Japanese space development venture company Space One said Sunday that it will launch the second unit of its Kairos small satellite-carrying rocket as early as in December, after the launch of the No. 1 unit ended in failure this spring.

The Tokyo-based company also said the failure of the No. 1 unit was determined to have been caused by the rocket's autonomous flight safety system judging the slower-than-predicted speed to be "abnormal" and causing the rocket to abort its flight.

The detailed schedule for the No. 2 unit will be announced two months before the launch. The No. 2 unit plans to carry one small satellite and four microsatellites.

According to Space One, the No. 1 unit, which exploded shortly after launch, had a lower thrust than previously calculated in the first-stage rocket as the predicted fuel burn rate was higher than reality. Also behind the explosion was the fact that the judgment criteria for the autonomous flight system had been strictly set to ensure safety.

At an online news conference, Mamoru Endo, director of Space One, said the company did not have a system to ensure reproducibility, explaining that improvements have been made to ensure correct predictions.

On March 13 this year, the No. 1 Kairos rocket was launched from Space One's liftoff site in Kushimoto, Wakayama Prefecture, but exploded five seconds later.

If the launch had been successful, the Kairos rocket would have been Japan's first fully-private-sector-developed rocket capable of putting a satellite into orbit.