Space Based Radar (SBR) Configuration
SBR will be built based on an approved, integrated set of user requirements and capabilities. Technology maturation, risk reduction and concept development are essential elements of the SBR program strategy. Investments in key technology areas are focused to mature technologies leading to component design and demonstration. Concept development activities will focus on reducing risk, integrating technologies, and demonstrating of a system level concept. Demonstrations as well as modeling and simulation will facilitate maximization of the operational capabilities of the SBR system.
Objective System design requirements include a complete system concept development to include Tactical GMTI w/SAR/Coherent Change Detection and Multilateration and bistatics. Flight Demonstration System design requirements include preliminary designs of a "bare bones" demonstration with EELV-Medium volume and mass constraints (with ESPA ring). The demonstration system objective and experiment plans and CONOPS Ground-based risk reduction demonstrations include: CAD deployment simulations; Scaled functioning structural models; and lab testing of RADAR on-transmit calibration techniques.
Requirements are to deploy, rigidize, and control a large -- approximately 80-100m linear -- structure. Dynamic and static structural metrology is required during deployment and operation. Thermal gradient and "snap" compensation and calibration are needed on transmit.
As of mid-2004 the program was in the design stage, with two contractors selected for this phase of the effort. The baseline system definition continued to evolve. The system was to use the spiral development approach with Increment 1 deployment beginning in 2010-2012.
SBR is to provide global, all weather, day/night, persistent access of areas of interest with Surface Moving Target Indication (SMTI), Synthetic Aperture Radar (SAR) imaging, and High Resolution Terrain Information (HRTI). The SMTI requirement is to track a 10-decibel (DB) target at 2,800km - a truck size vehicle with about a 10m2 radar cross section.
The system could be some combination of Low Earth Orbit (LEO) satellites at a nominal altitude of 1,000 km and Medium Earth Orbit (MEO) at a nominal altitude of 10,000 km. MEO will support SMTI with fewer satellites but would require long processing times to provide the needed quality of SAR images.
LEO will support both the SMTI and SAR imaging requirements with reasonable combinations of power and aperture. The options for a LEO system are characterized as 1X, 2X, and 3X. Available space launch capabilities could deliver three 1X systems on a single vehicle. The same space launch vehicle could deliver only one 3X system. For the 1X system, the power-aperture (power in kilowatts x aperture in meters2) is 35 kwm2. For reference, the average radiated power aperture for the Aegis radar system is 485 kwm2.
The baseline Surface Moving Target Indication (SMTI) and Synthetic Aperture Radar (SAR) imaging capabilities of the SBR could make a major contribution to locating and monitoring ballistic missile installations of interest and to tracking mobile systems. Both SMTI and SAR imaging capabilities are needed, with agile change between modes, to maintain track and monitor selected vehicles.
A LEO constellation requires some 21 satellites to provide persistent global access. As an example of the performance of smaller constellations, the nominal Increment 1 system of 9 satellites in LEO would provide access to North Korea with at least one satellite some 55-60% of the time. An expansion in numbers beyond Increment 1 will be needed to provide continuous monitoring during times and at places of high interest.
The concept of persistence does not lend itself to a single metric. It will depend on the nature of the objects of interest, the dynamics of the situation, and the supported task - detect, track, identify, and/or engage. E.g., persistent monitoring of the status of construction of a missile site might demand a weekly revisit using SAR imaging capabilities. Persistent monitoring of a missile launch site in a ready to launch status, using Air Moving Target Indicator (AMTI) track capability might require a revisit every few seconds. Tracking a large moving unit might require an SMTI revisit every few minutes while tracking a single vehicle might require a revisit each tens of seconds.
In any case, selecting and tracking specific objects of interest will require a capability to change rapidly between SMTI and SAR imaging capabilities. SAR imaging will be required to identify the specific locations and vehicles of interest before movement starts. SMTI can then track the moving objects but will lose tracking and monitoring when the vehicle stops. An approach is to wait for movement to resume. However, SMTI alone cannot determine that the new movement is the same vehicle. Only SAR imaging can provide that information. Further, in the case of tracking missile launchers, the need for information is even more critical when the vehicle stops since known systems must stop to launch.
A 21-satellite constellation could provide near full-time access to multiple theaters of interest. With less than a 21-satellite constellation, a combination of space-based and other assets will be needed to provide continuous access during times and at places of high interest. Continuous access does not imply unlimited continuous tracking.
Air Moving Target Indication (AMTI) track capability could be added to Increment 1 with low impact on cost and schedule if included in the initial design. SBR AMTI would not have a capability to search airspace and must instead either be cued by another system or maintain track from the point of launch.
Access depends primarily on constellation orbit and size. The maximum range for a SAR imaging from satellites in LEO at 1,000 km is 2,800 km. For a 9-satellite constellation at 53 degrees inclination, the distance between satellites is about 8,800 km, so the probability that a satellite is in position to cover a given target area is about 65%. A 21-satellite system would provide essentially continuous access to multiple theaters of interest.
Wide area SMTI uses a high area scan rate to monitor areas of interest. For example, within its area of access, the system can monitor road junctions in a 1000x760km area every 10 minutes. It could also monitor movements from individual garrisons distributed over a total area of 400x400km every 10 minutes. A few dozen high value moving targets can be tracked in the high-resolution mode in a 125x125km area with a revisit every 30 seconds.
The system can provide HRTI worldwide.
The combination of SMTI and SAR imaging with a 21-satellite constellation in LEO would provide detection, tracking and identification of targets of interest in areas of interest. To be useful for tracking high interest individual targets such as missile TELS, it will also be important to ensure that the system has both SMTI and SAR imaging capability with high agility between these modes.
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