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on board but is not available via Iridium. All communications electronics are contained in the lower portion of the electronics bay on a single circuit board, which also supports an inertial measurement unit (IMU), which is a MicroStrain (Williston, Vermont) 3DM-GX, and the electronics for the glider's depth sensor. The IMU provides heading, pitch and roll information to the navigation software and also provides Z-axis acceleration data to flter the depth-sensor signal. The existing IMU cannot be reliably used for inertial navigation due to high drift rates. Initial Development and Testing The process of determining the overall desirable specifcations began in 2005 by ANT LLC, followed by building and testing a prototype in 2006. By 2007, a full version of the glider's vehicle control software was ready for initial testing. Three prototype units of the Littoral Glider (LG) were built and designated LG01 through LG03. Initial navigation results were very poor, with the vehicle unable to hold a heading due to an incorrect IMU calibration procedure. A new calibration method and software utility was developed and implemented, resolving navigation issues. Tests also showed the reliability of the initial design of the roll control system to be poor. Several modifcations were tested before implementing the present design, which has not had problems with reliability or operation. Another problem was the reliability of the internal communications bus between the main navigation processor and the electronics bay. The glider also exhibited quality 36 st / DECEMBER 2012 control issues with leakage and damage in external cables, and with an antenna that resulted in lost communications modes. These issues have since been identifed, corrected and tested. In 2009, pilot production began, and 15 more LG units, LG04 through LG18, were built for ONR in the following two years. Applications The Coastal Gliders have logged 5,000 hours of combined fight time, and 12 of the initial 15 units are still in operation. The have been used in a variety of environmental monitoring applications. ONR Involvement. ONR has directed two gliders to Georgia Tech and three to the Navy Postgraduate School. The gliders are being modifed to incorporate acoustic sensors, specifcally Wilcoxon (Germantown, Maryland) vector sensor units. These organizations are conducting independent development of control-system modifcations to implement application-specifc behaviors. ONR has also directed two gliders to Naval Undersea Warfare Center Division Newport. Equipped with AML Oceanographic (Sidney, Canada) CTD units, one glider recently collected oceanographic information for a NASA project, operating for three days at the mouth of a fjord near Tiniteqilaaq, Greenland. During most of this testing, the glider was commanded at 1.5 knots to compensate for the expected high currents (greater than 1 knot). Power consumption was correspondingly high at 14 watts average over the fight. Approximately 32 percent of the alkaline battery was used. www.sea-technology.com