1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-06a71 Center Point of Contact: MSFCa71 Submitted by: Wilson HarkinsSubject: Guideline for Developing Reliable Instrumentation for Aerospace Systems Practice: The development of in-flight instrumentation, vehicle health man
2、agement systems, and sensor systems for control and monitoring should be thoroughly integrated into the requirements generation, preliminary design, and early planning for payloads and space flight systems. Multi-disciplinary Product Development Teams (PDTs) must include instrumentation consideratio
3、ns at the very front end of the development process. This will allow maximum advantage to be gained from current and emerging technologies to provide both real time and postflight diagnostics that will reliably and consistently reflect the systems condition. The result will be improved vehicle and p
4、ayload system reliability through accurate and well-planned access to performance information. Emphasis must be placed on early definition of instrumentation and measurement requirements to reduce the time and cost to develop reliable instrumentation systems and ensure mission success.Programs that
5、Certify Usage: N/ACenter to Contact for Information: MSFCImplementation Method: This Lesson Learned is based on Reliability Guideline number GD-ED-2215 from NASA Technical Memorandum 4322A, NASA Reliability Preferred Practices for Design and Test.Very early consideration of instrumentation (Note: fo
6、r purposes of this lesson, the term instrumentation refers only to sensor and signal conditioning subsystems and will not include the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-data management subsystem) requirements compatible with vehicle or p
7、ayload system monitoring and control requirements will result in: (1) Choice of sensor technology and sensor hardware/software that is cost-effectively matched to specific vehicle environment, design, performance, and configuration requirements; (2) Up-front consideration of the effects of instrumen
8、tation system and sensor maintainability, calibration, and reliability during the operational phase over the specified lifetime; (3) Optimum sensor location, avoidance of failures due to vibration, shock, thermal and stress effects, efficient cable design and routing; and (4) Lower costs of instrume
9、ntation system integration due to well thought-out and preplanned designs that are less subject to change during the development process.Implementation:It has been the general practice in past programs and projects to conceive and design instrumentation systems and related sensors, hardware, and sof
10、tware well after requirements for the system have been established. Instrumentation considerations have frequently waited until well after the design of the parent hardware has been approved, and many times the instrumentation design has not been initiated until the initial test hardware is well int
11、o fabrication. In general, this practice has not been seriously detrimental to past programs because of the luxury of ample resources and schedule time to iterate the instrumentation configuration many times prior to flight. Furthermore, the technologies available were not as advanced as those becom
12、ing available in the present age of computer-aided analysis, engineering, design, testing, and manufacturing. New concurrent engineering methods and tools that are now available, and the use of integrated product engineering development teams allow instrumentation considerations, designs, and techno
13、logies to be introduced at the earlier phases of the project life cycle. Earlier consideration of instrumentation issues will result in greater efficiencies and more effective total instrumentation support of the space system development and flight operations.Background:There are three main purposes
14、 of instrumentation systems, (1) to perform measurements, (2) to provide for system control, and (3) to relay information. Measurements are needed to obtain information on system operation and the operational environment. Based upon this information, feedback and adjustments can be made to control l
15、oops to maintain system control. Finally, the information generated by the measurements must be processed and relayed from the operational system to data collection and analysis centers. Data processing and relay are outside the scope of this guideline and will not be discussed further.There are thr
16、ee types of measurements: (1) measurements for design, test, and evaluation; (2) measurements for calibration; and (3) measurements for control (Ref. 1). Each of these types of measurements impose unique requirements on the vehicle or payload instrumentation system.Science, design, test, and evaluat
17、ion measurements seek to answer questions about a physical process Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-or environment about which little or nothing is known. A key consideration in these types of measurements is the effect of the instrume
18、ntation system itself on the phenomenon being measured.Control measurements are made to ensure the process or system is working properly. This usually involves making adjustments in control loops so as to maintain an operating point within some acceptable range.Calibration measurements are made to c
19、haracterize part of the instrumentation system, such as a sensor, in a known environment with specific boundary conditions.I. Key Instrumentation Considerations:There are a number of instrumentation issues that need to be addressed as early as possible in the system life cycle. The earlier these iss
20、ues are addressed the more reliable the measurements, and thus the overall system, will be. Close communication and interaction among instrumentation engineers, system users, and system designers are essential if these issues are to be adequately addressed. These key issues are briefly discussed in
21、the following paragraphs.A. What is the “real“ measurement requirement?Experience has shown that often the user does not state the real measurement requirement but rather an implementation. This must be avoided early-on as it results in limiting potential measurement solutions and affects reliabilit
22、y. A good question to ask to get at the core requirements is, “If you could only have one measurement, what would it be?“ In addition to the answer to this question, the type and purpose of each proposed measurement must be understood.B. Operating environmentThe environment in which a measurement mu
23、st be made significantly impacts the selection of sensors and ultimately the reliability and accuracy of the resultant information. Examples of important environmental factors include vibro-acoustics, atmosphere, temperature, and pressure.C. Required accuracy and frequency responseThis is an area wh
24、ere significant tradeoffs and compromises must be worked out between the user and the instrumentation engineer. Since accuracy and frequency response of sensors are directly related to cost, it is incumbent on the instrumentation engineer to make program participants aware of the cost to the project
25、 of satisfying stated accuracy and frequency response requirements. Often, it will turn out that less stringent requirements in these areas can satisfy the “real“ requirements at significant cost avoidance to the project.D. ConstraintsProvided by IHSNot for ResaleNo reproduction or networking permit
