assumed use of the “Americanized” version of the Russian NK-33 oxygen-rich staged combustion (ORSC) engine (i.e., a domestic AJ-26 engine). Under this baseline scenario, the time frame of the AFRL-funded hydrocarbon-fueled booster technology development does not significantly impact the booster main propulsion system.

Scenario 2: Extended EELV. The EELV program is extended with operations until 2040, which allows completion of the AFRL-funded hydrocarbon-fueled booster technology development and development of an RD-180 replacement engine for the Atlas V. This engine would be of the thrust class of the RD-180 and would be built using technology currently under development in the AFRL Hydrocarbon Boost Technology program. This same replacement engine would be used in an RBS system. The mid-scale RBD is again assumed in the development program.

Scenario 3: Accelerated RBS. This scenario was explored to examine implications of accelerating the end of the EELV program to 2025. This scenario uses the domestic version of the AJ-26 engine but eliminates the mid-scale RBD and proceeds directly to full-scale RBS development.

Scenario 4: Commercial partnership. This scenario assumes a government-funded program to develop and conduct the RBD using the domestic AJ-26 engine, with the full-scale RBS developed by industry to support both Air Force and commercial spacelift needs.

Additional variations were explored within each of these four scenarios, including options to not include the heavy-lift vehicle in either the RBS development or its operations. These options were explored because the committee believes that the heavy-lift requirement places great challenges on a system that is already challenged by the technical risks discussed in Chapter 3. The requirement for a dual-reusable booster heavy-lift configuration adds significantly to the complexity of the launch system with respect to balancing structural loads, conducting safe separation, and simultaneously managing two autonomous reusable boosters in the same airspace. Given ongoing trends for smaller electronics and emerging desires and capabilities for disaggregation of large satellites, the committee believes that the heavy-lift requirement should not drive the basic conceptual design for the RBS, because this requirement may disappear in the future or be addressed with alternative space lift capabilities. Thus, the committee explored cost options that pose no heavy-lift requirement for the RBS.

An additional factor that requires consideration is the existing Air Force requirement for two independent launch capabilities to meet its assured-access-to-space goal. The scenarios described above are all based on the assumption that the current EELV launch systems would be fully retired and that the RBS satisfies the complete Air Force launch manifest. In this case, a problem identified in the RBS system could potentially jeopardize the entire Air Force launch capability. One possibility for avoiding this possibility would be to maintain the Delta IV production capability and use this launch system to satisfy the heavy-lift requirement.

The evaluations to follow principally focus on Scenarios 1 and 4. Scenario 2 allows for development of the hydrocarbon engine technology prior to proceeding with RBS development, so any decision regarding RBS development would be delayed for several years. This use of an RD-180 replacement engine would complicate the RBS vehicle design by requiring large engine throttling, as discussed in Chapter 3. Scenario 3 was also not addressed in detail as it was viewed by the committee as being too risky given the existing concerns about the rocketback return-to-launch-site (RTLS) maneuver. In the evaluations that follow, a subdesignation “-A” is used for a modification to the baseline scenario that does not include the RBS-heavy variant. In these scenarios, the implications of carrying the alternative heavy launch system were not factored into the cost analysis.

The costing analysis covers a 47-year life cycle (2014-2061), with EELV costs provided by the Air Force’s Space and Missile Systems Center (SMC) Launch and Range Systems Directorate and RBS costs estimated by the SMC’s Developmental Planning Directorate. The approaches used for the RBS cost estimates are shown in Table 4.1. The NASA/Air Force Cost Model (NAFCOM) is used for the costs of design, development, test and evaluation (DDT&E), and production and contractor proprietary approaches are used for cost estimations of the vehicle and engines. The Aerospace Corporation’s operations design model and its facilities model are used for operations and facilities.

A conservative approach was taken to the flight rate assumption. Air Force analyses are based on only eight flights per year, with one heavy-lift payload every year, and commercial markets were not considered. The mission model for the assumed flight rate is provided in Table 4.2.

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