4
Assessments of Proposed Upgrades

Based on information NASA presented to the committee on numerous ongoing and proposed upgrades to the space shuttle (see list of upgrade topics: Appendix C), it is clear that a great deal of creative and useful design and development work has been performed. The committee conducted a top-level technical assessment of the upgrades and developed findings and recommendations about some of the ones that had not yet been developed and/or implemented. (see Table 4-1). 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. Those decisions must be based on careful and thorough assessments of requirements, costs, and benefits using analytic tools as well as engineering judgment (see Chapter 3).

Phase II Upgrades

Checkout Launch and Control System

The checkout launch and control system (CLCS) is an upgrade to the launch processing system used to check out, control, and process shuttle flight systems, ground support equipment, and facilities at Kennedy Space Center. The current system is growing obsolete; approximately one-fourth of its components are no



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 38
--> 4 Assessments of Proposed Upgrades Based on information NASA presented to the committee on numerous ongoing and proposed upgrades to the space shuttle (see list of upgrade topics: Appendix C), it is clear that a great deal of creative and useful design and development work has been performed. The committee conducted a top-level technical assessment of the upgrades and developed findings and recommendations about some of the ones that had not yet been developed and/or implemented. (see Table 4-1). 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. Those decisions must be based on careful and thorough assessments of requirements, costs, and benefits using analytic tools as well as engineering judgment (see Chapter 3). Phase II Upgrades Checkout Launch and Control System The checkout launch and control system (CLCS) is an upgrade to the launch processing system used to check out, control, and process shuttle flight systems, ground support equipment, and facilities at Kennedy Space Center. The current system is growing obsolete; approximately one-fourth of its components are no

OCR for page 38
--> TABLE 4-1 Upgrades Discussed in Chapter 4 Upgrade Phase Status Checkout launch and control system II Ongoing Micrometeoroid and orbital debris protection II Ongoing Auxiliary power unit replacement III Under study Avionics II Component replacement ongoing   III Major upgrade under study Channel-wall nozzle III Under study Extended nose landing gear III Under study Long-life fuel cell III Under study Nontoxic orbital maneuvering system/ reaction control system III Under study Water membrane evaporator III Under study Five-segment reusable solid rocket booster IV Under study Liquid fly-back booster IV Under study longer supported by vendors, it uses a unique software language, it is unable to support new tasks, and its operations and maintenance costs are estimated to be $50 million per year and rising. The CLCS upgrade will replace this system with modern commercial hardware and software. The upgrade, which was approved and funded in December 1996, is intended to reduce operations and maintenance costs by at least 50 percent without impacting flight hardware or software. As of September 1998, approximately $60 million had been spent and about 50 percent of the system software and 10 percent of the applications software had been developed. The system, which is designed not to impact the shuttle schedule as it is phased in, is expected to cost a total of $183 million by its completion in FY02. The committee believes that an upgrade to the launch control system is necessary and worth pursuing. 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.

OCR for page 38
--> Figure 4-1 Historical software coding rates. Source: The Aerospace Corporation, 1998. The CLCS is a large, distributed, heterogeneous computer project involving the development of more than 3 million lines of new software, much of it automatically generated. The program schedule has already slipped once, and most of the projected software has yet to be developed. Programmer productivity is projected to be 300 lines per programmer per month, which is substantially higher than industry norms. (The historical average for software tasks of this type is closer to 85 lines per month, as illustrated in Figure 4-1). The CLCS project management appears to be confident that the project is on track and will be completed on time, although it will consume some of the management reserve budget. Management is satisfied that the problem that caused the delay has been corrected and should not cause further delays. Based on their experience with similar NASA projects (notably the Johnson Space Center's Mission Control Center), 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.

