Space Based Radar (SBR) and Missile Defense
In accordance with the National Defense Authorization Act for FY2004, the Defense Science Board (DSB) was asked to assess the potential contributions of a Space Based Radar (SBR) to missile defense. In response, the Undersecretary of Defense for Acquisition, Technology and Logistics (USD (AT&L), and the Director, Missile Defense Agency (MDA) directed that the DSB Task Force on the Contribution of a Space Based Radar to Missile Defense perform the following tasks:
- Assess the impact of adding a missile defense mission on the ability of SBR satellites to conduct their primary missions;
- Assess how different SBR architectures and technical approaches might affect the ability of the satellites to achieve their primary missions and to contribute to missile defense;
- Assess the value of potential SBR capabilities in the context of the family of sensors being developed by the Missile Defense Agency; and
- Recommend any future actions that might be desirable related to SBR contributions to missile defense.
AMTI could provide early warning of missile launch from known launcher locations and some capability to search a given area on the surface for launches from unknown sites. Using conservative assumptions, about 10% of a single satellite's SMTI/AMTI resources are needed for each monitored site. Using other assumptions, SBR, using AMTI, could monitor multiple sites and also search a significant area for launches from unknown sites. Single satellite access should be capable of providing information on a single digit number of simultaneous launches.
Early launch detection (before cloud break) could cut valuable tens of seconds from the time to cue other missile defense systems. The AMTI capability could also provide sufficient trajectory information to commit an interceptor for earliest engagement. Earliest commitment is critical to success for boost/ascent phase and some mid-course intercepts.
The presently planned missile defense system depends primarily on the Defense Support Satellite system (DSP) for global launch warning. Since DSP is an IR system, it cannot provide launch detection until cloud break. In addition it does not provide sufficient trajectory information for early commitment of missile defense interceptors. Consequently, to defend against short time of flight attacks, e.g., a forward-based radar is required. In the near term, the Aegis radar system is to provide that capability for launches from North Korea. In the longer term, a global system of forward sensors will be required.
With the addition of a high pulse repetition frequency capability (HPRF) waveform, the SBR system should be able to screen out ground clutter outside of the main lobe directly below the satellite. That should provide for SBR to detect targets moving faster than a minimum detectable velocity (MDV). Further work by the SBR Program Office is required to quantify the cost and risk of this addition, but the needed radar components are available and the cost and risk should be low.
With this system addition, the SBR could monitor known sites with high reliability and provide early engagement quality trajectory information for launches from known sites or when cued by other sensors. The system could also be used for uncued area search within a specified area.
For this mode of operation to be most effective, the AMTI capability would need to be cued, which could be provided by the SMTI/SAR imaging capability of SBR or other surveillance assets to include IR systems when cloud conditions permit. Given such cues, a conservative estimate of the maximum AMTI dwell time required to detect a launch from a range of 2,800 km is less than 1 second. Against boosting missiles with larger radar cross-sections, the dwell time could be a fraction of a second. Considering expected initial missile acceleration, and the near vertical initial trajectory, the planned vertical dimension of the AMTI beam will ensure that the missile will remain within the beam size for at least 10 seconds.
Using other reasonable assumptions, single satellite access could provide the capability to monitor multiple sites of known location and search a designated area to detect launches from unknown locations. While this uncued search approach will not provide reliable access over large areas, the capability provides an added problem for an adversary since they cannot know what part of their territory is being scanned in this mode at any given time.
With the larger constellations needed for continuous access to ground target areas of interest, there will be more than one satellite providing access to a given area a significant percent of the time. In this case, the uncued search capability is significantly enhanced and/or the impact on other missions is reduced.
Using conservative assumptions, a single satellite could monitor at least 10 missile sites within the satellite's area of access if all of the satellites MTI resources are devoted to that task. With the same conservative estimates, a single site could be monitored using about 10% of the single satellite's resources. With other reasonable assumptions, a much smaller percent of the satellite's resources would be needed for this level of contribution to missile defense. Building a SAR image at these range from a LEO satellite requires about 16 seconds. However, that process can be divided into shorter segments so that it would be possible to monitor multiple launch sites while also using some resources to meet SAR imaging needs. Again, with larger constellations, more than one satellite will have access a significant percent of the time further reducing impact on other missions.
