Washington, May 2 (IANS) The launch of US space shuttle Endeavour on its 25th and final flight has been delayed again due to technical problems, NASA announced Sunday.

A new date for Endeavour's launch, which was originally scheduled last Friday, has not yet been set, Xinhua reported. It will deliver the $2-billion Alpha Magnetic Spectrometer (AMS) particle detector to the International Space Station.

The launch was, however, called off after engineers detected a failure in one of two heater circuits associated with Auxiliary Power Unit (APU) 1. Heaters are required to keep the APUs' hydrazine from freezing on orbit.

NASA hoped Endeavour would lift off Monday.

AMS, a particle physics detector, is designed to search for various types of unusual matter by measuring cosmic rays. Its experiments are designed to help researchers study the formation of the universe and search for evidence of dark matter, strange matter and antimatter.

Endeavor, which has been promised to the California Science Centre in Los Angeles upon its return, was the replacement ship for Challenger, which was lost in a 1986 explosion as it ascended over the Atlantic that killed seven astronauts.

It will be the second of NASA's three surviving shuttles to be retired. Sister ship Discovery, which will be transferred to the Smithsonian National Air and Space Museum, completed its last flight in March. Atlantis' final launch is scheduled for June 28.

The Russian space programme's Soyuz capsule will be the only method for transporting astronauts to and from the station when the US space shuttle programme ends later this year.