System Requirements Document (SRD) Summary

This is a System Requirements Document (SRD) for the Lunar Exploration Ground Sites (LEGS) Public Private Partnership (PPP), a space communications ground station network procurement by NASA's Space Communications and Navigation (SCaN) Program. The document establishes technical and operational requirements for a commercial contractor to procure, integrate, and operate lunar-focused direct-to-earth (DTE) communications ground stations. LEGS is designed to support NASA's Moon-to-Mars architecture with service coverage in the 36,000 km to 2,000,000 km range, including cis-lunar and lunar region communications. The network is planned in three phases: initial configuration of three operational DTE sites by October 2027, full redundancy configuration of six antennas by October 2028, and enhanced coverage of nine antennas by October 2029. Two government-furnished dual-band (X-band and Ka-band) antennas will be provided by NASA; LEGS 1 is installed at White Sands Complex in New Mexico, and LEGS 2 will be stored. The contractor is responsible for monitor and control equipment, signal processing, network infrastructure, antenna integration, site facilities for subsequent stations, and defining communications external interfaces to end users (Johnson Space Center Mission Control Center and Goddard Space Flight Center Flight Dynamics Facility) via the SCaN Program Operations Cloud (SPOC).

The document specifies comprehensive Level 3 requirements across RF performance, frequency bands, modulation standards, data services, and operational capabilities. Key performance metrics include G/T (gain-to-noise temperature) of ≥39 dB/K for X-band and ≥47.5 dB/K for Ka-band at specified elevations; forward services EIRP of 66-89 dBW (X-band) and 71-94 dBW (Ka-band); return service BER of 10^-5 (uncoded) and 10^-9 (coded) for both bands; return latency of ≤1 second; and forward latency of ≤125 milliseconds. System availability requirements are 0.98 for critical events and 0.95 for non-critical events, with 95% of service outages restored within one hour. The contractor must support X-band and Ka-band simultaneous operation, multiple uplink/downlink configurations per CCSDS standards, autotrack handovers, and radiometric services including 1-way and 2-way Doppler measurements and PN ranging. Facility requirements address antenna location accuracy (2 cm horizontal, 3 cm vertical), seismic design per ICC IBC 2024, NFPA compliance for fire protection and life safety, lightning protection per NFPA 780, electrical safety per NFPA 70/70E, physical security with 24/7 monitoring, and weather station integration. The SRD traces requirements to parent documents including SCaN Network SRD, Moon-to-Mars Artemis Requirements, and International Communication System Interoperability Standards (ICSIS).