Ballistic Missile Defense System Sensors and the Role of Space Systems
Scott J. Prouty
The Aerospace Corporation is assisting the Missile Defense Agency with defining requirements, identifying new technologies, and integrating existing sensor capabilities for the Ballistic Missile Defense System. Aerospace is also applying rigorous testing and systems engineering expertise to the development and operation of the system.
The mission of the Missile Defense Agency (MDA) is to develop and field an integrated Ballistic Missile Defense System (BMDS) that provides the homeland, deployed forces, friends, and allies with a layered defense against ballistic missiles of all ranges in all phases of flight. To fulfill this mission, the agency is developing, testing, and integrating sensors, interceptors, and a Command and Control, Battle Management, and Communications (C2BMC) system into a global architecture that must work to detect, track, and intercept enemy missiles.
MDA relies on a variety of sensor systems operated on land and sea and in space to provide the information required to engage missile threats. Sensors used by the BMDS to detect and warn of upcoming threat launches include radio-frequency and electro-optical infrared sensors, MDA-developed sensor capabilities, and sensor capabilities developed by other agencies that are integrated into the BMDS. Except for the MDA Space Tracking and Surveillance System, space systems fall into the sensor capabilities developed by other agencies.
Aerospace is extensively involved in the integration of these sensor data from sources developed by agencies outside MDA into the BMDS. Integrating these data allows MDA to take advantage of the significant investment in hardware, software, and talent that exists in the nation’s space program. In cross-agency integration, MDA engineers and acquisition professionals work with other agencies to develop products and services that interface between systems.
Aerospace works across the development process to make space sensor data a valuable tool for the BMDS. These Aerospace activities are integral to BMDS systems engineering and also to the assessment of the utility of current and future space capabilities to support the BMDS. Aerospace has developed MDA requirements for current space systems, defined architectures for future systems, and identified key technologies that require development to meet future BMDS needs. In addition, Aerospace provides systems engineering expertise to the development and testing of BMDS-dedicated ground processing that takes sensor data from space sensors-to include the Space-Based Infrared System (SBIRS) and others-and develops products that could potentially support BMDS operations.
One product from this work is the fusion of infrared sensor data to develop boost-phase track messages that can identify missile position and velocity to support cueing of BMDS ground radar assets. This cueing allows for much more efficient use of radar resources, thereby increasing BMDS performance. This capability has been demonstrated in MDA flight tests and is now in the process of being folded into more rigorous BMDS testing. Once proven in testing, it will be a candidate for transition to operations.
The Sea-Based X-band radar arrives in Pearl Harbor aboard the heavy-lift vessel Blue Marlin on Jan. 9, 2006. |
BMDS Sensor Architecture
BMDS relies primarily on fixed and transportable radar assets located around the world. These radars include X-band radars in the forms of the Sea-Based X-band (SBX) radar and the AN/TPY-2 forward-based radar; the SPY-1 S-band radar on Aegis ballistic missile defense ships; the Theater High Altitude Air Defense (THAAD) radar; the Upgraded Early Warning Radars (UEWR); and the Cobra Dane radar. The space sensor assets that can most readily be incorporated into BMDS are overhead nonimaging infrared assets. These systems include the SBIRS and Defense Support Program satellites, which were designed to sense the infrared energy from a missile in flight.
An X-band (wavelength 2.5-4 cm; frequency 8-12 GHz) radar can search, detect, and track missiles, and distinguish between warheads and countermeasures. The SBX radar is built upon a movable sea platform that will improve the ability to acquire, track, and discriminate countermeasures during the midcourse phase of flight. The AN/TPY-2 radar provides information early in the flight of a potential ballistic missile launch and helps discriminate threat reentry vehicles from associated countermeasures. The THAAD radar is an X-band, phased-array, solid-state radar that will provide extended coverage and the ability to engage incoming missiles more efficiently. The Aegis Ballistic Missile Defense Program provides an early line of defense against ballistic missiles. The Aegis S-band (wavelength 8-15 cm; frequency 2-4 GHz) radar ensures target detection in adverse weather where X-band radars can potentially be heavily affected by sea or rain clutter.
The Ground-Based Midcourse Defense system also includes the UEWRs and the L-Band Cobra Dane radar. These radars provide long-range missile surveillance, acquisition and tracking, and object classification, as well as update information for the BMDS exoatmospheric kill vehicle(s).
Functionality and Support
Space sensors fulfill five functions in supporting the BMDS. In the first, "situational awareness," a number of national systems provide information to the warfighter/operator about the actions and intent of an adversary. Next, sensors send a wakeup call-the "bellringer"-informing an operator that a threat missile launch has taken place and that the defense system should be alerted to be ready to respond. The Overhead Nonimaging Infrared (ONIR) missile-warning satellite system, to include the SBIRS, is the primary provider from space systems of this type of information.
