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Aerial Common Sensor: The Eyes and Ears of the 21st Century Warfighter

by Lieutenant Colonel Thomas D. Smart (USA, Retired)

The primary business of the Army is to focus its warfighting capabilities at a given time and place to achieve a military objective. The Army’s ability to do that depends largely on each ground com- mander’s ability to “see” the battlefield. The commander must know with real-time certainty and a high degree of confidence where both friendly and enemy forces are, accurately interpret enemy intent, and operate within the enemy’s decision cycle.

Gaining Information Dominance

This ability to gain information dominance—to achieve battlefield situational awareness—is a prominent and well-documented goal, clearly outlined in Joint Vision 2010 and Army Vision 2010. As we build Army XXI and shape the Army After Next, we continue to invest heavily for its attainment.

The Army ground commander has a wide array of platforms and sensors on which he can draw to “see” his battlespace and to gain information dominance. These include organic assets, national assets provided through the Tactical Exploitation of National Capabilities (TENCAP) systems, and joint assets such as the E-8 Joint Surveillance Target Attack Radar System (Joint STARS), RC-135 Rivet Joint, and the U2. The most robust organic capability, however, resides in the Army’s airborne sur- veillance and reconnaissance assets: Guardrail Common Sensor (GRCS) and Airborne Reconnaissance Low (ARL). For Army XXI and the Army After Next, the capabilities of the GRCS and ARL will combine in a single platform, the Aerial Common Sensor (ACS). ACS, like its predecessors, will be one of the most responsive and prolific contributors to tactical commanders’ knowledge of their battlespaces.

The GRCS and ARL Legacy

The Guardrail system has been the Army’s workhorse for airborne signals intelligence (SIGINT) collection for more than 25 years. Over this period, several versions of the Guardrail have been developed and fielded, each system providing the tactical commander an enhanced capability. Three variations of the current system, GRCS, are operational today. The Army will field the final and most capable GRCS system to III Corps’ 15th MI Battalion in 1999.

The GRCS provides near- real-time SIGINT and targeting information to tactical commanders throughout the corps area. Each system consists of 6 to 12 RC-12 Guardrail aircraft, which normally fly operational missions in sets of two or three. Processing of the collected signals is performed on the ground by the Integrated Processing Facility (IPF). Interop- erable datalinks provide the connectivity between the airborne systems and the IPF. The Commanders Tactical Terminal (CTT) or Joint Tactical Terminal (JTT) accomplishes near-real-time reporting.

The ARL grew from a Com- mander in Chief U.S. Southern Command (SOUTHCOM) urgent requirement for a low-cost, low profile airborne system to aid in the detection and monitoring of illegal drug traffic. Initially fielded in communications intelligence (COMINT) and imagery intelligence (IMINT) (ARL-C and ARL-I, respectively) variations, the multifunction ARL-M combines these capabilities. It provides the commander with varied imagery capabilities:

Although all ARL-Ms are configured for a COMINT capability as well, only two ARL-Ms will be equipped with the Superhawk COMINT subsystem. Although there are requirements for nine ARL aircraft, funding is available for only eight.

The Army’s airborne reconnaissance systems provide the ground commanders with an unmatched ability to conduct surveillance and reconnaissance in their areas of operation and across the entire electromagnetic spectrum. The V Corps’ 1st MI Battalion flies daily GRCS missions in support of Operation JOINT FORGE. Since deploying in December 1995 (and as of September 1998), they completed more than 2,400 sorties, achieved 14,000 accident-free flying hours, and generated more than 5,000 intelligence reports. The U.S. Army Intelligence and Security Command’s (INSCOM) 3d MI Battalion in Korea flies nightly indications and warning missions an average of 27 days per month using the ARL-M’s MTI and SAR sensors. The ARL-I and ARL-C platforms assigned to INSCOM’s 204th MI Battalion continue to operate throughout SOUTHCOM in support of the counterdrug mission.



Why ACS?

Why should the Army invest scarce resources in an enhanced aerial surveillance and reconnaissance capability, currently planned for fielding in 2009? Why not rely on enhancements to current Army systems and the systems of the other Services, such as Joint STARS, EP-3E Aries II, Rivet Joint, the Predator medium-altitude endurance (MAE) unmanned aerial vehicle, national systems, and future high-altitude UAVs such as Global Hawk?

To be sure, each has its place on the battlefield, and each fits into the overall reconnaissance, intelligence, surveillance, and target acquisition (RISTA) scheme. The final answer, however, lies primarily with the fact that we will design and build ACS, like its predecessor systems, to support the tactical commander on the ground. ACS will be an all-weather responsive intelligence, surveillance, and reconnaissance (ISR) capability dedicated to supporting Army tactical requirements. ACS will provide unique precision locations to support the deep targeting of Army weapons systems. The system will be capable of sustaining a continuity of coverage during periods of high operating tempo, maintaining a high level of reliability at an affordable cost, while supporting the production of predictive, timely intelligence.

The Aerial Common Sensor represents a logical migration path from the legacy systems. Combining the capabilities of GRCS and ARL into a single platform will give ground commanders an unprecedented ability to know and understand their battlespaces. The ACS design will include the internal ability to cross-cue sensors and conduct multisensor correlation, thereby providing immediate con- firming information.

