Military

New Sensors are Force Multipliers

By Geoff Fein | May 1, 2007

The global war on terrorism, shoulder-fired rockets and threats the military hasn’t even thought of yet are in part helping drive advances in sensor technologies.

Raytheon, Northrop Grumman, Lockheed Martin and BAE Systems are developing technologies that will not only provide advanced capability for the challenges of the new global threat environment but will also widen the battlefield by enabling the passage of data to ground forces and sharing of data among multiple platforms and coalition partners.

The U.S. military has a lot riding on these advances. Besides the hundreds of millions of dollars invested in development and testing, many are part of what the Air Force and Navy are counting as fifth-generation fighters. Some of these technologies are close to being deployed and others already are equipped on aircraft in operation.

Raytheon’s APG-63(V)2 Active Electronically Scanned Array (AESA) radar is fielded on 18 F-15Cs in Alaska. Also, the Air Force is installing APG-62(V)3 systems on upward of 48 Air National Guard F-15Cs, and is looking to broaden that effort to include 160 additional aircraft.

The Air Force also is planning to install AESA radars on its F-15Es. The system is installed on the F-22A Raptor, and will be included on the F-35 Joint Strike Fighter (JSF). Raytheon also is developing a system for the Global Hawk unmanned aerial system (UAS). Additionally, the Navy is testing the APG-79 AESA on its F/A-18E/F Super Hornet. A classified report on those tests was published in March.

The military and radar manufacturers say AESA radars improve reliability and survivability. The radars have no moving parts, and instead rely on an array with solid-state transmit and receive modules, which also reduces lifecycle costs.

At the time same, AESA radars, when operating in concert with other systems like digital radar warning receivers on the host aircraft, could transmit data in a manner that has a low probability of being detected by enemy sensors, although this "is more of a challenge," said Michael Henchey, Raytheon’s business development director for radar programs. Such transfers are critical for stealth platforms to evade being detected.

Raytheon, which designed and built the first operational AESA radar in 2000, is reorganizing its AESA team for the second time in two years. The team has been combined with the electronic warfare (EW) group to become Tactical Airborne Systems. In 2005, the company combined the Navy and Air Force programs because they had been experiencing a spiral and sharing of technology, Henchey said.

The reorganization made sense, Henchey said, because of the huge synergies involved when moving to digital electronic systems between the radar, the radar warning system and the onboard jammer, all comprising the EW suite.

"Now you have systems that are digitally linked. You are providing some sort of high-speed interface, be that fiber channel or however you mechanize that, but you have a direct link," Henchey said.

Linking the EW suite and AESA allows pilots to use the radar to transmit and receive in an EW sense, Henchey said. "Of course you have to work in the band of the radar, but you have a high-power transmit and receiver that provides great capability and can be used to do a couple of things from an EW standpoint," he said. "You can transmit to either protect yourself or provide a capability against a threat that would allow a separate platform to employ."

The combination of technologies brought another added benefit to AESA — the ability to move synthetic aperture radar (SAR) maps at very high rates of speed, a task that had been a problem until this point, Henchey said.

In December, Raytheon and partner L3 Communications demonstrated the ability to make a SAR map of the ground and transmit it at 274 megabytes per second. Henchey said they could go beyond that.

"Previously you couldn’t do that all," Henchey said. "That means we took that map, sent it to a ground station, did the processing at the ground station as maybe a rear command and control facility might do, and identified targets, things and points of interest, and then sent it back to the airplane," he said.

"What does that do? All of a sudden, when you can send that kind of data, identify it and send it back, you’ve created the network we keep talking about and are trying to get to," he said. "All of a sudden you have shared data. Everybody has the picture and now you have a network." It will be possible to have the platform collect the data even without telling the pilot to do it, Henchey said.

"When it’s under a tenth of a second, the aircrew doesn’t even have to bother with that. So now you have a game-changing situation because you no longer have a data rate problem," Henchey said.

The Air Force Research Laboratory (AFRL) tasked Raytheon with developing the protocols and standards so all AESA radars will be able to move data seamlessly between platforms.

Multi-Platform radar

Northrop Grumman is building upon active arrays for fighter aircraft, inserting a technology to improve surveillance capability. The company has partnered with Raytheon on the Multi-Platform Radar Technology Insertion Program (MP-RTIP), an effort to build the next generation airborne surveillance radar for multiple platforms.

