29 April, 2003 Update:

In order to prove the point, I have started building a low-cost cruise missile of my own on a budget of no more than US$5,000. The project will be documented here. 17 June 2002 Update:

Wired News now reports that the Bush administration wants to ban the export of some of the technologies I've outlined here as having potential use in a low-cost cruise missile.

You Can Already Buy All The Bits

Cruise missiles such as the Raytheon Tomahawk have proven themselves as an extremely cost-effective method of delivering a wide range of ordinance with pin-point accuracy against targets that may be up to 1,000 miles from the launch point.

By using mil-spec GPS, highly sophisticated terrain recognition systems and a raft of other previously top-secret technologies, the cruise missile allows its owner to deliver a powerful offensive strike against an enemy with no risk to its own troops or vehicles.

However, during the past decade, huge strides have been made in commercializing much of the technology on which the cruise missile is based and it is my firm belief that building a low-cost, autonomous, self-guided, air-breathing missile with a significant payload capability is now well within the reach of almost any person or small group of persons with the necessary knowledge and skills.

Targeting/Guidance

As mentioned above, one of the key components of a cruise missile's guidance system is a mil-spec satellite-based GPS system.

Today, compact, high quality, high accuracy GPS receivers are readily available for just a few hundred dollars. The inclusion of an easily used computer interface in many of these units makes them well suited for use in a low-cost cruise missile (LCCM).

While the GPS provides information necessary for tracking waypoints and identifying the final destination, smaller course corrections (for stability) can be provided by the solid-state gyro systems now readily available for use in model helicopters and aircraft.

Instantaneous measurement of altitude and groundspeed can be provided by a semi-forward looking radar and doppler radar units (possibly built around components such as these and these. This allows a the LCCM to fly lower than would be possible if relying solely on GPS and offers a degree of contour-hugging even when the exact nature of the terrain is not available.

The gyroscopic and radar-based systems could also provide an inertial backup guidance facility in the event that the GPS system was lost, blocked or simply turned off when an attack by such LCCMs was imminent or underway.

Onboard Computing

As Moore's law continues to produce a rapid rise in the speed and fall in the cost of computer chips, we've already reached the point where obtaining sufficient number crunching capability is no longer difficult or expensive.

Single-board computer systems are another readily available off the shelf component that can be recruited for use in an LCCM. Even the sophisticated realitime operating systems necessary for supporting the type of software needed to interface the guidance/targeting systems to the control servos are just a download away.

Airframe

Since an LCCM would be designed to fly at subsonic speeds (probably around 450-500 mph) the aerodynamic design of such a craft is relatively simple and there is plenty of resource material available to assist in such an undertaking.

Indeed, the fact that so many very successful radio-controlled model aircraft have been designed and built from scratch by talented amateurs testifies to the viability of such an option.

LCCM-specific factors that need to be taken into account when designing and constructing the airframe include the need for a low heat signature and low radar profile.

The use of materials such as fiberglass and kevlar composites would go a long way towards reducing the radar profile of such a craft, as would the insight gained from a close inspection of the masking techniques used on the existing generation of stealth craft.

Experimentation with coatings containing finely ground ferrites may even offer some degree of radar absorbsion. The heat signature of a suitable engine could be significantly reduced by judicious entraining of slipstream air to dilute and cool the jet exhaust prior to ejection behind the craft. At the cost of some thrust, the jet efflux could also be channeled so that the engine itself is not visible even from a rear view.

Powerplant

The realization of just how practical an LCCM has become came to me when I was doing development on my pulsejet engines -- since they would make an ideal low-cost powerplant for such a vehicle.

The fact that the German V1 "flying bomb", perhaps the first practical implementation of the cruise missile concept, was also powered by a pulsejet speaks volumes for the practicality of using such a powerplant today.

Traditional pulsejets would not be the best choice for an LCCM however as their very hot exhaust would make them an easy target for even the most primitive heat-seeking missile and their astonishingly poor fuel-efficiency plus limited reliability would reduce the LCCM's practical range.

A small turbojet (or the XJet) engine with 100lb-500lb of thrust however, would be the perfect powerplant -- offering a high level of reliability and longer ranges without the need for an excessive fuel-load.

Launch Facilities

Most existing hi-tech cruise missiles are designed for launch by way of a solid-rocket booster to get them up to flying speed, or they're dropped from an aircraft already flying at speed and altitude.

The V1s of WW2 were launched using a catapult system powered by a mix of nitric acid and hydrogen peroxide.

None of these systems would be required for an LCCM. A simple launch attachment could be fitted to the roof of an SUV or truck that would allow the takeoff speed of around 70mph to be achieved. At that point the engine could be ignited and the craft released.

Using this method, a reasonable sized LCCM could be transported by road to a position within range of the desired target, unpacked, prep'd and then launched from a deserted stretch of roadway within a few minutes.

Payload

Cruise missiles can carry just about any payload required in the theater of war.

High explosives are the most common payload but probably the least attractive to a terrorist group -- since, to be effective, these explosives do require very accurate targeting and represent a higher level of risk during the transport and launch phase.

More attractive would probably be some form of biological agent (anthrax, nerve gas, poison, etc) or even some type of nuclear material. the LCCM could be programmed to disperse its payload over a large area of high population with massive potential for death and injury in a manner that would be very difficult to defend against.

