Time for SpaceX’s Falcon Heavy rocket to fly: Watch live video of the final countdown

SpaceX's Falcon Heavy sits on Launch Pad 39A at NASA's Kennedy Space Center in Florida. (GeekWire Photo / Kevin Lisota)

CAPE CANAVERAL, Fla. — The maiden launch of SpaceX’s Falcon Heavy rocket is arguably the biggest thing to hit NASA’s Kennedy Space Center since the retirement of the space shuttle fleet in 2011.

RELATED: SpaceX launches Falcon Heavy rocket for first time, putting a sports car in space

Liftoff was set for 3:45 p.m. ET (12:45 p.m. PT) today, amid concerns about upper-level winds.

Hundreds of journalists have signed up to cover the launch from NASA’s historic Launch Complex 39A, where Apollo moon rockets and space shuttles have blasted off in the past. (NASA leased the launch pad to SpaceX in 2014.) Thousands of spectators swarmed to viewing areas surrounding the launch site. The backup to get into Kennedy Space Center’s visitor center stretched for more than 5 miles this morning.

More than 2 million viewers are watching the launch webcast.

“I’d say, tune in. It’s going to be worth your time,” SpaceX CEO Elon Musk said during a teleconference on the eve of the launch.

So what’s going on? We’ve boiled down the basics as answers to nine questions:

What’s a Falcon Heavy? It’s designed to be the most powerful rocket in operation since the Apollo era’s Saturn V rocket, in terms of its capability to loft payloads. The 230-foot-tall rocket combines a modified Falcon 9 rocket core in the center with a recycled Falcon 9 cores to the left and to the right. That means SpaceX aims to have 27 of its Merlin rocket engines firing at once.

As a result, the Falcon Heavy can launch 141,000 pounds — the equivalent of a Boeing 737 jet fully loaded with fuel, passengers and their luggage — to low Earth orbit. In terms of liftoff thrust, its 5-million-pound punch is the biggest since the shuttle’s 7-million-pound thrust capability.

What’s the big deal? If the Falcon Heavy works as advertised, it could provide a low-cost means to send expensive, hefty satellites directly to a particularly desirable altitude known as geostationary orbit, 22,000 miles up, where the satellites can remain permanently stationed over a given spot on Earth. Success would extend SpaceX’s market reach into a new space frontier.

What’s the payload? There’s a lot that could go wrong with this first flight, so Musk has arranged to send an expendable (and silly) cargo into deep space. It’s Musk’s pre-owned red Tesla Roadster, complete with a spacesuit-wearing mannequin in the front seat. Musk already has called attention to an “Easter egg” sitting on the dashboard: a tiny toy model of the Roadster, with an even tinier toy astronaut sitting inside. More Easter eggs, perhaps including a micro-sized copy of Isaac Asimov’s Foundation Trilogy, could be revealed during today’s webcast.

SpaceX’s Falcon Heavy stands 230 feet tall. (GeekWire Photo / Kevin Lisota)

Where’s it going? As far out as the orbit of Mars, roughly 250 million miles (400 million kilometers) from Earth at the farthest, and traveling at a relative speed of nearly 25,000 mph (11 km/sec), according to Musk.

“It’s going to be in a precessing elliptical orbit, with one point of the ellipse being at Earth orbit, the other point being at Mars orbit,” he told GeekWire. “So essentially it’ll be an Earth-Mars cycler, and we estimage it’ll be in that orbit for several hundred million years, maybe in excess of a billion years. At times, it will come extremely close to Mars, and there’s a tiny, tiny chance that it will hit Mars.”

I asked Musk if he could quantify that chance more precisely. “Extremely tiny,” he replied. “I wouldn’t hold your breath.”

The enormous size of the Falcon Heavy is clear when compared to the cars parked below it. (GeekWire Photo/Kevin Lisota)

What happens to the rockets? After the upper stage separates and heads further out into space, the three first-stage cores are programmed to execute an autonomously controlled pirouette to return to Earth. The two side cores should come down with a one-two punch of sonic booms at SpaceX’s twin landing pads on the Florida coast. The central core should touch down on “Of Course I Still Love You,” a fancifully named drone ship stationed hundreds of miles out in the Atlantic Ocean. It should be an impressive sight.

When can we tune in? Because this is strictly a demonstration mission for SpaceX, don’t expect NASA TV to carry the webcast. Instead, go to SpaceX.com/webcast. Right now, liftoff is scheduled for 3:45 p.m. ET (12:45 p.m. PT), later than originally planned, to give upper-level winds time to diminish to acceptable levels. If the launch has to be delayed, there’s a backup window from 1:30 to 4 p.m. ET on Wednesday. For more background, check out SpaceX’s press kit for the launch.

What’ll we see? In addition to the countdown and liftoff, SpaceX traditionally wires its first-stage booster up with a rocket-cam to provide an in-flight view of the ascent. This time around, there could be as many as four separate rocket-cam views on the screen, from the three first-stage boosters as well as the upper stage. There could be an extra video treat: Three cameras have been mounted on the Roadster, with the intent of beaming back deep-space views of the mannequin sitting in the car. “They should really provide some epic views if they work and everything goes well,” Musk said.

What’s the soundtrack? Musk said he wants to have David Bowie’s “Space Oddity” playing for liftoff, and that’s not the only Falcon Heavy tribute to the late rocker. The Roadster’s dummy driver has been nicknamed “Starman,” evoking another Bowie song. And Bowie’s “Life on Mars” provides the soundtrack for an animation highlighting the Falcon Heavy’s mission.

What’s next? SpaceX’s launch manifest lists four more missions for the Falcon Heavy, including the U.S. Air Force’s STP-2 test program as well as satellites for Arabsat, ViaSat and Inmarsat. The STP-2 mission is of particular interest because one of its planned payloads is the Planetary Society’s LightSail 2 spacecraft, which is designed to test solar-sailing technology.

In the long run, the Falcon 9 and the Falcon Heavy may be surpassed by the BFR, the “Big Falcon Rocket” that SpaceX is developing for passenger flights to Mars. But that, as they say, is another story.