SpaceX's newest rocket, the Falcon Heavy [wikipedia.org], is set to be launched at around 1:30 PM EST (6:30 PM UTC) today. The launch window extends to 4:00 PM EST (9:00 PM UTC).
SpaceX will attempt to recover all three boosters during the launch [floridatoday.com]. The two previously-flown side boosters will attempt to land nearly simultaneously at Cape Canaveral Air Force Station's Landing Zones 1 and 2. The center core will attempt to land on a drone barge hundreds of miles off the coast of Florida.
The dummy payload for the Falcon Heavy is Elon Musk's personal 2008 Tesla Roadster [wikipedia.org]. It is carrying a mannequin wearing SpaceX's
space suit flight suit [soylentnews.org] that will be used when the company begins to send astronauts to the International Space Station. The car will be launched into a heliocentric orbit that will bring it close to Mars (and back near Earth) periodically [wikipedia.org], and is equipped with three cameras. Its stereo system will be playing David Bowie's Space Oddity [wikipedia.org].
If the launch is successful, the Falcon Heavy could be flown within the next 3 to 6 months for a customer such as the U.S. Air Force, Arabsat, Inmarsat, or ViaSat.
Falcon Heavy will be capable of launching 63,800 kg to low-Earth orbit (LEO), 26,700 kg to geosynchronous transfer orbit (GTO), 16,800 kg to Mars, or 3,500 kg to Pluto (New Horizons [wikipedia.org] was 478 kg). It will supplant the Delta IV Heavy [wikipedia.org], which is capable of launching 28,790 kg to LEO or 14,220 kg to GTO. Space Launch System [wikipedia.org] Block 1 will be capable of launching 70,000 kg to LEO (Block 1B: 105,000 kg to LEO, Block 2: 130,000 kg to LEO).
Musk has suggested that an additional two side boosters could be added [theverge.com] to Falcon Heavy (perpendicularly?) to make a "Falcon Super Heavy" with even more thrust. This may not happen if SpaceX decides to focus on the BFR [wikipedia.org] instead, which as planned would be able to launch 150,000 kg to LEO while being fully reusable and potentially cheaper than the Falcon 9 (or capable of launching 250,000 kg to LEO in expendable mode).