scope:

Purpose

Direct field acoustic testing (DFAT) is a method of exposing space hardware to high intensity acoustic levels utilizing the direct field generated by an array of acoustic sources, typically loudspeakers. The DFAT methodology presents a number of significant logistical advantages over conventional RFAT in a dedicated acoustic chamber. However, certain technical limitations and nuances, variability in practice, and technical maturity relative to RFAT make it incumbent for a program to understand and carefully balance the benefits and limitations of the use of DFAT with the needs of the program.

The purpose of this NASA Technical Handbook is to provide information and guidelines on the applicability and use of DFAT testing. This NASA Technical Handbook is intended to provide an approach that may be consistently followed by those who choose to use this method for qualifying flight hardware for acoustic environments. The NASA Technical Handbook describes the following:

a. DFAT testing background. b. Configuration.

c. Instrumentation, test control, and data acquisition and reduction.

d. Theoretical considerations for designing a DFAT test setup.

e. Guidelines for DFAT testing.

The information provided herein is intended to guide engineers and engineering managers in making more informed decisions in the planning and execution of DFAT test activities. Additionally, the fundamental basis is provided for the development of procedures to facilitate execution of the DFAT testing process based on standards and recommendations developed in the past decade.

Applicability

This NASA Technical Handbook is applicable to all acoustic tests using the DFAT method for National Aeronautics and Space Administration (NASA) flight and non-flight hardware, including but not limited to, built-up spacecraft, spacecraft experiments and components, aircraft and launch vehicle equipment, launch vehicle pads, and ground support equipment (GSE).

This NASA Technical Handbook provides baseline information for designing coherent and consistent test planning, setup, and implementation approach for DFAT testing. The use of this NASA Technical Handbook is recommended for engineers and managers within the NASA Centers and NASA contractor organizations for acoustic acceptance, protoflight, or qualification testing using the DFAT test method. The applicability of this NASA Technical Handbook is to provide the means of planning and testing equipment and structures to wide-frequency acoustic induced vibration environments. The test equipment for acoustic testing, as well as details on test implementation are provided in this NASA Technical Handbook. It is expected that the user of this NASA Technical Handbook will have a mid- to high-level of understanding of acoustic testing techniques in the aerospace industry with commensurate education. The users of this NASA Technical Handbook are to apply the recommended steps with care and with an understanding of their purpose and limitations. Since the test equipment can be brought onto location without the necessity of transporting test articles, this method can present considerable cost savings and schedule flexibility where there is not the availability of an on-site acoustic chamber. Without the need of a reverberant chamber to produce the desired sound levels, DFAT testing can conveniently be performed to meet programmatic needs, if proper steps are taken to ensure this testing method provides the intended objectives and meets the flight hardware requirements.

Given the aerospace industry's body of knowledge and successful heritage based in RFAT, some comparisons will be presented between DFAT and RFAT. The primary purpose of this NASA Technical Handbook is to define the current state of DFAT and to highlight its strengths and potential technical problems that users need to know before making a decision to perform a DFAT test. Future revisions of this NASA Technical Handbook will provide updates to new developments and improvements, as the community continues to address technical issues with this method of acoustic testing.

This NASA Technical Handbook is approved for use by NASA Headquarters and NASA Centers and Facilities. It may also apply to the Jet Propulsion Laboratory (JPL) and other contractors only to the extent specified or referenced in applicable contracts

This NASA Technical Handbook, or portions thereof, may be referenced in contract, program, and other Agency documents for guidance. When it contains procedural or process requirements, they may be cited in contract, program, and other Agency documents.