Bombs With Brains

Dr Duncan L Copp

March 2003

The countless aircraft sorties of the Second World War left their legacy on many European cities. In ham-fisted attempts at destroying a few specific targets, planes would drop a myriad of bombs, indiscriminately flattening the towns below. Whole swathes of post-war architecture sprang up from the razed city centres and suburbs. But now, unless an aggressor is hell bent on inflicting the maximum number of casualties, this form of mass destruction can be avoided. Rapid technological advances allow a different type of assault from the air, employing bombs and missiles with brains that can talk to satellites in Earth orbit. although far from infallible, future conflicts will almost exclusively rely on a new power – the power of the computer processor.

Sixty years of technological development since the Second World War has bred a new generation of bombs, known as Precision Guided Munitions (PGMs), or smart bombs. Smart bombs have brains, as opposed to dumb bombs, which are little more than explosives packed into shells. Using installed computer hardware and software, smart bombs are able to receive and act on information sent to them prior to and during their flight. Smart bombs increase the frequency with which targets are hit, which in turn reduces the number of sorties that need to be flown. And, in theory, the greater accuracy should reduce the number of casualties, both soldier and civilian.

The first generation of smart bombs made use of lasers. The bomb detects laser light reflected off the target. Laser light is aimed at the target either by the plane that released the bomb, by another plane, or by soldiers on the ground. The laser light is coded by transmitting it in a specific series of pulses, one which the bomb recognises. Laser-guided bombs were first used during the Vietnam conflict and later during the Gulf War in 1991.

Many of us marvelled at the technology shown on the grainy black and white video footage of a laser-guided bomb shooting down the chimney of an Iraqi Air Force building, blowing it sky high. But laser-guided bombs do have considerable problems. The bomb needs to lock-on and see the reflected laser light at all times. If the laser light is lost the bomb flies blind, so the target must always be illuminated. But the real Achilles' heel of the laser-guided bomb is the atmosphere. Cloud, heavy rain, fog, mist, dust and haze can easily obfuscate laser light, again forcing the bomb to fly blind. During the Gulf War many such bombs missed their targets because of atmospheric problems. Pilots were often forced to call off bombing sorties because of the effect that weather, smoke or dust would have on the faint laser light.

Next generation bombs

As a result of the rather lacklustre performance of the laser-guided bombs during the Gulf War, the US turned to new and more sophisticated PGMs. Exploiting the rapid rise of global communication technology, they began using a network of orbiting satellites to guide bombs to their targets – bombing with geolocation they call it.

It works like this. First the enemy target must be located. This is achieved in a number of ways – by highflying U2 spy planes, by patrolling surveillance planes, or by lower flying aircraft that monitor radio transmissions from the enemy. This last method measures the direction of the radio transmissions in relation to the moving aircraft and terrain below. Using a number of sources to locate the enemy, the exact co-ordinates can be pinpointed on the ground with considerable accuracy. The location details are passed on to a plane, aircraft carrier, submarine or wherever the smart bomb is to be launched from. The target co-ordinates are then programmed into the bomb's computer.

The smart bomb can then be launched. But that's not the end of the story; the next stage is when the bomb becomes smart. The bomb carries a global positioning system (GPS) receiver, similar to those used in some cars today. By receiving signals from a constellation of satellites the bomb uses its GPS to calculate its exact position, through the method of triangulation. Since the smart bomb knows the position of the target and its own position it can accurately steer a course towards the target, making any midcourse corrections during flight. And how accurate are these smart bombs? The recent conflict in Afghanistan marked the first use of GPS-guided bombs, in support of ground troops. In one case, bombs were fired at an enemy target in the dark, just a few hundred metres away from friendly troops, destroying the enemy position.

This is a state-of-the-art smart bomb. No longer does the aircraft from which the bomb is launched need to stay in the vicinity to guide the bomb home. Furthermore, GPS is not hampered by poor visibility. However, though the weather is not a concern they are susceptible to sabotage. The satellite signals they receive which are so pivotal for their precision are incredibly weak, equivalent to identifying a fridge light over a distance from London to Sydney. Consequently, the enemy can bombard the flying bombs with white noise, effectively jamming any communication the smart bomb has with GPS satellites.

