The Senate on Tuesday approved its version of the fiscal year 2016 defense authorization bill that included a compromise on the RD-180 issue.Sen. Bill Nelson’s (D-Fla.) amendment gives the Air Force 18 additional Russian rocket engines to be acquired before the end of 2022 to help bridge the gap until a domestic next-generation engine is ready for use, The amendment also restricts the use of Russian engines to phases 1(a) and 2 of the Evolved Expendable Launch Vehicle (EELV) procurements,…