 Like its predecessors, ACS will be a standoff system. This characteristic not only enhances the survivability of the aircraft and its crew, but also permits the aircraft to fly at the appropriate altitudes to optimize sensor performance and cover the extended area required by a corps. The ACS design will permit it to operate as a system with tactical UAVs, giving the commander flexibility for situations where an overflight sensor is required or when the threat situation dictates an unmanned platform.

Today, the GRCS is the only DOD aerial platform able to provide precision geolocation of targets using time differential of arrival and differential Doppler, giving an unequaled targeting capability for precision-guided munitions. ACS will expand this capability through improved collection and processing with organic SIGINT sensors and by dynamically interacting with national systems. The result will reduce targeting circular error proba- bility, increase the number of targets identifiable at a given time, and enhance the ability to locate and track short duration and moving emitters. The latter functionality is not available with single platform, long baseline systems.



Army airborne surveillance and reconnaissance assets are an active component of the tactical commander’s battlefield. They are an integral part of operational, targeting, and movement planning and are capable of supporting scenarios across the full range of military operations. These aerial assets are significant and direct contributors to Force XXI corps operations and relate directly to the imperatives in Army 2010. Specifically, they enable commanders to operate throughout the depth, width, and height of their areas of operations. These airborne collectors:

System Overview

ACS will consist of three major component groups. They are the Ground Processing Facility (GPF), the Airborne Platform Subsystem (APS), and a modular, reconfigurable suite of sensors, processors, and reporting equipment known as the Airborne Mission Equipment Subsystem (AMES).

GPF. The GPF will evolve from the mini-IPF, an enhancement currently under development for GRCS. The deployment of the mini-IPF will address the significant shortfall in the ability of GRCS to deploy rapidly. The GPF will be a tailorable, scaleable, modular, and C-130 Hercules transportable, intelligence processing system. The function of the GPF will be to control Army and the other Services’ airborne sensors and direc- tion-finding systems. It will receive, process, display, and generate SIGINT- and IMINT-derived intelligence reports and rapidly disseminate these reports to ground commanders at all levels.

The GPF will be compliant with both Joint Airborne SIGINT Architecture (JASA) and Joint Interoperable Network (JOIN). It will interoperate with the TENCAP Tactical Exploitation System (TES).

With a modular configuration and small footprint, both the near-term mini-IPF and the objective GPF will give the tactical commander a responsive, deployable, expandable analysis and dissemination cap- ability. Satellite communications (SATCOM) links will permit analysis in sanctuary for early entry op- erations and will enhance the dissemination of refined products.

APS. The ACS Airborne Platform Subsystem will be a non-developmental aircraft. The essential operational parameters for the airframe include:

The aircraft will also be equipped with workstations for conducting initial onboard analysis. The ACS will have a common datalink (CDL) capability for communicating air- to-air and air-to-ground for ACS-UAV operations, as well as connectivity to tactical operations centers and sanctuary processing centers (Regional Security Operation Centers).

AMES. The primary mission of the ACS Airborne Mission Equipment Subsystem will continue to be to locate, identify, and produce targetable precision geolocation information on high-payoff threat signals and to provide that information to the tactical commander in near-real-time. The AMES suite will include DOD-compliant SIGINT, IMINT, and measurement and signature intelligence (MASINT) sensors. They will be able to operate against the most sophisticated threat technologies of the future. Many of these technologies will be openly available in the commercial market, resulting in a proliferation of inexpensive, difficult-to-defeat communications and electronic systems in the hands of potential adversaries.

The ACS will support the corps commander, but will have the capability to support ground commanders at all levels. Based on the corps commander’s priorities, it could provide a “pull” system to respond to queries of specific interest to lower echelon commanders. Needed information, such as images of a specific road junction, could come from established databases or directly from mission aircraft. Much of the collateral locational information that is currently not used is valuable to the shooter and could be provided to them directly via the Intelligence Broadcast Service (IBS) and Global Broadcast System (GBS). There is no reason why an Army Tactical Missile System (ATACMS), an attack aircraft, or a light-force battalion commander engaged in a peacekeeping operation could not receive real-time data within a set of parameters defined by the commander or crew.

Bottom Line

“Where am I?” “Where are my friends?” “Where is the enemy and what is he doing or going to do?” The commanders who can answer these questions clearly will have a tremendous advantage. They will be able to concentrate forces at locations and times of their choosing while accepting informed risk elsewhere. Ultimately, they will be able to focus combat power to destroy the enemy and protect their own.

The Army’s ACS, like its legacy systems GRCS and ARL, will make a vital contribution to the commander’s comprehensive awareness of the battlespace. It will give the ground commander an organic, responsive capability that (in conjunction with the assets of the other Services and national means) clears away much of the “fog of war.” ACS and its predecessors are integral and vital to achieving information dominance today and in the foreseeable future. ACS will be the eyes and ears of the 21st century commander.

Lieutenant Colonel Tom Smart (USA, Retired) was commissioned in armor and served in a variety of armor, cavalry, and staff positions culminating as a member of the Louisiana Maneuvers Task Force and the Center for Land Warfare. He is a graduate of Gettysburg College with a Bachelor of Arts degree in Psychology and has a Master of Business Administration degree from Florida Institute of Technology. He is currently a Project Manager with SY Technology, Inc., supporting Product Manager ACS. Interested readers can contact the author via E-mail at, or telephonically at (703) 769-1406.