OCR for page 38
--> Recommendation 14. NASA should conduct an audit of the requirements, specifications, plans, schedules, development budgets, status, and life cycle costs of the checkout launch and control system project. The objective of this audit should not be to cancel the upgrade but to estimate more accurately the time and cost required to complete it and to identify potential problems early enough to rectify them. Protection from Micrometeoroids and Orbital Debris The space shuttle was not originally designed to withstand the impacts of orbital debris. As the threat (and the understanding of the threat) has increased, the shuttle program has taken steps to protect the orbiter. As part of the Phase II upgrade program, the shuttle orbiters will be modified during 1999 and 2000 to protect the radiators and the leading edges of the wings from meteoroids and debris. Once these upgrades have been completed, the predicted risk of a penetration that could cause the loss of the orbiter or its crew in a worst case scenario will typically be in the range of 1 in 800 per mission compared to 1 in 400 before the modifications (Johnson, Loftus, 1998). A 1997 National Research Council report, Protecting the Space Shuttle from Meteoroids and Orbital Debris, noted that the proposed modifications to the radiator and the leading edges of the wings appeared to be positive steps towards protecting the shuttle from meteoroids and debris and recommended that NASA investigate additional modifications to the orbiter to improve its survivability (NRC, 1997). The committee chose not to revisit the orbital debris issue, deferring to the 1997 report. However, considering the relatively high predicted level of risk to the orbiter and crew even after the initial modifications are made, and considering the high priority of safety as a goal of the upgrade program, the committee concurs with this recommendation. Recommendation 15. 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. The APUs use hydrazine propellant to drive a high-speed turbine that produces mechanical power. The APUs pose a hazard because they use toxic fuel, and they have experienced problems during testing and flight, including a fire involving the hydrazine fuel after the landing of the STS-9 mission.

OCR for page 38
--> Existing APUs could support the shuttle program through 2014 at current flight rates. After that (or earlier if flight rates increase) the APUs will start to reach their 75 hour operational life limit, resulting in shortages and requiring cannibalization of APU systems. In an exercise to determine the long-term operational costs of the current APUs, contractors estimated that the cost of keeping the current system operational until 2030 would be approximately $550 million. NASA is studying a number of options for replacing the APUs with an electric system to support a decision in 2000 on proceeding with the upgrade. NASA is now exploring different battery chemistries and ultracapacitors to provide energy storage and peak power production. Most of the electric systems under consideration would weigh slightly more than the current APUs but would be less toxic. NASA has spent about $650,000 so far, and total development and implementation costs are estimated at $100 to $150 million. Total costs of developing the system and operating it until 2030 are estimated to be about $350 million. Few systems are more important to the safe operation of the shuttle than the APUs. These flight-critical systems are essential for the important launch and reentry phases; they involve high concentrations of mechanical energy and a very toxic, corrosive, and combustible fuel; and in spite of redundancy against single failures, they are spatially vulnerable to common cause failures, such as fire, explosion, and leaks. Not all of these vulnerabilities would be eliminated with the proposed upgrade, but the very important vulnerability from chemical energetics would be eliminated. 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), as well as the development of electric cars (by many companies, including Ford, General Motors, Honda, Toyota, and Nissan). By learning from and applying the technologies developed elsewhere, NASA could greatly leverage its funding for development of a replacement for the APU. However, considerably more study will be necessary to determine the benefits and costs of the upgrade. Probabilistic risk analysis can be used to estimate the safety impact of improving APUs and compare it with other safety improvements. Further analysis can be performed to determine more accurately the viability of other approaches to upgrading the APUs (including purchasing additional spare parts for the current APUs). Additional analysis is also warranted to determine whether the hydrazine-driven units that power the solid rocket booster's thrust vector control system (and which have similar problems and concerns as the current APUs) should also be replaced as part of the APU upgrade.

