Beacon Message Encoder
Self-Contained Beacon Telemetry Encoder with FEC
Self-contained microcontroller-based encoder that builds the beacon's data packet (Ark identity, geographic coordinates, time, basic health bits) and applies forward error correction before passing to the transmitter.
Purpose
Construct a robust, low-bit-rate distress message that includes enough information for a receiver to identify the Ark, locate it, and infer the type of distress without requiring detailed bidirectional communication.
Context
Companion module to L3-COM-BEAC-XMIT; reads simple sensor inputs (Ark presence, internal temperature, perhaps a redundant 'all systems offline' bit from a watchdog) and produces a periodic encoded message. No software updates over mission life — burned-in firmware only.
Principles
- ▸Cospas-Sarsat 406 MHz beacon message is 144 bits long with BCH(82,61) error correction and includes country code, beacon ID, position
- ▸Short messages with strong FEC achieve reliable decode at very low SNR; trade-off is bit rate vs. integration time
- ▸Time-bit packed encoding can fit identity, lat/lon (or x/y/z fixed-frame), UTC, and 16 status flags in ~256 bits
- ▸Hard-coded firmware (mask-programmed ROM) is more reliable than rewritable flash for 100-year mission
- ▸Watchdog input from main CDH allows the beacon to switch from 'all-ok' to 'distress' mode without complex protocol
- ▸Position encoded in ICRF-aligned lunar fixed frame (e.g., Mean Earth/Polar Axis) avoids dependence on Earth-fixed coordinate systems
Typical implementations
- ▸Cospas-Sarsat T.001 specification — message format and FEC for 406 MHz beacons
- ▸Mass-programmed ROM (one-time-programmable) for unchanged firmware over decades
- ▸RH (Radiation Hardened) PIC or RISC-V microcontroller — milliwatts active consumption
- ▸Hardware-described state machines in rad-hard CPLD as alternative to MCU
- ▸ESA secondary payload telemetry-only beacons on small satellites
Lunar considerations
- ▸Beacon message format must be human-decodable from first principles — assume future intelligence may not have Earth standards documents
- ▸Include a 'Rosetta key' preamble: known mathematical constants (π digits, primes) that prove the signal is artificial
- ▸Use Lunar Mean Earth/Polar Axis (MEPA) or ICRF-aligned position rather than Earth-tied frame
- ▸Long-life ROM (fused metal mask, optical) survives radiation and aging better than flash
- ▸Status flags should be self-explanatory: a few thermometer bits (temperature too cold/hot), pressure (sealed/breached), main bus (alive/dead)
Specifications
Functional
| primary function | Encode periodic beacon message with FEC |
| inputs | Internal sensors: temperature, accelerometer, RTG voltage, Watchdog signal from main CDH (alive heartbeat), Pre-burned identity ROM (15-hex Ark ID, base coordinates) |
| outputs | Encoded bit stream to L3-COM-BEAC-XMIT (~256 bits per burst), Local diagnostic LED |
| message length bits | 256 |
| fec code | BCH (256, 192) — corrects 8 errors |
| preamble rosetta bits | 32 |
| fields | preamble, ark_id, position_xyz_lunar, utc_time, health_flags, fec_parity |
| max encode time ms | 50 |
| firmware immutability | Mask ROM (no field reprogramming) |
Physical
| mass kg | 0.2 |
| dimensions | 80 × 60 × 10 mm card inside beacon enclosure |
| materials | Rad-hard PIC/RISC-V MCU (mask ROM), ATEX-compatible ceramic package, Single-layer PCB |
| operating temperature c | -100, 100 |
| radiation tid krad | 200 |
Operational
| power consumption mw idle | 0.2 |
| power consumption mw active | 50 |
| thermal range c | -100, 100 |
| lifetime years | 100 |
| mtbf hours | 1000000 |
Interfaces
Provides
- Encoded message bit stream
Requires
- 3.3 V from beacon power source
- Optional watchdog heartbeat (absent = distress)
Cite this entry
Lunar Ark Codex. "Beacon Message Encoder" (L3-COM-BEAC-ENC). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-COM-BEAC-ENC
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.