The vehicle is the largest of all of the underwater gliders (6.1 meter wing span), which is an advantage in terms of hydrodynamic efficiency and space for energy storage and payload. The glider’s primary function is to track quiet diesel–electric and the new fuel cell submarines operating in shallow-water. According to military doctrine it can “be deployed quickly and covertly, then stay in operation for a matter of months. It can be programmed to monitor large areas of the ocean (maximum ranges exceeding 1000 km with on-board energy supplies). The glider is very quiet, making it hard to detect using passive acoustic sensing” (ONR, 2006).
The vehicle was designed for easy and rapid deployment and retrieval, as well as payload carrying capability, cross-country speed, and horizontal point-to-point transport efficiency which is better than existing gliders. Liberdade XRay’s first major ocean test was performed in August 2006 in Monterey Bay, California, where it reported real-time via an 3.0 to 8.5 kHz underwater acoustic modem as well as with an Iridium satellite system while on the surface.
The vehicle had an array of 10 kHz bandwidth hydrophones located in the SONAR dome and across the leading edge of the wing. The XRay exceeded a 10 to 1 glide slope ratio (D’Spain et al., 2007). Later deployments were in the Philippine Sea, near Hawaii, and in Monterey Bay using the hydrophone array “to detect low frequency source signals, marine mammals (blue and humpback whales), and ambient ocean noise” (APL, 2007). The XRay glider is hoped to achieve 1–3 knot cruise speeds, have a 1200–1500 km range, and be able to remain on-station up to 6 months in partial buoyant glides.