1. ASCMD,
4.2 ARMY MISSILE DEFENSE R&D PROGRAMS .1 Theater High Altitude Area Defense System
4.2.2 Patriot PAC-3
PAC-3 (Figure 4.2) is the latest of three upgrades to the Patriot air defense system to provide a robust capability against theater ballistic missiles. The PAC-1/PAC-2 system, used in the Gulf War against Scud ballistic missiles, demonstrated a threshold level of capability against this threat, but a need for improved capability was evident. The PAC-1 and PAC-2 modifications to
ASSESSMENT OF CURRENT AND PROJECTED R&D PROGRAMS 107
Patriot, largely in radar coverage and missile warhead design, were made only a short time before the Gulf War, leaving little time for test and evaluation before they were used in combat. While the ability of the system to intercept Scud missiles was demonstrated, including field upgrades performed to cope with tumbling missiles, it was not clear if there were any warhead kills, so further improvements were warranted.
The need for a theater ballistic missile defense capability has been recog- nized by the Army for several decades, and the quest for a defense system to meet this need has been marked by a number of shifts between single- and multiple-mission approaches. In the late 1950s and early 1960s, the field army ballistic missile defense system (FABMDS), a self-contained, mobile defense system designed expressly to engage free-rocket-over-ground (FROG)-type bal- listic missiles (Soviet short-range ballistic missiles), was under development, but FIGURE 4.2 PAC-3 system.
• Endo-atmospheric, lower-tier TMD system
• C-band phased-array radar
• RF active homing guidance
•16 PAC-3 missiles/launcher
• FUE September 2001, IOC 2005
• 5 for 5 successful HTK intercepts, 3 vs. ballistic missile, 2 vs.
cruise missile targets (as of 9/00)
it was phased out largely because of the difficulties of packaging a complete system in a single vehicle. Also, FABMDs gave way to a shift in Army priori- ties from TMD to air defense, the mission objective of a study conducted from 1963 to 1965 called Air Defense Systems of the 1970s (AADS70).
The SAM-D system, which was the product of AADS70 studies, began with a requirement for a dual-mode capability (TMD and air defense). To reduce its cost, the SAM-D system was reoriented to a single mission, air defense, in the early 1970s, and its name was changed to Patriot. It remained a single-mission air-defense system until the PAC-1 and PAC-2 modifications were incorporated just prior to Desert Storm.
The ABM Treaty, signed in May 1972, prohibited the upgrade of such sys- tems to provide an ABM mode. While the treaty does not proscribe TMD system development or deployment, the ambiguities and controversies surround- ing the distinction between TMD and ABM systems inhibited the development of that class of system for a number of years.
The main elements of a PAC-3 battery are a radar set, an engagement control station, and a launch station. The launch station consists of a mobile launcher carrying 16 PAC-3 missiles. In the basic battery, launchers can be located up to 10 km from the engagement control station. With the remote launch communi- cation enhancements upgrade, currently under development, launchers can be located up to 30 km from the basic battery, thus extending the TBM-defended area significantly. The radar is a mobile, multifunction, phased array operating at C-band.
In a modern Patriot battery, there are 8 launchers, 4 of which are loaded with 16 PAC-3 missiles each (total of 64 PAC-3s) and 4 of which are loaded with 4 PAC-2 missiles each (total of 16 PAC-2 missiles). The PAC-2 missiles, originally designed to enhance TBM lethality through the use of large fragment size, are now inventoried for use against all classes of targets. The mixed inven- tory of PAC-2 and PAC-3 missiles gives the Patriot battery flexibility in engage- ment of ballistic and air-supported targets.
The original guidance system for the Patriot air defense, still used in PAC-2, was RF semiactive homing, with a downlink to allow implementation of target- via-the-missile (TVM) processing. The TVM approach was initially selected largely because the onboard computers did not have the required throughput, a limitation that has been diminishing rapidly with the march of Moore’s law. The PAC-3 missile uses a Ka-band active seeker for endgame homing. This guidance system was developed and demonstrated in the experimental extended-range interceptor (ERINT) program, culminating in three consecutive hit-to-kill inter- cepts, before transitioning to the Patriot system.
