Complex sentence: Dmitrii Evgenievich Okhotsimsky, an outstanding Soviet/Russian space scientist, pioneer of space ballistics in the USSR, author of fundamental works in applied celestial mechanics, control in space and robotics.
Split into simpler sentences: Dmitrii Evgenievich Okhotsimsky was a Soviet Russian space scientist who was the pioneer of space ballistics in the USSR. He wrote fundamental works in applied celestial mechanics and control in space and robotics.