Wikipedia
JPTS stands for Jet Propellant Thermally Stable (high thermal stability, high altitude fuel), and was created specifically as fuel for the Lockheed U-2 reconnaissance aircraft. It is officially called Thermally Stable Aviation Turbine Fuel. JPTS has a lower freeze point, higher viscosity, and higher thermal stability than standard Air Force fuels. In 1999 the United States Air Force spent approximately $11.3 million on fuel for the Lockheed U-2 aircraft, and was looking for a lower cost alternative. The U-2 has used JPTS since the aircraft's development in the 1950s. The high viscosity is needed to overcome the partial solidification of the fuel in low temperatures. The fuel also serves as coolant of engines and aerodynamically heated surfaces. As the fuel flow at U-2 operation altitude at cruising flight is about sixteen times lower than at sea level, the dwell time over hot surfaces is longer and increases the chances of thermal breakdown; high thermal stability is therefore desired to avoid coking and deposition of varnishes in the piping.
JPTS is a specialty fuel and is produced by only two oil refineries in the United States. As such, it has limited worldwide availability and costs over three times the per-gallon price of the Air Force's primary jet fuel, JP-8. Research is under way to find a cheaper and easier alternative involving additives to generally used jet fuels. A JP-8 based alternative, JP-8+100LT, is being considered. JP-8+100 has increased thermal stability by 100 degrees F more than stock JP8, and is only 0.5 cents per gallon more expensive; low temperature additives can be blended to this stock to add the desired cold performance.
JPTS is specified to have a flash point of 43 °C (110 °F) and a freezing point of -53 °C (-64 °F). Its flammability limits are 1 and 6 percents. It has an appearance of a water-white clear liquid with specific gravity of 0.816. It is insoluble in water. It is composed of a complex mixture of petroleum hydrocarbons.