Encyclopedia Astronautica

Credit: via Andreas Parsch
American surface-to-air missile. Standard Army surface-to-air missile. Later versions had anti-tactical missile capability.

The Patriot surface-to-air missile was designed to replace both the Hawk and Nike Hercules in US Army inventory. Subject to continuous improvement, 21st Century models had anti-ballistic missile capability.

Studies began in 1961 and Raytheon was selected as prime contractor in May 1967. First test launches began in November 1969. Full scale development was delayed to January 1976 by a switch to track-via-missile guidance in order to improve accuracy and decoy discrimination. It was not until 1984 that the Patriot began to deploy with Army units. Patriot is boosted by a single solid-propellant rocket motor and armed with a high-explosive blast-fragmentation warhead detonated by a radar proximity fuse. The missile is transported, loaded, and launched from a canister. Four of these are loaded onto a towed launching station. Mid-course guidance is inertial with command updates. Terminal guidance uses semi-active radar, with command updates based on track-via-missile data downlinked to the ground computer. A single G-band pulse-doppler phased-array radar replaces the multiple radars of earlier Army SAMs.

Later versions and updates of the Patriot included:

  • MIM-104B deployed in the late 1980s, with standoff jammer countermeasure capability. This allowed the missile to home on surface jammers while retaining surface-to-air capability.
  • PAC-1 with anti-tactical ballistic missile capability. This was tested in September 1986 and deployed in July 1988.
  • PAC-2 with an improved warhead, new proximity fuse, and greater anti-missile capability. This was deployed in 1990 and achieved international notice when used against Iraqi Scud missiles in 1991.
  • PAC-2-GEM with better performance against stealthy targets, and an improved fuse for high-speed ballistic missiles. This was deployed in 1995.
  • PAC-3, a three-step upgrade, with many changes to ground and missile systems, including Link 16 JTIDS to communicate with other battlefield systems, and improved capability against stealth and anti-radiation targets, and improved target discrimination in cluttered radar environments.
  • PAC-3 ERINT, a completely new missile optimized for the anti-missile role and using hit-to-kill instead of an explosive warhead. Four ERINTs can be launched from the same canister as a single earlier Patriot.

Initial Operational Capability: 1982.

Historical Essay © Andreas Parsch

Raytheon MIM-104 Patriot

The MIM-104 Patriot is the most advanced medium-long-range surface-to-air missile in current operational U.S. Army inventory, and is the only SAM to have intercepted ballistic missiles in combat. The Patriot system, complemented by the new PAC-3 missile, will remain the Army's main tactical air-defense system for some time in the future.

Studies for an advanced surface-to-air missile to supplement and eventually replace the MIM-23 Hawk already began in 1961 under the FABMDS (Field Army Ballistic Missile Defense System) program. The name was later changed to AADS-70 (Army Air-Defense System - 1970), and finally in 1964 to SAM-D (Surface-to-Air Missile - Development). Specifications were vague and changed frequently, but always included not only the ability to counter aircraft threats of all types, but also an anti-TBM (Theater Ballistic Missiles, a.k.a. short-range ballistic missiles) capability. In May 1967, Raytheon was selected as prime contractor for SAM-D development, and firing trials of SAM-D test missiles began in November 1969. The engineering development phase began in 1973, but in January 1974, a major change in the requirements occurred. It was directed that SAM-D should use Track-Via-Missile (TVM) guidance, i.e. target tracking information is not received by the ground radar directly, but by the missile which transmits it to the ground control station. Because the missile is always nearer to the target than the ground radar, this method significantly enhances accuracy and the ability to discriminate decoys from the real threat. This new requirement of course significantly delayed the development, and full-scale development didn't start until January 1976, after TVM had been demonstrated in tests in 1975. Around that time, the official designation XMIM-104A was assigned, and in May 1976, SAM-D was named Patriot. Testing of the missile and the Patriot ground equipment continued through the late 1970s, and in October 1980, the first production contract for the MIM-104A Patriot missile was issued. In 1984, the Patriot finally reached Initial Operation Capability with its first U.S. Army units.

The MIM-104A missile is powered by a single Thiokol TX-486-1 solid-fueled rocket motor, and armed with a high-explosive blast-fragmentation warhead. The missile is launched from canisters, four of which make up the M901 launching station transported on an M860 semi-trailer. In mid-course, the Patriot is inertially guided with command updates, and for the terminal phase a semi-active radar homing guidance with TVM is employed. The main item of the ground equipment is the AN-MPQ-53 G-band pulse-doppler phased-array multipurpose radar, which is controlled by the AN-MSQ-104 ECS (Engagement Control Station). The ECS is the central control agency for all missiles of a Patriot unit, and automatically coordinates the assignment of missiles to identified targets, and the launches of the individual missiles. The AN-MPQ-53 is used for tracking, IFF, and target-illumination purposes, and also includes the command uplink and TVM downlink channels. The TVM guidance method is particularly efficient in long-range and-or low-altitude engagements, when the ground radar can "see" much less of the energy reflected from the target than the MIM-104's monopulse seeker. Then the "radar image" in the missile's seeker can be used, together with the high computing power of the ECS, to discriminate decoys and calculate the interception path. At the interception point, the missile's warhead is detonated by a radar-proximity fuze.

The MIM-104B, fielded in the late 1980s, is also known as the SOJC (Standoff Jammer Countermeasures) missile and uses a modified guidance and navigation hardware. The MIM-104B adds a surface-to-surface capability against ground-based radar jamming sources to the Patriot system. The missile can fly an optimized (lofted) trajectory towards the jammer, and use its seeker to select the strongest emitter for terminal homing. The anti-aircraft-anti-missile capability is the same as for the MIM-104A.