OCR for page 38
--> Recommendation 16. NASA should continue studying potential modifications to the APUs to better determine the costs, benefits, and appropriate scope of an upgrade. Developments in electric power systems worldwide should be monitored to identify technologies and techniques that could be useful for an APU upgrade. Avionics The orbiter's current avionics system was conceived in the early 1970s but contains hardware added during the 1980s and 1990s (including the current computers, which were installed in the late 1980s). The system consists of more than 270 components and approximately 500,000 lines of code. Its primary functions include flight control, guidance and navigation, communication, and orbiter landing support. A secondary, but important, task is to provide operational services for nonavionics systems, such as data handling for the payloads and caution and warning alerts to the crew. 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.) To date, $3.5 to $4 million has been spent on studies and on replacing some hardware elements. Total costs will depend on the eventual scope of the avionics upgrade. Obsolescence probably affects avionics more than any other system, particularly when the avionics include interfacing computers and software. Obsolescence is primarily a cost issue because obsolete components can usually be repaired or replaced if sufficient funding is available. NASA appears to be doing a good job of identifying components that are becoming obsolete, prioritizing potential upgrades in terms of their payback and the urgency of the situation, and applying its limited budget to addressing the most pressing near-term needs. The proposed partitioned avionics architecture would reduce the cost of development and testing as well as improve safety by lessening the impact of subsystem changes on the remainder of the avionics as well as the current software. Progressing efficiently from the current system to the long-term architecture, however, will require that NASA create scaleable, long-term requirements and interface definitions for the future architecture. If NASA does approve a large-scale avionics upgrade (presumably as a part of a year 2000 decision not to replace the shuttle in the near-term), the availability of long-term requirements would be critical to smooth systems integration.

OCR for page 38
--> Recommendation 17. NASA should continue its strategy of judiciously replacing obsolete avionics components while developing a plan for a future improved architecture. Consistent with the year 2000 decision process, NASA should develop scaleable, long-term requirements and interface definitions for the future architecture. Channel-Wall Nozzle The channel-wall nozzle is a proposed replacement for the current SSME nozzle. Employing a process developed in Russia and used for the Russian RD-0120 rocket engine, flat stock is roll formed into a conical shape, which serves as the nozzle liner. The liner is slotted to form channels for the nozzle's liquid hydrogen coolant to flow through. A jacket is then installed over the liner and welded at the ends. The entire assembly is then furnace brazed. The channels in the liner take the place of the 1,080 tubes that regeneratively cool the current SSME nozzle. The channel-wall nozzle is a relatively simple design that has fewer parts and welds than the current complex SSME nozzle. (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. The new nozzle is also expected to improve engine performance slightly (although any gain in payload capacity may be canceled by the increased nozzle weight), to cost less and take less time to produce, and to cost less to operate. NASA and Rocketdyne (through Aerojet) have spent $0.8 and $1.2 million respectively to study this upgrade, and development could start at the beginning of 1999. The proposed upgrade would cost an estimated $63 million over four years for development and testing, plus an additional $71 million to build 18 certification and production nozzles. The committee believes that this upgrade could improve the safety of the shuttle because eliminating the tubular construction should eliminate the major source of nozzle leaks. After a recent SSME failure during test firing was attributed to the current nozzle, replacement with the channel-wall nozzle was endorsed by NASA's Mishap Investigation Board. Although adding a new part to the shuttle might increase risk, it seems unlikely in this case because the channel-wall design is based on an established technology that appears to be quite robust (although the technology has not previously been applied to reusable nozzles or any U.S. programs). The channel-wall nozzle upgrade may also have additional benefits. It appears to be simpler to fabricate than the current SSME nozzle, for example. In addition, the technology may be broadly applicable to other engines and launch vehicle programs, which might benefit from the lessons learned applying the

