Requirements Flowdown Research Articles

A synthetic Roman Space Telescope High-Latitude Imaging Survey: simulation suite and the impact of wavefront errors on weak gravitational lensing

ABSTRACT The Nancy Grace Roman Space Telescope (Roman) mission is expected to launch in the mid-2020s. Its weak lensing program is designed to enable unprecedented systematics control in photometric measurements, including shear recovery, point spread function (PSF) correction, and photometric calibration. This will enable exquisite weak lensing science and allow us to adjust to and reliably contribute to the cosmological landscape after the initial years of observations from other concurrent Stage IV dark energy experiments. This potential requires equally careful planning and requirements validation as the mission prepares to enter its construction phase. We present a suite of image simulations based on galsim that are used to construct a complex, synthetic Roman weak lensing survey that incorporates realistic input galaxies and stars, relevant detector non-idealities, and the current reference 5-yr Roman survey strategy. We present a first study to empirically validate the existing Roman weak lensing requirements flowdown using a suite of 12 matched image simulations, each representing a different perturbation to the wavefront or image motion model. These are chosen to induce a range of potential static and low- and high-frequency time-dependent PSF model errors. We analyse the measured shapes of galaxies from each of these simulations and compare them to a reference, fiducial simulation to infer the response of the shape measurement to each of these modes in the wavefront model. We then compare this to existing analytic flowdown requirements, and find general agreement between the empirically derived response and that predicted by the analytic model.

Designing a Systems Engineering Process and Toolset for the Giant Magellan Telescope

AbstractThe Giant Magellan Telescope (GMT) Project has used Cognition Cockpit™ to facilitate and implement systems engineering processes such as operational concept development, requirements development and management, interface management, failure modes and effects analysis, hazard analysis, and verification. This paper discusses the structure of the GMT Systems Engineering process, the flowdown of requirements throughout this process, and how Cockpit features are utilized to ensure traceability within the project.

The elephant in the mist: What we don't know about the design, development, test and management of complex systems

The authors survey the literature on complex systems to develop a fundamental critique of the systems engineering methods that value-driven design will attempt to replace. The current approach to systems engineering applies industrial revolution methods to information revolution problems. Not only the flowdown of requirements, but also the ability to verify and validate large engineered systems is brought into question.

Use Cases for Systems Engineering—An Approach and Empirical Evaluation

AbstractThis paper describes a use case driven approach for functional analysis/allocation and requirements flowdown. The approach utilizes use cases and use case realizations for functional architecture modeling, which in turn form the basis for design synthesis and requirements flowdown. We refer to this approach as the FAR (Functional Architecture by use case Realizations) approach. The FAR approach is currently applied in several large‐scale defense projects within BAE Systems Hägglunds AB. This paper also presents an empirical study where FAR is applied and evaluated in two large‐scale defense projects. Our results indicate that the FAR approach performs better than the previously used document based approach in the organization. © 2007, Wiley Periodicals, Inc. Syst Eng

Non-Contacting Interfaces: A Case Study in Modular Spacecraft Design

The benefits of modularization, such as reusability and upgradeability, remain underutilized in space. Exploiting these advantages after a spacecraft is launched introduces too much cost and risk in the current paradigm of spacesystem design. This gap between modular design and its benefi ts has inspired us to focus attention on interfaces. Many of the obstacles to bridging this gap lie in mechanical attachment of spacecraft subsystems. This paper reexamines the function of mechanical interfaces among spacecraft components and describes a new realization in which flux-pinning superconductors and permanent magnets provide stable, but unpowered, connections among spacecraft components that appear to hover at some distance from one another. Beginning with functional abstraction, this study identifies a new set of unexploited possibilities that add versatility to space-systems architectures. First, the limitations imposed on modularity due to mechanical coupling in spacecraft architecture are identified. These limitations are then used to back out the requirements for a non-contacting interface. With several technologies that enable adhesion without mechanical contact identified, requirements flowdown and functional analysis is performed to quantify technical performance measures for the interface.

