#trajectory__flight  the path followed by an object moving through space
  supertype:  #mechanical_phenomenon  a physical phenomenon associated with the equilibrium or motion of objects
  subtype:  #ballistic_trajectory__ballistictrajectory__ballistics  the trajectory of an object in free flight
  subtype:  #gravity-assist__gravityassist  (spaceflight) a trajectory that passes close to a planetary body in order to gain energy from its gravitational field

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