Loral is developing ERINT, a highly agile upgrade for the Patriot missile system.

Graham Warwick/DALLAS

Praise for the Raytheon Patriot air-defence system during the Gulf War turned to expert criticism afterwards when the missile's performance against Iraq's Scud tactical ballistic missiles (TBMs) was analysed, with the benefit of hindsight. If the praise was overstated, then the criticism was overdone, as the Patriot was not conceived for TBM defence.

Recognising that the existing missile was a more effective deterrent against TBMs than it was a defence, the US Army initiated a competition to develop an advanced-capability Patriot (PAC-3) which would provide effective theatre-missile defence (TMD). The two contenders, were an improved Patriot missile, with active radar seeker and Loral Vought Systems' hit-to-kill, extended-range interceptor (ERINT).

The Army chose the ERINT as its PAC-3 winner in February 1994. The disputed decision was reviewed and ratified by independent panels, and approved by the US Department of Defense in May 1994. The Dallas, Texas based company was awarded the $515 million, 47-month, PAC-3 engineering- and manufacturing-development (EMD) contract in October 1994.

"Gulf War use of TBMs showed that the steps to weapons of mass destruction were technologically simple," Loral says. "The threat is here today. Delivery systems are for sale and Third-World countries can manufacture chemical-warfare agents or buy them on the black market," the company emphasises.

"The PAC-3 competition was about which missile could best defend against TBMs," says Loral. The company says that the two contenders had their origins at opposite ends of the spectrum. The Patriot is an air-defence missile designed to counter aircraft and cruise missiles, while the ERINT has its roots in strategic ballistic-missile defence.

Gulf War experience showed that the Patriot's proximity-fuzed blast-fragmentation warhead had difficulties coping with the high closing speeds between missile and target when engaging a TBM. Raytheon's solution, was to use a multi-mode seeker with active-radar capability, to guide the missile closer to its target than was possible, with the present semi-active guidance using a ground radar. The target was still to be destroyed by the fragments blasted outwards when the Patriot warhead exploded.

The ERINT has no explosive warhead. The missile is designed to collide with the target at high velocity and destroy it with kinetic energy. According to Loral, the Army decided that only hit-to-kill provides enough energy on target to assure its complete destruction. The service feared that blast-fragmentation could rupture, rather than destroy a TBM warhead and that spread its chemical-warfare payload.

Loral says that independent reviews of the Army's decision concluded that the ERINT has the capability to counter TBMs, and also cruise missiles "with some risk", while the multi-mode Patriot had the capability to counter cruise missiles, but could not assure the destruction of TBMs.

The ability to counter advanced cruise missiles and electronic countermeasures (ECM) was given less priority than TBM defence in the PAC-3 competition, Loral says. "The low-altitude, low cross-section, cruise-missile threat is evolving now and has longer-term operational consequences," the company says, emphasising that "-PAC-3 is required to counter advanced cruise missiles, and ECM and the capability will be in the system when it is fielded".

Developing the ERINT's ability to counter air-breathing targets is part of the current EMD effort, which is finalising the PAC-3 missile design and moving the system to production. Compared to the original ERINT "ballistic-missile killer", the PAC-3 will feature a "lethality enhancer" for use against "soft" targets such as aircraft or cruise missiles.

The enhancer consists of two concentric rings of heavy tungsten fragments, which are blown outwards to increase the lethal radius of the missile, as it approaches the target. Loral says that its analyses indicate "a very high probability of kill on a cruise missile".


The PAC-3 missile is 4.9m long and 255mm in diameter, and weighs 316kg at launch and 151kg at burnout of the composite-case solid-rocket motor. Eliminating the warhead results in a much smaller, faster, more agile, missile and 16 ERINTs, in four-pack canisters, will replace four Patriots on each launcher.

The Army plans to equip two to four of the eight launchers in each Patriot battery with PAC-3 missiles and the rest with the present PAC-2 weapon. Two PAC-3 launchers in each of the six batteries consisting of a Patriot battalion would result in a mix of 192 PAC-3s and 144 PAC-2s, compared with 192 PAC-2s at present - a firepower increase of 75%.

