Below are some excerpts of an up-to-date independent assessment made by the renowned Institute for Defence Analyses (IDA) at the Pentagon's own request.
The "Study on the Mission, Roles and Structure of the Missile Defense Agency (MDA)" concludes that there should be no rush to deploy components of missile defense – instead of it, further research and development is recommended.

By the way, the assessment repeatedly asserts that the United States has been building global, multi-layered complex of various missile defenses (BMDS) that are to be constantly expanded and improved, both in qualitative as well as in quantitative terms. The so-called "limited" missile defense can thus soon 
transform into the robust version not unsimilar to the initial "Star Wars" project.


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The Institute for Defense Analyses (IDA) was tasked by the Department of Defense to carry out an independent study to examine and make recommendations with respect to the long-term missions, roles, and structure of the Missile Defense Agency (MDA). /page ES-1/

Specifically, the MDA is directed per Executive-level and DoD-level guidance as follows:
• To defend the United States, deployed forces, allies and friends from ballistic
missile attacks of all ranges in all phases of flight.
• To develop and deploy, as directed, a layered BMDS.
• To enable the fielding of elements of the BMDS as soon as practicable.
• To provide capability in blocks, improving the effectiveness of fielded capability
by inserting new technologies as they become available. 

The BMDS is not subject to the traditional 5000 series acquisition directives or the Joint Capabilities Integration Development System and Joint Requirements Oversight Council (JROC) approval processes. /page ES-2/

TOP-LEVEL RECOMMENDATIONS
• Retain centralized management with significant special authorities, which will continue to be essential to growing BMDS capability to meet future needs.
• The primary role of the MDA should be the RDT&E needed to continue to develop and improve U.S. capabilities to deal with existing and future ballistic missile threats. In this context RDT&E includes initial procurement and deployment of a component of the BMDS. /page ES-3/

While the independent study group agrees that there is a need to move toward more normal acquisition processes, the need for continuous evolution of the BMDS will require that the approach to setting requirements for increments of capability and developing and fielding those increments remain as special authorities with oversight of the MDEB. /page ES-3, ES-4/

For mid-course intercept systems, the balance between qualitative improvements and deploying more of existing capabilities should be strongly in favor of qualitative improvements. Without such a focus, the current system capabilities will become obsolete regardless of the numbers of interceptors deployed. /page ES-4/

... the Ballistic Missile Defense program was exempted from the Joint Staff requirements processes and DoD 5000 acquisition regulations and program review procedures; and in 2002, President Bush gave guidance to begin deployment of a set of initial missile defense capabilities in 2004. The MDA was also given control of the missile defense budget and was not subject to the normal program assessment and budget reviews by staff in the Office of the Secretary of Defense (OSD). /page II-3/

Relief from these treaty (ABM) constraints permitted a move toward a unified, global BMDS to defend against all ranges
of ballistic missiles in all phases of flight. /page II-3/

A set of Presidential Instructions, Congressional Acts, and DoD Instructions pertaining to ballistic missile defense are listed below, in chronological order, with their key points highlighted. /page II-3/

National Policy on Ballistic Missile Defense, National Security Presidential Directive-23, 16 December 2002 – “… the United States plans to begin deployment of a set of missile defense capabilities in 2004. These capabilities will serve as a starting point for fielding improved and expanded missile defense capabilities later.” /page II-4/

The ballistic missile defense mission requires a continued focus on qualitative improvements in sensors, interceptors, command and control, and battle management. The pressures for continued deployments of current capabilities can have an adverse impact on investments in RDT&E needed to increase capability to deal with a wide range of possible threats. Such a trend toward more deployments of current capabilities would seriously degrade the ability to increase the future capability of BMDS. /page III-2/

The appropriate balance between fielding current capabilities and investing in improving capabilities varies with specific systems. There is a particular need for the MDA to invest more in improvements for exoatmospheric intercepts, where future success will require improvements in multiple components of the BMDS (e.g., interceptor capabilities, sensors and sensor networks, and battle management systems). /page III-2/

The approach that provided rapid development and fielding of an initial BMDS capability has been less successful in fostering the planning and preparation needed to adequately address future operations of deployed systems and follow-on procurement and sustainment. /page III-2/

E. RECOMMENDATIONS FOR THE FUTURE MISSIONS, ROLES, AND
STRUCTURE OF THE MDA
The missions of the MDA should continue to be:
• To lead the integration of a complex set of global-scale ballistic missile defense activities that cut across OSD, the joint establishment, the Military Departments, government agencies, a wide spectrum of the defense industry, and allies.
• To develop and mature a diverse set of current and evolving technologies applicable to the challenging problems of ballistic missile defense.
• To maintain a long-term focus on constantly improving U.S. capabilities in order to deal with a wide range of ballistic missile threat characteristics. /page III-10/

The BMDS will need a continuing focus on qualitative and quantitative improvements to deal with the wide range of potential threat capabilities. This will require intense focus on technology, system development, and initial deployment of new capabilities. As the BMDS expands in scope and depth... /page V-4/

Many of the BMDS components have other functions and must be closely integrated into the broader set of capabilities that the Military Departments provide for joint operations. For example, the Standard Missile 3 is hosted by the Aegis cruisers and destroyers that perform vital surveillance and air defense and strike missions for fleet operations. The THAAD system needs to be closely integrated with other Army air and missile defense systems.

Defenses that must be provided for BMDS components may also provide multipurpose protection. The information available from BMDS sensors may be an important contributor to other joint operations. The MDA should be expected to take those needs into account while meeting the demand for continuing growth in ballistic missile defense capabilities. /page V-5/

The Air Force also currently operates the Cobra Dane radar in support of intelligence missions. /page V-6/