Sun Planet Vectors orbit type parameters

The Sun Planet Vectors orbit type lets you define steady state or transient spacecraft orientation with respect to the Sun and planet, and to the altitude of the spacecraft at that position.

The solver calculates all orbital heating effects at each position without calculating an orbit.

• To model steady state orbital heating at a given position in the orbit, define a single set of Sun and planet vectors, and an altitude or radius.

• To model orbital heating for a complete orbit or orbit segment, define a set of Sun and planet vectors and an altitude for each simulation time. The simulation times in the table are the calculation positions at which the solver calculates thermal effects.

Sun Planet Vectors specify a series of time-varying vectors modeling the position of the Sun with respect to the global coordinate system by specifying sets of Cartesian or spherical coordinates. Use the model's global coordinate system to define the Sun vector and the planet vector.

Defining model orientation with the Sun Planet Vectors method

If you choose Sun Planet Vectors from the Orbit Type list, you can specify a series of time varying vectors to model the position of the Sun with respect to the global coordinate system by specifying sets of Cartesian or spherical coordinates.

• Define the time-varying vectors with Cartesian coordinates by selecting Cartesian from the Coordinates list and clicking Select a Field to define a table field in the following format:Sun Planet Vectors defined with Cartesian coordinatesIndependent variableDependent variablesAnalysis time (sec)Sun vector coordinatesPlanet vector coordinatesSpacecraft altitudeSun-X valueSun-Y valueSun-Z valuePlanet-X valuePlanet-Y valuePlanet-Z valueAltitude value

• Define the time varying vectors with spherical coordinates by selecting Spherical from the Coordinates list and clicking Select a Field to define a table field in the following format:Sun Earth Vectors defined with spherical coordinatesIndependent variableDependent variablesAnalysis time (sec)Sun vector coordinatesPlanet vector coordinatesSpacecraft altitudeSun-Theta valueSun-Phi valuePlanet-Theta valuePlanet-Phi valueAltitude value

Spherical coordinate systems

This software uses the mathematics convention to define a spherical coordinate system, but the thermal solver uses the physics convention.

• Mathematics convention (r, θ, φ): radial distance, r, azimuthal angle, θ, and polar angle, φ.

• Physics convention (r, θ, φ): radial distance, r, polar angle, θ, and azimuthal angle, φ.

The user interface convention	The thermal solver convention

Because of this difference, with this software you enter the values using the mathematics convention, and at export, the software swaps the θ and φ values to comply with the physics (thermal solver) convention before the values are written to the INPF file.

Displaying the spacecraft in the Orbit Visualizer

The Sun and planet vectors do not uniquely determine the spacecraft position.

To accurately display the spacecraft's position in the Orbit Visualizer, for which you defined its position using the Sun and planet vectors, you must define the spacecraft's latitude and longitude coordinates for each set of Sun and planet vectors, which uniquely determine the spacecraft's position around the planet. You set these coordinates in a user-defined ASCII file called SunPlanet.dat, which you store in the run directory.

Example:

Assuming you defined two simulation times with its own set of Sun and planet vectors and altitude, you need to provide two pairs of latitude and longitude coordinates in the SunPlanet.dat file. Here is an example of the SunPlanet.dat file in this case:

LATITUDE  LONGITUDE45.5      -73.5749.3      -123.12

The Orbit Visualizer uses the latitude value and the Sun and planet vectors to compute the possible spacecraft's positions. There could be at most two possible positions, for which the solver computes the two longitude values. The Orbit Visualizer uses the computed longitude value that is closest to the provided value to display the spacecraft.

Note:

If this file is not present or the latitude and longitude data provided is not accurate, the Orbit Visualizer displays the planet as a blue sphere and positions the spacecraft arbitrarily.

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Sun Planet Vectors orbit type parameters, Simcenter 3D 2021.1 Series

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