From Earth to Orbit: An Assessment of Transportation Options (1992)

The Congressional committees that authorize the activities of the National Aeronautics and Space Administration (NASA) requested that the National Research Council (NRC) assess the requirements, benefits, technological feasibility, and roles of Earth-to-orbit transportation options that could be developed in support of the national space program.

This summary contains the NRC Committee's assessments, principal conclusions, and recommendations that were judged by the Committee to be of highest importance.

• The United States must make a long-term commitment to new infrastructure and launch vehicles. The United States is now competing with other nations that are able to make long-term commitments to large undertakings in space.¹ In order to meet national needs and be competitive, the United States must find a way to commit to the long term. Multiyear appropriations could be an important step toward this goal.

• The United States should undertake extensive design of new East and West Coast launch facilities as soon as possible. Existing facilities are deteriorating and are expensive to operate due to customization for specific vehicles. The construction of the new facilities should be coordinated with the design of a new launch vehicle to achieve the desired improvement in reliability and efficiency while involving fewer people and shorter launch schedules. Preliminary designs and costing are required to demonstrate

the feasibility of the various infrastructure proposals. This is an urgent national need and the Committee recognizes that it will take time. A conceptual schedule is suggested in Figure 1, Chapter 4, and Figure 5, Appendix A. The Committee also recognizes there must be a planned transition from the current facilities to the proposed new facilities. During the transition time, it is possible that limited modernization of existing facilities for some of the current vehicles would prove economically useful.

• The 20,000-pound payload class, National Launch System (NLS-3) vehicle, should be the first of the proposed NLS family to be designed and built in coordination with new launch facilities. It is the least complex and least expensive member of the NLS family and the one most likely to have possible commercial, as well as national security applications. In addition, based on the projected traffic models presented by the National Aeronautics and Space Administration (NASA), Department of Defense (DoD), and industry, there appear to be requirements for 20 to 30 launches per year, with the greatest potential growth of unmanned launch vehicle traffic suitable for the 20,000-pound class vehicle. Starting the smaller NLS vehicle first will allow more time to refine the requirements for the larger NLS vehicles. Also, the 20,000-pound payload class vehicle would utilize most of the new technologies now contemplated for introduction in the NLS family. Therefore, the Committee believes that developing this vehicle first is of highest priority and will better suit national needs.

• Investment in improvements for the Space Shuttle Orbiter and its subsystems should be continued. The Orbiters are complex, sophisticated vehicles and are the heart of the Shuttle system, and as such, critical to human access to space. At present, there are no plans for increasing the size of the four-Orbiter fleet, and the fleet is fully scheduled for many years. Therefore, all Orbiters must be maintained in as effective an operating condition as possible.

• Reliability should have top priority in the design of new systems, even at the expense of greater up-front costs and lower performance. The cost of failure in terms of time, money, and national prestige far outweighs the costs of built-in reliability. Improved reliability should be sought for all expendable launch vehicles (ELVs), many of which carry high-value cargo, as well as for manned vehicles.

• A one-third to one-half reduction in launch and operations costs is required if the United States is to remain competitive in the launch vehicle market.² This is second

in importance only to reliability. In a market where policy pricing³ is clearly at work, the U.S. government may have to rethink its policies. The United States should look at successful overseas operations to see what can be learned.

• Development and qualification of the Space Transportation Main Engine (STME) should proceed immediately and vigorously. The initial use of the STME is to propel the NLS vehicles, and its development is crucial.

• Efforts underway to improve the reliability, reduce the cost, and simplify production and refurbishment of the Space Shuttle Main Engine (SSME) should be continued since the nation may need to rely on the Shuttle well into the first decade of the next century. It is important to pursue both the alternate oxygen and hydrogen pumps under the Alternate Turbopump Program, as well as improve the SSME hot gas ducts and heat exchangers.

• The growth of a family of vehicles can best be accomplished by using strap-on boosters that, to enhance reliability, would be designed to allow pad hold-down with engine shutdown capability, as well as to be throttleable. The Committee believes that these capabilities are important characteristics that should be considered in the design of future launch vehicles. Liquid, solid, and hybrid boosters could all be candidates as long as they incorporate these attributes. However, in its discussions, the Committee found a number of considerations that favor liquid as compared to solid propulsion systems. Liquid rocket engines permit a more flexible approach to modular clustering and are amenable to verification before launch. The most compelling characteristic favoring liquids is throttleability and thrust termination capability, which can enable first-stage booster designs to incorporate an engine redundancy capability. Hybrid motors may be able to meet these criteria in the future, but currently the technology is at a very early stage and should be brought to the point where it can be evaluated.