OCR for page 38
--> technology to the shuttle. It is not clear whether the upgrade will result in cost savings; that will depend on the durability of the nozzles, as well as on the shuttle's longevity and flight rate. The committee is concerned, however, about possible problems arising from NASA plans to build the nozzle in Russia (through Rocketdyne) to reduce development costs. NASA will have to be extremely careful in drafting the agreements related to Russian production and technology transfer to ensure that potential problems in Russia do not compromise the shuttle schedule. Although it would probably increase the cost of the upgrade, NASA could ensure that the nozzles could be fabricated in the United States by licensing the technology and know-how to build the nozzles to a U.S. firm. By procuring sufficient numbers of Russian-fabricated nozzles before the U.S. production begins, NASA could also ensure that unanticipated delays in this project would not jeopardize the shuttle's ability to meet its manifest. Recommendation 18. 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. The proposed extension would include a new middle segment for the landing gear, a redesigned upper strut housing, and a gas supply cylinder for pneumatic actuation. The upgrade would add approximately 70 to 90 kg to the landing gear system but would either increase the safety margins during shuttle landing or, at existing safety margins, allow the shuttle to land with a higher maximum weight. About $200,000 has been spent to date on this upgrade, culminating in the development and testing of a prototype unit. The proposed upgrade appears to be a good design for reducing landing loads for the shuttle. However, extensive improvements have already been made to the landing and deceleration systems since the return-to-flight after Challenger, existing hardware meets current requirements, and there are no other apparent benefits to implementing this upgrade. The expected total cost for design and production is $15 million dollars over 28 months. Recommendation 19. NASA should pursue the extended nose landing gear only if future plans require that the shuttle land with heavier payloads than are currently allowable.

OCR for page 38
--> Long-Life Fuel Cell. The orbiter's fuel cells provide electric power for the orbiter and water for the crew. Ninety-six fuel cells in three stacks convert hydrogen and oxygen into electrical power, water, and heat via an alkaline electrolyte. The fuel cells require approximately four overhauls (at about $3.5 million per overhaul) and four repairs (at approximately $100,000 per repair) each year. With continuing overhauls and repairs, the current inventory of fuel cells could support current shuttle flight rates beyond 2012. If the flight rate increases to 12 per year or more, additional fuel cells will be needed. Two distinct upgrades—longer-life alkaline fuel cells and proton exchange membrane (PEM) 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. The modified fuel cells would operate at reduced reactant temperatures and would be designed to inhibit corrosion and improve reliability. Their electronic controls would also be upgraded to enable new monitoring capabilities and to preclude obsolescence. The lifetime of the upgraded fuel cells is estimated at 5,000 hours. The present fuel cells are certified to 2,600 hours before overhaul. In reality NASA is experiencing an average overhaul time for the current fuel cells of 2,100 hours. It should also be noted that the current fuel cells are operating in the vehicle for an average of only 1,200 hours before they must be removed to repair system component failures. The contractors estimate that certification of the units to fly on the shuttle would cost about $14 to $17 million, with a production cost of approximately $3 to $4 million for each of the four power plants, assuming that many of the current fuel cell components are reused. The development of advanced alkaline fuel cells could begin in 1999. The contractors estimate that the certification program would take three years, with the first production unit delivered a year later. Because the longer-life alkaline fuel cells appear to be straightforward engineering modifications of the existing orbiter fuel cell power plants and the changes are relatively minor, these estimates of cost and schedule should be reasonably accurate. If this upgrade were implemented, the primary benefit would be to reduce operations and maintenance costs and time. NASA estimates yearly savings from reducing the number of overhauls and annual repairs would be $22 million. The current fuel cells have flown successfully with an excellent reliability record, so the new cells would have no major functional or safety advantages. The advanced alkaline cell could, however, support longer missions and an increased flight rate, and the associated electronics upgrade could enable improved health monitoring of the fuel cells.

