The Three-Dimensional Battlefield

byJackTodd Navigation played a key role in enabling armored units of the coalition forces to crush Saddam Hussein’s vaunted “fourth largest army in the world.” The lesson has not been lost on military planners around the world.

In the relatively flat, featureless, desert environment of the Persian Gulf, the satellite-based Global Positioning System (GPS) provided far greater accuracy than the traditional tools of compass and map. The resulting enhanced navigation capability facilitated rapid maneuver, and improved coordination of the allied forces tipped the scales and ensured victory.

However, there should be no expectation that all the battlefields of the future will be as conducive. Factory technician makes final adjustments on a to the use of space-based naviga-POS/NAV navigation system processing unit. Unlike the sat-tion assets as was the Southwest elliie-dependent Global Positioning System, POS/NAV uses Asia desert terrain. nor can com-inertial guidance and is self-contained. I manders of armored units count on external navigation systems to remain invulnerable to determined enemy countermeasures, physical as well as electronic.

III The reality is that the battlefield is threedimensional. In order to direct fire effectively, annod units must know not only their location on the earth’s surface, but also the attitude of their vehicles relative to that surface. To make sure that allied forces can fight and win in this environment, the armored vehicles of the future will need self-contained navigation systems to complement GPS and other external means. Other vehicles, ammunition loads, and metallic objects can make a magnetic compass useless at crucial times.

The benefits of land navigation systems go beyond the restraints of landmarks. In addition to obstacles imposed by the enemy, the tank commander must worry about simple errors in orientation. Should a tank deviate from its prescribed course, the leader of an advance column could lead a whole unit into confusion and possible defeat.

Inertial navigation is a technique that has demonstrated its effectiveness in other military vehicles operating in threedimensional environments. It has progressed technologically to the point where it has been accepted for installation in the U. S. kny’s new M1A2 main battle tank (JBT), which has also been ordered by the armies of Saudi Arabia and Kuwait.

In September 1992, the Aerospace & Defense Systems Division of Smiths Industries, Grand Rapids, Michigan, began delivering production units of its most advanced military vehicular navigation system to the tank manufacturer, General Dynamics Land Systems Division.

This autonomous positiodnavigation (POS/NAV) system, under development since January 1989, represents more than 12 years of development and operational experience with gyroscope-based inertial navigation for military vehicles. The basic technologies of modular strapdown systems have been validated in Smiths Industries’ Vehicle Navigation Aid System (WAS, pronounced “vee-nass”) used in more than 25 types of tracked and wheeled combat vehicles around the world and updated for the demanding challenges of the future.

POSMAV uses the powerful 32-bit Motorola 68020 microprocessor and other state-of-the-art electronics, such as Application-Specific Integrated Circuits (ASICs), to control two gyro-scopes providing pitch, yaw and roll axes information. The system is integrated into the M1A2 through an interface to the one-megabit per second MIL-STD-1553 data bus.-All hardware is hardened to M1A2 standards, and the software is written in the DOD-mandated ADA language.

Specifically designed for the M1A2 and other main battle tanks, POSMAV is an improvement over comparable earlier navigation systems in its ability to counter nuclear, biological and chemical (NBC) threats, as well as survive ballistic shock. The system is contained in a single box qualified to full military environmental specifications. It weighs 20 pounds and measures 6 x 7 x 12 inches. The electronics suite, within the POS/NAV chassis, has room for expansion to accommodate other features.

POS/NAV serves as a force multiplier by allowing armored foxmations to move rapidly toward objectives on the basis of accurate and reliable navigation data while enhancing firepower and lethality. The system provides vital information to both the tank crew and the battlefield commander. By using the Intervehicular Information Sys-the location of all MSPOSINAV-advantages over manual navigation tem (IVIS), in combination with the equipped vehicles periodically and methods: 96 percent increased accu-single-channel ground and airborne automatically updating them on the racy in reaching checkpoints, 42 per-radio system (SJNCGARS), and POS/ display. In addition, it can share tar-cent less time to complete road NAV, the commander can track the lo-geting information between elements marches,.33 percent greater success in cation of all other vehicles equipped of the force to coordinate attacks. bypassing NJ3C threats, 12 percent with IVIS and POSINAV on the Com-less fuel expended, 10 percent less manders Information Display (CID), POS/NAV allows crews to move ac-distance traveled, and 99 percent more thus improving control of armored curately at combat speeds without accuracy in position reporting. formations while moving and during a stopping to read maps or orient land-battle. The M1A2 CID provides the marks or terrain features. Preliminary information on a grid map showing results indicate the following potential Other than a one-time alignment during initial installation, no calibration or maintenance is required for the system during normal operation. Projected Mean Time Between Failures (MTBF) is about 6000 hours. The system operates through a vehicle reference unit that aligns itself to true north, computing vehicle heading and sensing attitude and motion. In the tank, the vehicle system odometer provides distance information to the POSINAV. In other vehicles, a separate sensor can be used to provide distance information.

