Which statement is NOT a reason for the resilience of GPS against attacks in space?

• A. The GPS satellites have significant shielding against both kinetic and directed-energy attacks, and the ground antennas are highly defended.
• B. The satellites are designed to be semi-autonomous; they can go for days to weeks without ground support, and then they degrade gradually.
• C. Some receivers are designed to use alternative sources, e.g., Galileo, GLONASS, and Beidou.
• D. Terrestrial backups, such as VOR radio beacons, LORAN-C, surveying equipment, and atomic clocks, exist for many applications.

Answer: (A)

Resilience here comes from redundancy and the ability to keep operating even when parts of the system are compromised. GPS is designed as a large constellation so if some satellites are affected, others can continue providing coverage. Onboard fault management lets satellites function for extended periods without immediate ground support, so service can persist even during disruption. Receivers can also supplement GPS with signals from other GNSS constellations like Galileo, GLONASS, or Beidou, improving availability if GPS is degraded. Terrestrial backups such as VOR beacons, LORAN-C, and precise time sources provide alternative navigation and timing references when space assets are challenged.

The idea that resilience comes mainly from significant shielding of satellites and highly defended ground antennas isn’t how the system stays usable under space threats. Shielding adds mass and isn’t a guaranteed safeguard against space-based attacks, and defending ground stations against space threats isn’t the primary driver of GPS resilience.