Upgrading the Space Shuttle (1999) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-8
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Additional upgrades were approved in the early 1990s to enable the shuttle to visit the Mir space station and support the International Space Station. In 1996, however, the shuttle program effectively ceased approving new changes to the space shuttle design to concentrate scarce resources on developing potential replacements for the shuttle.
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In spite of budget uncertainties, technical risks with the development of a reusable launch vehicle (shuttle replacement strategy) , and existing national policy restrictions on shuttle use, the committee believes that NASA' s approach to upgrade planning is appropriate.
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The committee believes that when this system is more mature, it will be a valuable tool. However, the current Decision Support System will require significant modifications before it can be a reliable input to the prioritization process.
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ASSESSMENTS OF PROPOSED UPGRADES From the information presented to the committee, it is clear that a great deal of creative and useful work has been done to design and develop ongoing and proposed upgrades to the space shuttle system. The committee was able to assess the potential of some key upgrades to meet Space Shuttle Program goals, point out areas of technical or programmatic risk, and suggest alternatives.
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. vlonlcs Water membrane evaporator V Liquid fly-back booster or Five-segment reusable solid rocket booster Auxiliary ~ , ,, power unit 7~% , ~ Extended nose landing gear ik ~ Long-life fuel cell Protection from ~ micrometeoroids >~ and orbital debris if\ Nontoxic orbital SSME channel-wall nozzle FIGURE ES-1 Location of assessed upgrades.
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Based on work performed to date, the proposed upgrade appears to be a good design for reducing shuttle landing loads. However, the existing nose landing gear meets current requirements, so NASA should pursue the upgrade only if future plans require that the shuttle land with heavier payloads than are currently allowable.
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Nontoxic Orbital Maneuvering System/Reaction Control System This upgrade would modify the shuttle orbiter's orbital maneuvering and reaction control systems to use nontoxic liquid oxygen and ethanol propellants and would connect both systems to common propellant tanks. NASA believes that the proposed upgrade would reduce hazards on the ground and in orbit, improve ground operations and turnaround times, save money, and increase shuttle performance.
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These facts, combined with the risks involved in changing to a relatively unproven booster on a manned vehicle with only minimal crew escape capability means that NASA is not likely to, and the committee agrees it should not, enter into any major new booster program without substantial national need for the performance enhancements and long-term safety and cost benefits. Five-Segment Reusable Solid Rocket Booster A recent proposal by Thiokol Propulsion, this upgrade would add a fifth segment to the shuttle' s RSRB, alter the grain of the solid fuel to provide a safer thrust profile, and modify the RSRB's nozzle and insulation.
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