26、ted without license from IHS-,-,-There are a number of constraints with which the instrumentation system must comply. Some are limited resource allocations for things like size, power, weight, volume, and cost. Other constraints will arise with regard to possible locations for sensors and signal con
27、ditioners, and feasible routing for cables and connectors. All of these constraints must be dealt with in designing reliable instrumentation systems to meet user requirements.E. Maintainability/ReusabilityInstrumentation system components such as sensors, signal conditioners, and even cables and con
28、nectors are subject to failure. Requirements for access to these components to affect repairs will also impact the instrumentation system design for long-life missions. Related to maintainability are requirements for sensor checkout, calibration, and diagnostics which must also be factored into the
29、instrumentation system design. Similarly, requirements for cleaning and refurbishment associated with reusable flight systems impact on the design.F. Electrical and mechanical interfacesOften early decisions are made on the avionics architecture and on the data management system which will impact th
30、e instrumentation system design. Such items as choice of flight computers and data bus standard will be driving requirements in selection of instrumentation system components. Likewise, specific requirements for mounting and other mechanical interfaces will affect instrumentation system design.II. I
31、ntegrating Instrumentation System Design into the Project Life CycleInstrumentation engineering is one of the engineering specialties which needs to be integrated into the overall system engineering process required to develop and operate reliable aerospace systems. The tendency has been to wait unt
32、il the design phase of the life cycle before seriously addressing instrumentation requirements and issues. Often it is even later, even after the design is complete, before instrumentation is considered. When this occurs, it can result in less than optimum instrumentation solutions to engineering an
33、d science requirements. One consequence can be less reliable systems due to the inability to gather information on the true condition of the flight system in operation. An example of this problem can be seen in the Space Shuttle Main Engine (SSME) program at MSFC. Only after the High Pressure Fuel a
34、nd Oxygen Turbopumps were designed did it come to light that the single most important measurement that the engineers wanted was turbine inlet temperature. However, because instrumentation considerations had not been addressed early enough, no provision had been made in the design to accommodate a s
35、ensor for this purpose, and it was deemed too costly to redesign the turbopump at that point in the program.A typical NASA flight system passes through several distinct phases in its life cycle as it proceeds from concept exploration to system disposal. NASA Management Instruction (NMI) 7120.4 (Ref.
36、 2) Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-and NASA Handbook (NHB) 7120.5 (Ref. 3) describe these phases and the associated activities and milestones associated with each. Figure 1 (Ref. 4) summarizes these phases and the major activities an
37、d outputs of each phase.refer to D descriptionD The appropriate instrumentation engineering activities for each phase are discussed in the following paragraphs.A. Phase A (Analysis Phase)This is a study phase in which mission needs are determined and preliminary concepts are explored. Project object
38、ives, new technology requirements, and potential system concepts are developed and analyzed to determine the project feasibility and cost-effectiveness. Performance tradeoff analyses are conducted to refine the system concepts and to identify risk areas. A key activity in this phase is the definitio
39、n of preliminary system requirements and the development of a Preliminary Program Plan. Early point designs and even configuration layouts are a product of this phase.Even in this earliest of project phases, instrumentation issues should be addressed. First, the instrumentation engineers should be i
40、nvolved in developing the preliminary system requirements to ensure the key considerations discussed in Section I above are addressed. Obviously, point designs and configuration layouts can have significant impacts on instrumentation concepts and solutions and need to be reviewed carefully. Armed wi
41、th knowledge and understanding of the system requirements Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-and objectives, the instrumentation engineers can begin to define both the purposes and types of measurements that will be needed and to develop
42、 preliminary instrumentation concepts. The instrumentation concepts, preliminary measurement definitions, sensor technology development needs (if any), instrumentation risk assessments, schedule and resource requirements should all be documented in a Preliminary Instrumentation Plan which should be
43、an output of this project phase. Phase A ends upon approval of the Mission Need Statement.Instrumentation Guidelines for the Analysis Phase:1. Ensure user needs and mission requirements are understood by the instrumentation engineers.2. Ensure preliminary system requirements include appropriate inst
44、rumentation considerations.3. Prepare a Preliminary Instrumentation Plan that addresses instrumentation concepts, measurement definitions, sensor technology needs, risk areas, and resource requirements.4. Ensure the Preliminary Instrumentation Plan is reviewed by all program participants in conjunct
45、ion with a Preliminary Requirements Review or other formal review.B. Definition and Preliminary Design Phase (Phase B)This phase accomplishes the refinement and baselining of system requirements, cost estimates, schedules, and risk assessments prior to final design and development. Alternative syste
46、m concepts defined in Phase A are refined and a final selection is made. System analyses and simulations are conducted and further tradeoff analyses are made to refine system and support requirements. Preliminary manufacturing and test requirements are also defined and assessed in this phase. Key ou
47、tputs of this phase include a baselined System Specification and a Preliminary Design Review (PDR) baseline.Instrumentation engineering involvement should increase in this phase with activities focused on influencing the system specifications and preliminary designs to facilitate reliable vehicle in
48、strumentation and measurements. The Instrumentation Plan should be updated and baselined in this phase. Preliminary instrumentation system design and preparation of a preliminary Instrumentation Program & Command List (IP&CL) should be completed. The IP&CL is defined in MSFC-STD-1924 (Ref. 5).Instru
49、mentation Guidelines for the Definition and Preliminary Design Phase:1. Ensure the System Specification, lower-level specifications, and the preliminary system design include all appropriate instrumentation considerations and requirements and satisfy user needs.2. Update and baseline the Instrumentation Plan which defines the instrumentation concept and design, measurement definitions, sensor technology needs, risk areas, and resource requi