7.2.1 The FAR Approach – Functional Analysis/Allocation and Requirements Flowdown Using Use Case Realizations

AbstractThis paper describes a use case driven approach for functional analysis/allocation and requirements flowdown. The approach utilizes use cases and use case realizations for functional architecture modeling, which in turn form the basis for design synthesis and requirements flowdown. We refer to this approach as the FAR (Functional Architecture by use case Realizations) approach. The FAR approach is currently applied in several large‐scale defense projects within BAE Systems Hägglunds AB and the experience so far is quite positive. The approach is illustrated throughout the paper using the well known Automatic Teller Machine (ATM) example.

7.2.2 Performing Functional Analysis/Allocation and Requirements Flowdown Using Use Case Realizations – An Empirical Evaluation

AbstractThe FAR approach (Functional Architecture by use case Realizations) is a use case driven methodology for functional analysis/allocation, and requirements flowdown. The FAR approach is tailored towards the development of long lived software intensive defense systems, for example vehicles. In this paper, we present an empirical study where FAR is applied and evaluated in two large‐scale defense projects. Our results indicate that the FAR approach performs better than the previously used approach in the organization.

4 System Flowdown Using Enhanced QFD

AbstractIn defense/aerospace systems engineering the requirements are usually flowed down to lower, more detailed system levels directly as a self‐contained process. Commercial systems engineering takes a more eclectic view of the flowdown process. Here we set forth the complete commercial system flowdown process, which has two primary features: (A) a zigzag path through requirements, concepts, and improvement at system level N, which is then repeated at level N+1, and (B) three sources for requirements at level N: (1) higher‐level requirements from level N‐1, (2) the voices of external stakeholders (VOES) at level N, and (3) amplifications of the functions at level N. Thus, this approach expands on the narrow flowdown of requirements by integrating it with the VOES and functional analysis, and integrating all of requirements with concept selection and improvement. This is done by utilizing QFD, functional analysis and amplification, and Pugh concept selection. This process when implemented effectively provides competitive advantage in the global commercial competitive markets.

A Simplified Method for Requirements Flowdown and Test Limit Definition

AbstractA simple yet disciplined method for consistently flowing down requirements was created and implemented on a production radar program at Hughes Aircraft Company. This structured Requirements Flowdown Methodology was supplemented by a similar methodology developed for determining the limits at which the flowed down requirements are tested. These methodologies were created with the objective of producing a system that will better suit the needs of the customer. These customer needs include the need for proper operation of the product as specified for the entire product life under all specified environmental conditions, as well as improved system performance and increased reliability. With the structured definition of test limits as defined in the methodology described herein, a reduction in the number of field failures that cannot be duplicated at repair facilities is also accomplished. This reduces the amount of logistical support necessary to maintain an operational product in the field, minimizing the time necessary to isolate and repair failures, and resulting in increased customer satisfaction.

The Next Generation in Underwater Acoustic Detection

Since the 1950s, AT&T has provided underwater detection equipment to the U. S. Navy to satisfy the navy's two-tier mission of studying the ocean and developing and testing sonar systems. The latest generation of hardware is a fiber-optic system that has the transmission capacity of all the previous systems combined. Its design and development has provided a challenge both from the technical aspect of meeting stringent performance requirements and from the engineering aspect of managing a large defense program having a budget greater than $500 million. Following a brief summary of AT&T's history in the development and manufacture of underwater acoustic detection hardware, this paper provides a technical description of the fiber-optic system and a project history describing the processes used in bringing the equipment into production. During the period of program execution (1989 to the present), systems engineering management philosophy has evolved from strict flow-down of requirements via military standards to concurrent engineering and product-realization teams. The Fixed Distributed System (FDS) project has followed the same route, partly by design and partly by necessity. It provided some valuable lessons that have been learned and incorporated into the present AT&T Advanced Technology Systems (ATS) engineering process, which has been the basis for AT&T Best Current Practices in systems engineering.

