Sea Service Sets Missile Defense

September 2002
By Clarence A. Robinson Jr.

Shipboard sensors create worldwide network, offer multiple engagements, warhead cueing.

Buoyed by pinpoint impact and target destruction of successive ballistic missile test warheads in space, the U.S. Navy and the Missile Defense Agency are moving to more difficult engagement scenarios. This sea-based element of ballistic missile defense builds on the existing Aegis weapon control system and Standard Missile infrastructure to extend battlespace.

Sea-based assets can project homeland security through deployed forces, buying time and distance for detection and tracking of threats headed toward the United States. The Navy’s cooperative engagement capability, coupled to shipboard Aegis, fuses data to generate increased battlespace awareness through multiple sensor inputs, multiplying combat power. This system makes target engagement possible at greater ranges, expanding kill probabilities.

The Raytheon Standard Missile (SM)-3 is part of the Navy’s theaterwide protection of U.S. forces against medium- and long-range ballistic missile attacks. The weapon system employs a lightweight exo-atmospheric projectile, or LEAP, as a kinetic warhead. Once in space, the interceptor’s kill vehicle follows a target’s infrared energy to collide with and annihilate a warhead during midcourse flight outside the Earth’s atmosphere. LEAP’s design features a wide field of view, a large aperture and a long wavelength seeker that provide target acquisition at ranges greater than 300 kilometers (185 miles).

The second of two direct hits by the SM-3, on June 13 against a test warhead in space, clears the way for more complex evaluations, expanding the interceptor’s flight envelope, perhaps even for target engagements within the atmosphere. In this most recent test, the missile interceptor, fired from the USS Lake Erie (CG-70), slammed into a ballistic missile launched from Kauai, Hawaii. The Lockheed Martin Aegis weapon control system, with its powerful SPY-1 phased array computer-controlled radar, guided the SM-3’s trajectory toward the target, an Aries modified Minuteman I second stage. Once in space, the infrared seeker signaled the kill vehicle to maneuver for warhead collision.

An earlier warhead intercept also took place in late January over the Pacific, successfully destroying that target. Launched six minutes later than the Aries missile, and flying a trajectory of more than 500 kilometers (310 miles), the closing velocity between a target and SM-3’s kill vehicle is more than 8,500 feet per second. The impact produces more than 125 megajoules of energy, equivalent to a dump truck traveling 600 miles an hour. This force is sufficient to vaporize a missile’s warhead.

The LEAP program, with its hit-to-kill capability, is under development by Raytheon Electronic Systems and its missile systems unit, Tucson, Arizona. Major subsystems are from Alliant Techsystems, The Boeing Company, ARC, and Pratt and Whitney.

In spite of the Navy’s significant SM-3 exo-atmospheric intercept accomplishments, the service still faces significant challenges to provide an effective sea-based missile defense capability. Both the Navy and the Missile Defense Agency (MDA) require protection of seaports and airports near foreign coastlines in remote littorals. Effective missile defense is predicated on a layered system approach, capable of intercepting warheads both within the atmosphere and in space.

Nevertheless, the U.S. Defense Department’s December 2001 cancellation of the endo-atmospheric SM-2 Block IVA missile program restricts the Navy’s ballistic missile defense options and has the service and the MDA scrambling for alternatives. Poor performance, projected cost growth and schedule delays are the reported rationale behind Block IVA’s termination. This wide area missile defense program, capable of intercepts in the boost phase, or in flight regimes within the atmosphere, ran afoul within the Defense Department of Congress’ Nunn-McCurdy acquisition reporting requirements.

The Block IVA’s airframe and propulsion technologies are spinoffs of the more conventional SM-2 Block IV as well as the SM-3, and are considered mature. This two-stage SM-2 Block IV, for use against highly evasive aircraft and cruise missile targets, is in development and low-rate production, with limited but growing deployment at sea.

