SpaceX’s Falcon Heavy rocket has conducted its second flight on Thursday, carrying its first customer payload – the Arabsat-6A communications satellite into space. Following a delay on Wednesday due to unacceptable Upper Level winds, Falcon Heavy lifted off from the Kennedy Space Center at the start of a one hour, 57-minute window that opened at 18:35 Eastern Time (22:35 UTC), taking a little over 34 minutes to deploy its payload into geosynchronous transfer orbit.
The launch came fourteen months after Falcon Heavy made its successful maiden flight, sending founder and CEO Elon Musk’s old Tesla Roadster car into an interplanetary trajectory in lieu of using a more traditional demonstration payload.
The Roadster launch proved the Falcon Heavy design in flight, demonstrating that the rocket could deliver more valuable payloads to orbit. Wednesday’s launch sees the rocket entrusted with an advanced telecommunications satellite for Saudi Arabian operator Arabsat.
Arabsat-6A was constructed by Lockheed Martin. It is built around the LM2100 satellite bus, a modernized version of the company’s successful A2100 platform. Arabsat announced that it had contracted Lockheed Martin to build the satellite in April 2015, along with a second satellite: HellasSat-4/SaudiGeoSat-1. HellasSat-4/SGS-1 was successfully deployed by an Ariane 5ECA rocket in February.
The Arabsat-6A satellite has a dry mass of 3,520 kilograms (7,980 pounds), but fully fuelled it weighs in at over 6,000 kg (13,200 lb). The satellite will operate in geostationary orbit, a particular class of orbit where the satellite takes exactly one day to complete a revolution, remaining in the same position relative to the ground. Arabsat-6A will be stationed at a longitude of 30.5 degrees East, where it will join and later replace the nine-year-old Arabsat 5A.
In 2015, SpaceX announced that Arabsat had awarded it a contract to launch Arabsat 6A, with the company’s Falcon Heavy rocket tapped to deliver the satellite to geosynchronous transfer orbit.
This elliptical orbit is the first leg of the satellite’s journey to geostationary orbit: Arabsat-6A will later use its own propulsion system for a series of orbit-raising maneuvers which will circularise the orbit, raising the perigee – the point closest to the Earth – until it is at the same altitude as the apogee – the point farthest from Earth.
Once it takes up its slot, the satellite is expected to operate for at least fifteen years.
From its position high above the Earth’s equator, Arabsat 6A will use a suite of Ku- and Ka-band transponders to support television and radio broadcasting, internet access and mobile telecommunications across the Middle East, Africa, and Southern Europe.
The satellite is also designed to support other frequency bands – likely replicating the S-band and X-band coverage that Arabsat 5A provides to Turkey and the Arabian Peninsula, and that satellite’s wide C-band footprint which stretches from Northern Europe to South Africa and Central Asia.
The 30.5-degree-East slot is core to Arabsat’s operations. It was first occupied by the company’s third satellite, Arabsat-1C, which launched in February 1992. Arabsat-1C was replaced with Arabsat-2B, which launched in late 1996, with the older satellite sold to ISRO the following year as a replacement for a failed Indian spacecraft. Arabsat-2B remained in service until Arabsat 5A relieved it in 2010.
This launch was the first mission that SpaceX has undertaken for Arabsat. The Falcon Heavy rocket that was used is the most powerful rocket currently flying worldwide, capable of delivering a 63,800 kilogram (141,000 lb) payload to low Earth orbit or 26,700 kilograms to geosynchronous transfer orbit.
Seventy meters (230 feet) in length, Falcon Heavy is a two-stage vehicle with two liquid-fuelled boosters strapped either side of the first stage to provide additional thrust. All of Falcon Heavy’s twenty-eight Merlin engines burn RP-1 propellant – rocket-grade kerosene – and liquid oxygen.
Falcon Heavy was developed from SpaceX’s Falcon 9 rocket, with the two additional boosters and a modified center core that has been reinforced to cope with the additional stresses it experiences as part of the Falcon Heavy stack.
