scope:

Purpose. The objective of this NASA Technical Standard is to provide a consistent methodology for developing pyroshock test criteria for NASA spacecraft, payload, and launch vehicle hardware during the development, qualification, flight acceptance, and/or protoflight test phases of the verification process. Various aspects of pyroshock testing are discussed herein, including test environments, methods and facilities, test margins and number of exposures, control tolerances (when applicable), data acquisition and analysis, test tailoring, dynamic analysis, and prediction techniques for pyroshock environments.

Applicability. This Standard recommends engineering practices for NASA programs and projects. It may be cited in contracts and program documents as a technical requirement or as a reference for guidance. Determining the suitability of this Standard and its provisions is the responsibility of program/project management and the performing organization. Individual provisions of this Standard may be tailored (¡.e., modified or deleted) by contract or specification to meet specific program/project needs and constraints.

Background 

Pyrotechnic applications. Current launch vehicle, payload and spacecraft designs often utilize numerous pyrotechnic devices over the course of their missions. These devices are generally used to separate structural subsystems (e.g., payloads from launch vehicles), deploy appendages (e.g., solar panels), and/or activate on-board operational subsystems (e.g., propellant valves).

Pyroshock characteristics. Pyroshock is often characterized by its high peak acceleration (up to 300,000 g), high frequency content (up to 1 MHz), and short duration (less than 20 ms), which is largely dependent on the source type and size or strength, intervening structural path characteristics (including structural type and configuration, joints, fasteners and other discontinuities) and distance from the source to the response point of interest. Because of the high frequency content, many hardware elements and small components are susceptible to pyroshock failure while resistant to a variety of lower frequency environments, including random vibration. High frequencies may make analytical methods and computational procedures inapplicable for system verification under pyroshock loading. Thus, pyroshock verification should be accomplished experimentally, and pyroshock testing is considered essential to mission success. 

Potential hardware effects. Many flight hardware failures have been attributed to pyroshock exposure, some resulting in catastrophic mission loss [5]. Specific examples of pyroshock failures include cracks and fractures in crystals, ceramics, epoxies, glass envelopes, solder joints and wire leads, seal failure, migration of contaminating particles, relay and switch chatter and transfer, and deformation of very small lightweight structural elements, such as microelectronics. On the other hand, deformation or failure of major structural elements is rare except in those regions close to the source where structural failure is intended.

Summary of pyroshock environmental cateqories. In this Standard, the pyroshock environment has been divided into the following three categories, depending on the shock severity and frequency range: (a) near-field, (b) mid-field, and (c) far-field. Detailed definitions are provided in Section 3.2.3. The intent of this categorization is to assist hardware and test personnel in the selection of appropriate test techniques and facilities. For the near-field, only pyrotechnic devices should be used. For the mid-field, either mechanical impact or pyrotechnic devices should be used. For the far-field, electrodynamic shakers, impact or pyrotechnic devices may be used. 

Summary of Pyroshock test criteria. Specific pyroshock test requirements are selected based on: (a) the flight or service pyroshock environment as defined in Section 3.2.3; (b) the environment test categories described in Section 3.2.5; (c) the level of assembly defined in Section 3.2.6; (d) the maximum expected flight environment as specified in Section 4.2; (e) test margins as discussed in Section 4.3; (f) test specifications described in Section 4.4; and (9) the test method and facility as outlined in Section 4.5.