midcourse
adjective
mid·course ˈmid-ˈkȯrs 
: being or occurring in the middle part of a course (as of a spacecraft)
a midcourse correction
Example Sentences
Recent Examples on the Web This isn't the first time the nation has managed it; in 2010, China used a midcourse interceptor, likely another DN-3, to destroy a target missile in the exoatmosphere, or roughly 62 miles above the earth's surface. 
Popular Science, 13 Feb. 2018 On the way down As with all ballistic missiles, gravity takes over after the midcourse phase, and the warhead falls toward its target. Gerry Doyle, The Seattle Times, 11 Aug. 2017
Popular Science, 13 Feb. 2018 On the way down As with all ballistic missiles, gravity takes over after the midcourse phase, and the warhead falls toward its target. Gerry Doyle, The Seattle Times, 11 Aug. 2017 Word History
First Known Use
circa 1951, in the meaning defined above