1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-03-30a71 Center Point of Contact: GRCa71 Submitted by: Wilson HarkinsSubject: Maintenance Concept For Space Systems Practice: Develop a maintenance concept early in the program life cycle to provide a basis for full maintaina
2、bility support. It should be used to influence systems design to ensure that attributes for ease of maintenance, minimization of repair and down time, and logistics support will be present in the final design.Programs that Certify Usage: This practice has been used on Space Acceleration Measurement
3、System (SAMS), Combustion Module-1 (CM-1), Shuttle/Station Experiment.Center to Contact for Information: GRCImplementation Method: This Lesson Learned is based on Maintainability Technique Number PM-3 from NASA Technical Memorandum 4628, Recommended Techniques for Effective Maintainability.Effective
4、 development of a maintenance concept can enhance the effectiveness of maintenance support planning and aid both logistics planning and design of a maintainable system. The maintenance concept can also provide assessments of cost savings for maintenance activities and resources allowable at each mai
5、ntenance level.The maintenance concept provides the basis for overall maintainability design requirements for the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-program, and contains detailed planning of maintenance policy for the operational system
6、. It establishes the scope of maintenance responsibility for each level (echelon) of maintenance and the personnel resources (maintenance manning and skill levels) required to maintain a space system. Early development and application of the maintenance concept in structuring the maintainability pla
7、n can eliminate or reduce occurrence of problems that may interrupt system operation.The maintenance concept for a new system must be systematically formulated during the early conceptual design phase of a program to minimize maintenance problems during the operational phase. This proactive approach
8、 is being used on Space Station-based experiment development programs at LeRC to incorporate current Space Station Program support principles, prescribed Space Acceleration Measurement System (SAMS) and Combustion Module One (CM-1) operational and repair policy, and identified sparing requirements.E
9、lementsThis maintenance concept will aid in logistics planning and will guide design by providing the basis for establishment of maintenance support requirements in terms of tasks to be performed, frequency of maintenance, preventive and corrective maintenance downtime, personnel numbers and skill l
10、evels, test and support equipment, tools, repair items, and information. Inputs to the maintenance concept should include: a mission profile, system reliability and availability requirements, overall size and weight constraints, and crew considerations. The concept should support the following desig
11、n elements as they apply to a manned orbital space program where on-orbit and ground maintenance is planned.Repair PolicyThe repair policy should consider the support to be provided at the maintenance echelons (levels) summarized in Table 1.Table 1. Echelons of MaintenanceOrganizational Maintenance
12、Depot MaintenanceWhere Performed On-orbit NASA Center or ContractorSystem Maintainer Flight Crew Center Engineers and TechniciansBasis Repair and retain equipment Repair and return equipment to stock inventoryType of work accomplishedInspect equipment Repair at module, ORU, and component levelProvid
13、ed by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Remove and replace modules and ORUsRepair and maintain ground support equipmentAdjust equipment Calibrate equipmentOrganizational MaintenanceOrganizational maintenance is maintenance performed by the using or
14、ganization (e.g., flight crew) on its own equipment. This maintenance consists of functions and repairs within the capabilities of authorized personnel, skills, tools, and test equipment. Organizational level personnel are generally occupied with the operation and use of the equipment, and have mini
15、mum time available for detailed maintenance or diagnostic checkout; consequently, the maintenance at this level is restricted to periodic checks of equipment performance. Cleaning of equipment, front panel adjustments, and the removal and replacement of certain plug-in modules and Orbital Replaceabl
16、e Units (ORUs), referred to as black boxes, are removed and forwarded to the Depot Level.Depot MaintenanceDepot maintenance is maintenance performed at NASA Centers or contractor facilities for completely overhauling and rebuilding the equipment as well as to perform highly complex maintenance actio
17、ns. The support includes tasks to repair faulty equipment to the part level, if deemed necessary. This level of maintenance provides the necessary standards for equipment calibration purposes, and also serves as the major supply for spares.System AvailabilityOperational Availability (Ao ) is defined
18、 as the probability that at an arbitrary point in time, the system is operable, i.e., is “up.“ It is a function of the frequency of maintenance, active maintenance time, waiting time, logistics time, administrative time, and the ready time of the system, and is expressed as:refer to D description D(
19、1)Where:UPTIME = the total time a system is in an operable state, and TOTAL TIME = the combination of uptime and downtime, in which downtime is the time in which a system spends in an inoperable state.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-R
20、epair vs. Replacement PolicyNormally, on-orbit repair should not be performed on any plug-in modules or ORUs. If any on-orbit repair actions are planned, they should be clearly identified in the concept. At the organizational level, failed items should be either discarded or sent to the NASA Center
21、or contractor for exchange and repair in accordance with repair/discard policies identified in the system requirements. Corrective maintenance, limited to replacement of faulty ORUs and plug-in modules, should be specified to be performed during the mission period. Prime equipment should be designed
22、 to have ready access for maintenance. Quick-opening fasteners should also be specified.Level of ReplacementThe design for proper level of ORU definition should consider compatible failure rates for hardware parts within the same ORU. Relative ranking of ORUs through reliability and maintainability
23、considerations and mission criticality analysis can also contribute toward the proper level of replacement definitions. The required level of replacement should be specified at the plug-in module and ORU levels. Maintenance and support of a system should involve two-tier maintenance echelons. The fi
24、rst level provides for repair of the end- item on-orbit by replacing select faulty or defective plug-in modules and ORUs identified through use of specified diagnostic procedures. Faulty ORUs should then be evacuated to the second level of the maintenance echelon (depot level), which will be at a NA
25、SA Center for repair if deemed necessary. The particular NASA center/ facility should act as the depot for repair of faulty items.Skill Level RequirementsHardware should be designed to aid on-orbit and ground maintenance, inspection, and repair. Special skills should not be required to maintain a sy
