Readers turn searchlight on stealth controversy

Does 'mobile phone' detection system really pose a threat?

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Our article yesterday on UK company Roke Manor Research's stealth detection system provoked some interesting discussion. Nick Brown, features editor of Jane's Defence Weekly, was kind enough to send us a heads-up about the F-117 shot down over Kosovo:

As it happens, our major feature last week at Jane's Defence Weekly was on stealth (Low Observable) technology and how to counter it. I spoke to Roke Manor and they were very helpful - not clammed up at all.

The system that was rumoured to have had something to do with the stealth shootdown is the 'Tamara' system from HTT-Tesla Pardubice in the Czech Republic. How big a part it played is debatable though. It might give a general heads up that something sneaky is on its way, but it is no real help in interdicting stealthy aircraft as it's a passive detection system that only works if it can pick up electronic transmissions, IFF, radio comms and so forth. Stealthy missions are always carried out 'quietly' with things like IFF switched off.

A system that may be more helpful is Lockheed Martin's Silent Sentry passive detection system. They don't market it as stealth detection, but it effectively works as a comprehensive multi-static radar, without the expense or complication of setting one up. More worryingly for the States in light of recent events are consistent reports that the PRC have perfected the maths of a similar system.

There's more about the F-117 shootdown in this New Scientist article.

In fact, claims of stealth detection are nothing new, as several readers have pointed out. According to an article from The Naval Institute, British boffins were apparently able to track a B-2 during a visit to the 1988 Farnborough Air show. In this case, however, the aircraft was given away 'by the IR glow of its aerodynamic heating'.

The current detection technology, including that of Roke Manor, is based not on IR, but on 'bi-static' radar. This is where the transmitting and receiving stations are separated. One reader explains why this is necessary:

Stealth aircraft do not absorb most incoming RF energy, instead they reflect it to somewhere other than from whence it came. Thus if the radar transmitter and receiver are co-located, as in a traditional radar system, the radar receives no return signal. Note the strange polyhedral shape of the F-117: a flat surfaces returns RF energy in only one direction just as a flashlight beam on a mirror. Unless the radar signal is normal to some surface (extremely low probability) the radar receives no return. Newer stealth A/C achieve the same effect with more sophisticated smooth geometry at the expense of returning energy in many more directions - but not to the source.

It is possible to defeat such stealth by moving the receiver away from the transmitter and by using multiple receivers and/or transmitters. One simply floods the sky with RF energy from multiple sources and scans the sky with highly directional antenna at multiple locations. A stealth A/C will show up as an RF source on some of the receivers as the reflected energy goes somewhere if not back to the transmitter. Cell phone systems should do quite nicely to flood the sky with RF from multiple locations, but there's nothing special about cell phones that makes them behave any differently from other RF sources with regard to stealth aircraft. One might also note that cell phones systems should be quite vulnerable to being suppressed by ARMs (missiles that home on RF emitters) as, unlike military radar, they are not designed to shut down when being targeted by an ARM.

Interesting. But do the stealth aircraft not have absorbant coatings? Bill Jenkins concurs that mobile phone networks might be vulnerable to attack. Then, of course, what about the GPS element? To recap, Roke Manor's system relies on the reflected signals receivers being synced to a GPS satellite. A computer then collates this information and calculates the aircraft's position:

First and foremost, the system requires GPS to work. The US military OWNS the GPS constellation. While there are European and Russian starts to a non-US analog, there is currently nothing of the sort that works to the near-perfect precision of GPS. The military has the capability to degrade or deny the signal at any point on the globe it wishes. If, for some reason, a hostile nation began using GPS against us, they would not hesitate to turn Selective Availability back on.

Secondly, you must remember that all of these hordes of mobile-phone towers must be powered. A few cruise missiles through the front door of the offending power station, or a rain of carbon-fiber shards over some electrical substations, would render the entire system at least temporarily useless.

Third, even if you have a rough idea of where the plane might be, it is still far from "easy prey for convential ground-to-air missiles". Remember that in the Yugoslavian shoot-down of the American F-117, they expended well over 2000 missiles in an attempt to knock it out of the air. (More than likely, the loss of the aircraft was due to over-confidence on the part of the US military.) The most dangerous (to any aicraft) surface-to-air missile is the shoulder-fired type. They use infra-red (heat) homing, not radar, to find their targets. All US stealth aircraft are fitted with sophisticated systems to mitigate their heat signature, making it difficult to obtain the necessary missile lock. Add to this the fact that the stealth planes fly almost exclusively at night, and it makes it nigh-well impossible.

So is this a credible threat? I don't really think so. You are taking a bunch of cell phones and trying to find multi-billion dollar planes with them, after all.

You may have a point. Nevertheless, the US would still need to render GPS unavailable to the enemy, then disable its phone network before even attempting to attack other strategic targets. This must increase the chances of further aircraft losses. However many missiles it takes to down a stealth, the threat is a real one. If someone eventually manages to bag a B-2, that's a cool U$1bn worth of scrap metal - missiles, on the other hand, are cheap. ®

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