Req. 5.4.2.2: "Observatory Coordinates"

The FSW shall be capable of translating to observatory coordinates, as defined in [1].

Basis (help)

[1] (3.3.1.6.2-4)

1: "Mission System Spec." (NASA 433-SPEC-0001)

3.3.1.6.2: "Body Fixed"

The observatory shall use a right-handed coordinate system fixed in the observatory body, as shown in Figure 3-1. The origin of the body-fixed coordinate system shall lie in the separation plane of the launch vehicle Payload Attachment Fitting (PAF). The Z-axis shall be collinear with the geometrical centerline of the observatory. The +Z direction shall lie along the center of the LAT field of view. The Y-axis shall be parallel to the solar array drive axes. The -X axis shall be the anti-sun side. The +Y-axis shall be the cross-product of the +Z-axis and the +X-axis. The terms Roll axis, Pitch axis, and Yaw axis shall refer to the X, Y, and Z observatory axes, respectively.

3.3.1.6.3: "Orbit Fixed"

An orbit-fixed frame ("orbit frame") is defined as follows:

The origin is coincident with the origin of the Body-Fixed frame defined above.

The +Zo axis points to the instantaneous Zenith direction.

The +Yo axis points along the positive orbit normal.

The +Xo axis is the cross product of +Yo and +Zo.

For a circular orbit, +Xo points along the positive velocity direction.

The orbit-fixed frame rotates with respect to the inertial frame at orbit rate about the +Yo axis.

The orbit plane coincides with the +Xo-Zo plane.

A vector direction is defined with respect to the orbit frame by specifying two angles: an in-plane angle and a rocking angle. The rocking angle is the angle between the vector and the orbit plane, and is positive when the vector's Yo component is negative. The inplane angle is the angle between the vector's projection onto the orbit plane and the +Zo axis, and is positive when the vector's Xo component is positive.

3.3.1.6.4: "Pointing Axis"

The axis for pointing direction of the observatory is defined as the +Z axis.

Context (help)