The most important changes to the Patriot system were made by the PAC (Patriot Advanced Capability, originally Patriot Anti-TBM Capability) program. The interim PAC-1 modification, first flight tested against an MGM-52 Lance target missile in September 1986, incorporated only software changes to the search and track algorithms and the phased-array radar (the maximum elevation angle of the latter was increased from 45 to almost 90). Because the Patriot missile itself was unchanged, no new MIM-104 designation was allocated. The first PAC-1 systems were fielded in July 1988.

The PAC-2 upgrade includes further software changes, and an improved MIM-104C missile. The MIM-104C has a blast-fragmentation warhead with larger fragments (45 g compared to 2 g for the MIM-104A-B warhead) to increase lethality against ballistic missile warheads. It also has a new pulse-doppler proximity fuze with two beams, a narrow one for missiles, and a broader one for slower aircraft targets. The first test firing of an MIM-104C (against another Patriot missile!) occurred in November 1987, and the first PAC-2 systems were delivered to the field in late 1990. During Operation Desert Storm (ODS) in 1991, PAC-1 and PAC-2 systems were used against Iraqi "Al-Hussein" (modified SS-1 Scud) SRBMs. In most of the ODS engagements, two missiles were automatically fired at an incoming target. The success rate was not bad, but not as overwhelmingly good as the first reports suggested. Furthermore, the "Al-Hussein" was far from the state-of-the-art in missile and countermeasures technology.

The MIM-104D, also known as PAC-2-GEM (Guidance Enhanced Missile), is a further improved MIM-104C. It has a seeker with better performance against low-RCS targets, and an improved fuze against high-speed ballistic missiles. The MIM-104D entered production in 1994.

The designation MIM-104E has been allocated to a variant with further improved detection capability and lethality. I have no details about the upgrades, and don't know whether the MIM-104Es are new-built missiles or conversions of older rounds.

The PAC-3 system incorporates many changes to the ground equipoment and the missile, and is fielded in incremental steps, called Configuration 1, 2, and 3. PAC-3-Conf.1 was first fielded in 1995, and incorporates changes to the ECS, a new pulse-doppler radar processor, and the MIM-104D missile. PAC-3-Conf.2, introduced in 1996, includes Link 16 JTIDS (Joint Tactical Information Distribution System) compatibility and further radar improvements against low-RCS targets and anti-radiation missiles.

The ultimate PAC-3-Conf.3 includes radar upgrades to increase detection in high-clutter environments, an to improve discrimination of closely spaced objects (better decoy recognition). The most important feature of this new Patriot system, however, will be a completely new missile, a variant of the Lockheed-Martin ERINT (Extended Range Interceptor) commonly called PAC-3 (which is a bit confusing because the interim PAC-3 systems don't use this missile). The PAC-3 missile is highly optimized for the anti-missile role (employing a hit-to-kill capability enhanced by a fragmentation warhead), so that operational PAC-3 Patriot units will probably be equipped eventually with both MIM-104D and ERINT-PAC-3 missiles. The latter is significantly smaller than an MIM-104, so that 16 missiles instead of four can be carried in a single launch station. ERINT was first flight-tested in 1992, and selected as the ultimate PAC-3 missile in 1994. The PAC-3-ERINT integration tests took place from 1995 to 1997, and the missile is currently in LRIP (Low Rate Initial Production) status. The operational testing phase began in late 2001, and Initial Operational Capability is currently planned for 2003 (four years after the originally planned date). However, the operational tests in the first half of 2002 were only partially successful, and the decision for full-rate production, initially expected for mid-2002, may be postponed. The PAC-3-ERINT was also selected as the missile component of the joint US-European MEADS (Medium Extended Air Defense System).

A detailed description of the ERINT-PAC-3 missile, which has for unknown reasons not yet received a standard missile designation (as of February 2002), is outside the scope of this article about the MIM-104.

More than 12000 MIM-104 Patriot missiles have been built so far by Raytheon, and production is continuing with the MIM-104D version.


Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!

Data for MIM-104A-B, ERINT-PAC-3 (except where noted):

Length 5.31 m (17 ft 5 in) 5.2 m (17 ft 1 in)
Finspan 84 cm (33 in) 51 cm (20 in)
Diameter 41 cm (16 in) 25 cm (10 in)
Weight 900 kg (2000 lb) 320 kg (700 lb)
Speed Mach 5 Mach 5+
Ceiling 24000 m (80000 ft) 15000 m (50000 ft)
Range 70 km (43 miles) 20 km (12 miles)
Propulsion Thiokol TX-486-1 solid-fueled rocket Solid-fueled rocket
Warhead M248 91 kg (200 lb) blast-fragmentation
MIM-104C-D: 84 kg (185 lb) blast-fragmentation
Hit-to-kill + fragmentation
Main Sources

[1] Bill Gunston: "The Illustrated Encyclopedia of Rockets and Missiles", Salamander Books Ltd, 1979
[2] Hajime Ozu: "Missile 2000 - Reference Guide to World Missile Systems", Shinkigensha, 2000
[3] Bernard Blake (ed.): "Jane's Weapon Systems 1987-88", Jane's, 1988
[4] Redstone Arsenal Historical Information Website
[5] HAWK Site Denmark

AKA: MIM-104; Patriot.
Status: Active.

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Associated Countries
See also
  • Patriot Standard Army surface-to-air missile. Later versions had anti-tactical missile capability. More...
  • missile Guided self-propelled military weapon (as opposed to rocket, an unguided self-propelled weapon). More...

Associated Manufacturers and Agencies
  • Raytheon American manufacturer of rockets and spacecraft. Raytheon, USA. More...

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