Private space firm SpaceX said Saturday an engine throttle valve problem was to blame for the failure of its second attempt to land the Falcon 9 rocket's first stage on a drone ship in the Atlantic Ocean.

"Cause of hard rocket landing confirmed as due to slower than expected throttle valve response," SpaceX founder and CEO Elon Musk wrote in a tweet.

The problem, however, seems to be easy to fix. "While the rocket does look rather tall and tippy, a stable landing is no problem with proper throttle response," Musk said.

SpaceX made its second attempt to land a Falcon 9 first stage on the drone ship on Tuesday, during the launch of its sixth cargo mission to the International Space Station.

The first stage did land on the ship but came down "a little bit too hard," leading to a tip-over and a subsequent explosion.

The company's first attempt in January ended in a crash on the boat, because the rocket's steering fins ran out of hydraulic fluid.

Musk revealed that another attempt will be made in two months, during the launch of its seventh cargo mission to the space station.