More on the Electro Optical Targeting System and other components
With ample experience in building some of the world's most advanced targeting systems, scientists and engineers working for Lockheed Martin's Missiles and Fire Control in Orlando, Florida, were in a good position to take targeting capability even further when the requirements for the F-35 were received. The resulting AN/AAQ-40 electro-optical targeting system (EOTS) leverages on the experience gained from producing the LANTIRN targeting system ('the genesis of night, precision weapons employment'), the AN/AAQ-33 Sniper advanced targeting pod, and the AN/AAS-42 infrared search and track (IRST) system used on the F-14D Super Tomcat. "The EOTS is the first sensor to combine a targeting FLIR and IRST. Marrying the two capabilities into one sensor was the big technical challenge in developing the system," said Don Bolling, Lockheed Martin's Business Development Manager for EOTS.
Principally viewed as an air-to-ground targeting pod, the EOTS was initially destined for
every third F-35 produced. But the US Navy successfully argued for EOTS to be fitted
to every F-35 built citing the capability as an absolute indispensible part of the sensor
suite used throughout the mission spectrum. The EOTS provides laser designation, laser spot tracker for cooperative engagements, air-to-air and air-to-ground tracking FLIR, digital zoom, wide area IRST and generation of geo-coordinate to support GPS- guided weapons.
Space is limited to such an extent that a standard targeting system with a straight
optical path is physically impossible to house in the space available. The EOTS optical path is therefore folded via mirrors and prisms to refract the light off several different surfaces to direct it on to the focal plane array and fit within the space. "We are effectively bending light at least four times from the point where it enters the window and is finally directed onto the focal plane array or the detector, which was a significant challenge," Don Bolling extolled.
"What makes the F-35 truly magic is that for the first time you have a fused sensor suite. The APG-81 radar is much more accurate in range presentation against an airborne target than an IR system can be, and the EOTS is much more accurate in azimuth down to a single pixel than radar can be. Combine the two capabilities together and you get a much smaller target location uncertainty, which means your weapons effect will be greater and if required your designation accuracy to cue somebody else to that spot will be much tighter. You are able to share the capabilities of each of the sensors and reduce uncertainty," he said.
The EOTS sits behind a faceted window assembly comprising seven sapphire panels. A panel refers to an individual part that fits into a frame and is secured in place to comprise the whole window assembly. Driven by the requirement to comply with the aircraft's radar signature, the EOTS window assembly is the first such design in existence. By comparison, Lockheed Martin's
AAQ-33 Sniper pod has four smaller panels with a much shallower angle of incidence between the sensor and the window. Maintaining the required optical performance and complying with radar signature requirements presented a real challenge according to Bolling. Internally the EOTS has unique designs for the gimbal and the main entry lens called the A-focal or
azimuth assembly which provides the horizon-to- horizon view. It is positioned right up against the window with about a ¼ inch (6mm) of sway space. This intricate design was driven by the requirement for multiple fields of view with a digital zoom in a low-observable application. A second lens known as the elevation assembly is an innovatively designed mirror that sits opposite
and at a 45˚angle to the main A-focal and rotates to provide vertical coverage. The elevation assembly directs the light into the optical path. At the top of the system is the laser, the same type of laser used in the Sniper ATP but with a different output
path. Just below the laser on top of the gimbal assembly are two circuit boards or electronic control assemblies. One provides control to the power servo and the other is an image processor mechanism. A fibre- optic channel feeds data from the sensor directly to the integrated core processor. The entire EOTS assembly has a composite shroud to provide cover from debris and act as a structural element that assists with stabilising the system. System stabilisation is hugely important for holding a spot on the ground and very steady so a geo coordinate can be derived and fed to a GPS-guided weapon for targeting.
On stealth platforms like the F-35 the aircraft's signature must be carefully managed. With IRST the aircraft has a passive IR sensor that creates no emissions unless the laser is used. If the APG-81 radar detects something out at range, using IRST mode the pilot can feed the data to EOTS and passively track the contact with high fidelity while minimizing transmission of RF energy and the aircraft's signature. The EOTS IRST uses a gimbal, an inertial measuring unit, and a fast steering mirror to provide precise stabilization. Passive in operation, the IRST has a wide area search capability comparable to the APG-81 radar with very high scan and slew rates because of the unique gimbal design. Looking to future capabilities Don Bolling told AIR International: "We are looking at options where we might be able to apply the very fast IRST scan volume across the ground for an IR ground moving target indicator, which has some unique applications for the ISR role."
