gps-denied-onboard/_docs/00_problem/restrictions.md

Restrictions

Last revised 2026-05-07 (cleanup pass — design-independent, IEEE-830 style; only external dependencies, environmental constraints, integration boundaries). Subsequent revision 2026-05-07 (post-SQ6 research): the FC-facing communication protocol entries below were corrected — iNav firmware (master, post-9.0) has no inbound MAVLink external-positioning handler; the project must use a per-FC adapter (MAVLink GPS_INPUT for ArduPilot Plane; MSP2 MSP2_SENSOR_GPS for iNav). Rationale and L1 sources in _docs/00_research/02_fact_cards/SQ6_fc_external_positioning.md / _docs/00_research/01_source_registry/SQ6_external_positioning.md Sources #4, #9, #10, #12, #13.

UAV & Flight

• Fixed-wing UAVs only; navigation camera fixed downward (no gimbal).
• Operational area: eastern/southern Ukraine (east of Dnipro).
• Mission profile: 8-hour flights, ~60 km/h cruise. Sector ≤150 km² + transit corridor ~50 km². Total cached area ≤~400 km², persistent across flights.
• Altitude ≤1 km AGL; terrain assumed flat (rolling steppe / agricultural).
• Weather: predominantly sunny daytime; validation must cover seasonal/visibility classes (summer crops, autumn/winter bare fields, cloud/haze, snow if winter, low-texture repetition).
• Sharp turns are exceptions; consecutive photos may share <5% overlap (AC-3.2).
• No raw-photo storage (AC-8.5); storage bounded by tile cache + per-flight FDR (AC-NEW-3).

Cameras

• Navigation camera (pinned): ADTi 20MP 20L V1, APS-C ~23.6 × 15.7 mm, ~5472 × 3648 px (≈20 MP). Lens chosen so GSD lands in 10–20 cm/px @ 1 km AGL (frame footprint ~470×314 m to ~980×655 m). Intrinsics + camera-to-body calibration must be obtained pre-flight (e.g., checkerboard).
• AI camera: operator-controlled gimbal angle + zoom (consumed by AI detection systems). The GPS-Denied system supports object localization (AC-7.x) using gimbal angle + zoom only — UAV bank/pitch is not published to that path; AI-camera object localization is therefore scoped to level flight (AC-7.1).
• Camera-to-companion interface: USB / MIPI-CSI / GigE (lens-module dependent).

Satellite Imagery

• Source: Azaion Suite Satellite Service (separate Suite component). Onboard system is a consumer; upstream sourcing is the Service's concern.
• Onboard interface is offline-only: companion holds a local cache populated pre-flight from the Service for the operational area (AC-8.3). No in-flight Service calls.
• Mid-flight tile generation (AC-8.4): companion orthorectifies nav-camera frames into basemap-projected tiles, deduplicates, stores locally; uploads on landing.
• Storage policy: tile is the unit of persistence; no raw frames retained (AC-8.5).
• Resolution at cache interface: ≥0.5 m/px, ideally 0.3 m/px (AC-8.1).
• Tile manifest schema: CRS, tile matrix, dimension, lat-adjusted m/px, capture date, source, compression. Slippy/XYZ zoom (if used) is a provider convention, not a resolution proof.
• Cache budget: 10 GB persistent across the ~400 km² area, including manifests, overviews, and any precomputed indices unless the solution carves out a separate descriptor budget.
• Freshness: enforced per AC-8.2 / AC-NEW-6 (6-month active-conflict / 12-month rear). Mid-flight tiles timestamped current and treated as fresh.
• Sentinel-2 / free public imagery: not on runtime path; cache rejects below the 0.5 m/px floor.

Onboard Hardware

• Companion computer (pinned): Jetson Orin Nano Super — 67 TOPS sparse INT8, 8 GB shared LPDDR5, 25 W TDP. JetPack (Ubuntu) with CUDA / TensorRT.
• Cooling sized for 25 W continuous over 8 h at the upper environmental temp (AC-NEW-5).
• Storage budget ≥ tile cache (~10 GB) + per-flight FDR (64 GB, AC-NEW-3).

Sensors & Integration

• High-rate IMU available from FC via MAVLink (both ArduPilot Plane and iNav expose IMU telemetry over MAVLink outbound).
• Communication protocol (pinned): MAVLink for the GCS link (QGroundControl). Companion ↔ FC interface is per-FC: MAVLink for ArduPilot Plane (inbound external positioning + outbound telemetry); MSP2 for iNav (inbound external positioning via MSP2_SENSOR_GPS); MAVLink outbound from iNav for telemetry to the GCS is preserved.
• Supported flight controllers: ArduPilot Plane, iNav. PX4 out of scope.
• Output to FC: WGS84 GPS coordinates as a real-GPS replacement, via each supported FC's documented external-positioning interface — MAVLink GPS_INPUT for ArduPilot Plane, MSP2 MSP2_SENSOR_GPS for iNav (companion is the sole GPS source on iNav; iNav has no dual-GPS arbitration). Per-FC parameter wiring (EKF source-set on ArduPilot; GPS provider/UART selection on iNav) and source-label out-of-band channel are design choices; outcome contract is AC-4.3.
• Ground station: QGroundControl (Mission Planner out of scope). Telemetry link bandwidth-limited; per-frame data stays on local FDR (AC-NEW-3); GCS sees 1–2 Hz downsampled summary (AC-6.1).
• Representative data: see input_data/ (still images), input_data/flight_derkachi/ (cropped nadir video + synchronized SCALED_IMU2 + GLOBAL_POSITION_INT). Production acceptance still requires camera intrinsics, distortion, camera-to-body calibration, and synchronized representative flight data (frames + FC IMU/attitude/airspeed/altitude + emitted MAVLink + ground-truth trajectory).

Failsafe & Safety

• If no estimate produced for >3 s → autopilot falls back to IMU-only dead reckoning (AC-5.2). 3 s rides through one sharp turn at cruise.
• False-position safety budget: AC-NEW-4 (P(>500 m) <0.1 %, P(>1 km) <0.01 % per flight).
• Cold-start TTFF <30 s (AC-NEW-1); spoofing-promotion latency <3 s (AC-NEW-2).