The first launch of SpaceX’s Falcon Heavy is currently scheduled for Tuesday, 2018-02-06, with a two and a half hour launch window which opens at 18:30 UTC and closes at 21:00 UTC (since this is a test flight which need not enter a precise orbit, the launch time is not critical). If the launch is postponed, the same launch window will be used on successive days, subject to availability of the range. The Sunday weather forecast predicts 80% probability of favourable conditions for launch during the Tuesday window.
Falcon Heavy consists of three first stage cores derived from the existing Falcon 9 first stage. The centre core is specially strengthened to accommodate the structural loads of the boosters and heavier payload, and to attach the two side boosters, which are slightly modified Falcon 9 first stages (in fact, the two boosters to be used on this flight have previously flown on SpaceX Falcon 9 missions). The three cores ignite simultaneously on the launch pad, with a total of 27 Merlin 1D engines, nine on each core, providing liftoff thrust of 22,819 kN (5.13 million pounds of thrust). This compares to the 34,000 kN thrust of the Saturn V moon rocket, and 30,255 for the Space Shuttle (main engines plus solid rocket boosters).
But what matters isn’t thrust, but rather a launcher’s ability to deliver payload to where the customer wants it. Here, the Falcon Heavy, if it works, will become the heaviest lift launcher in service. Here, I’ll compare payload to low Earth orbit (LEO), since that’s the fairest comparison of launchers: regardless of the ultimate destination, any rocket must first achieve orbital velocity. The Saturn V could put 140 tonnes into LEO, while the Space Shuttle had a maximum payload of 24.4 tonnes (the reusable orbiter itself weighed 78 tonnes, but does not count as payload). Falcon Heavy can launch 63.8 tonnes to LEO, more than twice the payload of its closest competitor, the Delta IV Heavy (28.79 tonnes). Russia’s Proton M+ has a payload capacity of 23 tonnes, while the European Ariane 5 can deliver 21 tonnes to LEO.
This test flight will not carry a payload for a customer. Many things which can only be tested in flight, particularly the structural loads and aerodynamics of the three core first stage at max Q and separation of the two side boosters from the core (which runs at reduced thrust from shortly after liftoff until separation, and then throttles up to full thrust for the remainder of its burn), and customers who require this kind of lift capability aren’t likely to risk their payloads on a first flight. Instead, Falcon Heavy will be carrying a car.
This is Elon Musk’s Tesla Roadster with its Starman test dummy on board, attached to the Falcon Heavy payload adapter. It will be enclosed in the payload fairing for launch and, if the mission is successful, injected into an orbit around the Sun which will venture as far from the Sun as the orbit of Mars (but will not approach the planet). The payload serves only as a mass simulator, but has a lot more style than the usual steel or tungsten dummy payload carried on inaugural flights of other launchers.
The three first stage cores are intended to be recovered. After separating from the centre core, the two side boosters will return to the landing zone at Cape Canaveral for near-simultaneous landings. The centre core will fly downrange and land on the drone ship in the Atlantic.
The second stage is identical to that of the Falcon 9. Once the side boosters separate, a Falcon Heavy mission is essentially identical to that of Falcon 9; the white knuckle part will be from liftoff through booster separation.
You can watch a live webcast of the launch attempt on the SpaceX Web site. Coverage usually starts around 20 minutes before the scheduled launch time.