Defense Technology International - January/February 2008 - (Page 40) PATROL MARITIME GA-ASI BAMS requirements have pushed Lockheed Martin and General Atomics to increase the wingspan of the Mariner UAV, along with greater weight and payload. vy’s budget rules out a new UAV. It was therefore not surprising that the first contenders in the race were the two U.S. endurance UAVs, the General Atomics Aeronautical Systems Inc. (GA-ASI) Predator B family and Northrop Grumman’s Global Hawk. Northrop Grumman is the prime contractor for the RQ-4N program, while GA-ASI supplies the Mariner UAV to Lockheed Martin. Last summer, Boeing threw its hat into the ring with a di erent proposal: an unmanned version of the Gulfstream G550 business jet. This leaves the Navy with a range of choices. The RQ-4N is well over twice the weight of Mariner, and the G550 is almost three times heavier than the RQ4N. Mariner has a turboprop engine and operates around 45,000 ft.; the RQ-4N cruises around 60,000 ft. and the G550 at conventional-jet cruising altitudes. The G550 is by far the fastest of the three, but even with substantial extra fuel it is unlikely to match the endurance of its slender-winged rivals. Industry has improved its proposals under competitive pressure. The RQ4N is based on USAF’s RQ-4B Block 20 platform, but has a new suite of sensors. The most important of these is a specially developed radar, the Multi-Function Active Sensor (MFAS) from Northrop Grumman’s radar group. MFAS is an active electronically scanned array (AESA) radar, but with a mechanical 360-deg. azimuth scan to provide the desired all-round field of regard. It is an Xband radar and uses the same modules as the company’s radars for the Joint Strike Fighter, F-16E/F and F-22. The 40 decision to go with an AESA, Northrop Grumman says, was driven by the need for reliability and growth. The RQ-4N’s infrared sensor turret is based on the AN/DAS-1 Multi Spectral Targeting System B developed for the Reaper, with its very large optics for longrange target identification. Sierra Nevada Corp. is providing the Merlin electronic surveillance measures system. One device on all the BAMS platforms is an interrogator for the Automatic Identification System (AIS), originally intended to avert collisions and aid in rescue operations. It is mandated for passenger ships, and ships over 300 tons (some 40,000 vessels carry AIS). The AIS transmits the GPS position and identification of the ship, and the BAMS mission systems fuse that data with the radar image. AIS data can be correlated with a database showing the ship’s design, history, registered owner and recorded sailing plans. If the radar image does not match the ship’s supposed identity, or if the ship is in the wrong place or has a history of nautical shenanigans, it’s a target for investigation. The RQ-4N retains the primary Kuband satellite data link of the Global Hawk, but adds Inmarsat (also used on the P-8A) and the ability to use X-band and Ka-band wideband satcoms. The RQ-4N will have a nose-mounted, offthe-shelf radar to detect air tra c. The shore-based pilot will monitor the radar to meet air tra c authorities’ requirements to “sense and avoid” other tra c under all weather conditions. Northrop Grumman claims that the RQ-4N meets the Navy’s threshold time-on-station requirements with two aircraft rather than three, and that three aircraft will provide 80% coverage at 2,870 naut. mi. Lockheed Martin and GA-ASI have scaled up the Mariner UAV since the early days of the competition, reflecting the need for speed, range and capable sensors. The 88-ft. wing is one-third larger than Reaper’s, tail surfaces are larger and the payload bay is bigger. Takeo weight has been bumped by 2,500 lb., to 13,000 lb., and the total payload is up from 3,750 lb. on the Reaper to 5,350 lb. on Mariner (almost equal to the 5,600 lb. of the RQ-4N). Wind tunnel tests of the larger vehicle were carried out last summer. The team claims an e ective time on station of 94% at 2,000 naut. mi., reducing to only 90% if a low-altitude identification segment is involved. From the outset, Lockheed Martin has insisted that the Mariner’s turboprop propulsion, more e cient at low altitudes than Global Hawk’s turbofan, is best for BAMS. Northrop Grumman counters that the Global Hawk has the rate of climb and descent necessary to drop to low altitude to identify a ship below a cloud deck. The problem with that, regardless of platform, is the system loses its wide-area view. By the time it regains altitude, targets have moved and their identity must be verified again. The Mariner’s radar is the Elta EL/ M-2022A, a lightweight (200-lb. class) conventional radar with SAR and ISAR features, carried in a pylon-mounted ventral radome. The IR turret is the Star Safire from Flir Systems. Boeing makes strong arguments in favor of a literally “unmanned” aircraft. One is that the G550, as a commercial aircraft, is designed with higher levels of redundancy and reliability than any UAV. Boeing says the G550 is the right size for the mission, given the performance and sensor capability the Navy wants. With auxiliary fuel the G550 will meet the Navy’s time-on-station requirements “with margin,” Boeing says. Greater speed allows the G550 to cover a given area in less time than its competitors, and to revisit it more frequently. The BAMS mission is not like a Reaper mission, where the goal might be to maintain continuous surveillance of a small area. BAMS is designed to maintain persistent coverage only of suspicious targets. “Unmanning” a piloted aircraft is not as simple as it sounds. The G550 has a sophisticated flight management system (FMS), which, even in commercial operwww.aviationweek.com/dti DEFENSE TECHNOLOGY INTERNATIONAL JANUARY/FEBRUARY 2008 http://www.aviationweek.com/dti
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