OCR for page 38
--> The decision to upgrade to an advanced alkaline fuel cell is primarily a business decision, because the major benefit is cost savings. By calculating the return on investment and comparing this upgrade with other cost-saving upgrades with a high probability of success, NASA can ascertain whether this is a good business proposition. 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. Although PEM cells were flown in space before alkaline fuel cells, alkaline systems were chosen for the Apollo program and then the shuttle program. The proposed PEM fuel cells would have a lifetime of 10,000 hours (as opposed to an average lifetime of 2,100 hours for the existing fuel cells) and would produce more power than the equivalent mass and volume of alkaline cells. Like the advanced alkaline cell, the PEM cell upgrade would reduce operations and maintenance costs, support longer missions, and allow improved monitoring capabilities. Because the PEM cells do not involve hazardous materials, however, safety on the ground and in space would also be improved. NASA hopes that advanced PEM fuel cells will also be applicable to future extra-vehicular activity suits, human space exploration activities, and launch vehicles. To date, funding for the project has totaled about $1.5 million. NASA is now evaluating prototype PEM fuel cells from four different vendors. The development of PEM fuel cells for the shuttle would cost an estimated $25 to $34 million plus $2.5 to $4.5 million per fuel cell stack (approximately 15 stacks are required). NASA estimates that if the upgrade were approved, the development of fuel cells for the shuttle could begin in 2000 or 2001, with production commencing in late 2004. The committee believes that the development of PEM fuel cells for the shuttle would be difficult but is feasible. The development of a PEM fuel cell could, however, be substantially facilitated by work going on outside the agency. After a long hiatus, renewed interest in fuel cells for automotive, person-portable, and direct methanol applications has stimulated a major resurgence in PEM development. Thus, NASA has an opportunity to leverage long-life fuel cell development with U.S. Department of Energy and DoD money being spent on other applications. (Advancements to PEM technology developed for the shuttle may contribute in turn to the fuel cell development funded by other agencies.) One concern about PEM cell development is water management, a critical issue in providing a long-life PEM cell. The cell membrane must be maintained at 100 percent relative humidity. If any part of the membrane is allowed to operate at a lower humidity, reactant gas crossover increases, causing hot spots and accelerating membrane decomposition. This may be a bigger problem in a

OCR for page 38
--> microgravity environment than in other applications. NASA is aware that cell lifetime data from one contractor is not necessarily applicable to another contractor's design and is wisely evaluating fuel cell life with the appropriate water management scheme in full-size stack hardware. 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. However, the PEM cell upgrade would require an expensive and potentially open-ended technology research program, with delivery not expected until 2004. In addition, like any other completely new component, PEM cells might pose a slightly increased risk of failure to the shuttle until significant flight hours have been logged by the new power plant. (This concern could be mitigated by flying one PEM power plant with two alkaline power plants for a few missions.) Eventually, the decision to proceed with the PEM upgrade may depend on NASA's desire to pursue this technology for future space missions for which the 2,100-hour stack life of current alkaline fuel cells is unacceptable in terms of maintenance requirements or operational constraints. Planners of future space vehicles and missions could help determine the value of PEM cells for future missions, could influence the design of the shuttle's PEM cells so that it will be applicable to future missions, and, perhaps, provide funding. Recommendation 20. NASA should continue to explore the costs and benefits of PEM cells before making a decision on a future shuttle fuel cell. Planners of future space vehicles and/or missions that could benefit from PEM fuel cells should be closely involved in these studies. Nontoxic Orbital Maneuvering System / Reaction Control System The nontoxic orbital maneuvering system (OMS)/reaction control system (RCS) upgrade would modify the shuttle orbiter's OMS and RCS to use liquid oxygen and ethanol propellants instead of the current engines' toxic N2O4 and mono-methyl hydrazine propellants. The proposed upgrade would involve replacing the current engines with pressure-fed liquid oxygen/ethanol engines. In addition, the forward reaction control system would be connected to new common propellant storage tanks that would also be used by the OMS. (Currently, the forward RCS has its own propellant tanks in the nose of the orbiter). NASA believes that the elimination of toxic and corrosive propellants would reduce hazards on the ground and in orbit, improve ground operations and turn-around times, and decrease corrosion. NASA estimates that this upgrade would

