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Geometry

In the Geometry View, you can create properties related to the local geometry of your spacecraft: Body Frame Vectors, External Surfaces, and Fields of View.

Take care when establishing your principal directions and origin. If you have a CAD model of your satellite, align your Sedaro body frame with the coordinate system in the CAD model. This will make extracting key vectors straightforward.

Body Frame Vectors​

Body Frame Vectors are unit vectors fixed relative to the spacecraft body. Body Frame Vectors are used to drive Pointing Modes, define the orientation of sensor boresights and comm antennas, and to describe exterior geometry.

Create a Body Frame Vector by clicking the "+" button beneath the list of vectors. You can define a Body Frame Vector in either Cartesian or spherical polar (with the z-axis as the polar axis) coordinates of the principal axes.

Surfaces​

Surfaces are used as the mounting location for solar panels and to compute perturbations due to atmospheric drag, radiative heat transfer, and solar radiation pressure.

Create a Surface by clicking the "+" button beneath the list of surfaces. You will be prompted to define the area (m²) of the surface.

Motion Type​

Each surface must be given a motion type, which defines how they articulate relative to the spacecraft body.

  • Fixed Surfaces are fixed with respect to the satellite's local/body reference frame.
  • Sun Tracking Surfaces rotate about an axis that is fixed in the satellite's local/body reference frame. These surfaces maintain a rotation angle that maximizes alignment with the sun vector. Surfaces associated with a solar panel are often Sun Tracking.
  • Anti-Sun Tracking surfaces rotate about an axis that is fixed in the satellite's local/body reference frame. These surfaces maintain a rotation angle that minimizes alignment with the sun vector. This type is useful for creating the "back" side of a Sun Tracking Surface.

Surface Materials​

Every Surface will need to be defined using a Surface Material. Just as with other forms of hardware, you can specify a part number, manufacturer, temperature rating, etc. You will also define the radiative properties of the surface.

  • IR Emissivity - Percent of thermal energy radiated at IR wavelengths from this surface relative to a black body of the same temperature.
  • Solar Absorptivity - Percent of energy absorbed and trapped as heat by the surface at solar (visible) wavelengths.
  • Diffuse Solar Reflectivity - Percent of light diffusely reflected from the surface, used for solar radiation pressure calculations. Diffuse refers to light that is scattered on impact.
  • Specular Solar Reflectivity - Percent of light specularly reflected from the surface, used for solar radiation pressure calculations. Specular refers to light that is coherently reflected on impact.

Fields of View​

Fields of View (FoVs) are defined based on a direction (Body Frame Vector) and either a circular or rectangular sensor plane. These can be linked to Sensors or Directed Energy Devices and used to create FoV Conditions. When defining a Rectangular Field of View, you will need to choose a second vector which specifies the "height" direction.

Reference Vectors​

In the Reference Vectors board, you can create local direction vectors and vectors from the spacecraft to celestial bodies and targets. These vectors are used in other parts of the model to define behaviors such as pointing, condition compliance, targeting(/agentbranch/targets), and attitude determination. Reference vectors fall into four categories: Celestial, Local, Target, and Target Group.

Celestial Vectors​

Celestial Vectors point to the center of natural bodies such as the Earth and those outside of the Earth's atmosphere, like the Sun and Moon.

Local Vectors​

Local vectors are uniquely determined relative to the position, velocity, and orientation of the spacecraft. The available options are as follows:

  • Nadir - directly towards the center of Earth from the satellite.
  • Zenith - vector in the direction opposite nadir
  • Positive Cross Track - out of plane at right angle to position and velocity vectors (cross product of position and velocity, parallel to orbital angular momentum)
  • Negative Cross Track - out of plane at right angle to position and velocity vectors (negative direction of the cross product of position and velocity)
  • Positive Along Track - "forward", at right angle to position vector
  • Negative Along Track - "aft", at right angle to position vector
  • Ram - velocity direction
  • Anti-Ram - vector in the direction opposite ram
  • Magnetic Field - local magnetic field vector

Target Vectors​

If you have defined a Target, you can create a Target Vector which points from the spacecraft to that Target.

Target Group Vectors​

If you have defined a Target Group, you can create a Target Group Vector which points to the Active Target of a Target Group. The Active Target is determined based on which targets satisfy the Conditions associated with the Target Group and are tiebroken by Target Priority.