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The Combat Sent's mission is to locate and identify foreign military land, naval, and airborne radar signals. The collected data is provided to the joint war-fighting and intelligence communities for further analysis. Both the RC-135V/W Rivet Joint (RJ) and the RC-135U Combat Sent (CS) aircraft are United States Air Force (USAF) electronics reconnaissance platforms. The RJ is the USAF's standard airborne signals intelligence (SIGINT) gathering platform, while the CS is designed to collect technical intelligence on adversary radar emitter systems. Both aircraft are extensively modified C-135's characterized by protruding "cheek" fairings along the sides of the fuselage forward of the wings as well as the addition of numerous antennas along the top and bottom of the fuselage. The major distinguishing feature between the two variants is the nose radome, wherein the RJ has an elongated nose while the CS has the standard C-135 nose with a protruding "chin" radome along the underside.

COMBAT SENT is an RC-135 aircraft employed as a Scientific and Technical ELINT Collection System. There are only two Combat Sent aircraft in the Air Force inventory and both are assigned to the 55th Wing at Offutt AFB. The RC-135U aircraft are manned by Air Combat Command crews from the 45th Reconnaissance Squadron and the 97th Intelligence Squadron. USAF Rome Laboratory used computers and expert systems as enabling technology to re-engineer and improve COMBAT SENT Mission Management.

The Combat Sent is composed of a wide variety of commercial off-the-shelf and proprietary hardware and software. Its current configuration allows for both manual and automatic analysis of electronic signals. By combining manual systems with the Automatic Electronic Emitter Locating System, Ravens and intelligence specialists can simultaneously locate, identify, and analyze multiple electronic signals.

The Combat Sent records these signals for future reference or for extensive analysis by electronic systems theorists. Any information garnered from the data will help determine detailed operating characteristics and capabilities of foreign systems. Evasion techniques and equipment are then developed from this knowledge that will detect, warn of, or defeat these electronic systems.

The RC-135U Combat Sent provides strategic electronic reconnaissance information to the president, secretary of defense, Department of Defense leaders, and theater commanders. Locating and identifying foreign military land, naval and airborne radar signals, the Combat Sent collects and minutely examines each system, providing strategic analysis for warfighters. Collected data is also stored for further analysis by the joint warfighting and intelligence communities. The Combat Sent deploys worldwide and is employed in peacetime and contingency operations.

All RC-135U aircraft are equipped with an aerial refueling system, giving it an unlimited flying range. Communication equipment includes high frequency, very high frequency, and ultra high frequency radios. The navigation equipment incorporates ground navigation radar, a solid state Doppler system, and an inertial navigation system that merges celestial observations and Global Positioning System data. Although the flight crew stations are similarly configured, the reconnaissance equipment is slightly unique within each airframe.

The aircraft are identified by their distinctive antennae arrays on the "chin" and wing tips, large cheek fairings, and extended tail. Crew composition includes two pilots, one navigator, two airborne systems engineers, and a minimum of 10 electronic warfare officers, or "Ravens," and six or more electronic, technical, and area specialists. A minimum of an adjudicated Top Secret security clearance, an Interim SCI, and an open SSBI (single scope background investigation) is required.

An American RC-135U reconnaissance aircraft was buzzed by a Russian Sukhoi Su-27 fighter jet over the Baltic Sea near Russia’s Kaliningrad Region 07 April 2015, according to the Pentagon, which accused the Russian pilot of coming dangerously close to the US aircraft.

“On the morning of April 7, a US RC-135U, flying a routine route in international airspace, was intercepted by a Russian Su-27 Flanker in an unsafe and unprofessional manner,” Pentagon spokeswoman Eileen M. Lainez said. “The United States is raising this incident with Russia in the appropriate diplomatic and official channels,” she added.

The official said that a Russian Su-27 (NATO designation – Flanker) passed within a half-dozen meters of the unarmed reconnaissance aircraft, whereas the Sukhoi’s wingspan is 14.7 meters. The Pentagon spokeswoman dubbed the behavior of Russian pilot “reckless” and endangering the safety of the RC-135 crew.

Major-General Igor Konashenkov, spokesman for the Russian Defense Ministry, said that the interception was launched after “Russian air defense radars spotted an unidentified air target over the Baltic Sea making steady progress toward the national border.” The aircraft had its transponder turned off, Konashenkov said. However, Flightradar24 website said the transponder was on.


