A closed Brayton cycle thermal management system is proposed for a regeneratively cooled scramjet to reduce the hydrogen fuel flow for cooling, through converting part of the heat from fuel to other forms of energy to decrease the heat that must be taken away by hydrogen fuel. Fuel heat sink (cooling capacity) is thus indirectly increased. Instead of carrying excess fuel for cooling or seeking for any new coolant, the fuel flow for cooling is reduced, and fuel onboard is adequate to satisfy the cooling requirement for the whole hypersonic vehicle. A parametric study of an irreversible closed Brayton cycle thermal management system for scramjet has been performed with external as well as internal irreversibilities. It is known through performance analyses that closed Brayton cycle thermal management system has excellent potential performance over conventional regenerative cooling, due to the reduction in fuel flow for cooling and additional power output.