Nasa_Pyros (Раздаточные материалы), страница 2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3733.Percussion primer ignitability performance definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3834.Ignitability comparison of three ignition materials, each ignited by theM42C1 and M42C2 percussion primers.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3935.Schematic diagram of test fixture to monitor fragment patterns and velocitiesfrom rigid explosive transfer line end tips.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4036.Test fixture to evaluate the output of linear explosives.. . . . . . . . . . .

. . . . . . . . . . . . . . . 4237.Lockheed Super*Zip separation joint tapered plate test configuration. . . . . . . . . . . . . . . 4238.Graphic representation of statistical design margin, comparing normaldistributions of energy required to perform a function to energy suppliedby a cartridge. .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4539.Levels of pyrotechnic redundancy established by the Apollo Program. . . . . . . . . . . . . . 4640.Example of false redundancy in the use of explosive crossovers. . . . . . . . . . . . .

. . . . . . 4841.Depiction of the need for the pyrotechnic specialist to meet both safety andreliability requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4842.Cross sectional view of Viking pin puller.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6143.Statistical presentation of functional margin for redesigned HALOE pin puller. . . . . . . 6244.Shuttle/Centaur deployment system, using the Lockheed Super*Zip separation ring. . . 6445.Radial cross sectional views of three types of Super*Zip separation joints,and the programs to which they were applied.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64iv46.Identification of a portion of the parameters evaluated in the Super*Zipseparation joint.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . 6547.Severance performance, comparing web thickness to explosive load, of severalconfigurations of the Super*Zip separation joint . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66vChapter 1.- INTRODUCTIONAlthough pyrotechnic devices have been singularly responsible for the success of many of the critical mechanical functions in aerospace programs for over 30 years, ground and in-flight failures continueto occur. Subsequent investigations reveal that little or no quantitative information is available on measuring the effects on performance of system variables or on determining functional margins.

The threefollowing examples amplify these points. A pin puller design, that was used for the successful deployment of an antenna on the surface of Mars in 1976 in the Viking Lander Program, failed to function in asecond application in 1986 and was abandoned. A spacecraft separation joint failed to function in a1984 ground test after more than 20 years of flight successes; the same joint, which is designed for fullcontainment of explosive products, burst in 1994 during release of a payload from the Space Shuttlecargo bay.

A “fully qualified” valve design, that was created for the Gemini Program in the early1960’s, structurally failed and ignited hydrazine in 1994 through previously unrecognized failuremodes. Improved guidelines for pyrotechnic design, development and qualification are clearly needed.The purpose of this manual is to provide an overview of and recommendations for the design,development and qualification of pyrotechnic components and the systems in which they are used.

Thisis a complex field in which there are few specialists and even fewer guidelines on the approach to createa device and assure it will perform its required task. The field of pyrotechnics is generally considered tobe an art, not a science or engineering discipline. Also, pyrotechnics are considered to be readily available, and, therefore, can be managed by any subsystem in which they are applied, such as structure, propulsion, electric power or life support. This presentation is intended to dispel these misconceptions.The objectives of this manual are:(1) Remove the art from pyrotechnic applications.(2) Introduce engineering approaches.(3) Provide the logic for improved procurement, design, development, qualification, integrationand use.Tests methods and logic are recommended that quantify performance to improve widely cited go/no-go testing of under and over-loaded energy sources.

References are noted throughout to allow thereader to obtain more detailed information on all test methods.This manual does not provide “cookbook” answers and approaches for any aspect of pyrotechnicoperations. Not only are devices unique, requiring individualized approaches for design, developmentand qualification, but systems and operational procedures are also specialized.

The contents of this manual are not intended for direct incorporation into pyrotechnic specifications.1Chapter 2.- PYROTECHNICS DEFINITION, CONSIDERATIONS FORAPPLICATIONS2-1 Definition of PyrotechnicsIn aerospace technology pyrotechnics refer to a broad family of sophisticated devices utilizingexplosive, propellant and pyrotechnic compositions to accomplish:••••••••initiationreleaseseverance/fracturejettisonvalvingswitchingtime delayactuationReference 1The first use of the term “pyrotechnics” for explosive and propellant-actuated devices in the aerospace field was by Harry Lutz of McDonnell Aircraft Company during the Mercury program. Inresponse to a concern voiced by program management about using explosive devices in close proximityto the astronaut, Harry said, “Don’t call them explosives, call them pyrotechnics.” This was quicklyshortened to “pyros,” which sounded evenless threatening.2-2 Pyrotechnics Are Extensively Applied Because of Their High Efficiency••••High energy delivered per unit weightSmall volume, compactLong-term storable energyControllable initiation and output energiesReference 1Few sources of energy combine all four of these attributes.

Pyrotechnics contain the needed energyto accomplish a desired function within small volumes. The only external energy required is an initiation input. Initiation inputs to devices (mechanical, electrical, pneumatic, explosive transfer or laser)can be precisely established to prevent inadvertent initiation, as well as to assure adequate initiationenergy. Pyrotechnics utilize solid material compositions that are highly energetic and can be selected tobe stable under extremes of both thermal and vacuum conditions.2-3 Although Successful, Pyrotechnics Are Reluctantly Used• Unique Characteristics• Single shot• Cannot be functionally checked before flight• Short-duration, impulsive loads (pyrotechnic shock)• Safety issues• Contain explosive materials2• Inadvertent functioning:• only small forces sometimes required to initiate• static electricity• lightning• electromagnetically induced energy• stray energy in firing circuits• Limited engineering approaches/standards are available for pyrotechnic applications• Cannot apply approaches for commonly used energy sources (electric, hydraulic, pneumatic)• Lack of test methods and logic to demonstrate functional margin• Go/no-go testing• Failures continue to occur• Lack of understanding of mechanisms• Poor or no resolution of failures• Few sources for information (reliance on manufacturers)• Reliability estimate based on successful qualificationReferences 1, 2, 3 and 4Clearly, the advantages of using pyrotechnics often outweigh this burdensome list of disadvantages,concerns and challenges, or there would be no applications.

In the early stages of the Shuttle program,an edict was made that there will be no pyrotechnics used for the vehicle or for payloads. Pyrotechnicsviolate one of their first ground rules, which is that systems shall be reusable. However, over 400 pyrotechnic components fly on each Shuttle mission with some used on each flight and others only for emergencies. A primary requirement for Shuttle payload pyrotechnics is the assurance that on functioning,the Shuttle will not be damaged.Pyrotechnics normally are used only once, since often internal structural deformation is incurred in eachfiring.

These devices cannot be cycled like solenoid-actuated switches to assure their functionality. Thebest assurance of successful operation is that the devices are designed with functional margins and havebeen accurately manufactured.The explosive, propellant and pyrotechnic-composition energy sources will burn completely andquickly no matter if the ignition input is intentional or inadvertent. Selecting low- level energy inputs toignite these materials is a weight advantage, but can be a safety hazard.There are few guidelines for the design and application of pyrotechnic devices.

There is a lack ofaccepted test standards to evaluate functional performance of devices. Existing methods generally relyon go/no-go testing, which means that a device either does or does not work.No college courses are offered for this sophisticated aerospace field, and past experience in other energysources cannot be applied, primarily due to the single-shot, dynamic nature of pyrotechnic devices.Consequently, mission- critical functions are sometimes entrusted to pyrotechnic devices with less thanthe required reliability. The lack of understanding of these devices can lead to failures, as well as inadequate failure resolution.

Since there are few sources of information, users are forced into a reliance onmanufacturers. In using “off-the-shelf” hardware, component functional and system evaluation is oftenminimized with the assumption that qualification exists.