LIFE Closes the Loop

by Michael Puttré
Jul. 1, 2001

In May, the US Air Force (USAF) performed the first successful live-fire tests of a radical approach to directed infrared countermeasures (DIRCM) that adapts to the jamming head of a specific threat on the fly. The milestone that occurred at the US Army's White Sands Missile Range Aerial Cable Range in New Mexico represents a departure from the shotgun method of hitting a threat seeker with multiple jamming techniques.

The Laser IRCM Flyout Experiment (LIFE) testbed, developed by program prime contractor Lockheed Martin Naval Electronics and Surveillance Systems (NE&SS) (Akron, OH), includes a two-color infrared (IR) missile-warning sensor/processor subsystem, a large array IR track camera, a laser- specific gimbal, closed-loop infrared countermeasures (CLIRCM) signal processing, and a countermeasure- effectiveness-assessment capability. It is an extension of the Large Aircraft Infrared Countermeasures (LAIRCM) program. While many components of the LIFE are common to other directed IR countermeasures programs, such as Northrop Grumman's AN/AAQ-24(V) Nemesis and BAE Systems' AN/ALQ-212 Advanced Threat Infrared Countermeasures (ATIRCM), the so-called "closed-loop" threat classification and jamming subsystem is what sets LIFE apart.

Considered "blue sky" even in the leading-edge world of laser-based directed IR countermeasures, a closed-loop system classifies the threat and then counters with an IR jamming code unique to that threat. "Open-loop" systems, which make up the balance of DIRCM programs, hit the threat with a generic jam code covering an array of threats, or multiple jam codes that are repeated in sequence. "The closed-loop capability allows the jammer to quickly assess the characteristic of the missile seeker and then return a complex synchronized jam code that quickly causes an optical break-lock," said William Taylor of the Air Force Research Laboratory (AFRL) at Wright Patterson AFB, OH. "The jamming is so effective that it causes a high-G turn away from the targeted aircraft resulting in gross miss distances."

Many of the specifics of how a CLIRCM system identifies threats are, not surprisingly, classified. However, one industry expert speculated that it could work something like this: Missile seeker heads are necessarily transparent to IR energy, which they use to lock on and then track their targets. The interrogating laser beam of the CLIRCM system exploits this opening by shining inside, causing reflections off seeker components back to the protection system's two-color IR sensors. Some of these components will produce telltale signatures, such as the spinning reticle found on most IR-seeking missiles that modulate energy from the target for tracking purposes.

Reflections from the rotating reticle also create a pattern that can be compared with a database of such patterns to identify the threat.The concept is similar to jet engine modulation, where analysis of Doppler shift in a radar return is used to identify moving or rotating surfaces on a target. Once a CLIRCM has identified the threat, it then selects the specific technique for the jam head to defeat that seeker and cues a fine tracker for the countermeasures to be applied. As a result, all of the energy produced by the laser is modulated to one purpose with nothing wasted on blanket coverage and no interruption of the jam code.

The main benefit of the closed-loop approach over open-loop, proponents said, is that it defeats missiles more quickly and with greater miss distances -- provided the interrogation successfully identifies the missile seeker, of course. The same laser interrogates the threat seeker and provides the jamming energy, and remains focused on the threat for the entire engagement.

The two-color missile-warning sensor and processor provides the initial cue that the aircraft is under attack. "The two-color [sensor] allows the missile plume to be distinguished spectrally from the solar glints and clutter," Taylor said. "We went to two color to ensure the wide- field-of-view [90°x90°] warning sensor can a dig missile launch out of the clutter but not be plagued by large numbers of false alarms."

The LIFE tests conducted at White Sands saw man-portable air-defense- system (MANPADS) IR-seeking missiles launched from what Lockheed Martin termed an "operationally significant" range. Previous live-fire tests of Northrop Grumman's DIRCM system at White Sands in 1999 were conducted from three kilometers out to 16 kilometers, and included shoulder-fired as well as air-to-air threat types. Lockheed Martin officials declined to say what specific missile threats were tested nor their nations of origin, only that they were MANPADS-type. A second round of LIFE live-fire tests involving air-to-air missile types is scheduled for later this summer.

After this summer's battery of live-fire surface-to-air and air-to-air missiles tests at White Sands, plans are for the US Air Force to follow that evaluation with flight-testing on a C-17 jet transport. The $30-million program is funded though 2006 and will install 20 CLIRCM systems on twelve C-17s and eight C-130 turboprop transports. Phase II, which is currently not funded, plans to equip 59 other large aircraft with CLIRCM systems on through 2011, including twelve KC-135 tanker aicraft.

Still an Open Road

According to John Wojner, director of advanced programs business development at Lockheed Martin, the LIFE advanced technology demonstrator is finally achieving demonstrable success after more than 14 years of effort across several programs. The LIFE program, initiated by NE&SS-Akron in 1996, was defined by AFRL as a testbed to evaluate advanced aircraft self-protection technologies for detecting, tracking, and threat-adaptive countering of IR missiles.

Advanced laser-based IRCM systems efforts began at Lockheed Martin in 1987, when BAE Systems (Pomona, CA) awarded the company a $5.8-million subcontract from on the USAF HAVE GLANCE program to design, develop, and test an advanced laser - based CLIRCM processor and control - display unit. Lockheed Martin said HAVE GLANCE was the first program to design and test a laser-based CLIRCM for airborne applications. The program concluded in 1989 due to the lack of an operational laser. HAVE GLANCE was a pod-based laser CLIRCM system that would be used on tactical aircraft to jam surface-to-air and air-to-air IR guided missiles.

It is much too early to signal the decline of the open-loop approach to DIRCM. Paul Egbert, manager of the Jam Lab at BAE Systems and program manager for the Tactical Aircraft Directed Infrared Countermeasures (TADIRCM), pointed out that open-loop systems (of which TADIRCM is one) are more mature, having demonstrated a "very high success rate" in a series of live-fire tests involving MANPADS and air-to-air missiles. "This has been a very successful approach thus far," he said.

Having demonstrated itself at White Sands, the TADIRCM program for the US Navy is preparing to take on its own milestones. In June, QF-4 target drone was equipped with a TADIRCM advanced technology demonstrator at the Navy's China Lake Test Range in California. This month, the drone will undergo live-fire testing against MANPADS missiles. Assuming it survives, it will go up against air-to-air missiles in August.

Egbert said that one element in common to both open-loop and closed-loop systems is that the absolute necessity of having up-to-date libraries of threat-seeker codes and intelligence on what threats a force is likely to encounter. Furthermore, many of the underlying technologies are common between programs. "My view is that there is definitely opportunity for cooperation between various DIRCM development teams," Egbert said. "Sure, it is a very competitive business. But that's because we're working toward the same goal: affordable, feasible, and effective ways to protect aircraft and crews."