JAXA has been promoting research and development for hypersonic transports (HST) since 2004, following its long-term vision to demonstrate technologies for aircraft that can cruise at Mach 5. A precooled turbojet engine and Mach 5 flight experimental vehicle called Hypersonic Technology Experimental vehicle (HYTEX) are under development. Liquid hydrogen is the best fuel and coolant for the hypersonic turbojet, however safety standard in flight experiment tends to prohibit using hydrogen. Consequently we conducted the first flight experiment (Mach 2) of the hypersonic turbojet in September 2010 with gaseous hydrogen as a fuel and liquid nitrogen as a coolant. In this paper performance analysis of hypersonic turbojet engine using alternative fuel (methane and kerosene) and alternative coolant (liquid helium, liquid nitrogen, and other safe refrigerants) for the air-precooler during Mach 5 flight is discussed.