such as the potential for competition and the relationship of RBS to the launch needs of other U.S. space sectors are open at this time.
The Space and Missile Systems Center (SMC/XR),4 the Air Force Research Laboratory (AFRL),5 and the Aerospace Corporation6 extensively evaluated options to meet the Air Force, EELV-class mission requirements, and these evaluations will be augmented by newly commissioned economic analyses by industry. The RBS was judged to offer the best potential for both low-risk development and recurring cost reductions, relative to EELVs, of 50 to 67 percent.7
The baseline flight vehicles for the RBS concept,8 which are shown in Figure 2.1, consist of a reusable booster demonstrator (RBD), a medium-lift launch vehicle consisting of a reusable booster and an expendable upper stage, and a heavy-lift configuration consisting of two reusable boosters and expendable upper stages. All RBS variations are envisioned to be unmanned and to operate autonomously. As discussed in Chapter 1, the RBS concept involves a reusable first stage (or two first stages in the heavy-lift variant shown in Figure 2.1), which separates from one or more expendable upper stages at velocities between Mach 3.5 to 7 and then returns to the launch base by a “rocketback” maneuver using one of the first-stage rocket engines. Importantly, the staging velocities and altitudes were selected to optimize overall costs and risks rather than to optimize staging to maximize delivered payload. The main potential benefits of the RBS are said to include cost reductions via recovery of the expensive first stage, the corresponding reduction in expendable hardware, and more efficient ground operations.9
The RBD vehicle is a proposed midscale demonstration vehicle that would be developed as an intermediate step between today’s research program and a full-scale RBS system. The RBD would use a single NK-33 LO2/RP oxygen-rich, staged-combustion (ORSC) rocket engine to power the reusable first stage. The RBD would initially be used to demonstrate significant aspects of the rocketback return-to-launch-site (RTLS) maneuver, including expendable stage separation. Using a Castor 30 motor and a Star 63 solid motor to power the upper stages as a small expendable stage (SES), the RBD would be capable of launching small satellites to LEO.
The medium-lift RBS configuration (middle configuration in Figure 2.1) consists of a full-scale reusable booster and a large expendable stage (LES). The baseline configuration for the reusable booster is powered by five AJ-26 rocket engines; the AJ-26 is an “Americanized” version of the Russian NK-33 rocket engine. These engines operate using liquid oxygen and hydrocarbon fuels (e.g., RP-1) using an ORSC cycle. The baseline LES is powered by one RS-25E rocket engine using liquid oxygen and liquid hydrogen propellants. This RS-25E is an expendable version of a space shuttle main engine (SSME) being developed by NASA for use in its Space Launch System.
The heavy-lift RBS configuration (right configuration in Figure 2.1) consists of two reusable booster systems, one LES, and a solid-rocket-propelled third stage. This configuration, which would only be used by the Air Force for the largest national security payloads, would result in the additional complexity of having two reusable boosters separate simultaneously and execute their RTLS maneuver in the same airspace.
In addition to the proposed vehicles shown in Figure 2.1, AFRL is actively working on technologies to support the RBS concept. These include technologies for hydrocarbon-fueled boosters, integrated vehicle health management (IVHM), and adaptive guidance and control (AG&C). AFRL is also funding development of a small-scale demonstrator vehicle called Pathfinder, which aims to investigate the rocketback RTLS maneuver, including propellant management strategies, in a series of early flight tests. While the AFRL-funded activities are not part of the baseline RBS development program, these efforts serve to provide critical information leading into the larger-scale RBS development activities.
4 AFSMC, “Spacelift Development Planning,” presentation to the Committee for the Reusable Booster System: Review and Assessment, February 15, 2012. Approved for Public Release.
5 Air Force Research Laboratory (AFRL), “AFRL Portfolio: Responsiveness & Reusable Boost System (RBS),” presentation to the Committee for the Reusable Booster System: Review and Assessment, February 17, 2012. Distribution A–Approved for Public Release.
6 AFSMC, “Reusable Booster System Costing, SMC Developmental Planning,” 2012. Approved for Public Release.
7 AFSMC, “Reusable Booster System Costing, SMC Developmental Planning,” 2012; AFSMC, “Spacelift Development Planning,” 2012; AFRL, “AFRL Portfolio: Responsiveness & Reusable Boost System (RBS),” presentation to the Committee for the Reusable Booster System: Review and Assessment, February 17, 2012. Distribution A–Approved for Public Release.
8 AFSMC, “Reusable Booster System Costing, SMC Developmental Planning,” 2012. Approved for Public Release.
9 K.R. Hampsten and R.A. Hickman, Next Generation Air Force Spacelift, AIAA 2010-8723, paper presented at the AIAA Space 2010 Conference and Exposition, Anaheim, Calif., August 30-September 2, 2010. This meeting was unrestricted and open to the public.