Kansas City Star
June 17, 2001
Stealth's Unmasking Only A Matter Of Time
By Scott Canon, The Kansas City Star
For a decade or more the Pentagon has pointed to the Missouri-based B-2 bomber as typical of the military's future - high-tech weaponry that can deliver a strong punch while nearly invisible to radar.
Last week a British research firm said it had built a device - absurdly cheap by modern military standards - that used ordinary cellular telephone traffic to pinpoint stealth aircraft.
It is a system that turns the cloud of already existing radio signals from cell-phone towers into a passive radar detector. Where the B-2 can dodge most radar by reflecting the signals in odd directions, this system stations a new network of antennas to catch those diverted radio waves.
The British boast brought skepticism from the U.S. Air Force and American military experts, but not outright dismissal. Even if the device does not yet work as advertised, American experts said, it is based on technology that they think eventually will strip stealth aircraft of their virtual invisibility.
"There's no permanent military advantage," said John Pike of GlobalSecurity.org, a defense policy group. "Computational power made stealth aircraft possible a decade ago, and it will make stealth impossible in the future."
Flying from Whiteman Air Force Base near Knob Noster, about 60 miles southeast of Kansas City, the nation's fleet of B-2 stealth bombers made scores of bombing runs in Yugoslavia in 1999 without being hit.
Although it is unclear whether the angular, bat-winged bomber ever had to skirt Serbian radar, the jet has been seen as a stealth success.
Last week the British firm Roke Manor Research, a business owned by electronics giant Siemens AG, announced that it had developed technology that tapped existing cell-phone tower transmissions to foil stealth technology.
Roke Manor said its signal-detecting units - now the size of a sport-utility vehicle but soon to be the size of a briefcase - could sell for less than $200,000. America's 21 existing B-2s cost about $2 billion each, although Northrop Grumman recently has offered to build more for about a quarter of that cost.
"This latest technology breakthrough ... could prove to have phenomenal affects on the use of stealth aircraft in military situations," Roke Manor said in a news release.
Pike said that "you have to greet those claims with skepticism." Owen Cote, associate director of security studies at the Massachusetts Institute of Technology, said he also was doubtful that the company had a practical, working system.
In a prepared statement last week, the Air Force said reports about the technology "suggest a continuing misunderstanding of the practical applications of such an air-defense asset."
Still, among the experts, the consensus was that such a system could work and eventually would. The technological problem is chiefly one of computing power - something that is getting cheaper to solve. The primary practical problem is that a user would have to deploy a large network of receivers that shadow cell-phone towers.
Together the receivers and phone towers would form a passive radar system, which would prove a significant advantage to existing, active radar systems because a bomber pilot no longer would be aware that the jet had been spotted.
Traditional radar sends out radio signals. Those signals bounce off an object, such as a plane, and back to a receiver.
The time it takes for the signal to come back tells how far away the object is. With traditional radar, the modulation and frequency of the signal can be fine-tuned to produce the easiest-to-read echo.
Cell towers - along with TV and radio stations and air traffic control towers - send out almost constant streams of radio signals. But their frequencies are designed for talking, not for making echoes. They bounce back largely as noise.
For years deciphering the jumbled echoes proved too complicated. In the meantime, Moore's law, the prediction that computers would double their calculating speed every 18 months, has held true. Today's processors, experts said, should be strong enough to unscramble a cell-phone signal bouncing haphazardly off a passing bomber.
"You piggyback on all this radio frequency energy that's out there," Cote said. "I don't think anybody doubts that it can be done eventually."
The United States already has something like it. Lockheed-Martin's Silent Sentry system uses low-frequency FM radio and VHF TV signals to pinpoint low-flying objects such as cruise missiles. The Air Force said in its statement last week that early tests of Silent Sentry did not prove it to be "counterstealth."
But experts said they thought a system that relied on cell-phone frequencies easily could cover the areas traveled by high-flying B-2s.
Everything about the B-2 is aimed at avoiding radar. Its nearly seamless skin and special paint absorb radar, so there is not much of a signal to bounce back to a receiver. Its flying-wing shape of triangles and rounded edges is designed so that when radio signals do bounce off, they do not bounce back cleanly.
But with the cell-phone plan, radio signals fill the air to high elevations from different directions. It also relies on using many receivers - the devices the British firm would team with existing cell towers - to catch those radio signals deflected every which way by a stealth plane.
And that's a bit of a catch. Cote noted that building a detection system would be comparable in some ways to constructing a cell-phone network - expensive and requiring technological know-how.
"People have known for quite some time about this concept," Cote said. "The question is whether an adversary is ready to deploy something like this."
Experts said they doubted whether countries such as China, North Korea or Iraq are ready to sheath themselves in such a passive radar system.
"I can't see it happening within a couple of years," said Andrew Krepinevich, executive director for the Center for Strategic and Budgetary Assessments. "The difference between working in theory and working in practice can often be substantial."
Countries might be able to save some cost by stationing receivers as virtual fences rather than over vast areas. That way they could detect a plane entering a region instead of tracking it over long distances.
"The number of receivers you use is basically an economic argument," said Greg Duckworth, principal scientist at BBN Technologies. "So you could choose between barrier coverage and field coverage."
Duckworth and other experts said a system that caught radio signals from several locations eventually could trump the stealthy designs of the B-2 and the F-117 fighter-bomber.
That, however, might prompt a country with stealth aircraft to attack a series of cell-phone towers first.
"Measure and countermeasure are what military planning is all about," Pike said. "Airplanes that were impossible to shoot down in the First World War would have been child's play in the Second World War. Airplanes that would have been almost invincible in the Vietnam War are simply targets today.
"The stealth qualities of planes like the B-2 are safe for some time, but they will inevitably decline over time."