1、Best Practices Entry: Best Practice Info:a71 Committee Approval Date: 2000-04-19a71 Center Point of Contact: JSCa71 Submitted by: Wil HarkinsSubject: Maintainability Considerations in Extravehicular Activities (EVA) Design: An Astronauts Perspective Practice: Extravehicular Activities (EVAs) are ver
2、y demanding and specialized space flight activities. With the substantial costs from any unsuccessful EVA and the limited opportunities for work-arounds, careful maintainability design of payloads/systems and their operations are essential for complete mission success.Programs that Certify Usage: Th
3、is practice has been used on Shuttle Orbiter Missions with EVAs.Center to Contact for Information: JSCImplementation Method: This Lesson Learned is based on Maintainability Technique number OPS-19 from NASA Technical Memorandum 4628, Recommended Techniques for Effective Maintainability.Benefit:A wel
4、l thought out and properly designed EVA incorporating ease of crew maintainability leads to mission success. Failure to properly address crew maintainability in the EVA design can lead to time-consuming “work-arounds,“ the inability of the crew to fully complete the desired and/or required tasks, an
5、d may expose the crew to unnecessary safety hazards.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Implementation Method:BackgroundAstronaut Jerry Ross has participated in the development of almost all of the EVA hardware and procedures for the Spac
6、e program since 1981. This includes being the support crewman and EVA Capsule Communicator (CAPCOM) for the first manned maneuvering unit (MMU) flight (STS-41B), the Solar Max repair mission (STS-41C), the WESTAR and PALAPA retrievals (STS-51A), and the attempted “flyswatter“ activation of the SYNCO
7、M satellite. He has also performed four EVAs on STS-61B and STS-37 to investigate space construction techniques and prototype Space Station EVA equipment and to repair the Gamma Ray Observatory. In addition, he has participated in the testing of advanced space suits since 1984 and in the design of S
8、pace Station EVA systems since 1985.Primary Crew ConsiderationsFirst and foremost, a human being can do almost anything during a space walk that can be done on the Earths surface. However, working in zero gravity and in a spacesuit necessitates certain design compromises to facilitate the productivi
9、ty of the spacewalker and to enhance the probable success of the EVA. Two factors that must always be considered when designing EVAs are: (1) that the spacesuit is stiff, restricts visibility and movement, is fatiguing to work in, and all work is done with gloves that significantly reduce tactility
10、and dexterity; and (2) that all things must be tethered (including the crew persons) to preclude them from drifting away and becoming lost.EVA Design ConsiderationsThere are several design considerations that must be kept in mind when developing an EVA.a71 Compatibility - EVA equipment and tasks sho
11、uld be designed to be EVA compatible. This will maximize the probability of success, minimize the expense, eliminate EVA hazards, and prevent the need for inefficient, time-consuming operational workarounds due to bad design concepts.a71 Task Design - Tasks should be designed, when possible, so that
12、 tools are not required. For example, a doorknob should be used instead of bolts to provide access behind a panel. If tools are required, standard tools and interfaces should be used. This minimizes the number of tools that need to be flown and training required, and enhances the probability of succ
13、ess. Tools should be stowed at work sites when possible to minimize the movement of tools and equipment. Power tools should be used for tasks that are repetitive. This increases productivity and will reduce crew fatigue. For the most part, tasks should be designed so that only one hand is required.
14、This is due to considerations of working in the spacesuit and the frequent requirement to stabilize oneself Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-with the other hand. The maximum force to perform a task should be designed to 113 N (25 lbs.)
15、 and the task should be designed to use large muscle groups whenever possible to reduce crew fatigue.a71 Proven Design Concepts - Proven design concepts should be standardized and used; e.g., double high bolt heads, electrical wing tab connections, and ganged connectors. Designs should also minimize
16、 the number of loose parts by using self-retaining fasteners and panel hinges.a71 Good Visual Indicators - Good markings, feedbacks, and indicators need to be provided so the EVA crewperson can visually verify that the proper condition has been achieved, such as closed, locked, open, or over-center.
17、a71 Restraints - The right types of restraints, foot restraints, hand-holds, tether points, and translation aids need to be provided in the right locations. Their placement, type, and number must be determined through suited zero-gravity simulations in an underwater facility.a71 Involvement of Safet
18、y and Quality Assurance - The Quality Assurance and Safety organizations should be involved in the design process at an early stage. This will help to ensure a good and safe design and help minimize the need for costly redesign.EVA SimulationWater tanks provide an excellent analog simulation capabil
19、ity. They should be used early in the design process with mock-ups of the flight hardware and tasks to be performed. Astronaut participation in these early water tank evaluations is essential to a cost-effective and efficient design process. The mock-up should be upgraded as the design matures and t
20、he fidelity of the mock-up to the flight hardware can be critical to the success of an EVA.Functional Testing and Fit ChecksFunctional tests of EVA hardware and tools in a thermal/vacuum chamber have proven to be mandatory. Many design changes have resulted from such tests.Fit checks of all flight h
21、ardware to all flight (and flight spares) hardware and tools are mandatory. Develop a matrix of all interfaces and perform physical fit checks. Numerous on-orbit problems have been avoided through this process.Space Shuttle EVA OperationsFor the Space Shuttle, EVA is at least a three person task (tw
22、o EVA crew members and a third crewman on the aft flight deck to observe and act as an EVA activity manager). This third crewperson or activity manager serves as a time line prompter, procedure reader, picture taker, and keeps track of all of the loose hardware items. Crew coordination is essential
23、when EVA operations are combined with remote manipulator system operations and Orbiter operations.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Use conservative EVA timelines so that there will be time to deal with any unanticipated problems or del
24、ays. Convenient break points should be developed so that hardware can be left in a safe and stable configuration between EVAs. Backup procedures should be developed to overcome significant problems should they occur on orbit. Such preflight work saved the Solar Max repair mission and the WESTAR and
25、PALAPA satellite retrievals.Develop and maintain good documentation of flight hardware configurations. Closeout (prelaunch) photographs are important to the EVA design and development process. The lack of good closeout photos and other detailed information on the “as flown“ hardware configuration al
26、most caused the failure of both the Solar Max and WESTAR/PALAPA EVA missions.Impact of Non-Practice: Proper EVA design consists of working early and closely with the astronaut(s). Tasks and operations that are desired by the payload/system need to be reviewed early by the crew to ensure that the des
27、ign is directed toward ease of EVA operability and maintainability. This will increase the probability of EVA mission success.Related Practices: N/AAdditional Info: Approval Info: a71 Approval Date: 2000-04-19a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