The Navy and the MDA are examining alternatives for endo-atmospheric ballistic missile intercepts, according to Capt. Dallas G. Wilfong III, USN. He is the Pacific area theater ballistic missile defense representative for the Naval Sea Systems Command’s Theater Surface Combatants Program Executive Office. There is no current plan to replace the Navy Block IVA area missile defense program, the captain adds, “although, we have made a commitment to use available resources for experiments against endo-atmospheric threats, short- to medium-range ballistic missiles.”

Some of these experiments will involve SM-2 Block IV missiles. This weapon, the captain notes, has been developed over the past decade to deal with sea-skimming cruise missiles agilely pulling high-g turns. “We will look at whether it may also be possible to expand the missile’s footprint against a subset of endo-atmospheric and perhaps even some low exo-atmospheric ballistic missile threats,” Capt. Wilfong reports.

Earlier, modifications were made to the Block IV to convert the weapon to the canceled Block IVA. “But even our most optimistic assumptions are that the Block IV will have a smaller engagement footprint in comparison to the Block IVA,” the captain recounts. Simultaneously, the Navy also wants to see if the SM-3, which still has at least four planned flight tests scheduled against ballistic missile warhead targets, can handle some endo-atmospheric engagements, with an overlap between the two missile systems, he maintains.

The SM-3’s development is for engagement spectrums outside the atmosphere, the captain illustrates. As a result, the missile may not have the aerodynamic stability to deal with targets within the atmosphere. “However, it could just be possible for this missile to handle high endo- and low exo-atmospheric conditions, with anticipated exploration in these areas. This may, in fact, become part of upcoming flight tests,” Capt. Wilfong says. “We’ll see how much we can close this area down. A real strategic challenge will be in trying to establish a U.S. presence and force structure in areas where none is already ashore and no ground-based missile defenses exist.”

The captain points out that after years of facing numerous antiship cruise missile threats, the Navy has honed its battle management/command, control, communications, computer, intelligence, surveillance and reconnaissance (BM/C4ISR) to state-of-the-art technologies and skills. Forced into developing expertise to handle simultaneous missile and aircraft combat operations within a given battlespace, the Navy perfected an early warning and simultaneous target engagement capability. Salient real-time Navy planning functions also are available to meet U.S. ballistic missile defense requirements, he emphasizes.

In many cases, the U.S. Army and U.S. Air Force are facing some of the same BM/C4ISR challenges the Navy addressed years earlier through trial and error in realistic threat scenarios. The fleet must operate in engagement areas where a variety of missile and air defense systems require real-time coordination for maximum combat effectiveness. Aegis battle management and ballistic missile cueing could become a critical component of the MDA’s defense in-depth, offering multiple shoot-look-shoot opportunities and extremely high system lethality.

As part of a national ballistic missile defense strategy, especially within the BM/C4ISR architecture, the Navy is proposing to modify five of its Aegis cruisers, Capt. Wilfong offers. The CG-47, USS Ticonderoga, through CG-51, USS Thomas S. Gates, have extremely capable combat systems and crews. However, one of the major distinguishing factors of this class ship is its use of dual-rail Mk. 26 missile launchers. The Mk. 41 vertical launcher is in use on newer Bunker Hill-class cruisers. These five Aegis ships also operate with upgraded SPY-1A radars.

Vertical launchers are available from Spruance-class destroyer decommissioning, which could be made available for installation on the five early Aegis cruisers. The Navy is proposing that the vertical launchers be installed on the Ticonderoga-class ships and that some 20 SM-3s be procured to arm the vessels. Capt. Wilfong contends this could provide a limited sea-based forward missile defense capability circa 2004. The missiles could eventually be used in tests, if the weapons are not needed for homeland protection. “The approach is much like the MDA’s user operational evaluation concept, now morphing into a national testbed in Alaska. The missile defense testbed is always available for contingencies, as needed,” he explains.

The Aegis weapon system is deployed on more than 66 ships on station in vast ocean reaches, and 25 more Aegis-equipped vessels have been approved by Congress. Aegis also is approved for sale to Spain, Norway and Japan, so that allies also could contribute to BM/C4ISR functions. Aegis technology upgrades are continuing, with production of the system anticipated at Lockheed Martin’s Naval Electronics and Surveillance Systems–Surface Systems facility in Moorestown, New Jersey, through 2005. These Aegis improvements on fleet missile patrol cruisers and destroyers could make early warning and target cueing even more substantial missile defense functions.

