JED - March 2015 - (Page 28)

Conceiving of the Possible - of Directed Infrared Counter A By John Haystead The Journal of Electronic Defense | March 2015 28 Advances in technology, particularly dramatic advances in laser technology have driven major improvements in Directed Infrared Countermeasure (DIRCM) systems, allowing them to provide greater protection against IR-guided missiles for an increasing number of aircraft platforms. Over the last two decades, DIRCM system designers have been steadily reducing system Size, Weight and Power (SWaP) requirements, while simultaneously dramatically increasing performance and reliability, and reducing overall costs. Looking ahead, it appears this trend will continue, potentially opening up new platform opportunities, as well as very viable possibilities for the addition of significant new functionality and capabilities to the systems in the near future. LAMPS TO LASERS DIRCM technology has steadily evolved since the late 1980s, beginning with the transition from flashlampbased IRCM systems to laser-based optics. Two major IRCM programs underway at the time were pivotal in actually accomplishing this transition - what is now Northrop Grumman's AAQ-24(V) Large Aircraft IR Countermeasures (LAIRCM) program and, on the rotary-wing side, BAE Systems' ALQ-212 Advanced Threat Infrared Countermeasures (ATIRCM) system. The LAIRCM system actually grew out of the "Nemesis" IRCM program that Northrop Grumman began for the UK in March of 1989 (at the time, it was known as the "Operational Emergency Requirements 3/89" program), and which US Special Operations Command (SOCOM) later joined in 1993. As described by Jeff Palombo, Vice President and General Manager for Northrop Grumman's Land and Self Protection Systems Division (Rolling Meadows, IL), "At the time, lamps were really the only available technology for DIRCM." But, although the systems did provide protection for the aircraft, they also had a number of drawbacks including very limited useful lifetimes, high-cost, and high-power requirements. "As soon as we possibly could," Palombo says, "we looked at moving away from the lamps and into a laser-based technology." In general, the primary measure of protection that a DIRCM system provides to its host platform is reflected in its jamming-power-to-platform-heat-signature ratio. As observed by Palombo, this means that "for a large aircraft, such as a C-5 or C-17 with huge engines and therefore tremendous heat signatures, the system must provide a very substantial jamming-to-heat-signature ratio to be able to foil missile seekers." In fact, this requirement was an important consideration in the evolution from lamps to lasers. Would lasers be able to provide the needed jamming power levels? As it turns out, the jamming-to- heatsignature ratio of high-energy lamps would generally be in the range of about 50:1. Laser-based systems, however, can reach levels of 1000:1. In addition to providing adequate jamming power, DIRCM systems must also incorporate laser sources that can operate in the same frequency range as the missile seekers - generally in the 3-5 μm, Mid-Wave IR (MWIR) region of the spectrum, although some older IRguided threats may operate at lower frequencies. They must also be able to modify the power, Pulse Repetition Frequency (PRF) and spectral composition of the laser beam to adapt to a variety of threats. Referencing early laser research sponsored by the Defense Advanced Research Agency (DARPA) and the Air Force Research Laboratory (AFRL), David Rines, Advanced EOIR Systems Survivability & Targeting Solutions, BAE Systems (Nashua, NH), says that, "Laser technology was advancing in such a way that you could now provide coverage in the required (IR) bands that had previously only been practical for lamps." Principle among these advances was the move from early-generation CO2-based lasers to multi-band-capable solid-state and semiconductor lasers. As a result, although, the ATIRCM system originally utilized a combination of lamp and CO2 laser technology, as its development was completing in the late 1990s, advancements in multi-band laser technology allowed for complete replacement of the lamp-based functionality with a sole laser-based system. This, as Rines points out, also meant the removal of the lamps' large aperture requirements, which drove system size, as well as the large power systems needed to drive their high currents and pulse-forming networks. "Eliminating the lamps, together with the arrival of multi-band laser capability, was a significant enabler and brought about the ability to shrink the systems." LASER TECHNOLOGY CONTINUES TO ADVANCE Today, advancements in laser technology continue to drive improvements in both DIRCM SWaP requirements as well as system capabilities. According to Rines, "Our experience has been that, starting in the 1990s, about every five years or so, we've seen about a 2x reduction in SWaP in our lasers while maintaining similar or even higher output power." At the same time, however, he notes that new threats continue to emerge with some operating outside the mid-IR range where they have historically resided. "It's always a cat-andmouse paradigm, and spectrum shifting is one approach to gaining an edge, so there is always significant interest in developing new sources to address threats in this area."

Table of Contents for the Digital Edition of JED - March 2015

The View From Here
Conferences Calendar
Courses Calendar
From the President
The Monitor
World Report
Charting the Future for DIRCM
How Far Can We Take GaN Technology?
Book Reviews
EW 101
AOC News
2015 AOC Industry Member Guide
Index of Advertisers
JED Quick Look

JED - March 2015