OCR for page 38
--> result in $24 million in savings at Kennedy Space Center each year. The switch to liquid oxygen and ethanol could also improve the shuttle engines' performance in orbit, enabling it to better support the ISS program, and would provide increased redundancy during an engine malfunction. Technologies implemented in this upgrade might also be useful for other ISS support vehicles (e.g., the crew rescue vehicle), as well as for future space exploration missions. One potential advantage of a nontoxic OMS/RCS upgrade could be use of the system's liquid oxygen as an element of a contingency redundant life support system for the shuttle or the ISS. Approximately $4 million has been spent to study the OMS/RCS upgrade. The total cost of the upgrade is estimated at $90 to $100 million for development, plus $400 million to build the eight OMS pods necessary for a four-orbiter fleet. NASA is currently assessing the replacement RCS and OMS engines, including existing engines (such as the Ariane V upper stage engine), and designing the overall OMS/RCS system. NASA expects to be ready for a decision on whether to proceed with the upgrade by mid-2000. Although NASA has years of experience handling toxic, corrosive propellants, the removal of such materials from the shuttle could enable more rapid turnaround (and thus result in a cost savings) because fewer precautions would have to be taken to protect the ground crew. 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 Peace-keeper missiles.) The OMS/RCS upgrade has some disadvantages. Although the modified OMS pod would have fewer parts than the current system, it would be more complex because the liquid oxygen propellant would require additional tanks, insulation, and thermal controls. Structures and other subsystems in the vicinity of the liquid oxygen may also require thermal protection. Because the nontoxic propellants are not hypergolic, an ignition system would also be required, which might reduce reliability and could require additional maintenance. Because the engines being considered for the upgrade are not as well understood or tested as existing OMS and RCS engines, the risk to the shuttle may actually be increased during the early transition timeframe. Redundancy may be compromised by the proposed reduction in the number of separate propellant tanks and supply systems. Finally, the designers will have to ensure that the length of the feed system from the aft to the forward compartment does not compromise the rapid response characteristics of the RCS. The cost of ground system modifications will be significant and will require the existing ground systems to remain in place until all orbiters are modified.

OCR for page 38
--> Recommendation 21. Before NASA makes any decision on implementation, it should very carefully study the risks inherent in changing to a nontoxic OMS/RCS system and conduct trade-off studies to determine whether modifications to the existing system may be a more cost-effective means of meeting program goals. Commonality with the propulsion (and potentially life-support) systems of the ISS and other future NASA programs should be considered in any final design. Water Membrane Evaporator The water membrane evaporator (WME) is being considered as a replacement for the orbiter's flash evaporator system (FES), which cools the orbiter during ascent and reentry and provides supplemental cooling (in concert with the payload bay door ràdiators) in orbit. A replacement is being considered because the FES is experiencing corrosion, which creates a risk of freon leaks. Three FES units have been removed and replaced to date, and two more units have slow freon leaks which will eventually require repairs. NASA has already taken some steps to combat the problem, including cutting the iodine content of the water in the FES and replacing the FES's original aluminum material with aluminum that has a thicker anodized layer. The WME appears to be a simple passive device that can perform the FES's cooling function. The WME takes advantage of the hydrophobicity of microporous Teflon to evaporate water while maintaining excess liquid water in a hydrophilic layer behind the hydrophobic layer. Thus, the WME should be immune to corrosion and able to function longer than the FES. The team developing the WME also believes that the WME's simpler design and fewer moving parts will make it more reliable than the FES. NASA has spent approximately $200,000 on this project to date and estimates the total cost to place operational WMEs on the orbiters to be $15 to $20 million. The project team expects to be ready for a decision on whether to implement the upgrade by early 1999. The committee has some concerns about the WME. First, as the WME designers are aware, any trace of a surface-active impurity in the water will cause the WME's Teflon to become wet and fill with water, which could cause the loss of liquid feed water. Such surface-active impurities can be very difficult to prevent. (NASA might consider adding a sensor to ensure a high water surface tension.) Second, because this type of system is not used in any other application and thus will probably require an exacting development and qualification test program, the cost and schedule estimates may not be accurate. Finally, the committee believes that other options to reduce freon leakage (such as employing materials in the FES that are less susceptible to corrosion) might be lower-cost and lower-risk solutions to the problem.

