US space firm SpaceX on Friday successfully landed the first stage of its Falcon 9 rocket on a droneship in the Atlantic Ocean after launching a commercial communications satellite into orbit for a Thailand company.

"Falcon 9 first stage has landed," the California-based company said on Twitter, minutes after the satellite launch at 5:39 p.m. EDT (2139 GMT) from Cape Canaveral Air Force Station in Florida.

The success means that SpaceX has now landed three Falcon 9 first stages in a row on a boat in just two months.

The main objective of the mission was to deliver a commercial communications satellite called THAICOM 8 to a supersynchronous transfer orbit, which was used to move a satellite into a geostationary orbit about 36,000 km over the equator.

The 3,000-kg satellite, owned by Thailand's Thaicom, will provide communications coverage for South Asia and Southeast Asia and has an operational design life of 15 years.

Given this mission's high-orbit destination, SpaceX said before launch that a successful landing is "challenging" because the first stage of the rocket would be subject to extreme velocities and re-entry heating.

Prior to the three successful droneship touchdowns, SpaceX's four such attempts all ended in failure.

All of these landing attempts are part of SpaceX's effort to produce a fully and rapidly reusable rocket, which it said will dramatically reduce the cost of space transport.

Traditionally, rockets are designed for a single use only, burning up or crashing into the ocean after liftoff.