SpaceX has canceled Tuesday’s launch of a South Korean military satellite to “take a closer look” at the rocket’s staging.

The launch, which will send the satellite into orbit on its ANASIS-II mission, was delayed due to concerns over the rocket’s second stage. SpaceX tweeted that it will “swap hardware” for the rocket if needed.

A new launch date has not been set.

On Saturday, SpaceX announced it had completed a test of its Falcon 9 rocket ahead of the launch. The rocket had been loaded onto the launchpad and even fired its engines for a few seconds. “Static tests” like that allow engineers to measure pressure and temperature, as well as check that everything is working as it should.

The rocket booster that will be used in the ANASIS-II flight will be the same as the ones that lifted NASA astronauts into orbit during the historic Crew Dragon launch last month.

The ANASIS-II will be South Korea’s first military communications satellite. However, little else is known about the satellite due to its military background.