MP-RTIP began as an upgrade to the Air Force’s Joint Surveillance Target Attack Radar System (JSTARS) program. It eventually transitioned to the EA-10A, and then Global Hawk was added to the mix, said Pat Collins, Northrop Grumman MP-RTIP manager.

Right now, MP-RTIP is focused on the larger, manned EA-10A aircraft under the E-10A Wide Area Surveillance and MP-RTIP. That effort is scheduled for its initial test flight in 2010. MP-RTIP allows a much more dynamic use of the radar. Whereas traditional radar can perform moving target indication and then switch to SAR, MP-RTIP will provide the capability to do both simultaneously.

"The standard surveillance system you have out there today in Global Hawk and JSTARS are antennas that have one degree of steering electronically," Collins said. "This [system] has TR [transmit/receive] modules, which provide for steering in all directions instantaneously. Because you have much more dynamic control over where the radar beam goes and how it gets steered, you have a much more robust capability."

Collins said the Air Force spent millions of dollars developing radar arrays that use TR modules. The modules are very similar among all active electronically scanned radars, so the radar found on the F-22A Raptor and JSF are very similar, he said.

Having hardware that is similar among fighter planes, and Northrop Grumman’s use of an open architecture, provides the ability to think not only of future developments but any developments that get done in the active array field, Collins said.

Northrop Grumman designed MP-RTIP in building blocks. If, for some reason, the company needed to decrease the size of the antenna, it could be done without redesigning the whole system, Collins said.

"It is modular and expandable. It’s got a lot of components to it that are modular and scalable for different size platforms. The E-10 has 23,000 modules," he said. "It’s the same component that goes into Global Hawk, that goes into the Wide Area Surveillance Radar, there are just more of them."

Northrop Grumman also is developing MP-RTIP for the most recent version of the Global Hawk UAS, the Global Hawk Block 40. The Block 40 system that employs MP-RTIP is part of the Block VII Global Hawk production line. Northrop Grumman expects a contract to build those radars this year, Collins said. Each lot will have three MP-RTIP systems.

In September, the company conducted its first flight of the Global Hawk MP-RTIP aboard a high-altitude Proteus UAS. The system was tested in both its moving target indicator and SAR modes.

Under the current phase, Northrop Grumman has an $800 million MP-RTIP contract to build and test both radar systems for the Air Force, Collins said.

There is money in the fiscal 2008 budget for the Global Hawk variant of MP-RTIP, and the completion of development for Global Hawk is funded in FY’08 and FY’09.

"[Funding] to build production units comes from [the Global Hawk program] and that is funded in every year going forward that [the Air Force] has a budget for," Collins said.

The unmanned effort for NATO will use the Global Hawk Block 40 with MP-RTIP. The NATO manned aircraft program, based on an Airbus A321, uses a unique design being developed by a joint venture known as the Transatlantic Cooperative AGS Radar (TCAR). Northrop Grumman is part of that effort, said spokesman James Stratford.

Passive geo-location

Last fall, BAE Systems successfully completed its first test flight of a new passive geo-location capability that enables aircraft to identify enemy positions in crowded radio frequency environments.

"Geo-location is sort of the Holy Grail of electronic warfare in terms of being able to precisely locate where the emitter is," said Hugh Kao, BAE Systems technical director for electronic warfare programs.

Geo-location has traditionally been done by specialized platforms whose mission has been to locate emitters and collect information in order to build up an electronic order of battle, Kao said. Getting a very precise location in order to drop a weapon on a site requires multiple platforms. To get a near instantaneous location on an adversary requires a minimum of three platforms, Kao said.

"We demonstrated a multi-platform geo-location technique that could be very easily implemented on multi-purpose aircraft like fighters and so forth," Kao said. "It does not have to be a special mission type of aircraft."

Traditional multi-platform geo-location calculates the location of an emitter by measuring time difference of arrival (TDOA) of radio frequency waves. Three platforms have to be able to see the same pulse and by comparing the difference, determine the emitter’s location. But the problem with TDOA, Kao said, is the receiver sensitivity required for all the platforms to see the same pulse.

"[It’s] hard for all three platforms to see the same pulse at any given time, so it becomes very hard to get a solution using the standard TDOA approach," Kao said. "That is the technique that is used by most special-purpose platforms."

What BAE demonstrated is a new way of processing data allowing all platforms to calculate solutions even if they don’t see the same pulse simultaneously.

"Aside from its ability to get a solution more often than the standard TDOA, it’s easier to implement, because the standard TDOA requires the receivers on all the platforms to be synchronized and tightly locked, and again that coordination is often very difficult," Kao said.