At What Cost

The electronics (guidance/targeting, control systems, etc) could be purchased for less than $2,000. An airframe, built using the type of foam-composite construction found in a number of home-built light aircraft would cost between $1,000 and $5,000 depending on the size of the craft. The engine would cost between $500 and $150,000 depending on the type and size. Turbojets/turbofans are significantly more expensive than pulsejets and would be far more likely to ring "warning bells" if they were purchased in quantity by someone without an established track record or presence in the aviation marketplace so a simple pulsejet would be the most prudent option for a terrorist group.

The total component costs for an LCCM (less payload) could be as little as $6,000 for the smallest, simplest version, with a larger, more sophisticated design still requiring little more than $10,000 worth of parts and materials.

The real costs would come from the integration of all these components and the development of the software required to link the guidance/targeting systems to the aircraft's control systems. However, suitable resources are available in many eastern-bloc countries and doubtless could be purchased on a "no questions asked basis." This development cost is also a one-off expense that would be effectively amortized across the number of individual units constructed.

There is even a very good chance that the development costs could be quickly recouped by selling the resulting design to other parties interested in constructing similar LCCMs.

The cost of the payload carried by the LCCM would depend entirely on nature of that material -- but it would appear that those bent on terrorism have little difficulty in obtaining explosives or biological warfare agents.

Why Worry?

Personally, I'm more than a little worried at the prospect of terror groups or others constructing and launching their own LCCMs.

To date, the most effective method terrorist groups have had at striking against military or civilian targets has been the suicide bombing.

With the massively increased levels of security and surveillance that have been implemented in the September 11 attacks, the viability of such attacks are now in question.

June 10 Update:

The assertion that a heightened level of security in the wake of Sept 11 has effectively thwarted the traditional "suicide" attacks planned by terrorist groups has been effectively verified by recent events in which the US foiled a dirty nuke plan and Morocco stopped a planned attack against US and UK warships in the straights of Gibraltar. Could the effectiveness of such security measures now force al Quaeda to resort to more hi-tech tactics? Tactics including the use of low-cost cruise missiles that allow them to launch their attacks several hundred miles from the intended target?

The very fact that so many people with known anti-USA affiliations were turning up to have flying lessons and simulator time was enough to ring alarm bells at the FBI -- when it comes to the LCCM we might not be quite so lucky.

An LCCM can be built with items that are so readily available that, even if a group decided to build hundreds of them, there would be no way of easily detecting their activities. Although purchasing a number of turbojet or turbofan jet engines might pose a problem, pulsejets (even a sophisticated design such as the X-Jet) could be easily built from stainless steel using readily available tooling and machinery.

As someone with over 20 years experience in the design and construction of electronic control systems, realtime systems software, large model aircraft, and most recently, high efficiency pulsejet engines, I consider the design and construction of a simple yet surprisingly effective LCCM to be well within my own capabilities. If I could do it then you can bet that there are many others who have the ability to do the same -- and not all will be friends of the West.

In fact, if I had the time and the money, I'd love to build such a vehicle (albeit without the lethal payload) simply as a proof of concept.

If the LCCM concept was implemented by a terrorist group, they would likely carry out the design, development and testing work in a relatively safe, secure location within the borders of a friendly nation and then send the plans electronically (probably using something as simple as encrypted email) to agents operating in relatively close proximity to the intended target.

From there it would be a very simple task to purchase the required components and materials then fabricate and assemble the actual LCCM. The completed units would be loaded onboard trucks hired or purchased for the purpose and transported to within striking distance (100-300 miles) of a major city or military target. From any number of widely dispersed locations within the launch radius, the LCCMs could be launched simultaneously so as to stretch the defense capabilities of the party being attacked.

Imagine the effect of just one such LCCM reaching central NYC on a warm summer's afternoon, and dispensing a hundred pounds or more of highly radioactive material or anthrax spores in a fine dust across an area of (say) a square mile.

What Can Be Done About This Threat?

Unfortunately there's probably very little that can be done to reduce the magnitude of this potential threat.

Doubtless a country such as the USA has the technology to shoot down an LCCM -- but there's a very good chance that multiple launches from dispersed points relatively close (say 100 miles -- representing a flight time of just 12 minutes) to the intended target would likely make it impossible for a defending force to deal with all the LCCMs launched.

A small (say 5-foot long) target travelling at 500 mph, less than 200 feet above the ground while following an unknown and deliberately erratic course becomes an extremely difficult target to hit -- even if you're ready and waiting for it.

Given that, with a radioactive or biological payload, it would only require a single LCCM to reach its intended target in order to inflict a damaging blow, the capability of defending against such a strike must be considered just modest at best.

While one could argue that driving a large truck to the intended target and then detonating whatever device was onboard remains a far simpler option for terrorists -- it must also be acknowledged that this is not a particularly effective way of dispersing a bio or nuclear agent. Such a blast, especially in an area containing many high-rise buildings, would only provide minimal dispersal. A air-drop could cover a much wider area with resultantly greater effect.

The fact that the September 11 terrorists were obviously considering just such an aerial dispersal through the use of crop-spraying aircraft is clear indication that they are very much aware of this.

In the 21st century, technology plays no favorites -- it is the slave of anyone who chooses to master it.