美国航宇局、美国空军和美国国家航天委员会准备研制一种新的系列运载火箭。这种称作国家运载系统(NLS)的系列运载火箭将能把10～50吨的有效载荷发射到低地轨道。目前,美国空军正在运用先进的材料和加工技术研制共空间运输主发动机(STME)。这种可供NLS选用的发动机将使用液氧/液氢作推进剂,从而可减小对环境的危害。但NLS系列中 NASA, the U.S. Air Force and the U.S. National Space Commission are preparing a new series of launch vehicles. This series of launch vehicles, known as the National System of Vehicles (NLS), will be capable of launching 10-50 tonne payloads into low Earth orbit. Currently, the U.S. Air Force is using advanced materials and processing technologies to develop the main space transportation master engine (STME). This engine, which is available for NLS, will use liquid oxygen / liquid hydrogen as a propellant to reduce the environmental impact. But NLS series