Complex sentence: During the 1970s a leading advocate of the concept of travel in an evacuated environment was Robert F. Salter of RAND, he published two preliminary engineering articles in 1972 and again in 1978.
Split into simpler sentences: During the 1970s a leading advocate of the concept of travel in an evacuated environment was Robert F. Salter of RAND. He published two preliminary engineering articles in 1972 and again in 1978.