Satellite Security

GPS Signal Structure and Security

The Global Positioning System transmits navigation signals on three civil and military frequencies. Understanding the signal structure is essential for understanding its security properties:

C/A Code

The Coarse/Acquisition (C/A) code is a 1023-chip Gold code with a 1 ms sequence length. It is transmitted at 1.023 Mchips/s and is the primary signal used by mass-market GPS receivers. The C/A code is intentionally designed to be weak and easily jammed.

Selective Availability

Selective Availability (SA) was an intentional degradation of the C/A code to limit civilian accuracy to ~100 m. SA was turned off on May 2, 2000 by Presidential directive, giving civilian users full positioning precision (~10 m). SA remains off; there is no indication it will be reactivated.

Anti-Spoofing (A/S)

When Anti-Spoofing is active, the P-code is encrypted with a classified Key to produce the Y-code, which cannot be generated by an adversary. The Y-code requires the classified DoD modules for decryption. A/S protects military receivers against spoofed P-code signals.

GPS Jamming and Spoofing

Jamming

GPS signals arrive at -160 dBW (10^-16 watts) — far below the noise floor. Jamming is relatively easy:

• Low-power (1–10 mW): Disrupts receivers within ~100 m
• High-power (1–10 W): Affects aviation approaches and maritime navigation
• Military-grade: Capable of city-wide disruption

Documented Incidents

• 2012 Newark Airport: GPS jamming near the airport affected instrument landing system (ILS) approaches; FAA investigated
• 2016 FCC fine: FCC fined a Chinese manufacturer $48 million for marketing and selling illegal GPS jammers
• Russia Black Sea (2017): Mass GPS spoofing affected ~20+ ships; ships reported incorrect positions
• North Korea (2010–2016): Systematic GPS jamming of South Korean aviation and maritime systems

Spoofing

GPS spoofing broadcasts counterfeit GPS signals to mislead receivers. Unlike jamming (which causes denial-of-service), spoofing causes receivers to report false positions.

• Iran RQ-170 (2011): Iran reportedly captured a US military drone by spoofing GPS signals, causing it to land in Iranian territory
• Meaconing: Captures and rebroadcasts authentic GPS signals; harder to detect than synthetic spoofing

GPS III and Modernized Military GPS

GPS III satellites introduce significant security improvements:

• M-Code: Military code with higher power, anti-spoofing, and direct acquisition capability; designed exclusively for military use
• L1C: Civilian signal interoperable with Galileo E1; provides redundancy for safety-critical applications
• Modular design: Allows technology upgrades without replacing satellites
• CHIMERA: Military enhancement for GPS III providing signal watermarking for authentication

Galileo Authentication: OSNMA

Galileo's Open Service Navigation Message Authentication (OSNMA) provides the first operational authentication for any GNSS (Global Navigation Satellite System):

• Declaration: OSNMA declared operational November 17, 2023 (GSA/EUSPA)
• Mechanism: Digital signature embedded in Galileo navigation message
• Benefit: Confirms signal origin — receivers can verify they are receiving authentic Galileo signals, not spoofed copies
• Availability: Free to all users; already mandated for Smart Tachographs in the EU from December 2025
• EU regulation: eCall emergency response also mandates OSNMA

Satellite Signal Interference

C-Band and 5G Interference

The FCC's 2020 approval of Ligado Networks' low-power terrestrial 5G network in the L-band (1525–1559 MHz) adjacent to GPS L1 caused significant controversy:

• Adjacent Band Compatibility:DOT/DoD studies found GPS receivers would suffer interference at Ligado's proposed power levels
• NASCTN Report: National Advanced Spectrum and Communications Test Network (2022) analyzed interference in detail
• Executive branch opposition: National Telecommunications and Information Administration (NTIA) raised concerns about GPS protection
• Status: FCC approval stands but implementation delayed; debate ongoing

Interference Detection

• US Coast Guard Navigation Center: Accepts reports of GPS interference
• FCC enforcement: 47 CFR Part 15 / Part 333 prohibits marketing/jamming
• Jammertest (Norway): Annual government-sponsored GPS jamming tests

Military Satellite Communications Security

Frequency Bands

Link Encryption

• AES-256: Standard for military satcom link encryption
• MIL-STD-1553: Military satellite communications data bus standard
• Type 1 encryption: Classified algorithms for classified traffic

Ground Segment Security

TT&C (Telemetry, Tracking & Command)

Satellite command and control relies on:

• Uplink command authentication: Digital signatures on ground-to-satellite commands
• TT&C encryption: AES-256 for military satellites
• S-band vs Ka-band: TT&C typically on S-band (2–4 GHz); communications on Ka-band (26–40 GHz)
• Redundant ground stations: Multiple geographically separated stations prevent single-point failures

eLORAN as GPS Backup

eLORAN (enhanced Long Range Navigation) operates at 90–110 kHz and is being developed as a backup to GPS for timing and navigation:

• High power: 1 MW transmit power; difficult to jam
• High availability: Ground-based; not affected by space weather
• Accuracy: ~10–20 m (eLORAN, vs ~10 m GPS)
• US/UK development: Continued research as national resilience backup