OCR for page 38
--> Recommendation 22. NASA should reassess the costs (including those associated with surface tension issues and development testing) and benefits of all options for dealing with the corrosion problems in the flash evaporator system before choosing a solution. Phase IV Upgrades The only Phase IV upgrades briefed to the committee were two new first stage booster concepts: the five-segment RSRB (reusable solid rocket booster), and the liquid fly back booster (LFBB ). Each concept represents a major programmatic and technical undertaking. By the time either system would be ready to fly, the current reusable solid rocket booster will have demonstrated more than 100 flights (200 operational firings). As was the case with the cancelled advanced solid rocket motor program, any new booster design, no matter how many safety and reliability enhancements it contains, will necessarily pose additional risk to the first few crews who fly it. Part of the risk will be in the form of any failure uncertainties carried forward from the ground and/or unmanned flight tests, and part will be due to the continued lack of adequate crew escape capability in the shuttle. Because of all this, 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 promised performance enhancements and cost savings. 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. Thiokol, USBI, and Boeing have funded preliminary designs, estimated benefits, and examined systems integration issues. Estimated total costs for the upgrade are in the range of $1 billion with an estimated four year schedule from authority to proceed until the first flight. On the surface, the five-segment RSRB appears to be a relatively straight-forward approach to increasing the performance of the shuttle's boosters. The extra performance from this upgrade could either allow the shuttle to carry heavier payloads, eliminate the need to throttle the main engines during ascent (thus improving safety), or minimize or eliminate a high-risk launch abort mode. A full understanding of costs and risks will require more analyses of the cost and weight impacts associated with the RSRB's modified vehicle attachments, aero-dynamic and structural loads, control dynamics, separation rockets, and other integration issues

OCR for page 38
--> The potential improvements in performance and safety warrant a close formal examination by NASA of the five-segment RSRB. A recent initiative by the Office of Space Flight directing the Independent Program Assessment Office to perform an assessment of the five-segment RSRB and the LFBB is a good step in that direction. A complete assessment should also consider the possibility that some of the smaller improvements of the five-segment RSRB (e.g., grain shape optimization) might be more effective if they are considered as smaller stand-alone Phase II or III upgrades. Recommendation 23. NASA should formally evaluate the merits of the five-segment reusable solid rocket booster as it prepares for the decision on the future of the shuttle program. 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) after they have used up their rocket fuel and separated from the orbiter. Figure 4-2 illustrates some design concepts for the LFBB. The proposers of the upgrade believe that the LFBBs would improve safety by reducing or eliminating the need for some high-risk Figure 4-2 Representative LFBB concepts.

OCR for page 38
--> abort modes, save $400 million per year in operations costs (with seven shuttle flights per year), and increase the shuttle's payload capacity. The proposers also predict that the LFBB would enable a three-week turnaround time between missions, and (with three sets of LFBBs) could allow the shuttle to fly 15 times per year. Approximately $12 million has been spent by NASA to study the LFBB. Lockheed Martin and Boeing have also funded studies and produced some initial competing design concepts. NASA plans to continue studying the LFBB in preparation for a decision on whether to proceed at the end of year 2000. (Like the five-segment RSRB, the LFBB will be assessed by NASA's Independent Program Assessments Office.) If NASA decides to proceed, the upgrade proposers estimate that hardware fabrication and testing will take four years and will cost about $4 to $5 billion. The committee has a number of concerns about the LFBB. The most serious is that the fundamental configuration of a new shuttle booster seems to have been predefined without adequate trade-off studies to determine whether it is the most appropriate way to meet the needs of the shuttle and other programs. Low cost, but high-performance/highly reliable throwaway liquid boosters, an improved solid rocket motor, or relatively low-cost ocean-recovered reusable liquid boosters, for example, might be better choices. 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. A second important concern about the LFBB program is the accuracy of estimates of the total costs of the program from development through production and operation. Almost every aspect of the LFBB suggests that the development costs will be high. The LFBB: must be extremely reliable (“human rated”) will be a highly complex vehicle that uses both rocket and gas turbine propulsion will have all the systems and subsystems required to fly and land, including wings, a tail, and landing gear will modify the mold line of the shuttle (thus requiring major testing and analysis of the new configuration) More accurate estimates of the costs of developing the LFBB would require assessing these issues, as well as the feasibility and cost of achieving a three-week turnaround time, the cost of maintaining human-rated vehicles, and the cost of design and development testing to ensure that overall system risk is acceptable on the first few manned flights.

