Table of Contents ECSS Model Page
Background Information Radiation sources and effects
Geometry definition

The geometry definition tool constructs a representation of a spacecraft using simple geometrical objects (spheres, cylinders and boxes) as building blocks. The tool produces a Geometry Definition Markup Language (GDML) file, which can be used as input for a ray tracing analysis with the Sector Shielding Analyis Tool (SSAT).

On the first input page, the number of geometrical shapes is specified. The dimensions and orientations of the selected shapes are specified on the following input pages. When the input forms have been completed, a summary of the user inputs is presented and pressing the button will start the calculation and bring up the "Results" page.

Spacecraft configuration

The number of primitives is defined on this page. It includes the detector (or target) location. The detector location is defined on the last input page.

The user also has the option of selecting a material for the world volume (default is vacuum).

Geometry parameters

For each object defined on the first input page, material, dimensions and orientation and position have to be defined. In addition, each object is defined with reference to a parent object, which also has to be selected. The parent object for the first primitive is the world volume.

Depending on the choice of the primitives, different input parameters are requested on the page. One of the outputs of the tool is a VRML representation of the geometry, which can be used to check the geometry definition. This visualisation option is available at each step of the 'construction' process. The detector is represented by a red dot.

Material

For each primitive, a material can be attributed from a list compiled by NIST. The default material for each object is aluminium. Each object (except the detector) can be solid or hollow. For hollow objects, wall thicknesses must be defined; the space inside a hollow objects is filled with the material of the parent volume.

Dimensions

The size of each object is defined by its outside dimensions (in m). For hollow objects, wall thicknesses (smaller than half the smallest dimension) should be specified (in mm) for each dimension. Specifying a wall thickness larger than half the smallest dimension will results in an error.

Orientation and position

Each object is defined in a local coordinate system, i.e. the local origin is at the centre of the object and the axes are defined as: The local coordinate system of each object has to be attached to a reference coordinate system. This can be done by specifying a rotation and a translation - in this order - of the local coordinate system. The body of the satellite is always attached to the reference ('world') coordinate system, and can only be rotated. The components of the satellite and the detector can be attached to any of the previously defined components or the satellite or the reference coordinate system in a hierarchical way, to prevent circular references (e.g. unit 1 relative to unit 2 and unit 2 relative to unit 1 is not allowed). This hierarchy allows the user to define the detector relative to a box which is relative to the satellite. Moving the box position relative to the satellite in separate runs of the tool, without changing the detector, generally also moves the detector relative to the satellite.

Rotation

A rotation is specified by a rotation axis and an angle of rotation. The rotation axis is specified by giving the three cartesian components of the direction of the axis. Normalisation of this vector is performed by the tool. The rotation angle is specified in degrees. The detector can not be rotated, as it is defined as a single point.

Translation

A translation is specified by its three cartesian coordinates. The units of the translation are meters. The body of the satellite can not be translated with respect to the reference coordinate system.

Results

The geometry definition tool produces the files listed in the table below. The report file spenvis_stp.html contains the input parameters and summary tables. The GDML file spenvis_sec.gdml contains the GDML representation of the geometry. The plot file spenvis_stv.wrl contains a VRML representation of the geometry.

Output files generated by the geometry definition tool
File name Description
spenvis_stp.html Report file
spenvis_sec.gdml GDML description of the geometry for use with SSAT
spenvis_stv.wrl VRML representation of the geometry


Last update: Mon, 12 Mar 2018