Object Ephemeris Translation Software

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Description

The Object Ephemeris Translation Software is a flight software module that converts an object’s transform message into ephemeris and navigation translation message formats. This translation enables any simulation object with a transform to be represented in standard navigation coordinate frameworks, facilitating tracking, relative position calculations, and integration with navigation algorithms that expect ephemeris-formatted inputs.

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Example Use Cases

• Object Tracking: Convert arbitrary simulation object positions to ephemeris format for tracking system integration.
• Navigation Interface: Provide position data in navigation message format for guidance and control algorithms.
• Multi-Object Analysis: Enable relative position calculations between objects using a common ephemeris interface.

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Module Implementation

The Object Ephemeris Translation Software is a Software component that extracts position data from a transform message or tracked object and outputs it in both ephemeris and navigation translation message formats.

Position Extraction

The position is extracted from either the input transform message or the tracked object’s world transform. An optional offset in the body frame can be applied:

$${\mathbf{r}}_{B/N}^{\mathcal{N}}={\mathbf{r}}_{\text{transform}}+[BN]\cdot {\mathbf{r}}_{\text{offset}}^{\mathcal{B}}$$

where ${\mathbf{r}}_{\text{transform}}$ is the position component of the input transform, $[BN]$ is the body-to-inertial rotation matrix, and ${\mathbf{r}}_{\text{offset}}^{\mathcal{B}}$ is the configurable offset in the body frame. This offset allows tracking a specific point on the object rather than its origin.

Velocity Estimation

Since transform messages do not contain velocity data, velocity is estimated from the change in position between updates:

$${\mathbf{v}}_{B/N}^{\mathcal{N}}=\frac{{\mathbf{r}}_{B/N}^{\mathcal{N}}(t)-{\mathbf{r}}_{B/N}^{\mathcal{N}}(t-\Delta t)}{\Delta t}$$

where $\Delta t$ is the simulation time step. On the first update or when the previous position is zero, velocity remains zero.

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Assumptions/Limitations

• Velocity is estimated from position differences; this may introduce numerical artifacts at small time steps.
• The transform position is assumed to be expressed in the inertial reference frame.
• If both TrackedObject and In_TransformMsg are set, the tracked object takes priority.
• Both output messages receive the same position and velocity data.