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1 Background On June 15, 2011, the Air Force Space Command (AFSPC) established a new vision, mission, and goals to ensure continued U.S. dominance in space and cyberspace mission areas. Subsequently, and in coordination with the Air Force Research Laboratory (AFRL), the Space and Missile Systems Center (SMC), and 14th and 24th Air Forces, AFSPC identified four long-term science and technology (S&T) challenges critical to meeting these goals. One of these challenges is to provide full-spectrum launch capability at dramatically lower cost, and a reusable booster system has been proposed as an approach to realizing this lower cost. AFSPC requested that the Aeronautics and Space Engineering Board of the National Research Council (NRC) conduct an independent review and assessment of the reusable booster system (RBS) concept before decisions are made on whether to continue RBS-related activities in the AFRL research portfolio and whether to initiate a more extensive RBS development program. This chapter briefly describes the national security payload spacelift requirement now delivered by Evolved Expendable Launch Vehicles (EELVs), introduces the RBS program, and discusses the potential for emerging new-entrant candidates to enable the launch of EELV-class payloads. In this report, RBS is taken to mean both the reusable first stage and the expendable upper stages of the baseline reusable launcher concept. This chapter also summarizes the Air Force request for an NRC evaluation of the RBS program and the NRC's actions to support that request. More details on these items and further descriptive material are provided in Chapter 2. 1.1 SPACELIFT REQUIREMENTS AND OBJECTIVES FOR NATIONAL SECURITY PAYLOADS Assured access to space is an overarching requirement for national security payloads, and it is Air Force policy to provide launches for them. The present manifest1 for these payloads, which is illustrated in Table 1.1, comprises five different functional requirements, a variety of final orbits, and an average annual launch rate of eight per year. So far, EELVs have provided launches for these payloads with extremely high reliability. However, current plans call for the EELVs to be phased out in 2030 and it is now an objective 2 of the Air Force to achieve dramatically 1 Air Force Space and Missile Systems Center, "Reusable Booster System Costing, SMC Developmental Planning," presentation to the Committee for the Reusable Booster System: Review and Assessment, February 15, 2012. Approved for Public Release. 2 Air Force Space Command, "AFSPC Operational Requirements for Launch," presentation to the Committee for the Reusable Booster System: Review and Assessment, March 28, 2012. Distribution Statement: No Restrictions. 6

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BACKGROUND 7 TABLE 1.1 Satellite Launch Characteristics Showing Satellite Type and Associated Orbits, Launchers, and Effective Average Launch Rates Satellite Type Orbit Requirement EELV Used Average Annual Rate Communications GTO Atlas V 531 0.64 Meteorological GTO Atlas V 501 0.25 SSO Delta IV M 0.32 Navigation MEO Atlas V 401 1.96 Missile warning GTO Atlas V 411 0.31 SSO Delta IV M 2.12 Intelligence LEO (high inclination) Delta IV M+(4,2) 0.20 LEO (high inclination) Delta IV H 0.29 LEO (high inclination) Atlas V 541 0.20 HEO Atlas V 551 0.29 Polar Delta IV H 0.29 Polar Atlas V 401 0.16 GTO Delta IV M+(5,4) 0.50 GEO Delta IV H 0.50 Average annual launch rate 8.00 NOTE: EELV, Evolved Expendable Launch Vehicle; GEO, geosynchronous Earth orbit; GTO, geosynchronous transfer orbit; HEO, high Earth orbit; LEO, low Earth orbit; MEO, medium Earth orbit; SSO, Sun-synchronous orbit. SOURCE: Air Force Space and Missile Systems Center, SMC Developmental Planning, "Reusable Booster System Costing," presentation to the committee, February 15, 2012. Approved for Public Release. lower launch costs, while maintaining the reliability achieved by EELVs, considering the average launch rate of only approximately eight per year distributed among the missions shown in Table 1.1. 1.2 REUSABLE BOOSTER SYSTEM APPROACH AND POTENTIAL BENEFITS The proposed RBS must accommodate the reliable and cost-effective delivery of the manifest in Table 1.1 via appropriate vehicle designs and ground infrastructure/operations capabilities. After analyses 3 by the Air Force and the Aerospace Corporation, the RBS was proposed as an approach to meet overall launch requirements. The concept of operations (CONOPS) for the RBS is shown in Figure 1.1. An essential feature of the RBS is that it uses reusable first stages and expendable upper stages. For reasons of operational efficiency and performance, the first stage would employ an oxygen-rich, staged-combustion (ORSC) cycle engine with liquid oxygen and kerosene-type propellants. The baseline expendable upper stage uses liquid hydrogen and oxygen propellants. A solid motor is added as a final stage to the expendable upper stage for the most energetic missions. As will be explained in Chapter 2, the staging velocity, where the first stage and second stage separate, is selected to minimize overall costs and maximize operational efficiency. This is unlike the usual selection criterion for fully expendable launch vehicles, which is to maximize delivered payload and is a critical characteristic of the RBS concept. 1.3 POTENTIAL EXPENDABLE NEW ENTRANTS No alternatives to RBS-based launch approaches were presented to the committee; however, credible opportu- nities may soon be available that meet or exceed the Air Force goals for launches of EELV-class payloads. The U.S. 3 K.R. Hampsten and R.A. Hickman, Next Generation Air Force Spacelift, AIAA 2010-8723, paper presented at the AIAA Space 2012 Conference and Exposition, Anaheim, Calif., August 30-September 2, 2012. This meeting was unrestricted and open to the public.