There are other advantages. Since each platform can collect data independently, dissimilar platforms could contribute to a geo-location solution, Kao said. Also, the system does not require a lot of hardware.

"Basically if you have the ability to measure time of arrival of a signal of a pulse — if you can do it precisely enough — you have a sensor that can do very precise geo-location," Kao said. "It does not require putting complicated antenna arrays on airplanes, so it becomes relatively easy to implement. For electronic warfare, it’s not hard to incorporate this kind of capability into it."

BAE developed its geo-location technique through internal research and development funds. The JSF Joint Program Office funded the range time for the flight test at the Naval Air Weapons Station in China Lake, Calif.

"We also demonstrated you don’t need much data link capacity to be able to implement this," Kao said. "We used a commercial data link in the demonstration. You can get very good location answers with just a bunch of COTS (commercial-off-the-shelf) components."

The AFRL is interested in the technology for a possible demonstration later this year as part of its Advanced Threat Alert technology demonstration. "We are not on contract to do it, but the government is interested in seeing if they can add this capability," Kao said.

CATBird flies

At the same time, Lockheed Martin is testing its F-35 Cooperative Avionics Test Bed, or CATBird, a 737-300 modified by BAE that will develop and verify JSF’s capability to collect data from multiple sensors and fuse the information into a coherent situational awareness display.

In January, the CATBird conducted its first flight. By February, the aircraft completed eight test missions and logged 24.8 flight hours. Lockheed Martin said the aircraft was set to receive additional flight clearance.

Unlike legacy aircraft, the F-35’s sensors are different in that they are integrated into the aircraft.

"There are no sensor pods hanging out, no bubbles, no blisters," said Eric Branyan, Lockheed Martin vice president of mission systems for the F-35 program. "It’s all pretty much integrated into the aircraft in a single unified system and that’s part of the intrinsic design paradigm of a fifth generation low observable aircraft."

JSF will have an AESA radar, largely an extension of technology used on the F-22A Raptor but with much more capability, Branyan said.

JSF will not only include all the air-to-air capability of the Raptor, but also air-to-ground modes, and the ability to track moving targets and produce SAR maps. (The F-35 Lightning II achieved its maiden flight in December in Texas, beginning a 12,000-hour flight test program.)

The single-seat, single-engine fighter will have the Electro Optical Targeting Sensor (EOTS), which combines the capabilities of Forward Looking Infrared (FLIR), Infrared Search and Track (IST) and a laser designator — systems that were typically separate sensors on legacy aircraft, Branyan said.

Lockheed Martin Missiles and Fire Control in Orlando, Fla., developed the EOTS.

"We combined them all together on one single unit that’s integrated into the nose of the aircraft," Branyan said. "[It’s] half the weight and a third the volume of legacy FLIR-type sensors. Typically, to have a FLIR and laser target designator on legacy aircraft you have two pods. We found you can include all these with a single optical path and save a lot of development cost, weight, power and volume by packaging it all in one [system]."

While relatively contained, EOTS has a large field of view of nearly 270 degrees around the aircraft, Branyan said. "It’s a very, very powerful sensor in terms of being able to identify targets, track them, and once you have identified them, use the laser target designators for the ordnance you may want to use," he said.

The JSF also will be equipped with the Electronic Optical Distributed Aperture Sensors (EO-DAS) system, consisting of six cameras positioned around the airframe to provide full spherical coverage of the aircraft.

The positioning of the cameras will be the same on all three variants of JSF: Conventional Takeoff and Landing, Short Takeoff and Vertical Landing and Carrier Variant. Mission systems hardware and software are 98 percent similar on the variants.

The primary use of the system, developed by Northrop Grumman Electronic Systems in Baltimore, is to detect and track missile launches.

EO-DAS provides a 360-degree view around the aircraft, and, if the pilot chooses, he can obtain a mid-wave IR view overlaid with the rest of the scene, Branyan said. EO-DAS also will give pilots downward-looking capability.

"Those kind of things are only available today because of the significant technology pushes in imaging, the kind of devices like video cameras that are out there on the commercial market," Branyan said. "We are leveraging that technology in the mid-wave IR domain and putting them together on the aircraft, and those six cameras have a fusion engine that fuses all the video together seamlessly."

The first flight-test JSF is flying about twice a week, weather permitting. The aircraft doesn’t have a lot of sensors on it, Branyan said. Most of the sensors are being lab tested, and won’t fly until December 2008.

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