Flight-Test Program Accelerates for U.S. Navy''s E-2DBy David A. Fulghum
Within three years, the U.S. Navy's fleet will have fielded the technology for precisely locating small, flying targets. The target set embraces some of the Navy's latest nightmares, including the next-generation of stealthy - sometimes supersonic - cruise missiles.
Moreover, with the introduction of space-time adaptive processing (STAP) software, the hybrid APY-9 electronically scanned array (ESA) radar on board the new E-2D Advanced Hawkeye will be able to pick those elusive flying targets out of a background of rough terrain and urban sprawl, a far different mission than the overwater detection capability of earlier Navy airborne early-warning and control (AEW&C) aircraft.
The advanced radar capability on the 75 new E-2Ds will be parked 25,000 ft. above forward-deployed fleets so that those advanced enemy missiles can be detected at ranges great enough to allow for organization of an effective defense.
From that overhead perch, flying at an artificially slow cruise speed to maximize target observation time, the E-2D will be able to collect airborne target and electronic emitter data from well beyond the radar horizon of surface ships. The E-2D can then feed it to fighter aircraft, shipboard missile defenses and the newly emerging Global Information Grid.
"A big reason the E-2D is happening is to be able to detect these [small] targets over land," says James Culmo, Northrop Grumman vice president and program manager for AEW&C and battle management command-and-control networks. Therefore, "It is significant in that the first time we flew [the radar], we detected targets over water and land out to ranges [still classified, that] we expected."
Navy officials also are intentionally vague - often refusing comment - about the ranges, types and sizes of targets that can be spotted with the new, 360-deg. ESA radar the E-2D carries. They point out that the radar cross-sections of various targets will be analyzed by other specialized aircraft like the EP-X, with its massive AESA radar and advanced electronic surveillance arrays or even the carrier-based F-35B/C Joint Strike Fighter.
The E-2D will be there to detect and precisely locate those small targets first, often using information gathered from a variety of intelligence sources. To that end, the aircraft's radar was designed with a mix of technologies. The element that gives small-target detection is the ESA antenna. But the array has a limited field of view - 60-90 deg. or less. The solution for providing total coverage was to affix it to a second, mechanical array that rotates in a full circle.
"Our aircraft is not going to have the role of analyzing the signatures of aircraft," says Navy Capt. Randy Mahr, E-2D program manager. "But I will be able to use multi-sensor data from other platforms. I know where the target is. Somebody else may know what it is. I can put those pieces together. Sometimes it's going to be an aircraft that can see the target best. Other times it's going to be a ship or a ground unit."
The goal is "one piece of metal, one track," Mahr says. "That means everyone is looking at a single picture. I'm going to have server capability on the E-2D that can maintain some historical piece of the picture. Other parts are going to be resident in ships and with ground forces. I am the central airborne piece."
When cued by other intelligence sources, the ESA begins looking ahead and behind the mechanical scan so it can focus on a given piece of airspace to pick out small objects.
"I can track a fast target," Mahr says. "Whether I can acquire any other object is just a matter of how much [radar energy] I put on that particular target" and for how long.
New technologies always bring with them unexpected problems and occasionally an unanticipated solution. The E-2D is no exception. On the plus side, processor technology is shrinking, which has kept weight at least 1,500 lb. below predictions while producing excess processing capability.
But there may be concerns in future.
"I may need to see more things [outside the range of the new radar]," Mahr says. "As we move into the world of unmanned and remote vehicles, we're going to have a large amount of sensor data available. How we're going to operate with those unmanned vehicles is not fully understood. In some way, every airborne platform will be integrated. That challenge is coming at us."
Certainly, some problems have already been identified.
In the E-2D's early radar flights, the tracker was creating a new file for each target on each sweep, instead of tracking and building a history of the object. Target accuracy was good, but the tracks were not unambiguous. A software fix in the mission computer was required.
The radar's prototype power supply was also a problem early on, but it appears to be working smoothly now. There were malfunctioning circulators in the radar that let it power up and down. The two aircraft haven't accumulated enough flying time yet to produce reliability issues.
