Flexibility in engineering system design: •Flexibility in system design and implications for aerospace systems (Saleh et.al 2003) •A flexible and robust approach for preliminary engineering design based on designer's preference (Nahmet.al, 2007) •A real options approach to hybrid electric vehicle architecture design for flexibility (Kang et.al 2016) •Our research: •Simulation optimization •Long range uncertainty •Add flexibility and robustness to design