By John McHale
MIDDLETOWN, R.I. — Engineers at KVH Industries are designing a fiber optic gyro (FOG) sensor upgrade to their TACNAV navigation devices that ride in vehicles such as the U.S. Army Bradley Fighting Vehicle and the U.S. Marine Corps Amphibious Assault Vehicle 7 — better known as the AAV7.
The new T FOG Navigator inertial measurement unit is based on the FOG technology KVH officials purchased with their acquisition of the Fiber Optic Group of Andrew Corp. of Chicago in 1997, says John Manning, military sales manager at KVH.
The purchase and the release of FOG products now enables KVH officials to compete with the likes of Allied Signal, Litton Industries, and Honeywell in the navigation systems market, Manning says.
Preliminary performance specifications show the T FOG Navigator improves TACNAV pointing accuracy from 35 mils to 10 mils. This new integrated odometer/compass/gyro affords improvement of as much as 300 percent in global positioning system (GPS) accuracy.
FOG interfaces with GPS to deliver reliable, accurate navigation and targeting capabilities at a lower cost than traditional inertial systems, company officials say. The FOG device will start at about $15,000 compared to $30,000 to $35,000 for competing products, Manning says.
Blending GPS and inertial measurement units is a natural choice because each device compensates for weaknesses in the other.
The accuracy of GPS, for example, degrades when vehicle angle or terrain blocks one or more signals from the GPS satellites. Inertial systems, likewise, lose accuracy over time — which is called precession.
Yet when designers blend GPS and inertial systems, the inertial system can update GPS when signals are blocked, and GPS can periodically update inertial systems to compensate for precession.
The FOG system will improve heading accuracy, improve stability, and ensure the continuous delivery of attitude and azimuth functions on quickly maneuvering armored vehicles, KVH officials claim.
KVH designers have improved their series of solid-state FOGs by reducing the device`s size, weight, and power consumption, and by boosting its accuracy, KVH officials claim. KVH FOGs also have no moving parts to wear out. These characteristics make the devices suitable for applications such as train tracking, precision farming, and military vehicle navigation and stabilization, KVH officials say.
FOGs remain stable even when temperatures and time zones vary, and the rapid turn-on capability makes the system quickly available to users. Yet armored vehicles offer one of the most immediate benefits these devices can offer to military systems designers.
The ability to fire on the move, for example, is crucial for today`s fast-paced military operations. This ability requires precise turret stabilization. KVH FOGs feature greater accuracy and long-term durability than the mechanical gyros that typically have been used to stabilize turrets, and at nearly half the price, KVH officials claim.
The United Defense LP M2A3 Bradley Fighting Vehicle used TACNAV during the U.S. Army`s Task Force-21 Battle Command Brigade and Below (FBCB2) program.
While the onboard GPS is each vehicle`s primary source for location data, KVH`s TACNAV system will provided 100 percent position availability and essential backup.
TACNAV integrates magnetic headings and GPS data to deliver constant, positioning and targeting information. It can interface with the vehicle`s new or existing systems, including the odometer, turret angle encoder, laser rangefinder, and/or GPS to provide interactive navigation and far target location information.
TACNAV also integrates data from the vehicle`s odometer and heading sensor to generate accurate dead reckoning data should the GPS fail due to intentional, geographic, or catastrophic reasons. As a result, crews are ensured complete availability of essential tactical navigation data, even if the GPS is blocked, jammed, or disabled.
The TACNAV`s GPS is from Rockwell Collins in Cedar Rapids, Iowa. The first Marine Corps AAV7 using TACNAV Light rolled out earlier this summer, Manning says.
The basic TACNAV Light system provides continuous heading data to vehicle drivers with the smart electronic compass detecting and compensating for any distorting effects of the vehicle.