• A plan is needed to provide an array of engines with a range of thrust levels and propulsion system capabilities for all stages of future launch vehicles. The proposed STME can be used for first stages of future launch vehicles. In addition, the Rocketdyne F-1A and the current Russian RD-170 engines should be evaluated for liquid booster

applications. Hybrid engine technology should be investigated to determine its suitability for new launch systems. The propulsion system technology for second-and third-stage applications should emphasize low system cost and high reliability as in the initial booster stage. Revival of the Roeketdyne J-2 or upgrading of the Pratt & Whitney RL10 liquid-oxygen/liquid-hydrogen engines could provide upper-stage engines fitting the range of desired propulsion capabilities.

• In addition to pad hold-down and engine shutdown capability, incorporation of active redundancy for fail-safe capability should be considered in the design of new launch vehicle first stages having multiple engines. Active redundancy implies the capability of throttling the propulsion system down with all engines operating and throttling up if an engine fails, and may involve the use of an extra engine. The Committee believes that the advantages of this approach are worth the investment for an extra engine and are compelling in view of the costs of vehicle failures, payload loss, and schedule disruption.

• It is the opinion of the Committee that increased emphasis on propulsion system tests, including the whole propellant feed system, should be a major aspect of any new launch system program. Increased emphasis is also required in the design phase to include innovative methods to monitor propulsion system health and implement any required shutdowns at appropriate locations.

• The Committee believes that NASA should rely on the current Redesigned Solid Rocket Motor (RSRM) and that the Advanced Solid Rocket Motor (ASRM) program should be reconsidered. The current RSRM is capable of meeting all operational requirements of the Space Shuttle. The Committee believes that the balance of costs, technical and programmatic risks, and potential benefits tips in favor of avoiding integration of the ASRM into the Space Shuttle system at this time. Regarding the utility of the ASRM for other future space launch systems, the Committee understands its potential as a strap-on for the heavy payload end of NLS, (i.e., NLS-1); however the Committee has found no compelling rationale for such use other than the fact that it might be introduced in a reasonably short time. The Committee believes that NASA and the nation would be well served if the development of the NLS were directed toward strap-on boosters that have pad hold-down with engine shutdown capability and throttleability as means toward increased reliability.

• Because of concern over the potential detrimental environmental effects of some launch vehicles, the Committee endorses continuing research to better identify and understand these effects. Data suggest that pollution due to combustion products from

launch vehicles, at the frequency and scale that is anticipated, is not significant in comparison with other anthropogenic pollution on a global scale. It is, however, a serious local concern in the vicinity of launch test sites and deserves further investigation.

• A greater investment in long-term technology must be made to build the technology base for future systems. Critical, enabling technologies not specifically associated with an ongoing program are chronically underfunded. Underlying research and development provide technical stamina for the future. Today's decisions are hampered by the absence of research and development in the past decade. Specifically, the following areas of technology offer high payoff:

  Manufacturing methodology;

  Automatic, unmanned docking procedures and methodology;

  Modern, miniaturized guidance, navigation, and control;

  Propulsion advances;

  Propulsion system health monitoring and control; and

  Ceramic and intermetallic composite materials.

• Research and technology development with the goal of developing a new personnel carrier should be continued. New, enabling technology is needed for Orbiter replacement or a new personnel carrier. The oldest Orbiter will be over 20 years old in the year 2000 and long lead times are necessary for a new, human-rated space vehicle.

• An investment should be made in demonstrating the technology necessary to validate the engineering practicality of the hybrid rocket motor ⁴ for large, high-thrust, strap-on applications. Hybrid rocket motor development should be advanced to the point that it can be quantitatively evaluated in competition with solid and liquid bipropellant systems designed to directly comparable criteria.

• The Committee has three specific recommendations in regard to the Delta Clipper (DC-Y) in the Strategic Defense Initiative Organization (SDIO) Single-Stage Rocket Technology Program: (1) SDIO should continue a vigorous research and development effort directed at adding depth of detail design and analysis; (2) SDIO should examine

the use of other, already existing engines or engines under development; and (3) SDIO should reconsider the value and timing of the proposed one-third scale model flight tests relative to the more critical need for demonstrating the adequacy of the required low-weight structure and heat protection.

• The Committee believes that the National Aero-Space Plane (NASP) is a stimulating and productive research and development program and that the materials and air-breathing hypersonic propulsion technologies that have grown out of the NASP program deserve continuing and vigorous support. The Committee recognizes that the scramjet engines cannot be fully developed on the ground and must be tested in flight. It endorses such flight research as soon as the basic technology development is at a stage to make it worthwhile.

The body of the report covers in some detail the background and reasoning leading to these principal recommendations. Additional recommendations are included in the report. More detailed information is contained in the appendixes.