Spacecraft Ephemeris Translation Software

SWITCH TO API

Description

The Spacecraft Ephemeris Translation Software is a Software component that converts a Spacecraft body state message into ephemeris and navigation translation message formats. This translation enables spacecraft state data to be represented in standard navigation coordinate frameworks for use with guidance, navigation, and control algorithms.

---

Example Use Cases

• Navigation Interface: Provide spacecraft position and velocity data in ephemeris format for navigation algorithms.
• Component Tracking: Track the position of a specific point on the spacecraft using the body frame offset.

---

Module Implementation

The software extracts position and velocity data from the spacecraft state message and outputs it in both ephemeris and navigation translation message formats.

Position Extraction

The position is extracted from the spacecraft state message with an optional offset in the body frame:

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

where ${\mathbf{r}}_{\text{spacecraft}}^{\mathcal{N}}$ is the spacecraft position in the inertial frame, ${\mathbf{r}}_{\text{offset}}^{\mathcal{B}}$ is the configurable offset in the body frame, and $[BN]$ is the body-to-inertial direction cosine matrix derived from the spacecraft’s MRP attitude ${\sigma }_{B/N}$. This offset allows tracking a specific component or point on the spacecraft rather than its origin.

Velocity Extraction

The velocity is copied directly from the spacecraft state message:

$${\mathbf{v}}_{B/N}^{\mathcal{N}}={\mathbf{v}}_{\text{spacecraft}}^{\mathcal{N}}$$

The navigation translation message also includes the accumulated delta-velocity from the spacecraft state.

---

Assumptions/Limitations

• The software automatically connects to the parent spacecraft’s state message on attachment.
• The offset is applied in the body frame and rotated to the inertial frame using the spacecraft attitude.
• Velocity output does not account for rotational effects from the offset position.