The Global Positioning System (GPS) provides critical timing and positioning information world–wide. An emerging mode of attack is spoofing, which aims to “high jack" a receiver by sending it erroneous navigation information via fake GPS signals. Unlike GPS jamming attacks which are high-power and hence easily detectable, spoofing can often go unnoticed by the targeted receiver, rendering its Position, Navigation and Timing (PNT) solutions unreliable. Here we present an array–based spoofing detection and mitigation prototype, and report results from live sky trials.