distribution for a blackbody at Ts = 5780 K is used for the radiation in case of multiple spectral bands. The solar flux intensity (SI unit W/m2) is defined according to Table 6-6.

The Solar flux can also be set to User defined and User defined per band in case of multiple spectral bands. In case of gray surface model, only User defined is available.

When the Sun direction is set to User defined, the Sun vector in ECS field is editable. The Solar flux can be defined similarly as above except that the Automatic option is not available.

When the Solar flux is set to User defined for each band, enter a value for the Solar flux, q0s,i (SI unit W/m2, default value 0 W/m2) for each spectral band. Within a spectral band, each value is assumed to be independent of wavelength.

When Solar flux is set to User defined, define q0s,λ (SI unit W/m3, default value 0 W/m3). The wavelength may be accessed through the otl.lambda variable. This distribution is integrated on each spectral band to obtain the source heat flux q0s,i for each spectral band.

Any Clear sky noon beam normal irradiance defined from an Ambient properties node can also be selected to define q0s. In this case spectral the bands the solar flux distribution per band is defined following Plank's distribution for a blackbody at Ts.

Physics tab with Orbital Thermal Loads selected: