Bombs Away!

The Air Force is working overtime to redefine its role in warfare in light of using UAV’s, drones and autonomous weapons. What is at stake is the very nature of what the AF does. For the past 40 years, it has based its power and control on a three-legged table – bombers, fighters and missiles. Its funding and status in DoD is based on keeping all three alive and actively funded by congress.

The dying cold war and the end of the threat from Russia has largely diminished the role of ICBM missiles. The AF is trying to keep it alive by defining new roles for those missiles but it will almost certainly lose the battle for all but a few of the many silos that are still left.

The role as fighter is actively being redefined right now as UAV’s take over attack and recon roles. There is still the queasy feeling that we do not want to go totally robotic and there is a general emotion that we still need a butt in the seat for some fighter missions such as intercept and interdiction of targets of opportunity but even those are being reviewed for automation. There is, however, no denying that the AF will maintain this responsibility – even if non-pilots perform it.

The role of bomber is the one that is really in doubt. If the Army uses the Warthog for close combat support and the Navy uses A-6’s and F-18’s for attack missions, then the role of strategic bomber is all that is left for the AF and that is a role that is most easily automated with standoff weapons and autonomous launch-and-forget missiles. The high altitude strategic bomber that blankets a target area is rapidly becoming a thing of the past because of the nature of our enemy and because of the use of surgical strikes with smart bombs. To be sure, there are targets that need blanket attacks and carpet-bombing but a dropped bomb is notorious for not hitting its targets and the use of hundreds of smart weapons would be too costly as compared to alternatives.

The AF is groping for solutions. One that is currently getting a lot of funding is to lower the cost of smart bombs so that they can, indeed, use many of them in large numbers, necessitating the need for a manned bomber aircraft and still be cost-effective. To that end, a number of alternatives are being tried. Here is one that I was involved in as a computer modeler for CEP (circular error of probably) and percent damage modeling (PDM). CEP and PDM are the two primary factors used to justify the funding of a proposed weapon system and then they are the first values measured in the prototype testing.

CEP says what is the probably of the weapons hitting the target. CEPs for cruise missiles are tens of feet. CEPs for dumb bombs is hundreds or even thousands of feet and often is larger than the kill radius of the bomb making it effectively useless against the target while maximizing collateral damage. PDM is the amount of damage done to specific types of targets given the weapon’s power and factoring in the CEP. A PDM for a cruise missile may be between 70% and 90% depending on the target type and range (PDM decreases for cruise missiles as range to target increases). The PDM for a dumb (unguided) bomb is usually under 50% making the use of many bombs necessary to assure target destruction. In WWII, PDM of our bombers was less than 10% and in Viet Nam, it was still under 30%. The AF’s problem is to improve those odds. Here is how they did it.

Whether we call them smart bombs or precision guided munitions (PGM) or guided bomb units (GBU) or some other name, they are bombs that steer to a target by some means. The means changes from GPS, to laser to infrared or RF to several other methods of sending guidance signals. JDAM is one of the latest smart bombs but there are dozens of others. JDAM’s run about $35,000 on top of the cost of making the basic bomb. In other words, the devices (fins, detection, guidance) that make it a smart bomb add about $35,000 to the cost of a dumb bomb. The AF’s goal was to reduce this to under $5,000, particularly in a multiple drop scenario.

They accomplished this in a program they code named TRACTOR. It starts with a standard JDAM or other PGM that uses the kind of guidance needed for a specific job. The PGM is then modified with a half-dome shaped device that is attached to the center of the tail of the JDAM. This device looks like a short rod about 1 inch in diameter with a half dome at one end and a bracket for attaching it to the JDAM at the other end. It can be attached with glue, clamps or screws. It extends about 6 inches aft of the fins and is very aerodynamic in shape.

Inside the dome is a battery and a small processor along with a matrix of tiny laser emitting diodes (LsED) that cover the entire inside of the dome. It can be plugged into the JDAM’s system or run independent and can be modified with add-on modules that give it additional capabilities. This is called the LDU – laser direction unit.

The other side of this device is a similar looking half dome that is attached to the nose of a dumb bomb using glue or magnets. There is a plug-in data wire that then connects to a second module that is attached to the rear of the dumb bomb. This second unit is a series of shutters and valves that can be controlled by the unit on the nose. This is called the FDU – following direction unit.

Here is how it works. The LDU is programmed with how the pattern of bombs should hit the ground. It can create a horizontal line of the bombs that are perpendicular or parallel to the flight of the JDAM or they can be made to form a tight circle or square pattern. By using the JDAM as the base reference unit and keying off its position, all the rest of the bombs can be guided by their FDUs to assume a flight pattern that is best suited for the target. The FDU’s essentially assume a flight formation during their decent based on instructions received from the LDU. This flight formation is preprogrammed into the LDU based on the most effective pattern needed to destroy the target or targets.

A long line of evenly spaced bombs might be used to take out a supply convoy while a grid pattern might be used to take out a large force of walking enemy that are dispersed on the ground by several yards each. It is even possible to have all the bombs nail the exact same target by having them all form a line behind the LDU JDAM bomb in order to penetrate into an underground bunker.

It is also possible to create a pattern in which the bombs take out separate but closely spaced targets such as putting a bomb onto each of 9 houses in a tightly packed neighborhood that might have dozens of houses. Controlling the relative distance from the reference LDU and making sure that that bomb is accurate will also accurately place all the other bombs placed on their targets. This effectively creates multiple smart bombs in an attack in which only one bomb is actually a PGM.

The method of accomplishing this pattern alignment is thru the use of the lasers in the LDU sending out coded signals to each bomb to assume a specific place in space relative to the LDU, as the bombs fall toward the target. The lasers in the LDU send coded signals that cause the FDU bombs to align along specific laser tracks being sent out by the LDU and at specific distances from the LDU. The end result is that they can achieve any pattern they want without regard to how the bombs are dropped – as long as there is enough altitude to accomplish the alignment. It is even possible for the LDU dropped from on bomber to control the FDU’s on bombs dropped by a second bomber.

The low cost was achieved by the use of easily added-on parts to existing bomb types and devices and by using innovative control surfaces that do not use delicate vanes and flaps. The FDU uses rather robust but cheap solenoids that move a spoon-shaped surface from being flush with the FDU module to being extended out into the slipstream of air moving over the bomb. By inserting this spoon up into the airflow, it creates drag that steers the bomb in one direction. There are eight of these solenoid-powered spoons that are strapped onto the FDU that can be used separate or together to steer or slow the bomb to its proper place in the desired descent flight pattern.

Since these LDU and FDU devices are all generic and are stamped out using SMD – (surface mount devices) – the cost of the LDU is under $3,000 and the FDU is under $5,000. 25 dumb bombs can be converted into an attack of 25 smart bombs for a total cost of about $110,000. If all of them had to be JDAMs, the cost would have been $875,000 – a savings of more than 87%.

These have already been tested and are being deployed as fast as they can be made.

Update 2012:

A recent innovation to the Tractor program was initiated in March of 2012 with the advent of miniaturized LDU’s and FDU’s that can be easily attached to the individual bomblets in a cluster bomb. These new add-ons are small enough and custom fitted to the bomblets so that they can be very quickly added to the cluster bombs. In practice, a separate LDU bomb is dropped with the cluster bomb and the cluster bomb is dropped from a much higher altitude than normal. This gives the individual bomblets time to form complex patterns that enhance their effectiveness. For instance, an anti-runway cluster bomb would line up the bomblets in a staggered zig-zag pattern. If the intent is area denial to personnel and tanks, the submunitions would be directed into an evenly spaced blanket covering a wide but defined area. This allows the placement of the mines into a pattern that is much wider than would normally be achievable with a standard cluster bomb drop which is usually limited to only slightly wider than the flight path of the dropping aircraft. Now a single drop can cover two or three square miles if the are dropped from above 15,000 feet.

A similar deployment technique is being developed for the dispersion of clandestine sensors, listening devices, remote cameras and other surveillance systems and devices.

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