The US$79-million (S$115-million) effort will culminate in searching the crater for signs of a possible long-frozen water source and examining the unseen world's mineral makeup.

The Lunar Rerconnaissance Orbiter, or LRO, hopes to push forward the space effort's knowledge base through a one-year stay at an orbit of about 31 miles (50 kilometres) - the closest any spacecraft has continually orbited the moon.

LRO's US$500-million mission is designed to provide Nasa with maps of unprecedented accuracy, which will be crucial for scoping out possible landing sites.

Both missions, May said, will help Nasa model the nuances of lunar lighting and temperature range, and provide future moon travelers with information on the cosmic radiation the moon is exposed to due to its lack of atmosphere.

Finally, the probes' four-day, 238,000 mile (384,000 km) return to the moon forty years after humans first set foot on its surface is expected to illuminate our closest extra-terrestrial neighbor like never before.

Both LRO and Lcross missions, Mr May said, promise to teach the long distance explorers 'the process that formed the earth, the moon and the solar system.' The agency hopes the probes will answer a full plate of fundamental questions of cosmic history.

'Earth is subject to erosion processes from air and water,' noted Mr May. 'The moon itself doesn't have this process... LRO will send back pictures daily on things we have barely seen before.'

Meanwhile, the shuttle Endeavour was on track for launch Wednesday from Kenney Space Center at Cape Canaveral, Florida on a mission to take six Americans and a Canadian to the International Space Station, Nasa officials said.

The Endeavour's launch, now scheduled for 5.40am on Wednesday (0940 GMT), was delayed on Saturday because of a hydrogen leak in an external fuel tank. -- AFP