Thruster Fire Mapping Software

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Description

The Thruster Fire Mapping Software is a flight software module that converts high-level thruster burn commands into thruster fire request messages. The module determines when to initiate a thruster firing based on the commanded burn parameters and the current spacecraft attitude alignment. By incorporating attitude error feedback, the software ensures that burns are only executed when the spacecraft is properly oriented, preventing inefficient or off-axis thrust applications.

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Example Use Cases

• Orbit Maneuvers: Convert delta-velocity commands from a maneuver planner into thruster firing requests for orbit raising, lowering, or plane changes.
• Station Keeping: Execute planned maintenance burns when the spacecraft achieves proper attitude alignment.
• Collision Avoidance: Trigger emergency maneuvers with alignment verification to ensure thrust is applied in the correct direction.

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Module Implementation

The Thruster Fire Mapping Software is a Software component that processes burn commands and attitude error information to generate thruster fire requests.

Alignment Verification

Before initiating a burn, the module verifies that the spacecraft attitude is sufficiently aligned with the intended thrust direction. The alignment is evaluated using the Modified Rodrigues Parameter (MRP) attitude error:

$$\text{aligned}=\Vert {\mathbf{\sigma }}_{B/R}\Vert \le ϵ$$

where:

• ${\mathbf{\sigma }}_{B/R}$ is the MRP attitude error between the body and reference frames
• $ϵ$ is the configurable AlignmentTolerance parameter

If the attitude error exceeds the tolerance, the burn is inhibited and the output duration is set to zero.

Burn Gating

The module implements a multi-stage gating logic to determine if a burn should be executed:

Condition	Action
No burn message connected	Skip update
Thrust factor $\le 0$	Output zero duration
Attitude error $>ϵ$	Output zero duration
All conditions satisfied	Output burn request

Fire Request Generation

When all conditions are satisfied, the module generates a fire request with:

$$t_{\text{start}}=t_{\text{current}}$$ $$t_{\text{duration}}=100\cdot \Delta t$$

where $t_{\text{current}}$ is the current simulation time and $\Delta t$ is the simulation time step.

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Assumptions/Limitations

• The current implementation outputs a fixed duration based on the simulation time step; variable thrust durations are not yet supported.
• Frame-by-frame variable thrust factor burns are not implemented in this version.
• Attitude error checking is optional; if no attitude error message is connected, alignment verification is bypassed.
• The module does not compute required burn duration from delta-velocity and spacecraft mass; this must be provided externally.
• Only a single thruster firing mode is supported; pulse modulation or duty cycling is not