This paper reports the findings of a continuing study to examine the capabilities, flight dynamics, and operability of a new launch system predicated on a Reusable Booster System. This effort is part of the ongoing U.S. Air Force Future-responsive Access to Space Technologies (FAST) program. The authors considered a multi-stage launch vehicle with a reusable wing-body first stage and two expendable upper stages. The baseline propellants were selected to be LOX/RP-2 for all stages. A complete, Level 1 multidisciplinary conceptual systems assessment was performed on a baseline launch vehicle design and numerous trade study configurations to determine the impact to key performance metrics such as size, empty mass, and gross mass. The trade study variables of interest were the staging flight path angle, staging dynamic pressure, staging Mach number, and post-staging RTLS pitch over direction. Findings indicate that while minimal impact was seen for the top-level vehicle metrics like size, gross weight, and dry weight, there were more significant impacts to the vehicle's actual flight environment in terms of normal force loads, peak heat rate, and total heat load. Numerical results for all vehicle results from this effort are reported.
Partially reusable launch vehicle systems, featuring a reusable first stage and expendable upper stage(s), have been investigated as options for the next generation Air Force launch vehicle to meet future spacelift needs. An important area of research for the reusable first stage is the assessment of the aft end thermal environment in order to determine the influence of engine cluster packaging, plume characteristics, and engine protection and packaging approaches, particularly since the engines are to be utilized over again for multiple flights before refurbishment. Lockheed Martin's (LM) objective for the aft-end heating assessment was to generate a broad parametric understanding of engine-plume interactions and engine integration and packaging options to inform successful future configuration definition. Under contract from the Air Force Research Laboratory (AFRL), LM conducted CFD and thermal analyses for a wide baseline of engine cluster arrangements and packaging options for a small-lift 5000 lb payload baseline. The study matrix contains seven unique engine cluster arrangements that utilize from one to five rocket engines which are scaled to provide the same total performance as the baseline vehicle. For each engine arrangement, LM assessed the aft end thermal environment for two different engine packaging concepts. The first concept is an aft end boat tail engine packaging similar to what is seen on many other launch vehicles such as the Atlas V. The second packaging option places the entire engine in its own nacelle up to the engine mount. This second engine packaging concept is the baseline for AFRL's Fully reusable Access to Space Technology (FAST) study and is intended to simplify engine refurbishment and periodic replacement. The assessment of the thermal environment and flow behavior between these nacelles was a principal study goal. The resulting fourteen vehicle engine configurations were modeled in CAD and assessed utilizing Cart3d for CFD analysis. Parametric comparisons of convective heating derived from those solutions were produced in the base region for all cases over a range of Mach number and altitudes.
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