The 9-satellite system would not provide a useful early launch and trajectory warning capability since such a capability must be 24/7 during periods of high concern. With a 21-satellite constellation and the addition of HPRF, SBR could take over some, or perhaps all of the radar coverage tasks for launch and trajectory warning and free a system such as Aegis to devote more resources to other mission demands. However, this capability was not likely to be available before 2012 [as of 2004] and the planned missile defense architecture is to provide forward based land or sea-based radars well before the planned first SBR deployment.
Given the need for high-resolution global radar access (or access with some other set of high-resolution sensors) for discrimination, just adding early launch and trajectory warning does not significantly reduce the need for the planned elements of the currently defined missile defense architecture.
Providing the needed forward-based high-resolution sensor access for the evolving integrated layered system may not be feasible using only surface-based systems. It seems likely that space-based assets will need to have an expanding role and is likely to be the preferred, perhaps the only feasible, approach to meeting some important sensor location demands for the boost-phase layer of missile defense.
The 2004 DSB report concluded that the potential value of AMTI capability warranted adding it to the SBR program. To be useful for this mission, the constellation must eventually provide near continuous access during times and at places of high interest. While adding the capability inevitably has some impact on cost and risk, the task force believed the impact to be low. Adding the HPRF capability displaces no currently planned performance.
The 2004 baseline SBR was to have an inherent capability to measure velocity and velocity changes of major components of a missile system that are above the horizon with useful precision. Cueing is required for SBR to acquire the missile. This capability would provide an intercept error basket precise enough to direct the interceptor to its required acquisition and maneuver basket.
The 2004 DSB report concluded that the Missile Defense Agency needed to include the trajectory tracking capability of the baseline SBR in plans for the overall sensor architecture for an integrated missile defense.
Adding SBR capabilities for missile defense will place new demands on a number of key functions, e.g., signal processing, software development, communication links, and off-board system updates. An aggressive technology development and transition program would be needed to provide a netted, integrated, computer aided command and control and battle management system.
The 2004 Nominal SBR designs and constellations can search countries the size of North Korea or Iraq for moving targets of cross sections larger than about 10m2 about every 10 minutes. This would include moving missile Transport-Erector-Launchers (TELS). However, there can be thousands of 10m 2 vehicles moving at any time in a country the size of Iraq. Targeted monitoring of specific areas based on the full set of intelligence, surveillance and reconnaissance capabilities to include SBR SAR imaging will be required to direct the SMTI capability at areas of interest.
The command and control and battle management integration task is not appreciably changed by the addition of SBR to the intelligence, surveillance and reconnaissance (ISR) suite for many targets and operations. However, for the missile defense mission, since the need includes identifying the location of mobile TELS with low latency when they have the potential to launch, that is, when they stop moving, the timelines are more demanding than for most other operations.
The need for low latency includes supporting pre-boost operations where there is eminent danger of a launch. Here the acceptable latency is driven by the responsiveness of attack assets. Highly responsive support for attack operations against a wide range of targets is a current mission of SBR. Low latency is a requirement to support early launch and trajectory warning when SBR is committed to that role. Here the acceptable latency is measured in a few seconds.
Tracking fast moving vehicles in flight had not previously been an objective of the SBR program. There will be demanding near real time ISR (which can include SBR) integration needs to ensure that SBR AMTI capability is cued with enough precision to ensure that a missile in early boost phase is in the SBR beam. While this is no more demanding for fixed missile sites than for other fixed targets, it is highly challenging for moving targets. SMTI will lose track on the TEL as it slows to below SMTI threshold speed. When this occurs, there must be highly agile switching to SAR imaging mode for the SRB satellite to monitor the TEL when it stops. There will also be added command and control and battle management demands beyond detection of the launch to meet the latency requirements to make early launch and trajectory warning useful. Again, the information must be available and usable within a very few seconds.
Early attention would be needed to the added integration challenge generated by adding and exploiting AMTI capability. There may be substantial impacts on the demands on onboard signal processing, software development, and communication links. Full integration of SBR capabilities into the Task, Post, Process, and Update (TPPU) paradigm is needed to fuse SBR data with data from other sensor sources to offer multi-phenomenology detection, discrimination, and designation (D3) benefits. Such a system will contribute significantly to generating knowledge instead of just data, to meeting time sensitive targeting and response timelines, and to providing users a capability to quickly re-task sensors to optimize coverage of the evolving situation.
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