AN/ApG-81 Radar
Complex in design, the APG-81 radar has a variety of main components including the T/R modules, the beam steering computer, array driver, power supplies, inertial navigation systems,and an electronic warfare interface eunit. There are about ten assemblies for the antenna and 15 for the receiver-exciter, wideband and narrowband waveform generators.
Built by Northrop Grumman, the RF support electronics comprise a receiver module, an exciter module and power supplies. Each module is shipped to Lockheed Martin’s Fort Worth facility, where it is integrated into the aircraft.
“The front endif the radar comprises what we call the array,which has the T/Rmodules and the radiating element, and is bolted directly to the integrated forebody and positioned up front in the radome,” said Dave Bouchard, Program Director for the APG-81.
The size of the APG-81antenna or array is governed by the internal size of theradome and comprises many of hundreds of T/R modules.
Once installed into the aircraft, in theory, the radar’s front end should not have to be removed or replaced. “The array is designed to last the 30-year life of the platform, with a meantime between critical failure (MTBCF) rate greater than 10,000 hours,” Dave Bouchard asserted.
Items that drive the antenna, such as the power supply, are on the other side of the bulkhead (to the array) and their MTBCF rate is not as high. These components will eventually require maintenance and are easy to access without removing the radome.
Receiver-exciters are usually packed into one box but because of space restriction they are broken into two different boxes located behind the bulkhead and linked to the antenna with a very short cable.
The APG-81 has an electronically steered array controlled by a steering computer with no mechanical motion. Designed as a multi-mode system, the APG-81 has 32 modes of operation which are common to all three F-35 variants; 12 air-to-air, 12 air-to-ground (including two maritime modes ship target track and sea search), four electronic warfare (electronic attack and electronic protection), two navigation, and two weather. Some of the modes are high resolution and are supported by the sophisticated signal processing available.
Although Northrop Grumman would not confirm as such, the APG-81 can operate in LPI (low probability of intercept) and LPD (low probability of detection) modes that are used to minimize the aircraft’s signature to comply with its low observable (LO) requirements. The radar is optimised for agility, very low noise and high efficiency and fully supports the LO nature of the aircraft. Northrop Grumman claims that it is capable of detecting very small targets and tracking at ‘relevant tactical ranges’.
Sensor track information is sent into the aircraft’s integrated core processor (ICP). Tasked by the ICP, the mission system then fuses radar data with that sent from the DAS, EOTS, EW or CNI to provide what Lockheed Martin describes as unparallel situational awareness. Operational flight program (OFP) software for both the APG-81 and DAS reside in the ICP, which allocates processing power to each system. “What really helps is having the ICP provide more memory and throughput that gives the timeline to execute targeting,” said Dave Bouchard adding: “We send our radar and DAS information to the mission system and have an interface control that defines what messages are passed from radar and DAS to the fusion system.”
Another interesting aspect of the APG-81 is the interface with the ASQ-239 electronic warfare (EW) system. On most legacy aircraft the radar and EW are confederated systems that work separately of each other. On the F-35, radar and EW functions work collaboratively, and in some modes they work independently of one another.
Detection and tracking capability are two aspects in which the new APG-81 has set new performance criteria. But how does the system achieve the range accuracy required by the F-35 mission set. Dave Bouchard explained: “Range accuracy is achieved by multiple air-to-air waveforms that drive the dozen air-to-air radar modes. Range measurements are provided to the common filter, which uses algorithms to filter out drift or inaccuracies that arise over time, and thereby maintain track accuracy.”
In terms of type, the APG-81 is a pulse-doppler radar system that runs multiple waveforms for air-to-air and air-to-ground, with what Northrop Grumman calls ‘very robust electronic protection’ (EP), which helps the system to achieve its accuracy requirements. EP is a series of techniques that help prevent the radar from being confused or jammed and ensures that information presented to the fusion system is very accurate.
DAS, CNI, EOTS and the APG-81 radar all provide track information and track updates to the fusion system that in turn controls the portrayal of targets and symbology on the panoramic cockpit display and the HMD (helmet-mounted display).
In terms of ground target identification and coordinate generation, Dave Bouchard claims that the APG-81 outperforms current AESA radars in two ways. By processing synthetic aperture radar (SAR) data with multiple advanced algorithms, the system performs automatic target recognition (ATR) and automatic target cueing (ATC) on the SAR maps. “We can take a very high resolution ground map of a large area and use algorithms that pick out targets of opportunity that the pilot would be interested in,” Bouchard advised.
