Space Station Engineering Design Issues Report of a Workshop (1989) / Chapter Skim
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4 Issues Related to Systems Requirements and Design
4 Issues Related to Systems Requirements and Design
Pages 31-52
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From page 31... ...
In the course of its review of subsystem requirements and design approaches, the committee identified a number of issues related to the interactions and interdependencies of Space Station subsystems. It believes that more attention needs to be given to such overall Architectural considerations.
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From page 32... ...
However, increased damping would permit further simplification and accommodate future configuration changes without requiring major control system changes. Increased damping also would reduce the response in the microgravity laboratory areas to astronauts" movements.
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There are precedents for such an approach. One European contractor has intentionally introduced damping in the joints of a spacecraft structure to provide such conservative design margins that a costly structural analysis is not needed each time there is a configuration change.
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of an evolving spacecraft during construction, when the configuration changes with the arrival of a transport vehicle (initially the Shuttle) , and when an experimental payload or module is added or deleted.
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SPECIFIC SYSTEMS ISSUES The following sections identify issues and concerns raised by the committee with respect to specific Space Station systems. Software and Data Management Overview The Space Station software and data management systems are highly complex.
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From page 36... ...
Nonetheless, the committee is concerned about a number of aspects of the Space Station software and data management capabilities. Successful software development is characterized by well-understood, well-defined, and stable software requirements; elimination of high-risk software items; precisely defined interfaces between the software components; and a mature, in-place SSE.
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From page 37... ...
A particularly effective risk resolution capability for software design uncertainties is rapid prototyping. Early use of rapid prototyping in such areas as user interface systems, distributed processing, and critical algorithms should be much more strongly emphasized.
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The early schedule preferably should emphasize execution of risk management plans and resolution of risk items before software requirements are "cast in concrete. Finally, it appears that the first item in the critical path for the software is the DMS.
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From page 39... ...
Particular needs are Ada-compatible requirements and design aids and applications-level TMIS data definitions. Software Design for Supportability It does not appear that supportability is being adequately emphasized in the Space Station software design approach (e.g., having software requirements documents include a section on primary sources of requirements growth and change)
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From page 40... ...
Finally, current Space Station software integration plans emphasize postcoding activities. The Ada programming language enables software developers to begin integration during the design phase, by thoroughly defining Ada package specifications and verifying their consistency with other Ada package specifications via the Ada compiler.
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From page 41... ...
The additional complexities of having a single clearinghouse for commands, command checking, or transaction management underscore the need for continued emphasis on coordination in this area.
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From page 42... ...
The complexity of the Space Station program requires continuing analyses of all links from their origin to their final destination, inclucling command and control as well as experimenter data links. For example, signals should be traced from the source through the Space Station's internal processing steps and channels, Tracking and Data Relay Satellite System (TDRSS)
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From page 43... ...
Electromagnetic Interference The Space Station obviously is dependent on many communication links for its successful operation; it is equally obvious that the vulnerability of these links to deliberate or inadvertent interference or access will be a continuing concern. Similarly, the various connected components of the Space Station contain many potential sources of interference that must be shielded from one another.
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From page 44... ...
The relative inaccessibility of the Station and the relatively meager resources that will be available to the crew heighten the need for special attention to this potential problem. One of the more troublesome forms of electromagnetic interference is the generation of passive intermodulation products.
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From page 45... ...
The Space Station program should press forward strongly with its advanced automation initiative and foster a synergy with the NASA Office of Aeronautics and Space Technology automation technology efforts, but with a more problem-c~riven approach. Some important criteria for early AI applications to the Space Station are that they be low cost and low risk with high payoffs.
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From page 46... ...
However, Space Station program functional breakouts of crew time indicated that three times as much crew time will be spent on user operations as on system operations. From a productivity-leverage standpoint, more emphasis should be directed toward advanced automation tools and capabilities to improve efficiency of user operations, and toward training designers of Space Station user applications and experiments in the use of such tools and capabilities to make their applications more crew efficient.
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The committee has not had an opportunity to meet again to assess the merits of the decision.] The committee understands that the electrical power and thermal control systems are being developed by at least two NASA sites.
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The thermal control system programs for the thermal management of the photovoltaic power and space conditioning systems are presently at two locations: the NASA Lewis Research Center and the Johnson Space Center. Better coordination or even combination of the programs should be considered.
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The ECLSS, Man Systems, and EVA System are intimately interdependent and also are closely related to the Fluid Management System, which will be discussed subsequently. The committee identified a number of issues related to these systems that warrant attention.
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Medical Evacuation Situations are likely to arise in which Station personnel need to be evacuated after an initial medical stabilization by fellow crew members. NASA has considered the possibilities for evacuation from the Space Station under a variety of circumstances.
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From page 51... ...
and consideration of astronauts' requests for a smaller EVA backpack, more development efforts are needed on monitoring for nitrogen bubbles in the bloodstream and on a means for handling vomiting while an astronaut is engaged in an EVA. FLUID MANAGEMENT SYSTEM The plans for an integrated fluid management facility need to be carefully developed.
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From page 52... ...
The current design utilizes a single water and nitrogen supply system going to both the ECLSS and EMS systems. Although the design calls for check valves, the committee believes that a thorough analysis of this concept should be conducted prior to baselining an integrated system.
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