RPO Executive Software

Description

The RPO Executive Software orchestrates the terminal phase of Rendezvous and Proximity Operations (RPO) by coordinating the handoff between the formation controller and the docking adapter. It manages a capture gate that prevents premature docking during approach maneuvers, enables capture when the chaser reaches the final hold position, and optionally commands a retreat trajectory after undocking.

Example Use Cases

Docking Sequencing: Suppress capture during R-bar or V-bar approach until the chaser reaches the final hold with acceptable position and velocity errors.
Automated Undock and Retreat: Command a teardrop or other retreat trajectory automatically after the spacecraft undocks.
Port Alignment Gating: Hold capture until the docking adapters are aligned within tolerance.

Module Implementation

Phase State Machine

The executive maintains a phase state that reflects the current stage of the RPO sequence:

Phase	Description
Idle	No active approach; capture gate follows default policy
ProximityApproach	R-bar or V-bar approach in progress; capture suppressed
DockReady	Approach complete and aligned; capture enabled
Docked	Spacecraft are docked; propulsion optionally inhibited
Retreat	Undocked and retreating; capture suppressed
Undocked	Undocked with no retreat configured

Capture Gate Logic

The executive controls the docking adapter’s capture gate based on the current phase and approach status:

During Approach: Capture is disabled to prevent premature contact while the formation controller is maneuvering.
At Final Hold: Capture is enabled when:
- Position error $∣ e_{r} ∣ \leq ϵ_{r}$ (configurable tolerance)
- Velocity magnitude $∣ v_{re l} ∣ \leq ϵ_{v}$ (configurable tolerance)
- The approach segment duration has elapsed
- Port alignment is satisfied (if required)
While Docked: Capture remains disabled.
During Retreat: Capture is disabled until the retreat completes.

Approach Completion Detection

The executive determines that a terminal approach is complete when:

∣ e_{r} ∣ \leq ϵ_{r} and ∣ v_{re l} ∣ \leq ϵ_{v} and t \geq t_{s t a r t} + Δ t_{a pp ro a c h}

where $t_{s t a r t}$ is the approach segment start time and $Δ t_{a pp ro a c h}$ is the planned approach duration from the formation controller.

Undock and Retreat

When the spacecraft transitions from docked to undocked, the executive can automatically command a retreat formation mode (e.g., Teardrop) on the formation controller. This ensures the chaser moves to a safe distance before any subsequent operations.

Propulsion Inhibit

When StopPropulsionWhenDocked is enabled, the executive commands the formation controller to mode None and sets the device status to inactive while docked. This prevents thruster firings that could disturb the docked stack.

Assumptions/Limitations

Requires formation flying telemetry from an ROE Formation Controller Software.
Capture gate management assumes a connected Docking Adapter with capture command input.
Port alignment checking requires docking adapter telemetry; if unwired, the alignment gate is bypassed.
The retreat mode is commanded once on undock detection; subsequent mode changes must be handled externally.