Space shuttle endeavour's final launch postponed again

The final launch of the space shuttle Endeavour, scheduled for Monday, has been postponed again as NASA specialists have failed to fix technical problems with the spacecraft's engine compartment, the US space agency said. According to Russia's News Agency (RIA Novosti), no date for a new launch attempt has been set, but NASA said it would not take place before the end of the week, at the soonest. The Endeavour's launch was previously rescheduled from Friday after engineers detected a malfunction in one of two heater circuits associated with the auxiliary power unit (APU). Heaters are required to keep the APUs' hydrazine from freezing in orbit. Endeavour with the STS-134 expedition is to deliver a $2 billion particle detector to be mounted outside the International Space Station (ISS.) This will be Endeavour's final flight and the next-to-last shuttle mission. The U.S. space agency, which says its shuttles are outdated and too expensive to maintain, will begin sending astronauts to the ISS on board Russia's Soyuz rockets.