Complex sentence: After securing more funding in the 1990s, the initial design underwent radical revision and, since 2000, Reaction Engines has been working with the University of Bristol to develop an engine design vital to the success of Skylon.
Split into simpler sentences: After securing more funding in the 1990s, the initial design underwent radical revision. Since 2000, Reaction Engines has been working with the University of Bristol to develop an engine designs vital to the success of Skylon.