Complex sentence: It was launched on June 1,1990, with a Delta II rocket from Cape Canaveral for a 5 year initial mission, and operated for over 8 years until February 12,1999.
Split into simpler sentences: It was launched on June 1,1990, on a Delta II rocket from Cape Canaveral, on what was initially planned as a 5 year mission. ROSAT actually operated for over 8 years, finally shutting down on February 12,1999.