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This will assist in assuring that all interfaces are defined andthat the end goals are accomplished. Physical envelopes should be defined so as not to restrict the typesof devices and their functional approaches. Performance of devices should be defined in quantitativeparameters and margins, based on the functions to be accomplished, rather than attempting to specifyphysical details of design. For example, a pin puller should be described in terms of the loads to beaccommodated and the functional margins required (energy deliverable by the cartridge, versus energyrequired to accomplish the function).

In the field of pyrotechnics, it is very difficult to produce a devicewith a “build-to-print” specification, since very subtle changes can significantly affect performance.Every functional test should be designed to yield quantitative performance information; go/no-go testing should be eliminated.Once functional margins have been established for devices under system requirements and conditions,then the devices can be subjected to environmental qualification. The design and demonstration accomplished to this point should provide confidence that these devices should be capable of withstanding allenvironments.

At this point, quantitative measurements of performance must be non-invasive. Devicesmust be assembled as flight-configured units and measurements cannot influence the performance during functioning. However, external measurements can be made, such as observing the velocity of a pinduring stroking. Also, quantitative functional data can be obtained after a firing through x-ray and teardown of the device to reveal internal, precalibrated, metal deformation, such as an energy-absorbing cupor the amount of penetration of a piston in a tapered bore.Performance verification and functional margin demonstration should be accomplished for acceptanceof new lots of devices.

For example, the test should be configured to require a worst-case flight condition. Again, quantitative functional data should be collected non-invasively and/or from post-testevaluation.51Chapter 11 - PYROTECHNIC COMPONENT DESIGN AND DEVELOPMENT• Utilize engineering experience• Energy delivery capabilities• Materials/configurations• Scaling• Compatible materials• Pyrotechnic charge• Monitor functional performance• Determine/evaluate key functional parametersReference 4The first cut at selecting and sizing the device, its components, and its performance should be based onthe company’s experience with comparable hardware.

As described in chapters 3 and 4, the possibilitiesand combinations are nearly unlimited. One approach would be to use existing hardware with minimalmodifications and hardware that had been qualified previously on a similar application. The foundationto a successful design effort is to monitor performance to determine and evaluate key functional parameters; that is, those parameters, when slightly changed, that most influence performance.• Conduct development• Adjust performance to optimize• Conduct functional evaluation to limits of requirements• Forces/loads• Materials/conditions• Environments• Establish structural integrity• Locked shut• Pyrotechnic overload• At conditions of maximum stress, i.e. temperature• Dual-cartridge device must survive simultaneous firings• Determine functional margin/reliabilityReferences 4, 20 and 21Development should be conducted to optimize the first five parameters (energy delivery, materials/configurations, scaling, compatibility and pyrotechnic charge) by conducting functional evaluations to thelimits of requirements.Also affecting this optimization is the requirement to maintain structural integrity.

That is, the resistanceto rupture of the pressurized structure can be evaluated by a locked-shut test (preventing stroke ormotion of a piston), or a pyrotechnic overload at conditions of maximum stress, such as at temperatureextremes. For those devices that utilize dual energy sources, such as cartridges or explosive cords, forredundancy (the device must function with the output of either energy source) firings must be conductedwith simultaneous initiation of both energy sources. This must be done, even though in the system, onlyone cartridge is fired at a time; the possibility exists that both energy sources can be fired.

Functionalperformance measurements should be taken during these tests to quantify the degree to which structural52containment was achieved, or how close the structure was to failing. Maximizing the performance of adevice is contradictory to maintaining structural integrity. That is, using a large pyrotechnic charge toachieve a large functional margin will increase the potential of structural failure. A second contradictoryfactor is the generation of pyrotechnic shock, described in chapter 13, which is increased by greaterdynamics from large pyrotechnic loads.At this point, the structural margin and reliability of the device, as described in chapters 7 and 8 can bedetermined.53Chapter 12 - QUALIFICATION••••Determine the survivability of design to environmentsDemonstrate subsystem performanceCompile additional data on functionality (margin)Various test philosophies• Test all units through all environments• Subdivide test units to allow sequential exposures• Number of test units depends on:• Criticality of subsystem• Expense• Complexity• Ease of evaluation• Final firings should be conducted in system-level tests• Worst-case loads• Worst-case environments• Structural integrityReferences 2, 4, and 41The objectives of component and subsystem qualification are to demonstrate the capability to withstandenvironments and to compile additional information on performance.