OCR for page 38
--> The operations costs of the LFBB may also be higher than predicted. For example, current cost estimates do not include the potential need to replace LFBBs. NASA assumes that six LFBBs will be sufficient to support up to 15 flights per year. Table 4-2 shows the relationship between LFBB reliability and hardware requirements over time. Clearly, if the reliability of the LFBB is less than perfect, it may be necessary to purchase additional LFBBs. (NASA currently estimates that the LFBB will experience a catastrophic failure every 1,520 launches—an unprecedented level of reliability for a new, highly complex booster.) The committee's third concern is the programmatic status of the LFBB. If the LFBB were designed only for the shuttle (like the RSRB and the canceled ASRM), funding for development could be problematical, considering recent budgetary decisions and Congress's desire to finance new transportation initiatives through industry. If the LFBB is funded only from the shuttle program, it is also likely that it would be optimized to support the shuttle (thus making it less attractive for other uses). By finding other compelling uses for the LFBB (e.g., as a booster for a new heavy-lift vehicle) and by involving other potential users (e.g., the DoD) in the funding and design of the LFBB, NASA could both improve the overall value of the program and increase the likelihood that it would be funded. Recommendation 24. NASA should initiate a detailed independent assessment of configuration trade-offs, costs, and programmatic and technical risks for a new shuttle booster. TABLE 4-2 Required Inventory of LFBBs Number of LFBBs Probability that at least 6 LFBBsa remain in inventory after 30 shuttle launches,b assuming successful recovery of each booster   0.90 0.95 0.98 0.99 6 0.002 0.046 0.30 0.55 7 0.014 0.19 0.66 0.88 8 0.053 0.42 0.88 0.98 9 0.14 0.65 0.97 1.0 10 0.27 0.82 0.99 1.0 11 0.44 0.92 1.0 1.0 12 0.61 0.97 1.0 1.0 13 0.75 0.99 1.0 1.0 a Assumes dual booster configuration b 2 years at 15 flights per year, 3 years at 10 flights per year, or 4 years at 7 or 8 flights per year

OCR for page 38
--> Recommendation 25. NASA should coordinate closely with other government and industry transportation initiatives in determining the need and the resources for any new shuttle booster. References Aerospace Corporation. 1998. Aerospace Roles in Space Systems Architecting, Acquisition, and Engineering: Cost Management and the Aerospace Role. Los Angeles: The Aerospace Corporation. Johnson, N. 1998. Personal conversation between study director, Paul Shawcross, and NASA senior scientist for orbital debris research, Nicholas Johnson. August 18, 1998. Loftus, J. 1998. Personal conversation between committee chairman, Bryan O'Connor, and NASA Johnson Space Center Space and Life Sciences Directorate, Assistant Director for Engineering, December 21, 1998. NRC (National Research Council). 1997. Protecting the Space Shuttle from Meteoroids and Orbital Debris. Committee on Space Shuttle Meteoroid/Debris Risk Management. Washington, D.C.: National Academy Press.

OCR for page 38
This page in the original is blank.