Environment: Solar Flux

Description

The Solar Flux module always exists in the simulation at all times. All spacecraft will be reading the solar flux data regardless of where they are located. The solar flux module determines the energy per square meter produced by the sun acting on a surface. The solar flux uses the Eclipse module to determine the amount of flux from the sun at some object, keeping in mind the shadow factor due to a celestial body blocking the sun.

Example Use Cases

Use solar flux information to determine the amount of solar power that is generated from an array of panels.
Use solar flux calculations to determine the solar radiation perturbations influencing the dynamics of spacecraft

Module Implementation

The module assumes a constant solar flux value at the surface of Earth, taken as an average value with no atmospheric scattering at the distance of \(\mathrm{AU} = 149597870691\) m. This value is given as \(\Phi_{E} = \mathrm{SOLAR\_FLUX\_EARTH}\).

Given a vector relative to the inertial frame \(N\), \(\vec{r}_{BN} = \{x, y, z\}\), then a vector between the object and the sun’s centre \(\vec{r}_{BS}\) can be calculated, given the earth and sun’s vectors from the SPICE frame, \(\vec{r}_{PN}\) and \(\vec{r}_{SN}\). This assumes that the body \(B\) and the sun \(S\) vectors are also represented in the \(N\) frame.

\[ \vec{r}_{BS} = \vec{r}_{BN} - \vec{r}_{SN} \]

Then, the solar flux at the body location \(\Phi_{B}\) can be defined by the distance from the sun as calculated above multiplied by the shadow factor \(\epsilon\), where \(\epsilon\) is 1.0 when in shadow and 0.0 when in complete visibility of the sun. Any values in between will be defined when the surface’s entire surface is only partially blocked by a celestial body, in the case of a partial eclipse.

\[ \Phi_B = (1 - \epsilon) \times \Phi_E \times {\mathrm{AU}^2 \over |\vec{r}_{BS}|^2} \]

The flux expands as an inverse square law, defined by maintaining energy over an increased surface area of a sphere.

Assumptions/Limitations

Solar Flux takes into account shadows from celestial objects. It does not take into account shadows between objects
Solar activity is assumed to be constant on the Sun and the solar flux value not in eclipse at a particular distance from the Sun will remain the same always.
Celestial bodies are assumed to be spherical. If geometry is added to the surface of planets, these will not contribute to the shadow factor.
By default, unless a component is added, solar radiation pressure will not influence the spacecraft’s dynamics and will remain a lookup table.

References