Just an hour before Florida sunset, SpaceX’s gigantic Falcon Heavy—lauded by the Hawthorne, Calif.-headquartered launch services provider as the world’s most powerful active rocket, by a factor of two—successfully roared aloft tonight (Thursday, 11 April) from Pad 39A at the Kennedy Space Center (KSC) for its long-awaited first commercial mission. Fourteen months after a triumphant test flight, which boosted SpaceX CEO Elon Musk’s cherry-red Tesla Roadster onto a Mars-crossing heliocentric trajectory, the triple-cored booster got down to business by delivering the 14,320-pound (6,495 kg) Arabsat 6A communications satellite to orbit on behalf of Riyadh-headquartered Arabsat and King Abdulaziz City for Science and Technology (KACST).
Under the combined thrust of 5.1 million pounds (2.3 million kg), the Falcon Heavy performed with perfection during first-stage flight, before the side boosters plunged back to Earth and alighted smoothly like a pair of synchronized ballet dancers at Landing Zones (LZ)-1 and 2 at the Cape. Meanwhile, despite “challenging” conditions at sea, the core booster successfully touched down on the Autonomous Spaceport Drone Ship (ASDS) in the Atlantic Ocean, completing an objective left unfulfilled during last year’s Falcon Heavy test flight. All three boosters were previously unflown, although the side rockets are expected to be reused on the Falcon Heavy’s next mission in the summer.
As outlined in AmericaSpace’s Arabsat 6A preview, the mighty rocket was moved out of the Horizontal Integration Facility (HIF) to historic Pad 39A in the small hours of 4 April and successfully completed a customary Static Fire Test of its 27 Merlin 1D+ engines the following day. By this point, the targeted launch date had slipped from the 7th to no sooner than the 9th, although weather conditions were predicted to be only 30-percent-favorable and SpaceX later reported a slip to the 10th, in order to benefit from an improved meteorological outlook. In Twitter comments provided shortly after the static fire, Mr. Musk also explained that the Falcon Heavy for Arabsat 6A boasted three uprated Block 5 cores and would achieve a 10-percent increase in thrust over the February 2018 test flight. In subsequent tweets, he stressed that the possibility of failure lay in the range of 5-10 percent, but explained that many “good design improvements” had been implemented since last year’s test flight, but cautioned that they remained “unproven”.
Weather conditions for Wednesday’s opening launch attempt and Thursday’s backup opportunity both promised to be exceptionally favorable, with an 80-percent probability and 90-percent probability, respectively, of acceptable conditions. “A deep low-pressure center over the panhandle with an associated cold front will shift eastward today, bringing showers and thunderstorms into Central Florida,” cautioned the 45th Weather Squadron at Patrick Air Force Base in its L-1 briefing on Tuesday morning. “The unsettled weather will mainly occur midday into the early evening hours. On Wednesday, the low moves into the Atlantic with some residual moisture wrapping around it into central Florida with isolated showers possible through sunset.” It was noted that the primary weather concern for an on-time Wednesday launch was violation of the Cumulus Cloud Rule associated with this moisture.
Wednesday’s launch window opened at 6:35 p.m. EDT and closed at 8:32 p.m. Overnight, the Falcon Heavy—its center core this time capped-off by its bulbous payload fairing, housing Arabsat 6A, and boasting additional heat-shielding at its tip—was returned to Pad 39A and as dawn broke over Florida was elevated vertical. However, in an update late in the afternoon SpaceX announced that it was aiming for T-0 at 8 p.m., close to the end of the launch window, as it kept a wary eye on upper-level wind conditions.
This was subsequently moved to 8:32 p.m., right at the very end of the window, raising the very real probability that Wednesday’s attempt would be scrubbed. “Upper atmospheric wind-shear is very high,” tweeted Mr. Musk at 6:48 p.m. “Will have to postpone launch unless weather improves soon.” Alas, the weather did not improve and at 7:25 p.m. SpaceX declared a scrub and 24-hour turnaround. The backup launch date of Thursday promised an improved weather outlook, with a 90-percent probability of acceptable conditions, and a similar window length running from 6:35 p.m. through 8:31 p.m.
“Overnight, weather will remain benign with virtually clear skies and light onshore winds,” the 45th Weather Squadron noted in a post-scrub update at 8:15 p.m. Wednesday. “On Thursday, winds will become southeasterly as high pressure builds into the Spaceport, continuing the atmospheric drying.”
Loading of the Falcon Heavy first-stage with liquid oxygen and a highly refined form of rocket-grade kerosene, known as “RP-1”, commenced a little under an hour before Wednesday’s scheduled T-0. With 35 minutes to go, the loading of RP-1 into the second stage tanks got underway, followed by the onset of second-stage liquid oxygen tanking at T-18 minutes. Entering the final minutes of the countdown, the Falcon Heavy proceeded smartly through pre-launch engine chilldown and at T-90 seconds the flight computer was commanded to execute its final checks. At one minute, the giant rocket’s propellant tanks were declared fully pressurized for flight and shortly thereafter the SpaceX Launch Director announced a clipped “Go for Launch”.
Ignition of the two Block 5 side boosters—designated “B1052” and “B1053” and both making their first flights—occurred at T-2 seconds, followed by the ignition of the brand-new core, B1055, a fraction of a second thereafter. Pummeling the Pad 39A surface with an estimated 5.1 million pounds (2.3 million kg) of thrust, the second Falcon Heavy soared smoothly into a crystal-clear Florida sky at precisely 6:35 p.m. EDT.
A minute into ascent, the stack passed “Max Q”, the period of maximum aerodynamic turbulence on its flight surfaces. The side boosters shut down, as planned, at 2.5 minutes and separated, commencing an intricate “boost-back” sequence which saw them alight smoothly and in tandem on LZ-1 and 2 at the Cape. The time was 6:43 p.m. EDT, only seven minutes and 50 seconds after liftoff. Meanwhile, the core continued to burn for another minute, before it too shut down and separated to begin its much faster, higher-energy descent towards the Autonomous Spaceport Drone Ship (ASDS)—dubbed “Of Course I Still Love You”—positioned about 600 miles (960 km) offshore.
As if on cue, the video feed from the deck of the ASDS cut out at the last moment, almost if it knew the core booster was on its way and wanted to agonize its spellbound audience still further. But within seconds came confirmation that, for the first time, a Falcon Heavy launch had successfully achieved three smooth and intact first-stage booster landings. By the time the core’s landing legs touched the deck of the drone ship, less than ten adrenaline-fueled minutes had passed since liftoff.
Elsewhere, with the side boosters and the first stage of the core gone, the Falcon Heavy’s second stage picked up the baton to deliver Arabsat 6A to orbit. And from this point onward, its flight profile closely mirrored an “ordinary” mission by an Upgraded Falcon 9, with the single Merlin 1D+ Vacuum engine roaring silently into the void, followed by separation of the bulbous payload fairing at four minutes into the flight.
The initial burn ran for about five minutes, before the second stage fell silent and coasted for a quarter-hour, ahead of its second firing, just 85 seconds in length. This served to position Arabsat 6A for deployment into a high-apogee Geostationary Transfer Orbit (GTO), at 34 minutes into flight.