Complex sentence: On September 11,1962 an R-21, fitted to a Ye-8, exploded in mid-air after compressor failure; test pilot Mosolov survived the ejection at Mach 1.78, but he never fully recovered.
Split into simpler sentences: On September 11,1962 an R-21 exploded in mid-air after compressor failure. Test pilot Mosolov survived the ejection at Mach 1.78, but he never fully recovered.