Concept of Operation

The Horizon system consists of two identical hardware units — an Aircraft Hardware Unit mounted on the aircraft and a GCS Hardware Unit connected to the GCS laptop or terminal. Collectively, these are referred to as Horizon Hardware Units. The two units communicate using a 868-928 MHz radio link for LOS operations and a satellite constellation (Iridium, or Inmarsat on the Horizon Darkstar variant) for BLOS operations.

The GCS software is two pieces. Beam is Somewear’s background server — an API wrapper to the Somewear backend, shared across multiple product lines — which runs in the GCS computer’s system tray. Horizon UI is the Horizon-specific application Beam opens (from the tray, Open Horizon Manager). Horizon UI runs on the GCS computer alongside the GCS application (such as Mission Planner, QGroundControl, or Athena) and intercepts MAVLink traffic from the GCS application, routing it through the GCS Hardware Unit. When a LOS link is active, commands and telemetry flow over the radio link at low latency. When the LOS link is lost, the system automatically routes supported MAVLink commands and telemetry over the BLOS link, and will additionally use ISP/WAN connectivity if available. When the GCS computer has an active internet connection, the GCS Hardware Unit is not strictly required for BLOS operation — messages can be transmitted to the aircraft via Iridium through the Somewear backend.

LOS Communication

The LOS link uses two 868-928 MHz radios per unit (LOS1 and LOS2 ports). Both units must be configured with matching frequencies. The LOS1 and LOS2 radios use antenna diversity to maximize link robustness.

BLOS Communication (Iridium / Inmarsat)

Each Horizon Hardware Unit includes a satellite modem connected via the SAT antenna port. The BLOS link provides global coverage with higher latency than LOS. An active Iridium (or Inmarsat) satellite subscription (data plan) is required for BLOS operation. The Aircraft Hardware Unit requires a clear view of the sky for reliable satellite connectivity.

Automatic LOS/BLOS Handoff

The system monitors the LOS MAVLink packet reception from the aircraft. If no MAVLink packet is received for more than 3 seconds, it automatically routes supported MAVLink commands over the BLOS link (see BLOS Fallback During Flight). When LOS is restored, the system returns to LOS routing. The operator does not need to manually switch modes during normal operation.

MAVLink Passthrough Architecture

The GCS Hardware Unit connects to the GCS laptop over USB. Horizon UI manages the serial routing to and from the unit automatically and transparently to the GCS application — no manual COM-port selection is required in current versions. The GCS application connects to the aircraft via a local UDP connection managed by Horizon UI (127.0.0.1, port 14550), configured in Preferences.