Rome Lab's Expert Mission Manager is a "rule-based" automated tool which enables quick ELINT collection responses to short up-time or otherwise hard-to-collect signals. ELINT databases such as the National Signal Databases, EWO information sheets ("Raven Notes"), ELINT collection Concept of Operations and ELINT collection quality metrics, and heuristic rules are all embedded within the Expert Mission Manager to enable real-time operation.

The Expert Mission Manager operates in real-time on collected ELINT signals to

  • validate and re-identifies Electronic Intelligence (ELINT) signals
  • list ELINT collection priorities
  • recommend action based on location and priority
  • identify best geolocation of aircraft for optimum ELINT collection
  • recommend what assets to to tune for the collection.

This capability provides the ELINT Mission Coordinator with the tools to effectively direct the ELINT collection effort aboard the COMBAT SENT aircraft -- making sure that high priority, new or unknown signals are properly collected for detailed analysis.

Rome Lab's Expert Mission Manager program is sponsored by the Air Force's Consolidated Cryptologic Program for ELINT Analysis Techniques. The objective of this Consolidated Cryptologic Program effort is to apply advanced processing techniques to the COMBAT SENT aircraft in order to improve COMBAT SENT mission collections by automatically processing all the knowns and usuals -- leaving the more difficult signals and unknowns to the on-board personnel.

The COMBAT SENT Operator Workstation Upgrade procures and installs high resolution operator displays to improve target detection and signal recognition. Wide band fiber optic base audio distribution network to all operators. Wide band, high capacity COTS audio recorders. High capacity, digital, reprogramable, wideband demodulators and processors. Current display resolution is insufficient to allow accurate signal detection and recognition of modern modulation target signals. Several current target emitters exceed the bandwith of the current audio distribution system, resulting in unintelligible audio output. Several receiver outputs are routed to specific operator positions, limiting flexibility in responding to theater driven dynamic target environments. Bandwidth and capacity of current recorders is exceeded by an emerging class of wideband modern modulation target emitters. Bandwidth and capacity of current signal demodulators is exceeded by an emerging class of wideband modern modulation target emitters. Current demodulators are not reprogramable. It is expensive and time consuming to reconfigure them to process different target emitters.

Re-engining of RC-135 aircraft with CFM-56 engines modifies the airframes to support re-engining. This effort decreases cost of ownership and increases operational capability by installing new, fuel efficient engines. Reduces maintenance manpower and logistics costs; the new is more reliable than the current engine, and the engine is common with the AMC KC-135 fleet. Extends unrefueled range and time-on-station, and permits operations at higher altitudes, increasing airborne sensor field of view and effectiveness. Increased altitude range provides flexibility to airspace planners integrating aircraft into conjested airspace just behind the FEBA. Decreases dependency on tankers for air refueling. Provides capability to takeoff on shorter runways at increased gross weights. Facilitates two-level maintenance concept reducing costs by 32%. Supports improved aircraft environmental system prolonging sensitive sensor life.

COMBAT SENT Cockpit Modernization includes the COMBAT SENT in the Air Force PACER CRAG initiative to upgrade the C-135 fleet cockpit, and installs the GATM/FANS avionics required to operate in the evolving civil air structure. PACER CRAG installs new compasses, radar, multi-function displays, and global positioning system/flight management system. New fuel panel, Mode S IFF, TCAS, precision altimeters, and DAMA compliant, 8.333 KHz channel radios are included in this upgrade. Provides COMBAT SENT aircraft commonality with the C-135 fleet for training, logistics, and parts. Eliminated "vanishing vendor" problems associated with diverging from the KC-135 avionics. Permits aircraft to comply with ICAO navigation and communication standards to operate in the trans-oceanic and European portions of the commercial air structure. Improves safety, reliability, and maintainability of aircraft. PACER CRAG kits/generic installation funds provided by AMC. Aircraft will be denied access to increasing portions of civil air space without proper navigation/communications equipment. Current avionics systems will become unsupportable as KC-135 migrates to newer equipment. Commonality will be lost with the rest of the C-135 fleet. Common parts supply base will not be available.

