Complex sentence: The RD-0256 is an improved version of the RD-0228 (GRAU: 15D84), itself composed of an RD-0229 (GRAU: 15D84) main engine and a RD-0230 (GRAU: 15D79) vernier engine.
Split into simpler sentences: The RD-0256 is an improved version of the RD-0228 (GRAU: 15D84). Itself composed of an RD-0229 (GRAU: 15D84) main engine and a RD-0230 (GRAU: 15D79) vernier engine.