Massachusetts Institute of Technology (Systems Engineering Advancement Research Initiative (SEAri))

Multi-Attribute Tradespace Exploration for Survivability

Tradespace exploration as a conceptual design tool provides the ability to examine thousands of system designs. Comparing these designs within the tradespace can reveal performance trends based on design choices. Varying the environment in which the system is evaluated adds another layer of complexity on the analysis. Incorporating time and changing contexts in the conceptual design allows engineers to consider 'ilities', or time-dependent system performance characteristics. Flexibility, the ability to dynamically change the system to mitigate risk or take advantage of opportunity, is difficult to assess within static snapshots of tradespaces. Flexibility is valuable in the presence of future uncertainty, so conceptual analysis should also consider future context changes on the system. A metric to identify valuably flexible designs in a tradespace, Value Weighted Filtered Outdegree, is presented and applied to a satellite radar case application. The metric is able to identify design in the tradespace that would not have been identified with existing tradespace analysis metrics.

http://seari.mit.edu/documents/preprints/VISCITO_AIAA09.pdf

Quantifying Flexibility in Tradespace Exploration: Value Weighted Filtered Outdegree

Effects of the second order perturbative term of the Earth's geopotential on clusters of satellites are analyzed by adding the linearized J/sub 2/ force onto the right side of Hill's equations as a forcing function. A continuation of previous work, the equations of motion are generalized to orbits of all inclinations, and terms are identified that account for rotation of periapsis within the orbital plane, as well as precession of the longitude of the ascending node. The effect of the periapsis rotation on the cluster is identified as a 'tumbling' mode of the system. Accuracy of the linearization is determined by comparison of the analytic solutions with those obtained using an orbit propagator.

A perturbative analysis of geopotential disturbances for satellite cluster formation flying

A method of performing space based Ground Moving Target Indication (GMTI) using radar interferometric processing is presented The algorithm, referred to as Scanned Pattern Interferometric Radar (SPIR), uses the high angular variability of a sparse array Point Spread Function (PSF) to collect sufficient data from the signal return that the clutter and targets can be separated without an a priori assumption of the clutter statistics It is shown that clutter within the main lobe of the individual aperture pattern can indeed be separated from the targets, using the deterministic geometric relationship between observation direction and clutter Doppler shift If the computational domain is extended to the side lobes of the gain pattern, clutter entering through these lobes can also be extracted Constraints on the cluster geometry are derived from the invertibility of the PSF matrix

Space based GMTI using scanned pattern interferometric radar (SPIR)

Designing complex space systems that will deliver value in the presence of an uncertain future is difficult. As space system lifetimes are now measured in decades, the systems face increased risk from uncertain future contexts. Tradespace exploration increases the designer’s system knowledge during conceptual design and with dynamic analysis can predict the system’s behavior in many possible future contexts. Designing flexible systems will allow mitigation of risk from uncertain future contexts and the opportunity to deliver more value than anticipated by the designers. Flexibility is a dynamic property of a system that allows it to take advantage of emergent opportunity and to mitigate risk by enabling the system to respond to changing contexts in order to retain or increase usefulness to system stakeholders over time. Value Weighted Filtered Outdegree is introduced as a metric for identifying valuably flexible systems in tradespace studies in order to improve decision making during the conceptual design phase. Dynamic Multi-Attribute Tradespace Exploration (Dynamic MATE) is used as the basic tradespace exploration method for Value Weighted Filtered Outdegree, and applies decision theory to computer simulation of thousands of system designs, across hundreds of unique future contexts. Epoch-Era Analysis is used to parameterize future contexts for dynamic analysis of the designs’ performance. Although dominated in static analysis, flexible designs are valuable in the presence of changing contexts.

http://seari.mit.edu/documents/presentations/AIAA09_Viscito_MIT.pdf

Quantifying flexibility in the operationally responsive space paradigm

Efforts at fielding satellite based radar systems for performing tactical and strategic moving target indication (MTI), and synthetic aperture radar (SAR) imaging, have been underway since the 1960's. While some success has been achieved in SAR imagery, very little success has occurred for MTI. In 1995, an Air Force General Officer conference was held at which briefings were given on the feasibility of transitioning the MTI sensor functions of the Airborne Warning and Control System (AWACS) and the Joint Surveillance Target Attack Radar System (JSTARS) to space. These briefings concluded that although it would be too expensive to transition these functions in 1995, there was a real potential that by 2000 the problem might become affordable. Accordingly, the AF Chief of Staff directed that space based radar studies continue. This paper provides an overview of major studies and development efforts which have occurred since 1995.

R.A. DeLap

Papers

Recent and current Air Force space based radar efforts