Many radar systems have SAR capability with a set resolution such as 20ft, 10ft, 5ft (6m, 3m, 1.5m). In comparison the APG-81 has what Northrop Grumman calls ‘Big SAR’, which instantly generates a huge SAR map when commanded. The pilot can zoom in or out on a specific point for a higher fidelity image display without having to generate a new SAR map. The ATR and ATC work simultaneously on the entire area of the ‘Big SAR’ map, and greatly reduce pilot work load during the most demanding phases of air-to- ground operations.
In support of the two-level maintenance system to be set in place for the APG-81, maintainers will use the APG-81’s prognostic health monitoring system to check the status of the radar for flight line maintenance. Faults are presented on a display located inside a bay on the aircraft, indicating which line replaceable component (LRC)to change. This is a straight forward procedure requiring the maintainer to remove a cover, unplug the LRC, unfasten ten screws, remove the old LRC and replace with a new one, run a test and in theory the radar should be serviceable once again.
All other radar maintenance (the second level) will be undertaken either by Northrop Grumman or at the respective depot facility.
The radar’s antenna, housed inside the radome, has a MTBF (mean time between failure) rating of 10,000 hours, though the APG-81 as a system is not rated at that level. DaveBouchard explained:“One of the advantages of the system from
a reliability standpoint is based on the T/R module array that allows graceful degradation, meaning you can afford to lose T/R modules and still maintain the performance.”
The F-35 radar gained a significant amount of radar design heritage from the APG-77 used by the F-22 and the APG-80 AESA system used by the Block 60 F-16, both of which have thousands of hours of field data and robust reliability requirements.
Using field history of the T/R module architecture used on the APG-77 and APG-80, and sophisticated predictive modelling, Northrop Grumman is performing operational and support modelling to help support its performance-based logistics programme.
Because no single APG-81 array has reached the equivalent MTBCF hours yet, modelling of this nature must be performed to mitigate this situation.
Lockheed Martin received the first APG-81 radar units from Northrop Grumman in 2005, the same year that the system flew on Northrop Grumman’s BAC 1-11 test bed aircraft for the first time. In 2009 the radar made its maiden flight fully integrated onboard Lockheed Martin’s
Boeing 737 CATbird, and flew for the first time in an F-35 (F-35B BF-04) in April 2010. Since its first flight on the BAC 1-11, the radar has made 150 flights and accumulated 400 hours as part of a risk reduction effort. “We are flying with the integrated core processor[linked in to the radar]and using PAO cooling [the APG-81 is cooled with Polyalphaolefin or PAO a coolant], to represent an environmental condition that will be encountered in an F-35,”said the Program Director. According to Northrop Grumman, the radar system has demonstrated good stability and performance onboard the BAC 1-11 and also in Lockheed’s integration lab and on the CATbird. “The reliability we have seen in the field to date, even though it’s primarily in the lab and in test jets, supports what our modelling has predicted we will see from F-35,” extolled Dave Bouchard.
Electronic warfare
A fighter aircraft intended to enable control of both the air and of the electromagnetic spectrum, the F-35 Lightning
II was designed from the outset with its own electronic warfare (EW) system. With BAE Systems at Nashua, New Hampshire as the team lead, but including the participation of leading EW specialists worldwide, including Northrop Grumman, the F-35’s EW system is part of the basic design, alongside its avionics, communications, navigation and intelligence; and sensor systems.
While all the aircraft types that the F-35 will replace use EW systems, some highly capable against current threats, the F-35’s EW system enables its effective integration with all the other onboard systems. Each of the F-35’s systems is able to inform and operate with components of each other. This F-35 network can also link to larger multi-unit networks, other aircraft or terrestrial platforms via its built-in MADL (Multifunction Airborne Data Link), which allows the EW system to be networked either in attack or defence.
The internally mounted AN/ASQ-239 Barracuda EW system built by BAE Systems completed its flight testing in 2005 and was soon in low-rate initial production, with a unit cost estimated at $1.7 million. Weighing some 200lb (90kg), it was developed from the BAE Systems AN/ALR-94 EW suite fitted to the F-22 Raptor, using emerging technologies to produce greater capabilities with a goal of achieving twice the reliability at a quarter the cost.
The F-35 EW system provides radar warning (enhanced to provide analysis, identification and tracing of emitting
radars) and multispectral countermeasures for self- defence against both radar and infrared guided threats. In addition to these capabilities, it is also capable of electronic surveillance, including geo-location of radars. This allows the F-35 to evade, jam, or attack them, either autonomously or as part of a networked effort. The enhanced capabilities of the ASQ-239 (and integration with the F-35’s other systems) allow it to perform SIGINT (signals intelligence) electronic collection. The aircraft’s stealth capabilities
make it possible for an F-35 to undertake passive detection and SIGINT while operating closer to an emitter with less vulnerability. For the use of active deception jamming, the F-35’s stealth design also allows false target generation and range-gate stealing with less use of power.
