2015年12月14日,美国空军售出了3个小型发动机研究合同。空军称计划共售出6~8个合同,总价值3500万美元,旨在研制低成本推进部件。这是研制替代RD-180的美国发动机的第二轮合同,美国国会2016年拨款2.27亿美元用于加速开发新的推进系统。得到第二轮合同的是加州从事微电子设计的Tanner研究公司、Moog公司及约翰·霍普金斯大学怀廷工程学院,后者的合同是研究冷却液体火箭发动机 On December 14, 2015, the U.S. Air Force sold three small-engine research contracts. The Air Force said it plans to sell 6 to 8 contracts worth 35 million U.S. dollars in total, aiming to develop low-cost propulsion components. This is the second round of contract to develop a U.S. engine that will replace the RD-180. The U.S. Congress allocated $ 227 million in 2016 to accelerate the development of a new propulsion system. The second round of contracts was awarded to Tanner Research, a California-based microelectronics design company, to Moog and to the Johns Hopkins Graduate School of Waintin, whose contract is to study cooling liquid rocket engines