Innovative LOX/Methane upper stage for future launchersInnovative LOx/methane upper stage for future launchers

The trend is today to research easy to use and cheap solutions for the propulsion of future expendable launch vehicles but also with a high level of performances. Another point is to look for non toxic propellants but able to operate in space for long duration mission and with a high level of performances: LOx Methane is a good compromise. A way could be an extensive use of composite materials both for the structures, the tanks and the engines with use, as much as possible of automatic processes. In a near future a breakthrough or improvement of the fibers strength may increase the interest of such technologies. Liquid composite wound tanks can weigh three to four times less than a metallic one under the same operating conditions, the same results can be obtained for the chambers; So these technologies give a new interest to pressure fed solutions (as a first approach Vacuum Specific Impulse depends mainly on engine area ratio and less on operating pressure). It could lead to a stage easy to operate, reliable, needing no costly solutions (Expander engine, Turbopumps, Boost pumps). On an upper stage with a full diameter tankage system (with a common bulkhead), the use of composite tanks is enabling creation of room, or all around the aft dome of the tank or in length (moreover mass of composite tanks is less sensitive than metallic ones to the shape). Creation of thrust depends mainly on the possibility of implementing nozzles divergent surfaces. On another side, thermal fluxes depend greatly on the operating pressure: low pressure engine no longer needs regenerative cooling system (radiation+ film or transpiration cooled ceramic engines could be used). Increase of throat area ratio is not a major problem with respect to the available room. Moreover stage without turbomachinery is much less sensitive to the mission profile and become much more competitive with a multi-boost mission. As a previous study showed the interest of these solutions with cryogenic upper stage, the aim of this presentation is to demonstrate the performance improvement by replacing a conventional low pressure-fed NTO/MMH upper stage by an all composite designed LOx/Methane pressure fed stages and so the interest for R&D on this field.