On start-up, positioning is initialized and heading is determined through gymompassing. Heading can either be entered manually or recalled from memory at last system closedown. The memory is nonvolatile, retaining data when the system is turned off. Once the vehicle’s start position is entered into the data system, the navigation display unit reports the vehicle’s position in Military Grid Reference System (MGRS) coordinates. The system also provides grid heading in degrees. Other outputs provide information on pitch and roll angles and the vehicle’s azimuth rate. Used in conjunction with the vehicle computer, POSMAV can provide way points, target positions, and course line deviations.

POS/NAV maintains position accuracy to within 2 percent of distance traveled (20 meters per kilometer) and heading accuracy to within 1 degree per hour. The initial heading accuracy is better than 0.4 degree. This means that, when the system is updated, POS/NAV provides superior short-term attitude and position accuracy that can be critical during engagements to complement the long-term accuracy of external means such as GPS.

Based on its performance in the Persian Gulf war, it is clear that GPS has a definite place in future tank navigation systems. However, self-contained systems like POS/NAV offer at least two advantages over satellite-based systems in other combat environments.. Both the satellites in space and the antennas on the earth’s surface can be vulnerable to enemy actions. A technologically sophisticated enemy can jam satellite transmissions, and an enemy with only minimal technological capability can disable antennas with conventional munitions.. Navigation systems based on space assets are degraded if they must operate in areas out of assured line-of-sight to the satellites. This is a particularly difficult problem in a jungle environment, but it could also be troublesome in urban areas.

Another value is the threedimensional accuracy of POS/NAV in offset targeting, which derives a target map position from the known position of a vehicle and the range and bearing of the target using laser rangefinders. The 3D solution takes into account that the target may be above or below the targeting vehicle and that the targeting vehicle may not be level, thus introducing targeting errors that can be substantial at ranges of 3500 meters or beyond.

In a series of 900 computer runs conducted during 1992, Smiths Industries tested a mathematical model representing a realistic battlefield scenario: vehicle hull pitch and roll limited to pludminus 20 degrees, turret angles of pludminus 60 degrees (based on the assumption that engagements would tend to be frontal) and targeting ranges of 2500 to 3999 meters (the current operational range limit for the MIA2 laser rangefinder) based on the premise that targeting tasks may occur at ranges greater than those for engagement.

The objective was to isolate the targeting errors contributed by the lack of attitude (pitch and roll) information without POS/NAV. The results showed an average targeting error of 64 meters and a peak targeting e m of 400 meters and a more than tenfold improvement to a peak error of less than 38 meters with POSMAV.

An additional contribution from the POSMAV is in the targeting solution for the main gun. Steady improvements in the performance of the ammunition and basic gun system are providing the capability for longer range kills than the original design. With this longer range comes a need for improved computation for the ballistic solution for the gun. Computation that is not needed at shorter ranges becomes more important as engagement ranges increase. With full time pitch, and roll data from the POS/NAV, the fire control system in the M1A2 can provide dynamic cant correction to the firing solution. This permits “shoot on the move” engagements over uneven terrain while maintaining targeting accuracy. The combination of longer ranges and dynamic correction increases both lethality and survivability.

Enhanced lethality, in turn, provides advantages in two areas: the higher PK permits more effective use of ammunition and it improves crew survivability through increased range engagement, faster engagement times, and increased probability of first round hits.

Armored vehicle navigation systems of all types are now a fact of life for the armies of the world. The successful armies will be those that tailor these systems to serve as force multipliers in real world battlefield conditions.

Jack Todd is vice president for military development for the Aerospace & Defense Systems Division of Smiths Industries and is based at the company’s office in Arlington, Virginia. He is a former Army Aviator and a graduate of the Command and General Staff College and the National War College. He has served in the military in a series of Planning Strategy Development and Weapon System Evaluation activities. He is currently an associate member of the Scientific Advisory Board. His military awards include the Silver Star Medal, the Distinguished Flying Cross with oak leaf cluster, the Air Medal (33), the Bronze Star Medal, and the Defense Meritorious Service Medal.