Robust ballistic missile defense upgrades to Aegis are consistent with evolutionary improvements that emerged over the past decade to keep abreast of next-generation threats, Chris Myers discloses. The business development director, missile defense and radar programs at Lockheed Martin, he continues that recent SM-3 engagement successes are compatible with the Navy’s evolutionary weapons philosophy.

Myers clarifies that Aegis evolution is proceeding on three tracks. The first involves looking for technical improvements to the existing system “in as many ways as feasible to get as much performance as possible before moving on to newer technologies.” Modifications to existing software codes and additions of commercially available equipment provide system flexibility. The second avenue, he continues, takes Aegis into a larger sensor architecture as part of overall MDA use, relaying threat information via satellites. And the third direction is toward providing operational capabilities with whatever missile is selected to meet the emerging threat.

“The nation has invested $72 billion in the Aegis program, making it a natural lever to exploit early warning and battlespace expansion,” William Atwood stresses. He is Lockheed Martin’s director of air and missile defense development programs. “The importance reflected with SM-3 testing is the inherent mobility of ships operating forward on a routine basis, especially in areas of interest where ground-based missile defenses do not exist. Aegis can provide sensor input and target track displays to benefit the overall U.S. architecture.”

Many Aegis functions can assist the MDA as a cooperative element “netting together various systems—Patriot advanced capability (PAC)-3, theater high altitude area defense (THAAD), ground- and sea-based segments to prosecute layered missile defense engagements,” Atwood illustrates. He believes planned functional Aegis improvements will only enhance this concept, as LEAP test firings continue. There also is another upgrade on the horizon, primarily through software, for the SM-2 Block IV missile system.

Lockheed Martin is transforming Aegis into an open architecture system through an object-oriented design, Atwood explains. This approach capitalizes on commercial technology. A fully open system enables rapid responses to technology advances. Legacy software also is being translated to commercial languages. “The next step is to provide additional radar capability. The company is under contract to deliver a solid-state, phased array, next-generation SPY radar prototype by 2006,” he states.

As Aegis improvements unfold, Raytheon also is upgrading its SM family, including the SM-3, Dean T. Gehr, business development manager, ballistic missile defense systems, confirms. Advances in focal plane array technology provide the capability for two distinct wavelength infrared imaging bands within the same detector array. This approach also dovetails with the company’s advanced all-reflective seeker optics to reduce background noise and improve sensor performance.

Both the SM-2 Block IV and SM-3 use a common Mk. 72 booster for initial propulsion and liftoff from the Mk. 41 vertical launcher, the same steering and control section, and the Mk. 104 dual-thrust rocket motor. Unlike the SM-3, the Block IV uses an autopilot, warhead, fuze and radio frequency seeker. The commonality between the two missiles ends at the top of the Mk. 104 booster.

The SM-3 adds another staging mechanism for space flight. The third-stage rocket motor ignites and provides axial thrust and attitude control, propelling the kinetic warhead to very high burnout velocity during the midcourse phase. A global positioning system (GPS)-aided inertial navigation system (GAINS) in the guidance section positions the kill vehicle for intercept.

After launch, the SM-3 receives in-flight target updates from the Aegis ship, to further improve its trajectory. The two-pulse motor design and integral attitude control system provides mission flexibility. Once the kill vehicle is ejected in space, it immediately searches for the target based on data received from the third stage. The kinetic warhead’s sensor provides target discrimination and aim-point identification for an intercept guidance solution. A solid divert and attitude control system maneuvers the kill vehicle to ensure a lethal target collision.

The Aegis ship and SM-3’s high velocity and flexibility of sea basing provide multiple target engagement opportunities in various stages of flight. Inherent sea-based mobility allows an operational commander to defend an entire geographic region while maintaining a multimission capability.