Emergency Beacon Transmitter
Independent Low-Power 406 MHz / UHF Distress Beacon
Self-contained, low-power radio beacon transmitting Ark identification, location, and minimal health status on internationally-monitored distress frequencies (406 MHz Cospas-Sarsat style and a dedicated lunar 2.2 GHz channel), operating fully independently of the main communication system.
Purpose
Provide a last-resort 'we are alive' signal that any future intelligence — Earth-based, lunar-resident, or otherwise — could detect even if the entire primary communication chain (transceiver, CDH, power bus) has failed.
Context
Single-board self-powered unit with its own L3-COM-BEAC-PWR (long-life isotope or capacitor power), L3-COM-BEAC-ANT (omnidirectional antenna), and L3-COM-BEAC-ENC (message encoder). Wakes periodically (e.g., every 1 hour) to transmit a short burst, then sleeps to conserve power.
Principles
- ▸Cospas-Sarsat 406 MHz EPIRBs use a 0.5 s burst of digital data every 50 s containing identity, position, and beacon type
- ▸Constant-envelope modulation (BPSK, MSK, GMSK) is preferred to permit Class-C/E SSPA at high efficiency
- ▸Beacon power budget = TX energy per burst × burst rate / battery (or RTG) capacity; small RTG (e.g., 1 We Pu-238 GPHS) provides decades of continuous operation
- ▸Forward error correction (BCH, Hamming) enables successful decode at low SNR even with weak signal at receiver
- ▸Frequency stability typically ±5 ppm over temperature/aging — adequate for distress beacon detection
- ▸International beacon database (e.g., NOAA/USAF SARSAT) maps beacon IDs to assets — Lunar Ark would register a unique 15-hex code
Typical implementations
- ▸Cospas-Sarsat 406 MHz EPIRB / ELT / PLB beacons — international standard
- ▸Mars Express UHF beacon mode
- ▸Apollo Lunar Communication Relay Unit (LCRU) emergency beacons
- ▸RTG-powered ARTEMIS-style isotope beacons for long-duration retrofits
- ▸Galileo SAR repeater integrated with 406 MHz reception
Lunar considerations
- ▸Cospas-Sarsat satellites operate in LEO and detect 406 MHz beacons from Earth's surface — lunar visibility is unlikely without dedicated lunar relay
- ▸Better: a custom 2.2 GHz (S-band) beacon detectable by Lunar Pathfinder / LCRNS / Moonlight relays at lunar orbit
- ▸Power source must be independent of main Ark power — radioisotope thermoelectric generator (RTG, ~1 We for 100+ years) or sealed lithium primary battery (decades)
- ▸Beacon should survive scenarios that disable main systems: catastrophic regolith collapse, reactor scram, cyber compromise of CDH
- ▸Beacon mounted in hardened, geographically-distinct location from primary comms (separate mast or buried with antenna exposed)
Specifications
Functional
| primary function | Transmit periodic identity/location/health beacon on distress frequency |
| inputs | Encoded message bits from L3-COM-BEAC-ENC, Power from L3-COM-BEAC-PWR, Internal timing reference (local quartz) |
| outputs | RF burst at 406 MHz and/or 2.2 GHz, +20 to +33 dBm, Status indicator (LED for visual ground inspection) |
| frequencies mhz | 406.05, 2200.0 |
| rf output power dbm | 23 |
| burst duration s | 0.5 |
| burst interval min | 60 |
| modulation | GMSK BT=0.5 |
| data rate bps | 400 |
| frequency stability ppm | 5 |
| self test interval days | 30 |
Physical
| mass kg | 2.0 |
| dimensions | 200 × 150 × 100 mm hermetic enclosure |
| materials | Stainless steel enclosure (radiation/dust resistant), RF-transparent radome (PEEK or ceramic), Discrete GaAs/LDMOS PA, Rad-hard 8-bit microcontroller (RH-RICE or equivalent) |
| operating temperature c | -100, 100 |
| radiation tid krad | 200 |
| vacuum qualified | True |
Operational
| power consumption mw idle | 0.5 |
| power consumption w burst | 5 |
| duty cycle percent | 0.014 |
| thermal range c | -100, 100 |
| lifetime years | 100 |
| mtbf hours | 1000000 |
Interfaces
Provides
- Modulated RF signal to omnidirectional beacon antenna
Requires
- Pre-formatted beacon message
- Independent power source
- RF coupling to antenna
Cite this entry
Lunar Ark Codex. "Emergency Beacon Transmitter" (L3-COM-BEAC-XMIT). Retrieved 10 September 2026, from https://lunarark.com/entry/L3-COM-BEAC-XMIT
Licensed CC-BY-SA 4.0. You may reuse and adapt this entry with attribution, under the same licence.