26、stem. The following design features should be incorporated:a71 Plug-in module and ORU design to minimize installation/removal time and requirements for hand tools, special tools, and maintenance skills.a71 Plug-in modules and ORUs should be designed for corrective maintenance by removal and replacem
27、ent.a71 Plug-in module and ORU designs requiring preventive maintenance should be optimized with respect to the access, maintenance hours, and maintenance complexity.a71 Software and its associated hardware should be designed so that software revisions/corrections can be easily installed on-orbit wi
28、th minimum skill level requirements.a71 Flight crew training for payload flight operation should identify hands-on crewmember training, at the NASA center where the system is built, to familiarize crewmembers with the removal/replacement of hardware.Provided by IHSNot for ResaleNo reproduction or ne
29、tworking permitted without license from IHS-,-,-Spares PhilosophyTwo basic types of spares should be required to support a maintainable system: development spares and operational spares. Development spares are those that must be identified and acquired to support planned system test activities, inte
30、gration, assembly, check-out and production. Operational spares are those spares that must be acquired to support on-going operations on-orbit.The quantity of development spares required for each system, and the total quantities to sustain the required availability during the planned test activities
31、, integration, assembly, and check-out test should be determined according to the following:a71 Custom-made components/partsa71 Long-lead time itemsThe quantity of spares required for each system and the total quantities to sustain the required operational availability on-orbit should be determined
32、according to the following:a71 Items that are critical to system operationa71 Items that have high failure ratea71 Items that have limited lifeIn the initial spares provisioning period and to the maximum extent practical, spares should be purchased directly from the actual manufacturer; i.e., lowest
33、-tier subcontractor, to eliminate the layers of support costs at each tier. The initial provisioning period should cover early test and evaluation, plus a short period of operation, to gain sufficient operational experience with the system. This will provide a basis for fully competitive acquisition
34、 of spares.Spares with limited shelf life should be identified and should be acquired periodically to ensure that adequate quantities of spares are available when needed. Spares with expired shelf lives should be removed and replaced.Procurement of spares should be initiated in sufficient advance of
35、 need to account for procurement lead time (administrative and production lead time).The location of the spares inventory (on- orbit and on-ground) should be a function of the on-orbit stowage allocation capabilities and requirements. A volume/weight analysis should be conducted to determine the qua
36、ntity and types of spare items necessary to sustain satisfactory operational availability. The volume/weight analysis shall assure available or planned payload volume and weight limits, and planned or available on-board stowage area.Breakout should be addressed during initial provisioning and throug
37、hout the replenishment process in accordance with NMI 5900.1, Reference 1. Breakout is the spares procurement directly from the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-original equipment manufacturer, prime contractor, or other source, whiche
38、ver proves most cost-effective. A spare item requirement list should be maintained by procurement and technical personnel.Diagnostic/Testing Principles and ConceptsThe system should meet the following failure detection requirements as a minimum:a71 The system should have the capability to detect, is
39、olate and support the display of failures to the plug-in module level. Crew observations may be used as a method of failure detection of the following: visual displays, keyboards/buttons, general lighting, speakers.a71 System design should provide the capability for monitoring, checkout, fault detec
40、tion, and isolation to the on-orbit repairable level without requiring removal of items.a71 Manual override and/or inhibit capability for all automatic control functions should be provided for crew safety and to simplify checkout and troubleshooting.a71 All failures of the system should be automatic
41、ally detected and enunciated either to the flight crew or the ground crew.a71 Accesses and covers should be devoid of sharp corners/edges and be equipped with grasp areas for safe maintenance activities.a71 Systems/subsystems/items should be designed to be functionally, mechanically, electrically, a
42、nd electronically as independent as practical to facilitate maintenance.The concept should also describe operating/testing techniques to identify problems and consider the complexity of the various types of items in the space system and associated maintenance personnel skills (for all software, firm
43、ware, or hardware). The techniques will identify maintenance problems. In all cases of fault simulation, the safety of personnel and potential damage to system/equipment should be evaluated in the concept. The concept should request that a safety fault tree analysis be the basis for determining simu
44、lation. Also, a Failure Modes, Effects, and Criticality Analysis should be used to evaluate and determine fault simulation. Some of the fundamental maintenance actions to be evaluated, monitored, and recorded are as follows:a71 Preparation and visuala71 inspection timea71 Functional check-out timea7
45、1 Diagnostic time: fault locate and fault isolatea71 Repair time: gain access, remove and replace, adjust, align, calibrate, and close accessa71 Clean, lubricate, service timea71 Functional check-out of the repair actionResponsibilities for Contractor MaintenanceThe prime contractors maintainability
46、 program should provide controls for assuring adequate Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-maintenance of purchased hardware. Such assurance is achieved through the following:a71 Selection of subcontractors from the standpoint of demonstr
47、ated capability to produce a maintainable product.a71 Development of adequate design specifications and test requirements for the subcontractor-produced product.a71 Development of proper maintainability requirements to impose on each subcontractor.a71 Close technical liaison with the subcontractor (
48、both in design and maintainability areas) to minimize communication problems and to facilitate early identification and correction of interface or interrelation design problems.a71 Continuous review and assessment to assure that each subcontractor is implementing his maintainability program effectiv
49、ely.Responsibilities for Payload MaintenanceDirector of field installations responsible for launch preparation, maintenance, or repair activities should be responsible for maintenance planning and for providing the resources necessary to support the efficient identification of maintenance related problems in accordance with system requirements. These resp
