REG NASA-LLIS-0651-2000 Lessons Learned Environmental Test Methods for Ground Support Equipment.pdf

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1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-03-02a71 Center Point of Contact: KSCa71 Submitted by: Wil HarkinsSubject: Environmental Test Methods for Ground Support Equipment Practice: Defines test methods for determining the capability of ground support equipment (GSE

2、) and other facility hardware to function when exposed to the natural and induced environments peculiar to the prelaunch and launch conditions at Kennedy Space Center (KSC). Provides guidelines for the preparation of detailed test procedures and for the preparation of the environmental test portions

3、 of design specifications.Programs that Certify Usage: This practice has been used on the Space Shuttle Program, at the Kennedy Space Center, Launch Complex 39 Ground Support Equipment.Center to Contact for Information: KSCImplementation Method: This Lesson Learned is based on Reliability Practice n

4、umber GSE-3006 from NASA Technical Memorandum 4322A, NASA Reliability Preferred Practices for Design and Test.Benefit:The test methods described herein specify conditions obtainable in the laboratory that will give test results similar to actual service conditions.Provided by IHSNot for ResaleNo rep

5、roduction or networking permitted without license from IHS-,-,-Implementation Method:1. Design and Testing Considerations. a72 The basic purpose of this practice is to provide a guide to uniform testing of Ground Support Equipment (GSE) and other facility components to assess the ability of the hard

6、ware to withstand the environmental stresses it will encounter during its life cycle and to ensure that plans and test results are adequately documented.a72 a72 Tests should be conducted to the maximum extent practicable to ensure operational suitability of the item for the anticipated environmental

7、 conditions to be encountered during its required usage. Consideration should be given to natural and induced environments and to combinations and sequences of stresses.a72 a72 The environmental conditions to which GSE is exposed in the KSC area vary considerably by virtue of its location on the cen

8、ter. The environmental conditions of computer equipment installed in an air-conditioned, sound-absorbent room on vibration-isolated floors is negligible compared to the severe conditions a holddown system experiences; i.e., the daily natural environments and the blast of the launch vehicle during li

9、ft-off. Designing or testing all equipment to the most severe of these conditions is impractical and expensive.a72 a72 Design and testing should be accomplished with both the actual environmental and reliability requirements in mind. KSC-STD-164 may be used as a guide to define test conditions.2. 3.

10、 Testing Procedures. a72 Test Requirements. - The anticipated environmental conditions should be carefully considered before determining which tests are to be conducted. Generally, only those conditions that reflect launch and prelaunch usage of the test item should be considered. Where possible, da

11、ta should be obtained on actual operating and field environments to which the GSE will be exposed to aid in the test selection process.a72 a72 When considering the applicable environmental conditions, combined environmental testing should also be considered as a means for more closely simulating ser

12、vice conditions, and in fact, may be the only method of attaining valid test results.a72 a72 Test Sequence. - Those tests that require the successful operation of the test item during exposure to the environment should normally be conducted first, and those tests where the test item remains static t

13、hroughout the environment should be conducted Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-last. In either case, the test should be conducted in the order of the likely severity on the item; the least severe being conducted first. Unless otherwise

14、 stated in the test requirements, the following sequence is recommended; a73 Electromagnetic interferencea73 Low temperaturea73 High temperaturea73 Temperature shocka73 Acousticsa73 Vibrationa73 Shocka73 Humiditya73 Raina73 Icinga73 Solar radiationa73 Fungusa73 Salt foga73 Sand and dusta73 Explosion

15、a73 Lift-off blasta72 a72 Receiving Inspection. - Prior to conducting any tests, the test item should be subjected to a receiving inspection. This inspection should be made to determine conformance with applicable drawings and specifications to the extent possible without disassembly of the test ite

16、m. When quality acceptance tests are specified, they should be conducted as part of the receiving inspection.a72 a72 Functional Test. - The functional test is the means by which it can be determined whether or not the environmental tests are adversely affecting the performance capabilities of the te

17、st item. Because the functional test is required to monitor the very “pulse“ of the test item, it is obvious that it must be comprehensive enough to include all possible aspects which could affect the operation of the item.a72 a72 The determination of what checks to make as part of the functional te

18、st requires a good understanding of the operation and application of the test item and its possible failure modes. Prior to conducting a functional test, the functional parameters to be monitored should be specified and should include allowable limits on permissible degradation.a72 a72 Installation

19、in Environment Facilities. - The test item should be installed in the test facility at ambient conditions in a manner that will simulate service usage. Install instrumentation in, on, or around the item as required by the test. Plugs, covers, and Provided by IHSNot for ResaleNo reproduction or netwo

20、rking permitted without license from IHS-,-,-inspection plates used in service should remain in place. When mechanical or electrical connections are not used, the connections normally protected in service should be adequately covered in the same manner as service usage. The test item should then be

21、functionally tested to determine that no malfunction or damage was caused due to faulty installation or handling. The requirement to conduct a functional test following installation is applicable only when a functional test is required during exposure to the specified environments.a72 a72 Frequency.

