WASHINGTON — SpaceX is now planning to attempt the first launch of its Falcon Heavy rocket around the end of this month, the company’s chief executive said Jan. 4.

In a posting on the social media website Instagram that featured a video of the rocket, Elon Musk said the heavy-lift rocket would launch from Kennedy Space Center’s Launch Complex 39A after a static-fire test on the pad scheduled for next week.

“Hold-down test fire next week. Launch end of the month,” he wrote.

The company rolled the rocket, featuring three Falcon 9 first stages mounted side-by-side with a second stage mounted on top of the center booster, to the pad for the first time Dec. 28, raising it to the vertical position for fit checks there. The rocket was lowered and rolled back to its hangar the next day.

The Falcon Heavy will return to the launch pad in the next few days for the static-fire test, where the engines in the rocket’s three booster cores — 27 in total — will briefly ignite. That static fire test is not expected to take place until after the Falcon 9 launch of a classified payload codenamed “Zuma” from nearby Space Launch Complex 40.

SpaceX announced Jan. 4 that the Zuma launch had been rescheduled to no sooner than the evening of Jan. 7 because “extreme weather” in Florida had slowed launch preparations, an apparent reference to unseasonably cold weather in the region. That statement came despite forecasts that had, in recent days, offered a 90 percent chance of acceptable weather for a launch previously scheduled for Jan. 4 and 5.

The long-delayed inaugural launch of the Falcon Heavy — the company said in April 2011 that the vehicle would be ready for a first launch in 2013 — is a demonstration mission without a paying customer. In December, Musk announced the rocket would carry his own Tesla Roadster sports car on a trajectory that would take it past the planet Mars. SpaceX later released photos of the car being encapsulated in the rocket’s payload fairing.

If that demonstration mission is a success, SpaceX has at least two more Falcon Heavy launches planned for 2018, of the Arabsat 6A communications satellite and the Space Test Program 2 mission for the U.S. Air Force, although the timing of those missions is uncertain. SpaceX also announced plans to fly a Crew Dragon spacecraft, carrying two people, on a circumlunar mission in late 2018 using a Falcon Heavy, but the company has provided no updates on the status of that effort since announcing it in February 2017.

Musk, though, has lowered expectations for the first Falcon Heavy launch, something he also did in his Instagram post. “Excitement on launch day guaranteed, one way or another,” he wrote.