Extensive design trade-off analyses were conducted between a semiactive and an active RF guidance mode and the active seeker before final selection of the active mode for PAC-3. The main factor leading to selection of the active RF guidance mode was its demonstrated hit-to-kill lethality in an endo-atmo-
ASSESSMENT OF CURRENT AND PROJECTED R&D PROGRAMS 109 spheric environment. Since the hit-to-kill strategy obviates a warhead, the mis- sile is smaller and lighter, allowing a larger number of missiles per launcher (four times as many as PAC-2). This increase in firepower is a significant factor in handling large raid sizes and in implementing a salvo firing doctrine to im- prove kill probabilities.
The engagement sequence of PAC-3 is (1) inertial fly-out of the missile following initial detection and tracking by the radar to a nominal intercept point in space, (2) onboard seeker acquisition, (3) midcourse homing using rapid- response attitude control thrusters, and (4) endgame homing to achieve hit-to- kill of the target. Precommitment discrimination is performed by the radar, including a high-resolution waveform that enhances discrimination performance and provides growth options for non-TBM target classification. A critical on- board function is aim-point selection to assure warhead kill, a function that was not accurately executable by Patriot during the Gulf War. Aim-point selection has been effectively executed in the PAC-3 tests conducted to date.
As noted, PAC-3 is an endo-atmospheric, or lower-tier, TBM system, com- parable in altitude operating regime to the NAD system. The Army has analyzed PAC-3 from both an effectiveness and an operational viewpoint as an underlay to THAAD in a layered configuration, as well as an autonomous TMD system.
Since the elements of the PAC-3 system are separate and distinct from those of THAAD, they can provide a statistically independent tier of defense yielding very low overall leakage. With a lower tier having 20 percent leakage, net system leakage will be 4 percent (0.2 × 0.2 = 0.04). For the defense of high- value theater targets, this layered defense mode can be of immense value in providing a level of protection unachievable with a single system.
The PAC-3 system has had five consecutive successful tests, three tests against ballistic targets and two tests against cruise missiles. The active RF mode has proved to be effective against both classes of targets. Significantly, the tests conducted thus far demonstrate warhead kill against unitary warheads and high lethality against multiple canister warheads.
The PAC-3 system is currently in a low rate initial production phase, with 16 missiles scheduled for the end of FY01 and 32 in FY02. The full system FUE is scheduled for the fourth quarter of FY01, coincident with FUE for the PAC-3 missile. The PAC-3 IOC is scheduled for 2006.
Candidate technologies for block upgrades to Patriot PAC-3 include the following:
• Solid-state transmitter. Building on prototype development for PAC-3 performed in the atmospheric interceptor technology (AIT) program, this pro- gram would transition a K-band solid-state transmitter to production. It would provide an alternative to the traveling-wave-tube-based transmitter. The pro- gram includes producibility enhancements, consolidation of the support elec-
tronics through the use of application-specific integrated circuits (ASICs), and environmental stress testing of a prototype.
• IFOG. A COTS IFOG unit has already been configured for PAC-3 inser- tion, and it would be a relatively straightforward upgrade to improve navigation- al accuracy with lightweight, low-cost gyroscopes. An opportunity for further improvement exists in the MEMS implementation of an IMU, a design not ex- pected to reach maturity until at least 2005 or so.
• Upgrades either under way or being evaluated for the Patriot radar.
These include advanced A/D converters, advanced digital signal processors, and improved discrimination and classification. A recent example of improved dis- crimination was the successful demonstration of a wideband frequency-jump burst waveform to measure body length.
4.2.3 Joint Land Attack Cruise Missile Defense Elevated