22、 - Functional tests should be conducted at least three times before and after each test environment. If the functional test performed after an environmental test is satisfactory, the test item should be qualified for the succeeding environment without further testing, provided (1) the succeeding tes

23、t is started within 72 hours after the previous functional test and (2) installation changes are not required. When a test environment simulates conditions under which the test item would be required to operate during service, the item should be functionally tested at least three times during the te

24、st environment.a72 a72 Characteristic Tests. - Tests to establish the basic design characteristic of the item are also required. These tests should not be confused with the functional-type test which is repeated throughout the test program. Characteristic tests are conducted once, generally prior to

25、 the environmental tests, unless they are destructive in nature. Examples of characteristic tests for pneumatic components may include proof test, flow test, surge test, and the burst test which is destructive. For electrical components, characteristic tests may include voltage drop test, ampere tes

26、t, resistance test, and repeatability test.a72 a72 Life Cycle Reliability Testing. - Testing is conducted to provide statistical data for determining the reliability of the test item with a reasonable degree of confidence. Failures that would occur “once-in-a-thousand“ are looked for in the life-cyc

27、le test. After exposure to all the environments the item would normally be exposed to during use with no deterioration of operation found, the life-cycle test can provide a valid method for determining reliability. Failures that occur due to wearing out of parts beyond service life expectancy must n

28、ot be considered a design failure, but may be considered for establishing maintenance time periods. The number of life cycles to be conducted should be established by the testing agency.a72 a72 Documentation. - The environmental tests required for a particular hardware item should be documented in a

29、 test plan or test requirements document. Inspections, data requirements, test tolerances, functional tests, and installation requirements should be indicated along with any deviations from the standard tests established herein. KSC-Provided by IHSNot for ResaleNo reproduction or networking permitte

30、d without license from IHS-,-,-DF-107 may be used as a guide in preparing the plan. The testing agency should develop a detailed test procedure based upon the test requirements specified in the test plan. Test results should be documented, approved, and published in accordance with KSC-STD-128.4. 5.

31、 Test Methods. a72 Electromagnetic Interference. - The electromagnetic interference test is performed to determine if the electronic or electrical equipment under test will exhibit malfunction or degradation in performance when subjected to undesired external signals. Electrical and electronic equip

32、ment includes components that are susceptible to malfunction from external electromagnetic interference. Such interference can change the calculations of a computer, alter the sequence of planned commands of computer programs, and cause recorders to erroneously indicate that a function occured, fail

33、ed, or even altered the time of the recording function. Components, such as solenoid valves, power contacts, and signal relays that are not susceptible to malfunction from external electrical interference, generate transient pulses when deenergized. These impulses may exceed the normal operating vol

34、tage ratings of much associated connecting circuitry as well as transmit electromagnetic interference to external electronic circuits.a72 a72 Low Temperature. - The low temperature test is performed to determine the operational performance of the item at low temperatures which might be encountered d

35、uring its life cycle. The test item should be functionally tested during exposure to ascertain whether or not the environment causes degradation of performance. Some of the difficulties which may result from low temperature exposure are binding due to differential contraction of parts, loss of resil

36、iency of gaskets, and congealing of lubricants. Testing to this environment is applicable to components not installed in a temperature controlled environment.a72 a72 High Temperature. - The high temperature test is performed to determine the operational performance of the item at high temperatures t

37、hat might be encountered during its life cycle. The test item should be functionally tested during exposure to ascertain whether or not the environment causes degradation of performance. High temperature conditions may cause permanent setting of packings and gaskets, binding of parts due to differen

38、tial expansion, and cracking or bulging of rubber and plastic. This test is applicable to components that are not installed in a temperature controlled environment.a72 a72 Temperature Shock. - The temperature shock test is performed to determine the effect of an anticipated sudden change in temperat

39、ure on the operational performance of an Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-item. Cracking or rupturing of materials (particularly valve seats) due to changes in material characteristics and dimensions is the principal difficulty to be a

40、nticipated. A thermal shock is experienced when (1) gases expand upstream or immediately downstream of a pneumatic component, (2) hydraulic fluid is forced through restrictions at high flow, and (3) when cryogenic fluids are used in items that are not gradually chilled down.a72 a72 Acoustics. - The

41、acoustic test is performed to determine the effects on performance that acoustics will have on GSE and other facility hardware located at or near the launch pad at the time of launch vehicle holddown and lift-off. In an acoustic noise field, pressure fluctuations impinge directly on the equipment pr

42、oviding a distributed type of dynamic load. Broadband spectra of these loads contain resonance frequencies of most, if not all, structural components of equipment. The resulting resonant vibration is generally different from that which occurs when excitation is applied only at discrete points. Furth

43、er, components that are effectively isolated from a mechanical transmission of vibration from the supporting structure will be excited directly. Electronic chatter at friction-held contacts, chafing of wires, cracking and collisions of printed circuit boards, and malfunction/failure of waveguides an

44、d Klystron tubes are examples of acoustically induced problems. Acoustic! test specifications provide guidance for the performance of acoustic tests on GSE or other facility hardware. Acoustic tests are subject to restraints imposed by the capabilities of existing test facilities.a72 a72 Vibration.

45、- Vibration test specifications provide guidance for the performance of vibration tests on GSE or other facility hardware used to support the launch of a space vehicle. These specifications apply to a vibration environment occurring during a launch for the purpose of providing criteria for acceptanc

46、e and qualification of GSE. The extent of concern is limited to equipment located on and in the proximity of the launch pad, generally within a 300-meter (1000-foot) radius of the launch pad.a72 a72 Shock. - The launch of a space vehicle generates pressure acoustic environments that do not contain s

47、hocks. A pressure pulse generated by some engines at the time of ignition does not induce as a response a distinct vibration shock, rather it results in a transient vibration with peak amplitudes that are substantially lower than the peak vibration during a lift-off period. True vibration shocks occ

48、urring during a launch are true anomalies caused by collisions between structural elements and by bottoming of vibration isolators. High shocks can be generated by a hard bottoming of vibration isolators that do not have snubbers and that involve metal-on-metal impacts. Whenever possible, the cause

49、of shocks should be corrected rather than trying to qualify equipment for an operation in the shock environment by testing. Exceptional Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-shock occurrences covered by these specifications are those that canno