The EW system also sends and receives data and status and warning information from other onboard systems through the MADL data link.
The ASQ-239 has ten dedicated apertures, six on the wing leading edge, two on the trailing edge, and two on the horizontal stabilizer trailing edge. The system also has the potential to use the F-35’s other apertures, most notably that associated with its APG-81 AESA (active electronically scanned array) radar. In addition to functioning with the radar, this array, transmitting only at high-power, could function as a stand-off jammer.
When used in receive only mode, the APG-81 provides enhanced SIGINT capability. The radar could also be used, following future upgrades, as an electronic attack weapon,
burning out emitters with pure power or injecting hostile radars or command and control systems with computer inputs that would provide false targets, misleading information, or shut down an air defence system. Combining these capabilities and data links will give F-35s the potential to do more than defend themselves and jam or attack enemy emitters they locate.
Groups of F-35s could collect SIGINT from multiple directions, and then use the information gathered and analyzed to fire missiles, start jamming, or launch an electronic attack. Data links mean that F-35s can provide this information to other platforms in near real-time and have their actions coordinated ‘off-board’, where there will be more access to fused intelligence, greater situational awareness, and less chance of lethal information overload, than in the cockpit of an F-35.
The 513th Electronic Warfare Squadron part of the 53rd Electronic Warfare Group, formed in 2010 at Eglin AFB, Florida, is tasked with introducing the F-35’s EW capabilities at an operational level. A joint squadron with personnel from all US services, the 513th is co-located with the 33rd Fighter Wing, the F-35 school house for pilot and crew chiefs. Tactics, techniques and procedures (TTPs) to be used by the F-35 in electronic combat are being developed by the 513th. The unit will also provide and update the threat libraries and systems programming that will keep the F-35’s systems responsive to changing threats. To do this, the 513th will operate a new $300 million reprogramming laboratory at Eglin, scheduled to open in mid-2011.
EODAS
he sphere provides information on threats and feeds that information to the fusion system, which in turn displays the most relevant information into the HMD. Depending on which direction the pilot is working will dictate what frames or field of view from the sphere the pilotwill be able to see in the HMD.”“While the imagery provided to the pilot in the HMD is
the most tangible thing generated by the DAS and the one that people are most impressed by, in reality, the ability to simultaneously see different targets in all directions, feed information to the fusion system and provide warnings to the pilot, is the key advantage of the system.” he added.
But providing images to the HMD is not the limit of the system’s capability. The DAS also tracks airborne targets it detects surface- and air-launched missiles, while providing passive protection of the aircraft. It performs different functions simultaneously but does not operate in different modes as requested or commanded by the pilot. The six aperture sensors function in the infrared spectrum in all directions, run advanced exploitation algorithms to increase range, reduce false alarms, turn track information into useable data, feed it to the fusion system and add to the air picture displayed for the pilot. Each of the six apertures is interlinked to the ICP, which runs the software algorithms that generate geo-registered threat reports and imagery. These are fed to the fusion computer which outputs data using two channels, one to the HMD and one to the panoramic cockpit display. n the case of the HMD, whatever direction the pilot is looking, he will receive data from the sensor that supports his field of regard. With the panoramic cockpit display, the pilot can chose what he wants presented, which can be a permanent feed from one sensor or whichever sensor can view a given point on the ground, as two examples.
The DAS is designed to detect low intensity threats in a much cluttered background, and has the capability to detect threats such as ballistic missiles. In June 2010, Northrop Grumman collected data from a two-stage Falcon 9 ballistic missile launch from Cape Canaveral in Florida, to determine the applicability ofthesystemtodetect,trackandpotentiallytargetmissilesin the ballistic missile defence role. Northrop Grumman’s BAC 1-11 test bed tracked the multi-stage rocket with the DAS for over 808 miles (1,300km) while airborne over the coast of North Carolina. According to Dave Bouchard, the processing power available enables the DAS to simultaneously track thousands of targets, far more than is possible with any current infrared system.
“DAS is an omni-directional infrared system that can simultaneously detect and track aircraft and missiles in every direction, with no practical limit on the number of targets it can track. DAS truly revolutionizes the way we think about situational awareness,” said the Program Director.
An image of AN/AAQ-37 (EODAS) picking up Ground fire, and automatically geolocating it, feeding targets to the weapon and displaying all relevant information onto the MFD.
http://speedy.sh/bgc5E/F-35LightningII.pdf
. They'll keep repeating that nonsense ad-nauseam.
and Bofors ToT is another joke.
and I cant agree more with him.