The second test aircraft, AA-2, was producing an unusual sound in the left wing. A pair of hydraulic lines were found to be rubbing. All hydraulics and wiring were inspected and rebundled to ensure there was no chafing, which set back the radar flight-test program about three weeks.
Now Mahr is accelerating the schedule by increasing flight tests up to 4.6 hr. from 2.5 hr. "We're doing well, flying missions and we're now within weeks of our original plan," he says.
Between now and the end of summer, "we'll be testing the radar and its systems to get ready for [an] operational assessment," Culmo says. "We haven't tested the [electronic steering] modes of the radar. The first thing we want to do is make sure the mechanical scan works. We won't be testing the full ESA [capability] until late this year or early 2009. But the outputs of the radar are such that we're sure we can electronically steer it."
Culmo also notes that "the same thing that allows us to do electronic scanning, allows us to do STAP. Basically, [it's the product of] being able to control the amplitude and phase of each of the antenna elements. That allows the cancellation of a lot of electromagnetic interference," particularly from radar signals reflecting off of terrain and buildings.
A few details have drifted out of the aerospace industry about the capability. So far, the Advanced Hawkeye's radar has operated at only half power. Yet the radar's range already equals that of the E-2C's conventional radar and the volume of airspace it can monitor has tripled. Even a layman's extrapolation would put the new E-2D's range at least at 250 mi. More likely it's limited only by the aircraft's radar horizon.
Mahr will only say that, "The test team is seeing E-2C equivalent performance in the E-2D testing completed so far. There are no plans or requirements to do more extravagant things yet."
Electronic and network attack, for example, are not part of the Advanced Hawkeye's portfolio.
"Electronic attack is like [the E-2D] carrying bombs; there's no reason for it," Mahr says. "Other elements in the network do that."
A primary attraction of AESA radars is 2-3 times longer range than single aperture radars. They are also able to focus an array's energy on enemy sensors and antennas for jamming, placing false targets and even serving as a conduit for the digital attack of integrated communications networks.
So far, at least, the E-2D won't be operated with those missions in mind, but there are still some interesting electronic warfare applications.
"From an electronic attack perspective, one of the benefits of E-2D is that it has a UHF radar, which is different from most of the other [L, S and X-band] radars that we're going to be up against in our environment," Mahr says. "[That] adds a dimension to the [jamming] problem for any foe. It [also] gives the U.S. another dimension to work in. The more complicated we can make the electronic problem for somebody else, the better off we'll be."
Data links for pushing information off and on the E-2D are still being explored.
"The pipes aren't finalized yet," Mahr says. "Right now, I have the E-2C's data links as a threshold capability. But the Defense Dept. is still maturing the next generation of network radios. Whatever that is in [about] 10 years, the plane's open architecture will be able to make it compatible with our weapons system. That radio and the open architecture is the touchstone."
Program members have been jumpstarting the process of tying "into the giant network in the sky" with tests conducted from specially modified E-2Cs involving intra-battlegroup wireless networking.
"I look at broadband capabilities and waveforms on new radios that aren't in the fleet yet to move large pieces of data, whether that is imagery or an air tasking order," Mahr says. "We have talked to an F-18, AWACS and F-15, but it's not an operational capability. When it [is available], we'll be ready."
The team also is using the mission computer and communications system from an E-2C to build a core open architecture. That will make it easier to do in the E-2D, and make both aircraft compatible nodes on the network.
"Once I get the radars' final transmitter pieces and rig them out, I'll move them to the aircraft," Mahr says. "That's the end of the hardware stairstep. This summer, we'll get the transmitter operation in both aircraft. By the end of the summer, we'll turn the aircraft over to the commander of operational test force so that test squadron VX-1 can do an operational assessment."
That's the last hurdle before a low-rate initial production decision next spring. The aircraft will move to NAS Patuxent River, Md., this year. Aircraft carrier qualifications are scheduled for late 2009, followed by initial operational capability in 2013.
Source
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