The third function, "sensor-to-sensor cueing," allows a sensor with a threat missile in track to pass pertinent information on that missile to another sensor so that it can efficiently pick up the missile. Again, this is a function from space systems primarily fulfilled by the SBIRS and ONIR system. The fourth and fifth functions, "launch on" and "engage on," occur when the weapon system assigned to defend against the incoming threat is activated based on the space sensor information. Accuracy of the information available from the sensor system and the capability of the weapon system differentiate the criteria of these two functions. In other words, does the accuracy and timeliness of the information available for the sensor system allow for the weapon system to close the fire control loop and launch and negate an incoming threat missile?
Sensor accuracy, timing, information latency, coverage, and availability are all system attributes that determine if a possible sensor system is capable of supporting these five functions. For example, highly accurate information that is too late or timely information that is inaccurate can negatively affect the execution of the BMDS mission. This balancing act between accuracy and timeliness is one of the major design trades that continues to be investigated and analyzed within MDA and the external sensor community. In addition, limited coverage and availability can adversely affect the benefit of a sensor to support the mission.
The forward-based AN/TPY-2 radar consists of a solid-state phased-array X-band antenna supported by an electronics unit and a cooling unit. |
Why Space Sensors?
Space systems provide global coverage and a wide-area search capability, allowing space sensors to monitor the globe looking for missile launches. These space sensors provide the global look that ground- and sea-based radars cannot because of their more limited fields of regard. Though ground- and sea-based radars have a more limited field of regard, these radars generally provide more detailed and accurate information on the threat to the BMDS and provide the fire-control quality data for the weapon system. The persistent, global coverage of space assets when integrated with the accuracy of ground and sea-based radars allows the BMDS to take advantage of the best performance attributes of each sensor type for improved integrated sensor performance in support of BMDS mission capabilities.
One of the tools MDA has used in developing and demonstrating the synergies between different sensors within the BMDS is a rapid prototype environment that allows the developers to quickly and efficiently develop, integrate, and test new sensor-to-sensor concepts. This rapid prototype environment at MDA is the External Sensors Laboratory.
External Sensors Laboratory
The External Sensors Laboratory is an MDA research and development facility located at the Missile Defense Integration and Operations Center at Schriever Air Force Base in Colorado Springs, Colorado. The laboratory's mission is to develop and test concepts for using sensor data from external space systems-those systems developed by agencies outside MDA-to support the BMDS. The laboratory is a contractor-operated facility designed for the testing and evaluation of innovative ideas from industry, FFRDC/UARCs, and SETAs to determine their potential benefit to the BMDS mission. Promising ideas become candidates for further development, integration, and testing with the goal of fully mature concepts being transitioned to operations. Aerospace plays a key systems engineering role in this process of exploring innovative ways of using this sensor data and making products from the data available to C2BMC and other elements to increase the performance of sensor and weapon systems. Using data from external systems is allowing MDA to experiment with new algorithms and operation concepts for using the SBIRS and other ONIR sensor data to generate boost-phase track messages to cue a radar asset. This capability allows the radar to generate a more precise search volume from the track data.
Demonstrating a new capability in the External Sensors Laboratory is the first step in the process of maturing a new capability for the BMDS. Further efforts are under way in developing a robust interface to C2BMC, participating in MDA ground testing and flight testing, assessing end-to-end BMDS performance, and, finally, implementing and hosting the capability at an operational location. Aerospace is playing a key systems engineering role in this work.
The integrated Ballistic Missile Defense System (BMDS) consists of a set of sensors, including SBIRS, STSS, and various types of radars; more than half a dozen interceptor types; and a comprehensive C2BMC system of systems. The BMDS will know the location and state vector of a threat target during all of its system segments: boost phase, midcourse phase, and reentry. Each of the shooters and their sensing systems are designed for one of these segments. |
Interface to the Warfighter
The key interface for the External Sensors Laboratory is with C2BMC. The C2BMC provides the primary interface to the warfighter/operator and is responsible for providing the command and control, battle management, and communication functionality needed to execute the BMDS mission. Command and control provides the operator with situational awareness of the adversary's action and the operation status of the defense system mission. This situational awareness is provided by many assets, including space assets. Battle management takes place after an adversary missile is in flight. The many activities during battle management include determining if the missile is a threat, determining the best way to counter it, and allocating sensor and weapon resources to negate the threat.
As part of battle management, space systems provide the wake-up call to the BMDS that a threatening missile is in the air. Additionally, sensor data and the associated products of the External Sensors Laboratory can provide the track information necessary to cue ground radar in boost to help it quickly and efficiently acquire the threat. Providing this boost-phase cueing information from space assets has been demonstrated by the External Sensors Laboratory in flight tests. This capability is being refined and in the future may become part of the BMDS operational capability.
Summary
MDA is developing the BMDS to use a set of land-, sea-, air-, and space-based sensor assets that provide information to allow the BMDS operators to use sensor and ultimately weapon systems to negate adversary missiles. Space sensors bring persistent, global coverage and provide threat-missile information of sufficient accuracy and timeliness to support a variety of BMDS functions. Aerospace is providing systems engineering expertise to MDA's space systems development to include a lead role in systems engineering in a rapid prototyping development called the External Sensors Laboratory. The use of space systems within the BMDS will continue to evolve, and Aerospace will be an integral player in this evolution.
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