Upgrading the arsenal

The smart bombs used in the Gulf War were mostly Cruise missiles. The Cruise missile is basically an unmanned aircraft. It's launched using a 250kg solid rocket booster that falls away once the fuel is expended. A turbofan jet engine then provides propulsion, burning up to 450kg of fuel. The missile is stabilised in flight by wings. Also onboard is an inertial guidance system – a set of gyroscopes that help guide the missile by sensing changes in the missile's acceleration as it flies. An analogy can be made with the force you feel when rounding a corner in a car. Do this with your eyes closed and you'll still retain a sense of direction. That's thanks to the motion of fluid in your inner ear and the forces on your body telling your brain which way you're moving. This technology was used along with onboard terrain locating information. Legendary stories circulated of Cruise missiles flying low along the streets of Baghdad, navigating street corner turns with ease. The truth of the matter was that most Cruise missiles launched ended with 'no-shows' because the missiles simply got lost.

Cruise missiles have been updated considerably since the Gulf War. They've now metamorphosed into the Joint Air to Surface Standoff Missile (JASSM). Like Cruise missiles, JASSMs have a long range, up to 200 miles. Hence the name 'Standoff' since it can be fired well away from the action. It has the latest GPS guiding technology and carries an infrared imaging device to help visually identify the target. But such technology comes with a hefty price tag – each Cruise missile costs around one million dollars. Also, they carry a relatively small warhead for such an expensive weapon – just 450kg of explosives.

For standard dumb bombs, Boeing were contracted to devise an upgrade system which employed GPS technology. The result? Joint Direct Attack Munition. JDAM is not actually a missile but a strap-on conversion kit that makes an old-fashioned dumb bomb brainy. At a cost of $20,000 an existing dumb bomb undergoes a technological transformation. The bombs are fitted with a GPS receiver, a computer, an inertial guidance and control system, tail fins and a harness to strap it to the under wing of an aircraft, such as the US Navy's F/A-18 Hornet.

But no matter how smart your bomb is, there is always room for human error. Under the pressure of enemy attack, it's all too easy for a pilot to misinterpret information and enter the wrong co-ordinates. The results can be disastrous. Ultimately, smart bombs are only as smart as the people who use them.

Find out more

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Websites

Precision Guided Munitions and the New Era of Warfare
www.fas.org/man/dod-101/sys/smart/docs/paper53.htm
Article by Richard Hallion on the history of Precision Guided Munitions.

Frontline – The Gulf War
www.pbs.org/wgbh/pages/
frontline/gulf/weapons/
Gulf War site that looks at the aircraft and ground systems, munitions and space operations employed in Operation Desert Storm.

Desert Star US Military Space Operation/Desert Shield and Desert Storm
www.fas.org/spp/military/docops/
operate/ds/weather.htm
Looks at military operations during the Gulf War, with an in-depth analysis of the problems caused by unpredictable weather conditions.

FAS – Global Positioning System Aided Munition
www.fas.org/man/dod-101/sys/smart/gam.htm
This is currently the only all-weather, near-precision, 'bunker busting' weapon available.

GPS World
www.gpsworld.com
Lots of articles, information and a search facility on issues relevant to GPS.

AGM-158 Joint Air to Surface Standoff Missile (JASSM)
www.globalsecurity.org/military/systems/
munitions/jassm.htm
Everything you need to know about the JASSM, with lots of images.

Boeing – Joint Direct Attack Munition
www.boeing.com/defense-space/
missiles/jdam/flash.html
Boeing site that gives background information and technical specs on the JDAM. This is not a missile as such, but a strap-on conversion kit that makes a dumb bomb brainy.

Twenty First Century Warriors
They can see in the dark. They can sense the presence of the enemy by detecting body heat. They can pinpoint their own position in a vast and empty desert. They are the new world, hi-tech soldiers.

Books

	From Shield to Storm: High-tech weapons, military strategy and coalition warfare in the Persian Gulf by James Dunnigan and Austin Bay (iUniverse, 2001) Military analysts outline the weapons, strategy, motives and miscalculations of Operation Desert Storm with accounts that were not reported in the media. Get this book
	The Complete Idiot's Guide to the Gulf War by Charles Jaco (Alpha Books, 2002) The Gulf War was brief but the fighting was intense and involved over 25 countries. Written by a journalist, this book explores the history of the Iraqi region, the politics of oil and hundreds of years of the history that ultimately led to war. Get this book
	Using GPS: Finding your way with the global positioning system by Bruce Grubbs (Verulam Press, 1999) Filled with practical examples of GPS navigation, intended to make it useful for skiers, hikers, boaters, mountain bikers and backpackers. Low cost, lightweight GPS units are now widely available. Get this book

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