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8 REUSABLE BOOSTER SYSTEM--REVIEW AND ASSESSMENT Air Force: MNS 001 -01, Operationally Deploy Satellite D Responsive Spacelift, 20 Dec 01 or CAV ORS-LFT ICD, Mar 2006 Mach 5+ Separation Boost Back Reusable Booster + Expendable dable Upper Upp Stage FIGURE 1.1 Diagram of flight path of reusable booster with an expendable upper stage. Following separation, the first stage is rotated approximately 180 degrees as part of the rocketback return-to-launch-site maneuver. SOURCE: Air Force Research Laboratory, "AFRL Portfolio: Responsive and Reusable Boost System (RBS)," presentation to the committee, February 17, 2012. Distribution A: Approved for Public Release. Figure 1-1 R02338 vector editable Government Accountability Office (GAO)4 recently released a study of the EELV situation for the U.S. Congress. The study said that "domestic commercial launch providers are emerging that may satisfy some of [the Depart- ment of Defense's] EELV-class launch vehicle needs. According to DOD officials, the newer providers have not yet demonstrated adequate reliability to provide launches for critical satellites, but may be poised in the future to compete with the current sole-source EELV provider." The GAO report also indicated that DOD and the National Reconnaissance Office plan to spend about $3 billion per year for EELV launches over the 2013 to 2017 time frame. The Falcon 9 made by SpaceX is one of the more mature options as it has successfully flown three times, most recently delivering cargo to the International Space Station (ISS). In addition, SpaceX has entered more than 20 contracts to launch commercial satellites (COMSATs) and has a contract with the National Aeronautics and Space Administration (NASA) for more ISS cargo delivery missions. A brief review indicated that implementation of higher performance in-space propulsion or disaggregation of payloads would enable the Falcon 9 to deliver all or most of the national security payloads shown in Table 1.1. The reliability of the vehicle and its associated launch costs for Air Force payloads are not established, although it is noted that SpaceX has entered a fixed-price contract with NASA for 12 cargo missions to the ISS for $1.6 billion.5 The 2011 price for a Falcon 9 launch of a commercial COMSAT is $54 million.6 Perhaps more important, commercial launchers (1) could eliminate or greatly mitigate requirements for a new Air Force launcher development; (2) might be implemented much sooner than RBS; and (3) would have a large, intensively competitive customer base. 4 U.S. Government Accountability Office, Evolved Expendable Launch Vehicles, GAO-11-641, U.S. GAO, Washington, D.C., September 2011, p. 9. 5 The Economist, "Keep on truckin," Science and Technology, pp. 77-78, May 15, 2012. 6 See "Space Exploration Technologies Corporation, "Falcon 9 Overview," available at http://www.spacex.com/ falcon9.php.

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BACKGROUND 9 1.4 NRC EVALUATION OF THE REUSABLE BOOSTER SYSTEM Given the potential benefits offered by the RBS and by alternative launch approaches, the Air Force asked the NRC to conduct an independent review and assessment of the RBS concept. As defined in the statement of task (provided in Appendix A), the purpose of this study was to review and assess the SMC/AFRL RBS concept for the U.S. Air Force. The items to be addressed include these: Criteria and assumptions used in the formulation of current RBS plans; Methodologies used in the current cost estimates for RBS; Modeling methodology used to frame the business case for an RBS capability, including --The data used in the analysis --The models' robustness if new data become available; The impact of unclassified government data that had not previously been available; The technical maturity of elements critical to RBS implementation; and The ability of current technology development plans to meet technical readiness milestones. Accordingly, the NRC formed the Committee for the Reusable Booster System: Review and Assessment, which consists of experts independent of current RBS activities but with experience in the areas of launch vehicle design and operation, research and technology development and implementation, space system operations, and cost analysis. Brief biographies of the committee members are provided in Appendix B. The committee held meetings in February, March, and May of 2012. Air Force perspectives on issues asso- ciated with the RBS concepts were provided by representatives of AFSPC, SMC, and AFRL. Costing analyses supporting the RBS concept were provided by the Aerospace Corporation. NASA perspectives on space launch were solicited, and presentations were provided by representatives of the Marshall Space Flight Center and the Kennedy Space Center. Input from industry was solicited, and presentations were received from four commercial aerospace companies involved with launch systems, two propulsion system providers, and one small business. A listing of all presenters is provided in Appendix C. Using the materials provided, committee analyses, other available open sources of information, and its own experience and expertise, the committee developed the findings, conclusions, and recommendations contained in this report. These findings, conclusions, and recommendations represent a consensus view of the committee members regarding the RBS concept, and the bulk of this report aims to support the committee's view. 1.5 REPORT ORGANIZATION The RBS system, the launch approach, and the basis for the RBS business case are described in Chapter 2. Chapters 3 and 4 provide evaluations of the technical and economic aspects, respectively, of the RBS as presented to the committee. The potential implementation issues surrounding the RBS program are given in Chapter 5, followed by findings and recommendations in Chapter 6. Appendix E provides details on previous U.S. reusable vehicle developments and Appendix F provides committee thoughts on operability issues associated with the design of RBS boosters.