Upgrading the Space Shuttle (1999) / Chapter Skim
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4 Assessments of Proposed Upgrades
4 Assessments of Proposed Upgrades
Pages 38-56
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From page 38... ...
The committee points out areas of technical or programmatic risk, suggests alternate approaches, and addresses the potential of proposed upgrades to meet the goals of the Space Shuttle Program. With rare exceptions, however, the committee does not recommend particular upgrade candidates for implementation.
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From page 39... ...
A modern system that incorporates advances in both hardware and software could not only reduce costs related to obsolescence and personnel but could also facilitate future computer-intensive shuttle upgrades, such as an integrated vehicle health management system. However, the committee has some serious concerns about the CLCS project as currently planned.
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From page 40... ...
, management believes the predicted level of software productivity can be achieved with the aid of software generation tools. Based on other historical precedents, however, the committee believes that a system as large, complex, heterogeneous, and tightly scheduled as the CLCS has a high potential for running behind schedule and over budget.
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From page 41... ...
The Space Shuttle Program Development Office should solicit additional proposals for upgrades to protect the shuttle from meteoroids and orbital debris. PHASE III UPGRADES Replacement of the Auxiliary Power Unit Each shuttle orbiter has three APUs, which are used to power the vehicle's hydraulics during ascent and reentry.
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From page 42... ...
In addition, the replacement of the existing APUs by longer-life, less toxic, more efficient power units would reduce turnaround time during ground processing of the orbiter system. In its search for a replacement for the APU, NASA can take advantage of worldwide efforts to develop advanced electric power systems, including aerospace applications (e.g., the Joint Strike Fighter, the F-22, the Comanche helicopter, the X-33, and the X-34)
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From page 43... ...
The objective of NASA's proposed avionics upgrade strategy is to avoid the growing costs associated with obsolescence by judiciously replacing obsolescent hardware while, at the same time, positioning the upgrades as components of a modern, functionally partitioned avionics architecture. (Replacement of obsolete avionics hardware is considered to be a Phase II upgrade; the development of a complete modern avionics architecture is considered to be a Phase III upgrade.)
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From page 44... ...
(The current SSME nozzle takes two-and-one-half years to build, costs $7 million, and is currently flown no more than 12 to 15 times because of safety concerns related to hydrogen leaks.) NASA expects the channel-wall nozzle to be more reusable than the current nozzle and to have less risk of critical failure.
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From page 45... ...
If NASA decides to implement the channel-wall nozzle upgrade, it should take steps to ensure that channel-wall nozzles are available in the United States, either by stockpiling additional nozzles or developing a channel-wall nozzle manufacturing capability in the United States. Extended Nose Landing Gear The proposed extended nose landing gear is a modification intended to reduce the loads on the orbiter's landing gear.
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From page 46... ...
fuel cells are being considered to replace the current cells. Longer-Life Alkaline Fuel Cells This upgrade, proposed by International Fuel Cells and Boeing, would entail replacing the current fuel cells with modified alkaline cells.
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From page 47... ...
Proton Exchange Membrane Fuel Cells This proposed upgrade would replace the current alkaline fuel cells with PEM cells, which operate at a comparatively low temperature (70°C to 100°C) and use a moist polymer membrane as the electrolyte.
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From page 48... ...
A decision to develop PEM fuel cells for the shuttle would require more complex analysis than the decision to develop advanced alkaline fuel cells. The benefits of the PEM cells could include large savings in operations costs, improvements in safety through the use of nontoxic electrolytes, and an increase in power for the shuttle.
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From page 49... ...
However, the shuttle often carries payloads that use toxic hypergolic fuels, so this upgrade alone may not allow the shuttle program to completely scale back its safeguards against toxic propellants unless payloads carrying hypergolic propulsion systems could be loaded away from the shuttle and treated as sealed prepackaged systems. (This approach is used by the military in numerous programs, including the Minuteman and Peacekeeper missiles.)
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From page 50... ...
Water Membrane Evaporator The water membrane evaporator (WME) is being considered as a replacement for the orbiter's flash evaporator system (FES)
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From page 51... ...
Five-Segment Reusable Solid Rocket Booster This upgrade, informally proposed by Thiokol Propulsion, consists of modifications to the shuttle's four-segment RSRB intended to improve safety and performance and reduce overall systems costs. In addition to adding a fifth segment to the RSRB, the proposed upgrade would modify the RSRB' s nozzle and insulation and alter the grain of the solid fuel to provide a more risk-tolerant thrust profile.
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From page 52... ...
A thorough evaluation of the potential for the separate implementation of subsets of the proposal should be included in this assessment. Liquid Fly-Back Booster This proposed upgrade would replace the shuttle's two solid rocket boosters with winged liquid-fueled boosters that would automatically fly back to the launch site (using conventional gas turbine engines)
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From page 53... ...
Bringing in experts from inside and outside the agency to conduct and review trade-off studies to determine the most appropriate fundamental configurations for a new shuttle booster would help NASA ensure that it is spending its upgrade money wisely. Understanding the uncertain future of the program, these tradeoffs will most probably include various flight rate and mission scenarios.
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From page 54... ...
Recommendation 24. NASA should initiate a detailed independent assessment of configuration trade-offs, costs, and programmatic and technical risks for a new shuttle booster.
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From page 55... ...
1998. Personal conversation between study director, Paul Shawcross, and NASA senior scientist for orbital debris research, Nicholas Johnson.
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