The two-stage Naro rocket operated normally during and after lift-off from the country's space centre, science minister Ahn Byong-man said. But then communications with the rocket were lost after it reached an altitude of about 43 miles.
"We believe the Naro rocket is likely to have exploded," he said.
In the first attempt last August, the satellite failed to reach orbit because one of its two covers apparently failed to come off. The rocket worked, however, so South Korea saw that launch as a partial success.