Small Aircraft May Become Large Sensors

By David A. Fulghum, Douglas Barrie, and Robert Wall  
10/28/2006 10:15:07 PM  

SENSORS VS. AIRFRAMES

An emerging arena for new competition in the defense industry will involve the melding of airframes and what they traditionally have carried internally.

The debate about whether platforms or payloads are more important will soon shift fundamentally as systems--particularly sensors, communications and weaponry as they merge into one--move to the outside of platforms and become their skins. Moreover, there are moves afoot to integrate the two more closely, even on more traditional designs.

Conformal arrays are being eyed for manned and unmanned aircraft, ships and ground vehicles. But they seem to have a special niche in unmanned aircraft. There the operational and low-cost advantages of small, stealthy, missile-size unmanned combat aircraft can be fused with the benefits of a sensor that uses the whole exterior of the platform as an aperture to communicate, image, jam or function as a weapon that fires high-power spikes of energy into enemy electronics.

Aerospace officials generally will not address this new industrial battlefield on the record because they don't want to offend their commercial airframe partners. But some outline what they think is underway in the laboratories of major U.S. and European defense companies.

There's also a race underway for international supremacy. Europe has trailed the U.S. in development of active electronically scanned arrays (AESAs). This time, there's an all-out effort on to make sure that gap doesn't emerge when it comes to the next-generation of arrays.

Some view what's taking place--particularly in the U.S.--as a battle, with the sensor houses challenging the airframers for primacy.

In Britain, other fundamental question are under consideration. The Defense Ministry, for instance, sees no need to develop a manned, fast jet platform to eventually succeed the Eurofighter Typhoon or Lockheed Martin F-35 Joint Strike Fighter. What it does want to develop in the coming decade are high-end unmanned combat and reconnaissance air vehicles. Conformal multiaperture sensors, sometimes dubbed smart skins, will be central to this effort. Ownership of this technology would grant a contractor or nation, in an international competition or collaboration, significant input to the nature of the airframe.

U.S. industry observers believe there will be a continued effort to produce small numbers of large unmanned combat aircraft, based on designs like Boeing's X-45 and Northrop Grumman's X-47, because of the desire to conduct round-trip missions and avoid detection by enemy air defenses. At the same time, researchers are aware of the need for large numbers of sub-$100,000, missile-size unmanned aircraft that can perform missions with a single sensor. They see these aircraft decreasing in price while increasing in their range (due to more efficient engines) and payload capability. This would allow small unmanned aircraft to have operational parity with larger, more expensive designs.

Some companies are working toward networks of small, stealthy aircraft that provide many types of information that can be fused into a richer, more detailed image. Here, physics is maximized from both ends--with smaller, harder-to-detect platforms that carry antennas as large as the aircraft.

Moreover, researchers envision a number of aircraft working together as a single virtual array that would allow them to function at very low frequencies. They contend that experiments are already being conducted using Hunter- and Shadow-size unmanned aircraft.

So there's a push to build lightweight antenna arrays that serve as aircraft skins and require very little electrical power. While initially these arrays would be single function, there is some promise that eventually they could be designed as multifunction sensors. Even a small array with limited power could serve as a microwave weapon if it got close enough to an enemy emitter or other antenna arrays, they contend.

The U.S., Britain, Australia and Italy all have expressed interest in directed-energy weapons that can be produced through software modifications to the F-35's electronically scanned array radar. That nonexplosive technology is popular with left-leaning governments, and it's expected to be miniaturized enough over time to fit into much smaller unmanned aircraft.

Integrated arrays should produce vehicle designs that are optimized for low observability. But whatever the long-term road map for a transition to aircraft that are virtually flying antennas, the world's military establishments will continue to fly conventional, manned aircraft for the foreseeable future. A profitable avenue for industry will be upgrading these older aircraft with the new antenna technologies, and prolonging their operational lives by making them formidable weapons and sensor platforms.

In particular, front- or nose-positioned AESAs are likely to remain the central element of the sensor package of manned fighter aircraft for decades. As a result, researchers are working on reducing some of those system's disadvantages, since efforts to produce conformal arrays have in part been driven by the limitations in the conventional approach to building air intercept radars.

Both the U.S. and Russia have looked at adjunct antennas to supplement the primary nose-mounted sensor. The F-22 has "chin cheeks" for two small conformal arrays. In the 1990s, Russian designers experimented with using a secondary passive e-scan antenna mounted at the rear of an aircraft to provide greater radar coverage.

There are also low-observable and jamming implications for AESAs. Forward-positioned arrays are potentially large reflectors, which could compromise radar cross sections.

However, frequency-selective radomes can now be designed to let only signals pass through that operate in the frequency of the radar itself. This makes it harder for an adversary's sensor to penetrate the radome because it would have to be exactly in the same band.

Moreover, developers are working on tunable radomes that can change their filtering characteristics as the onboard array shifts frequency. Frequency agility provides added target-recognition benefits, while making it harder for an adversary's electronic warfare suite to characterize the threat. Being electronically agile while masking the array is seen as a huge boon to survivability.

Also being examined is plasma-shielding using a generator within the radome to produce a comparatively small field to ward off enemy electronic penetration. The U.S., Russia and European states have active programs in plasma research for airframe applications.

...Requisite post about the phased plasma rifle in the 40-watt range...