SM-5 Mountain Top
The STANDARD Missile program has been developing ship-based air defense missiles for decades, so there was an established program office that invested time in pre-Milestone-B planning and coordination with stakeholders. According to program officials, the original plan for the next generation missile was an aggressive, costly solution dubbed SM-5. After thoroughly considering alternatives, however, the Navy decided to take the more cost conscious, incremental approach of the SM-6 which program officials said addressed 80 percent of their capability needs for half the cost of the SM-5.
The Cooperative Engagement Capability (CEC) program allows the Battle Group surface ships and airborne elements to exchange integrated, fire control quality information in real time as both an electronic warfare countermeasure and an enhanced operating capability. The SM-5 designation was applied informally to the US Navy's plan for an over-the-horizon, networked missile to leverage AEGIS CEC. The program began in 1998, and was projected to give the Standard Missile the capability of intercepting cruise missiles over land. Intended to replace the SM-2(ER) Block IV, the missile would have been targeted by E-2D Advanced Hawkeyes and. SM-3 is the upper tier BMD missile and SM-4 the cancelled RGM-165 Land Attack Standard Missile (LASM).
In January 1996, the Navy and the Army demonstrated advanced, experimental capabilities in Cruise Missile Defense (CMD). In the CMD Phase I Advanced Concept Technology Demonstration (ACTD), also known as "Mountain Top", surface-to-air missiles were launched from an AEGIS cruiser to engage sea-skimming cruise missile test targets well beyond the ship's radar horizon. Approved by the Deputy Under Secretary of Defense (Advanced Technology) in May 1994, the CMD ACTD Phase I was a joint Army and Navy effort led by the Navy.
The focus of this ACTD was the detection of over-the-horizon cruise missile targets by an elevated sensor and target engagement by surface-based (sea and land) air defense systems. In practical terms, the extended horizon engagement concept involves deploying an airborne platform with a new surveillance and tracking radar to detect low-flying cruise missiles while they are still far beyond the horizon of protected areas and defending shooters. The airborne radar was envisioned to provide precision radar data for guidance of surface-to-air missiles launched from ships and land-based missile batteries to intercept cruise missile targets beyond the firing ship's horizon or batterys line of sight.
One of the technical challenges of achieving this capability was to develop a "networking architecture" to allow the individual radars and weapons systems onboard the firing ship or battery and airborne surveillance/tracking sensors to operate as a single composite air defense system. The networking architecture must meet the very stringent requirements necessary to transfer radar and missile status data with high accuracy and precise timing to provide for interceptor missile control and homing. This networking requirement was met by the Navy's Cooperative Engagement Capability (CEC). CEC provides an identical, real time, fire control quality picture of the battle space as though it were viewed through the collective eyes of all participants in the CEC network. Other technical challenges were modifications to surface-to-air missile performance, missile control, and airborne radar. Required changes to Navy STANDARD missile terminal homing performance were incorporated in several of the latest SM-2 Block IIIA missiles specially modified for this experiment.
Navy Mountain Top culminated in missile firing tests conducted on 20-21 January 1996. The AEGIS cruiser, USS Lake Erie (CG-70), fired four STANDARD missiles and achieved four target kills at ranges more than three times greater than typically achievable with deployed systems. A typical firing scenario began when a sea-skimming target was flown out beyond radar range, and turned back toward the ship or toward shore. The developmental radar detected the target and provided tracking data to USS Lake Erie via CEC. USS Lake Erie evaluated the threat, completed fire control solutions, and ordered the target engaged while it was still well beyond the ship's AEGIS SPY-lB radar horizon. When the missile passed beyond the ship's radar horizon it was guided to the target by reflected signal energy from the tracking radar illuminator. Because target tracking and terminal homing illumination were provided by the surrogate aircraft via CEC, the SM-2 could intercept a low-flying target at long range, thus dramatically extending the air defense horizon.
The termination of the STANDARD Missile-2 (SM-2) Block IVA program due to cost, schedule, and performance problems prompted the Navy to modify the next in its series of planned standard missile programs. Initially, the Navy proposed the STANDARD Missile-5 (SM-5) program, which was intended to develop sophisticated targeting capabilities.
Strong support from senior acquisition leaders allowed program officials to advocate for a more achievable and affordable "80 percent solution" which resulted in the SM-6 program. The key to the SM-6 supplanting the SM-5 was the SM-2(ER) Block IVA. SM-2 Block IVA was to be a lower altitude BMD tier (terminal phase) to complement SM-3 that would also have an extended range AAW capability to replace Block IV. Block IVA was cancelled in 2001 and the Navy needed a gap filler. Raytheon proposed the SM-2 Block IV with the AIM-120C-7 to create the RIM-174 SM-6 Extended Range AAW Missile (ERAM). The SM-6 has the over-the-horizon, networked capability of the SM-5 with the AMRAAM's active seeker autonomous terminal interception, rather than the E-2D supported solution of the SM-5.
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