COMBAT SENT Calibration Systems replaces obsolete and unsupportable components of the Emitter Source Van (ESV) and the Portable Calibration Van (PCV) used to generate test signals to calibrate aircraft antenna and RF distribution system. Provides modern modulation capability and millimeter wave frequency calibration. Returns aircraft system calibration accuracy to required level. It replaces failing components of the ESV and PCV. Modernizes computer assets which have become obsolete and unsupportable. Provides modern modulation capability to enable test and calibration of systems designed to exploit frequency agile, coded pulse, and coherent radar weapon systems. Provides high frequency millimeter wave calibration signals. COTS computer systems used in both ESV and PCV will become unsupportable in the FY05-06 years. Sensors designed to exploit modern weapon systems must be calibrated against similar signals to ensure accurate measurements. Increasing use of millimeter wave frequencies in direct threat systems makes calibration critical for weapon system characterization.

COMBAT SENT Wideband Acquisition/Frequency Hopping Receiver System (FHRS) provides wideband acquisition and frequency hopping receiver system (FHRS) capability for exploitation of frequency agile threat systems. Builds on previous efforts to provide unique capability for precision measurement and exploitation of modern, frequency agile radar. Uses shared antennas and pooled computer assets with high speed, JASA compliant network to integrate existing reconnaissance systems with wideband receiver and de-hopping systems. Allows real-time acquisition and exploitation of frequency-agile threats. Enhances probability of intercept for LPI systems and increases tip-off capability. Will enhance the unique capability to intercept and exploit radar transmission characteristics to include modern frequency-agile threats. Enables collection of data essential for electronic warfare system reprogramming and design. Modern threats are increasingly using frequency agility to counter fielded systems. These threat systems cannot be adequately characterized by existing collection systems. This increases the margin of error required to be used in mission and route planning, as well as increasing the cost of LO, HARM, and electronic warfare system design because of the inability to accurately characterize the threat system.

COMBAT SENT RF Distribution System Improvement procures and installs antennas and RF distribution system capable of intercepting frequency agile radars. Redesigns wing RF distribution system to permit installation of new RC-135 engines. Enhances power, beam pattern, and polarization (P3) collection on narrowband signals. Expands collection system field of view, increases sensitivity and implements standard data links for increased cross-platform cueing, near-real-time reporting, and tactical support capabilities. Installs industry standard ID-1 wideband recorders. Implements common aperture RF distribution/fiber optics (CARF) to allow re-engining and collection of frequency hopping radars. Enhances P3 collection by adding improved near-real-time processing and reporting along with narrowband collection capability. Allows near-real-time reporting and cross-platform cueing through common data links (TADIL-J/TIBS). Increases training and collection capacity through improved carry-on terminals. Increases ability to exploit wideband threats through higher bandwidth recorders. Cannot reinstall P3 collection system after re-engine without common aperture RF distribution/fiber optics (CARF). CARF allows 360° field-of-view and exploitation of frequency hopping radars. Improved processing and communication provides enhanced cross-platform tip-off, and P3 information in near-real-time for mission planning and threat avoidance. Operator workload is reduced by enhanced P3 system automation, data management, and reduced complexity allowing operation in more complex, more diverse threat environments.

The RC-135 Operational Systems Development and enhancement activities project supports design studies, engineering analysis, non-recurring engineering, and other efforts associated with the integration and modification of the RC-135 programs and their specialized mission systems -both air and ground. Extensive utilization of commercial-off the-shelf (COTS) based solutions allows rapid fielding of needed capabilities through continuous technology refresh cycles and diminishing manufacturing sources (DMS)/vanishing vendor items (VVI) logistics mitigation efforts.

The results of these efforts provide for preliminary assessments of technical feasibility, operability, or military utility as well as specific engineering implementations for integration into the various systems baseline configurations. These activities are managed by the Air Force through the 645th Aeronautical System Group (645 AESG, a.k.a. BIG SAFARI Systems Program Office or SPO), Aeronautical Systems Center, Air Force Materiel Command, Wright Patterson AFB, OH. BIG SAFARI manages engineering, ground and support systems modifications, integration, flight testing, product assurance, acceptance testing, logistics, and training activities.

Aircraft, aircraft sensor systems, and associated ground support system engineering planned for FY13 include support for two distinct RC-135V/W RIVET JOINT configurations [Baselines 11 & 12], two distinct RC-135U COMBAT SENT configurations [Baselines 4 & 5] and two distinct RC-135S COBRA BALL configurations [Baselines 4 & 5].

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Page last modified: 11-04-2015 20:15:44 ZULU