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Ticket 063 — Return-to-Home Reserve Check from Worst-Case Point

Status: Implemented

Problem

The current energy feasibility model computes reserve at the planned landing point (the last route item). For real BVLOS approval a more important question is: at every point along the route, does the vehicle have enough battery to fly straight home AND land with reserve intact?

Today there is no way to answer "can I RTH from waypoint 5 with reserve?" without manually running a scenario with a lost-link event. This is the single most common pre-flight question asked by real operators.

Acceptance Criteria

  1. EnergyEstimate gains an optional rth_reserve_timeline field: a list of per-leg RTH margin values (energy remaining after hypothetical RTH from that leg's endpoint minus reserve threshold).
  2. The RTH distance from each leg endpoint to mission.planned_home is computed geodesically (straight-line, same as landing-zone divert).
  3. RTH energy uses TAS-based cruise-power calculation (same model as landing-zone divert; wind correction from Ticket 062 can be applied later).
  4. MissionEstimate exposes a new rth_is_feasible boolean: true iff the vehicle can RTH from every leg with reserve intact.
  5. The Markdown report includes an "RTH Reserve Timeline" table.
  6. The GeoJSON export colours each leg by RTH margin (green/yellow/red).
  7. At least 6 tests cover: feasible RTH at all legs, infeasible RTH at one intermediate leg, short mission that is always feasible, missing home position handling.
  8. Existing tests are unaffected (opt-in; rth_reserve_timeline is None when not computed, i.e., when mission.planned_home is absent).

Scope

  • estimator/core/results.py — EnergyEstimate.rth_reserve_timeline
  • estimator/execution/energy.py — RTH distance + energy per leg
  • adapters/markdown.py — RTH section
  • adapters/geojson_export.py — RTH margin layer
  • docs/USAGE.md — document new output field
  • tests/test_estimator_energy.py — new RTH tests

Notes

  • planned_home is always present in MissionPlan; the planned home position is the RTH destination.
  • This feature directly replaces the need to run a full scenario just to answer "can I RTH at any point?"