North Korea has bristled at UN sanctions imposed after its April launch, which US intelligence officials say did not place a satellite in orbit but in reality was cover for a test of long-range missile technology.

Series of delays

Tuesday's South Korean launch took place after a series of delays put a hold on previous attempts.

Last week blast-off was aborted with just minutes to go after technicians discovered a software fault.

Ahead of the launch scientists had warned the first seconds of flight would be crucial as the main engine pushes the 140-tonne rocket off the launch pad.

"If there is a sudden gust of strong wind or any other slight problem in the stabilisation mechanism, the rocket can tip over and be lost," Min Kyung-Ju, head of the Naro Space Centre, told South Korea's Yonhap news agency.

'Successful launch'

A successful launch would make South Korea only the 10th nation in the world to send a satellite into orbit from its own soil.

Although the rocket's powerful first stage was Russian-made, South Korean experts said they had gained valuable know-how that could enable them to build their own launch vehicle in its entirety by 2018.

SOUTH KOREA'S SPACE DREAMS

Two-stage rocket dubbed Korea Space Launch Vehicle-1 (KSLV-1), aims to launch 100-kg satellite that will monitor Earth's radiant energy.

 Expected launch comes after 20 years of research and development that started with small, rudimentary solid-fuel machines.

 Rocket is 33 metres long and can generate 170 tonnes of thrust.

 Built at a cost of $400m in co-operation with Russia's Khrunichev space production centre which built main thrusters for first stage.

 South Korea aims to build a rocket completely on its own by 2018 and launch a probe to the moon by 2025, eventually sending its own astronauts into space.

Neighbouring North Korea launched its own three-stage rocket on April 5 claiming it sent a communications satellite into orbit, but there were doubts the mission succeeded.

The United States, Japan and others have called Pyongyang's rocket launch a cover for test of long-range missile technology.

The UN Security Council also condemned the launch, saying it was a violation of resolutions banning North Korea from ballistic missile-related activity.

The North responded by expelling inspectors and withdrawing from six-party talks on the disarmament of its nuclear programme.

Ahead of Tuesday's launch Won Tae-jae, a South Korea defence ministry spokesman, defended his country's space programme saying the launch vehicle differed vastly from the North's controversial rocket launches.

He told reporters during a regular briefing that the development of South Korea's space launch vehicle has been responsible and open to the international community.

"On that matter, we are not accused of launching a ballistic missile," he said.