South Korea was poised Wednesday for its third bid to send a satellite into orbit -- a watershed moment for the future of the country's space programme and a high-stakes challenge to national pride.

The pressure surrounding the mission has risen considerably in the wake of rival North Korea's successful launch of a satellite on an indigenously-built carrier in December.

Final preparations for Wednesday's launch were also being made under the North's threat of an imminent nuclear test, which would quickly deflate any congratulatory bubble arising from a successful mission.

After two previous failures in 2009 and 2010, the 140-tonne Korea Space Launch Vehicle (KSLV-I) was scheduled to blast off some time after 3:55pm (0655 GMT) from the Naro Space Center on the south coast.

Success would mean a huge boost for South Korea -- a late entrant into the high-cost world of space technology and exploration and desperate to get its commercial launch programme up and running.

Despite a very successful satellite construction programme, it faces a long slog to catch up with the other Asian powers with proven launch capability -- China, Japan and India.

A final dress rehearsal was carried out on Tuesday, involving launch simulations of both the rocket's Russian-built first stage and the South Korean-built second stage.

Initially scheduled for October 26, the launch has already been twice postponed for technical reasons.

Successful or not, this will be the last launch under the current agreement with Russia which agreed to provide the first stage for a maximum of three rockets.

"The pressure is on the South Koreans like never before," said independent space analyst Morris Jones.

"There are several converging factors -- the two previous failures, North Korea's success and the fact that this is the last chance with this particular rocket model," Jones said.

Seoul's space ambitions were restricted for many years by its main military ally the United States, which feared that a robust missile or rocket programme would accelerate a regional arms race, especially with North Korea.

After joining the Missile Technology Control Regime in 2001, South Korea made Russia its go-to space partner, but the relationship has not been an easy one.

In 2009, the rocket achieved orbit but faulty release mechanisms on the second stage prevented proper deployment of the satellite.

The second effort in 2010 saw the rocket explode two minutes into its flight, with both Russia and South Korea pointing the finger of blame at each other.

"Another failure would prompt a lot of mud-slinging," said Jones.

Whatever the outcome of Wednesday's launch, South Korea insists it remains committed to developing a totally indigenous three-stage, liquid-fuelled rocket capable of carrying a 1.5-tonne payload into orbit by 2021.