6.4.3 A Systems Engineering Approach to Optimize Customer Satisfaction on Complex Systems

AbstractAt McDonnell Douglas, a creative approach to resolving the issue of flowing down requirements to best meet customer needs has been developed. The approach provides guidance identifying and rank ordering preferred design choices, developing requirements flowdown, and illustrating the sensitivity of performance parameters based on the selection of optimal choices. The methodology determines a Customer Quality Model (CQM) using modified Quality Function Deployment (QFD) assessments[1] in combination with management science techniques for optimization to perform numerical suballocation of system level requirements. The approach provides guidance toward solutions which protect the customer's interests without the need for the customer to dictate design solutions and contractual requirements at these suballocated levels of detail. A computer application of this methodology has been produced by McDonnell Douglas and exists as an EXCEL software tool.

A CUSTOMER ORIENTED APPROACH TO OPTIMIZING SUBALLOCATIONS OF SYSTEM REQUIREMENTS

AbstractA proper Systems Engineering approach to aircraft requirements allocation demands that upper‐level performance requirements be flowed down and allocated to lower‐level subfunctions in a logical, traceable, structured process. Normally it is not in the customer's best interest to contractually specify suballocated values developed from the top requirement because such action borders on dictating hardware design solutions instead of focusing on communicating customer overall needs to the contractor. Because of this, the requirement flowdown process appears to offer opportunities for multiple feasible solutions which are all capable of meeting the customers top level requirement. Thus, there is need for a systems engineering process which is capable of identifying a “best choice” among these selections. At McDonnell Douglas, a creative approach to resolve this requirements flowdown issue has been developed. The approach provides guid‐ance identifying and rank ordering preferred design choices, developing requirements flowdown, and documenting rationale behind identification and selection of optimal choices. The process focuses on a guidance philosophy which identifies customer needs using Quality Function Deployment assessments in combination with linear optimization analyses to perform numerical suballocation of top requirements. The approach provides guidance towards solutions which protect the customer's interests without the need for the customer to dictate design solutions and contractual requirements at these suballocated levels of detail. An application of this process to the diagnostic requirements area has been packaged by McDonnell Douglas as a single integrated set of software modules which fit on a floppy disk capable of operating on a desktop PC.

Database Generated Software Requirements Specification

AbstractThe goal of software requirements management at Grumman is to provide Systems Engineering's internal and external customers with the right information to produce and evaluate a computer program that meets the system's needs. A valuable approach to requirements management is to model one or more aspects of a system and communicate and control the system and software requirements via a database of the model elements.Engineering models can range from abstract models such as a series of partial differential equations for the solution of harmonic vibrations to isomorphic models such as a data flow diagrams or perspective drawings. The modeling method chosen uses a graphical notation and an Entity‐Relationship‐Attribute (ERA) database to create four isomorphic models to define a system and is currently implemented using RDD‐100® from Ascent Logic Corporation.The models used to specify the system are:1) Design Knowledge Capture (DKC) model‐an ERA model of the requirements flowdown from the perceived need to the requirements specification. 2) Behavior model – built using entities that represent functions and items, along with temporal notations of the functional flow. 3) Physical model –sometimes called the system architecture, includes the hierarchical structure of the components that build the system, the interfaces between the components, and the physical links that comprise the interfaces. 4) Resource model‐allows the engineer to evaluate the amount of resources needed when specified behavior is exhibited by a system architecture and to determine the behavior of the system when resources are depleted.The customization of the RDD language and the augmentation of RDD with other tools to add the required capability is described. The elements of the model are mapped from the RDD database to the an expansive interpretation of the Data Item Description for a Software Requirements Specification (DI‐MCCR‐80025A). The interpretation is based on interchanges between the requirements provider and the requirements implementor.The paper describes the aspects of systems specified using the database of models method. The method is heavily driven by the need to meet the MIL‐STD 2167A requirements for a Software Requirements Specification. However; the main value of this paper may be in the identification of the information produced while engineering the system that is not in the Systems Requirements Specification (SRS).