The PAC-3 is a fire-and-forget weapon. The predicted intercept point, determined by the ERINT fire-solution computer from track data supplied by the Patriot ground radar, is loaded into the missile before launch.

"Fly-out" is on inertial guidance, with the intercept point updated in flight using the Patriot radar as a datalink if required. During the fly-out phase, the ERINT, spinning at 30RPM for stability, is controlled aerodynamically using cruciform tail fins.

In the terminal phase, the target is acquired by the missile's Rockwell-developed dual-mode, millimetre-wave (Ka-band), radar seeker. This provides "instantaneous" target data to the onboard guidance-processor and 180 "one-shot" attitude-control thrusters near the nose of the missile, now spinning at 180RPM, are used to refine its course to assure body-to-body contact with the target.

If the target is a TBM, the seeker identifies the nose of the missile and aims for an impact point further aft, where the warhead should be, to assure destruction of the payload. If the target is air breathing, the lethality enhancer is triggered "a few milliseconds" before impact. The fragments expand about 100 times more slowly than the forward speed of the ERINT. Triggering the enhancer separates the fore-body of the missile from the aft body, but both parts will still hit the target, Loral says.

Integration of the PAC-3 missile with the Patriot air-defence system, developed during ERINT demonstration/validation, will be "transparent" to the operator. An integrated missile-management system is being developed, enabling launchers to handle all the missile types. The ERINT fire-solution computer consists of three cards installed in the Patriot weapon-control computer in the engagement-control station.


Loral's PAC-3 missile has its origins in the Small Radar Homing Intercept Technology (SRHIT) proof-of-principle programme awarded in January 1983, and later renamed the Flexible Lightweight Agile Guided Experiment (FLAGE). Three test flights were conducted between 1984 and 1986.

The ERINT demonstration/validation programme began as a follow on to the FLAGE project, but was reshaped in April 1988 to develop the missile for use with air-defence systems such as the Patriot, Loral says. Six test flights were conducted between 1992 and 1994. Two seekerless control tests were followed by a series of guided flights.

A successful first guided test-flight in June 1992 was followed by a failure in August 1993, when the ERINT missed its Lance ballistic-missile target because of a guidance problem, later fixed. Three successful flights followed:

November 1983: the ERINT intercepted and destroyed a Storm re-entry-vehicle target carrying a simulated chemical-submunition warhead. The 5,000g impact "catastrophically destroyed" every submunition, Loral says.

February 1994: the ERINT intercepted and destroyed a Storm carrying a simulated bulk-chemical warhead. Airborne measurements showed that the chemical simulant had been "totally dissipated" by the heat of impact.

June 1994: the ERINT intercepted and destroyed an MQM-107D target drone simulating a diving aircraft. "It was a glinty target, making it difficult 'for the seeker' to develop a centroid," Loral says. The missile hit aft of the wing and "catastrophically destroyed" the air-breathing drone.

By the time of its last flight, the ERINT had already been selected and approved as the Army's PAC-3 missile. "At least ten" EMD flight tests are scheduled to begin in late 1996, for which a TBM target with "higher relative velocity" than that of the Orbital Sciences' Storm is being developed.

Low-rate initial production is scheduled to begin in 1997, leading to deliveries in mid-1998. The first operational unit will be equipped with PAC-3 missiles at the end of 1998, to give the Army a contingency TMD capability. A decision on full-rate production is scheduled to follow.


Future applications being studied by Loral, include offering the ERINT to meet the US/French/German Medium Extended Air Defence System requirement, formerly the US Army's CorpsSAM programme; integrating a vertical-launch ERINT with the US Navy's Aegis ship air-defence system to give it a TMD capability; and upgrading US Marine Corps Raytheon Hawk mobile air-defence systems to give them a TMD capability.

Source: Flight International