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Guardrail/Common Sensor (GRCS)

The Guardrail/Common Sensor (GRCS or GR/CS) is a corps-level airborne signals intelligence (SIGINT) collection and location system. It provides tactical commanders with near real-time targeting information. Key features include the following: integrated communications intelligence (COMINT) and electronic intelligence (ELINT) reporting, enhanced signal classification and recognition, near real-time direction finding, precision emitter location, and an advanced integrated aircraft cockpit. Preplanned product improvements include frequency extension, computer-assisted online sensor management, upgraded data links, and the capability to exploit a wider range of signals. The Guardrail common sensor shares technology with the ground-based common sensor, airborne reconnaissance-low, and other joint systems.

The GRCS is a tactical airborne SIGINT collection and precision targeting system. The GRCS consists of 7 RC-12X aircraft, a Guardrail Ground Baseline (GGB) exploitation and dissemination center, and a mission operations center. The mission is usually conducted with up to 3 aircraft in a synchronized constellation to optimize coverage and location accuracies at altitudes up to 35,000 feet mean sea level for durations of up to 5.5 hours. GRCS is managed by the corps it supports, while tasking may include requests from brigade, theater, and national organizations. GRCS may be deployed within hours of being tasked with an urgent/ad hoc mission supporting dynamic tasking in flight. The GRCS improves commanders' situational awareness and contributes to their understanding of the environment by providing COMINT and ELINT intercept, direction finding, precision geolocation, and special signals exploitation.

The initial Guardrail Common Sensor System (GRCS) system had integrated the improved Guardrail V for COMINT, the Communications High Accuracy Airborne Location System (CHAALS/CHALS-X) for COMINT and precision emitter location, and the Advanced Quicklook (AQL) for ELINT and precision emitter location into a single SIGINT system. Initially, the airborne elements were integrated into the RC-12K/N/P aircraft. Ground processing was conducted in the Integrated processing facility (IPF). Key performance requirements for the system included a real-time COMINT and ELINT collection and high accuracy target location capability in communications and radar frequencies. The Interoperable Data Link (IDL)/Multi-Role Data Link (MRDL) connected the airborne elements and the ground processing element. Key features included integrated COMINT and ELINT reporting, enhanced signal classification and recognition, fast Direction Finding (DF), precision emitter location, and an advanced integrated aircraft cockpit. Preplanned product improvements included frequency extension, computer assisted on-line sensor management, upgraded data links and the capability to exploit a wider range of signals.

GR/CS is an essential member of the Precision SIGINT Targeting System (PSTS). PSTS is a joint-service and defense-agency effort that uses both tactical and national systems to provide a near real-time, precision-targeting, sensor-to-shooter capability. The Guardrail Common Sensor (GR/CS). It is considered to be among the most accurate and timely of signal intelligence (SIGINT) reporting platforms.

GR/CS provides near real-time SIGINT and targeting information to Tactical Commanders throughout the corps area with emphasis on Deep Battle and Follow-on Forces Attack support. It collects selected low, mid, and high band radio signals, identifies/classifies them, determines locations of their sources, and provides near-real-time reporting to tactical commanders. The system uses an integrated processing facility (IPF) which is the control, data processing, and message center for the overall system.

Each system consists nominally of twelve aircraft which normally fly operational missions in sets of three. Up to three airborne relay facilities (ARF)/aircraft intercept communications, noncommunications emitter transmissions, and gather LOB and TDOA data. They then transmit this data to the IPF. The ARF/aircraft also serve as the relay platforms for communications between the IPF and the supported commands. The typical system configuration uses one Integrated Processing Facility (IPF), two or three Airborne Relay Facilities (ARFs), approximately nine (up to a maximum of 32) Commanders Tactical Terminals (CTTs), and an Auxiliary Ground Equipment (AGE) van. Special Purpose Equipment (STE) vans are included for maintenance and troubleshooting.

This system incorporates the Communication High Accuracy Airborne Location System (CHAALS) to achieve target locations for its COMINT system, and CHALS-X, which is a continuation of the project which developed the CHAALS precision location subsystem currently in GR/CS systems 4 and 1. The CHALS-X system provides the targeting capability required to support the Division Commander's requirements to locate and kill the enemy by providing for precise location of High Value Targets (HVTs). Airborne systems mixed with ground based systems will be capable of precisely locating enemy weapon systems and units (regardless of whether the enemy uses conventional or modern radios) producing target locations sufficiently accurate for first round fire for effect by organic artillery. It utilizes the previously developed Time-Difference-Of-Arrival/Differential Doppler (TDOA/DD) techniques and incorporates advances in electronics state of the art and distributed processing to provide for improved capabilities; increases frequency range, adds frequency hopping radios to the target set, and decreases size/weight/power requirements of processing subsystems (3 racks of computer equipment now reduced to two boxes which fit into a standard 19 inch rack). The continued evolution of Target Accuracy Geolocation capability using TDOA/DD is a technology advantage over any other country and has been restricted from release to foreign countries.

GR/CS Targeting accuracy is also provided by the ELINT system. Ground to ground (including CTT) communications links also provide an interface with fixed locations and tactical users. Automated addressing to CTT field terminals provides automated message distribution to tactical commanders in near real time. Planned improvements include expanded COMINT/ELINT collection, LPI capability, embedded training, CTT(3 channel) retrofit, and automated reporting.

The Radio Remote Receiving Set (AN/ARW-83) is commonly referred to as the Airborne Relay Facility (ARF). The ARF consists of equipment installed in a modified Beechcraft Super King Air aircraft with a military designation of RC-12. The ARFs are manned only by the pilots during a mission. ARF mission equipment is remotely controlled by operators in the Integrated Processing Facility (IPF). The Guardrail systems currently in service include the Guardrail V (RU-21H aircraft), the Guardrail Common Sensor Minus (RC-12H aircraft), and the Guardrail Common Sensor (RC-12K/N/P aircraft). Guardrail Common Sensor (GRCS) combines the Improved Guardrail V (IGRV) Communication Intelligence (COMINT) sensor package with the Advanced Quicklook electronics signals (ELINT) intercept, classification, and direction-finding capability, and a Communication High Accuracy Airborne Location System (CHAALS). GRCS shares technology with the Ground-Based Common Sensor, Airborne Reconnaissance Low, and other airborne systems.

GRCS comprises a series of special purpose detecting systems - AN/USD 9B thru E. The GRCS systems are tactical, remotely controlled, airborne mission equipment, and ground-based intercept and emitter location systems. They have an external near real-time reporting capability that can be operated in six modes (local, isolated, remote, interoperable, training, or maintenance/calibration). These systems are assigned to a B company, military intelligence battalion, aerial exploitation, as part of a corps military intelligence brigade.

The GRCS System 1, AN/USD-9C, and System 2, AN-USD-9E have the additional capability to operate worldwide via the GRCS Tethered Medium Earth Terminal (TMET) and the Direct Air to Satellite Relay (DASR) Aircraft (RC-12Q). Other major system improvements are:

  • The new UNIX-based work stations.
  • Faster (Micro 5) mainframe computers.
  • The fiber-optics distributed data interface (FDDI) local area network (LAN).
  • The GRCS Data Distribution System (DDS), elementary special signals processing.
  • The GRCS Integrated Processing Facility (IPF) rapid deployment capability (two vans minimum vice four).
  • The entire system (less aircraft) will be C-130 transportable.

Information is processed and reported to joint consumers via TRIXS broadcast primarily over the Joint Tactical Terminal (JTT) which is a subsystem of the GRCS DDS.

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