By determining the level of performance, based on dynamic or passive energy measurements, this data will provide further substantiation of functional margin demonstrations. Two basic approaches exist in regard to conductingenvironmental exposure tests: 1) exposing all test units to all environments, and 2) subdividing the testunits for sequential exposure to environments. For example, with 5 groups of test units and 5 environments, group 1 would be subjected to environment 1 and functionally tested, group 2 would be subjected to environments 1 and 2 and functionally tested, group 3 would be subjected to environments 1, 2and 3 and functionally tested, etc.

With a thorough understanding of the effects of environments fromthe developmental effort, qualification testing should produce no surprises. However, without a thorough development, test units are subdivided for sequential exposures. This allows for determination ofwhich environment had a deleterious effect on performance. At the conclusion of environmental exposures, the test units should be functioned at physical and environmental extremes, as well as demonstrate structural integrity.54Chapter 13 - PYROTECHNIC SHOCK• Pyrotechnically induced mechanical environment• Suspected cause of Galileo computer memory loss• Magellan, Mars Observer powered down before firing pyrotechnics• Dynamic, impulsive compressive/tensile waves generated by:• Rapid pressurization of gas-actuated mechanisms• Impact of mechanical interfaces• Sudden release of loads at loaded interfaces• Contains frequencies to over 40 khz• Dynamicists/accelerometers ignore readings above 10 khz• Accelerometers resonate, produce large output• Limitations on simulators• Assume higher frequencies do not damage• Viking project required pyrotechnic shock testing• Impacting mass simulator induced considerable damage• Abandoned above approach for system-level demonstrations• Recommend system-level demonstrations• Actual or closely simulated structure• Actual pyrotechnic devices• Test item mounted on structure as flown• Eliminates concern of simulation• Comparison testing• Use Hopkinson Bar with strain gages• Frequency response to 80 khz• Each pyrotechnic design generates reproducible strainReference 42Recent spacecraft failures have been associated with a mechanical environment called pyrotechnicshock.

Following the loss of memory on a backup computer in the Galileo spacecraft, the Magellan andMars Observer spacecraft have been powered down, prior to firing pyrotechnics. A firing command forpyrotechnically actuated valves was the last signal to be transmitted to the Mars Observer before communications with the spacecraft were lost. Since the spacecraft had no onboard systems in operation, nodiagnostic information could be obtained to analyze the failure of the spacecraft.When pyrotechnic devices are functioned, dynamic, impulsive waves of compressive and tensile strainare produced within the device and through the release of loads at structural interfaces.

On functioning,pyrotechnic devices produce strain by rapid, high pressurization of gas-actuated mechanisms and theimpact of these mechanisms at the limits of the function. An example of the sudden release of loads is abolted interface released by explosive bolts. These strain waves contain frequencies to over 40 khz.

A10 khz upper frequency level is an artificial constraint applied by dynamicists, due to the limitations ofaccelerometers and the equipment used to simulate pyrotechnic shock inputs. An assumption is madethat frequencies above 10 khz cannot damage structure. However, small-mass electronics have exhibited sensitivities in this regime.55Pyrotechnic shock testing was an early requirement on the Viking Program, the soft landing of twoinstrumented payloads on the surface of Mars. Impact test pyrotechnic simulations always producedsevere overtests, destroying many test items. The pyrotechnic shock simulation requirements were continuously reduced and, ultimately, were abandoned in favor of system-level demonstrations.Only system or subsystem pyrotechnic shock tests should be conducted, using the actual or closely simulated structure, with the actual pyrotechnic device and the test item mounted and functioned as inflight.