BEIJING - China's next generation carrier rockets using non-polluting propellants may fly as early as 2015, a top space scientist revealed on Monday.

The rockets fueled by liquid oxygen and diesel as well as liquid oxygen and liquid hydrogen, will make their maiden flights within the next two years, Lei Fanpei, chairman of the China Aerospace Science and Technology Corporation, the main contractor for the country's space program, said in an interview with Xinhua.

The next generation will include the heavy Long March-5 and the smaller Long March-7. It will take about 15 years for an overall upgrading.

The Long March-5 will have a payload capacity of 25 tons to low Earth orbits, or 14 tonnes to geostationary transfer orbit, about twice the current capacity, and could be a serious competitor to the US Delta-4H.

The Long March-7 will carry up to 13.5 tons to low Earth orbit or 5.5 tons to sun-synchronous orbit at a height of 700 km. It will carry cargo craft for the planned space station. Its maiden flight should be next year.