Nasa is preparing to launch its Dawn space probe later this month after two failed attempts.

The probe was due to be launched in July, but was delayed by adverse weather conditions.

A second attempt later in the month had to be abandoned because the right equipment was not available to carry out the launch to the required safety standards.

The Dawn probe has now been moved to its launch position ready for an expected lift-off on 26 September.

"From here, the only way is up," said Dawn project manager Keyur Patel of Nasa's Jet Propulsion Laboratory in Pasadena.

"We are looking forward to putting some space between Dawn and Mother Earth and making some space history."

The probe will investigate Ceres and Vesta, the two largest objects in the Asteroid Belt between Mars and Jupiter. It will reach Vesta in late 2011 and go into orbit for seven months before heading to Ceres and arriving in February 2015.

Ceres is thought to be covered by a 120km layer of ice, which offers the tantalising possibility of liquid water underneath.

Vesta is a dry asteroid, but its diameter of 530km means that it accounts for around 10 per cent of the total mass of the Asteroid Belt.

Together the two may answer some fundamental questions about the development of the Solar System and how planets are formed.