The side boosters are essentially unmodified Falcon 9 first stages with aerodynamic nosecones – and SpaceX intends to use boosters interchangeably for Falcon 9 missions and Falcon Heavy – although the center core’s modifications mean that a dedicated pool of stages will need to be reserved for this specialized role.
Like Falcon 9, SpaceX has designed and engineered Falcon Heavy fore reusability. During the launch the two side boosters are expected to fly back to Cape Canaveral after separating from the rocket, making powered touchdowns at Landing Zones 1 and 2, to the south of Falcon Heavy’s launch pad.
Both side boosters have landed! pic.twitter.com/lRTMOg3nhO
— Chris Bergin – NSF (@NASASpaceflight) April 11, 2019
The rocket’s center core successfully landed aboard a floating platform – the Autonomous Spaceport Drone Ship (ASDS), Of Course I Still Love You – in the Atlantic Ocean. SpaceX also deployed boats into the Atlantic that will attempt to recover the payload fairing – the rocket’s nose cone – after it separated later in the ascent.
Having perfected landing and re-using Falcon’s first stage, recovery of the rocket’s payload fairing has become SpaceX’s next focus. The company has conducted a series of relatively low-key tests during operational missions, with attitude control thrusters and parachutes fitted to each part of the fairing to guide and slow its descent.
To minimize contamination from sea water, SpaceX plans to catch the fairing as it descends using a large net mounted on one of its ships. This part of the recovery process has not yet been accomplished with a fairing returning from space, although several attempts have come close. During the launch SpaceX intends to allow the fairing to land in the ocean and then recover it, rather than trying to catch it before splashdown.
SpaceX sees recovery and re-use of components as a way to reduce the cost of access to space, with expensive hardware able to support multiple missions instead of just one as with competing expendable launch vehicles (ELVs). That said, and despite the considerable success that SpaceX has enjoyed to date, recovering parts of the rocket is secondary for any launch – the primary objective is always to deliver the customer’s payload to its pre-designated orbit.
Although Falcon Heavy can fly with a previously-used first stage or boosters, the launch used an all-new vehicle. The center booster – or first stage – for this mission was numbered B1055, while the two side boosters were B1052 and B1053. Together these three cores deliver over 22,800 kilonewtons (5,130,000 pounds-force; 2,330,000 kilograms-force) of thrust at liftoff. Each core is powered by nine Merlin-1D engines, arranged in an octagonal or OctaWeb layout. A single Merlin powers the second stage.
This launch was the first time Falcon Heavy flew with Block 5 components – an upgrade which was introduced for the Falcon 9 last year a few months after the debut Heavy launch. Seen as the ultimate outcome of SpaceX’s previous incremental upgrades to the Falcon 9 design, Block 5 froze the rocket’s design and incorporated changes mandated by NASA so that the rocket could be human-rated.
Additional changes were made to the first stage boosters to ensure that each core could be re-flown multiple times – as previous-generation boosters were only able to fly twice before retirement or disposal.
Falcon Heavy lifted off from Launch Complex 39A (LC-39A) at NASA’s Kennedy Space Center on Florida’s Space Coast. Launch Complex 39 was built in the 1960s to support the Apollo program, with two launch pads and the iconic Vehicle Assembly Building (VAB). LC-39A was the primary launch pad for Apollo’s Lunar missions, with all but one of the crews who visited the Moon departing Earth from this pad. Only Apollo 10, which tested the Lunar Module in orbit around the Moon, flew from the backup pad at LC-39B.
The first rocket to launch from LC-39A was AS-501, the maiden flight of the Saturn V which carried the unmanned Apollo 4 mission into orbit in November 1967. The twelfth and final Saturn V launch from Pad 39A came in May 1973 when a modified two-stage version of the rocket deployed the first US space station, Skylab. Following the Skylab launch, LC-39A was taken out of service to begin preparations for the Space Shuttle program, while crewed missions to Skylab and the later Apollo-Soyuz mission flew from LC-39B.
After the end of the Apollo program, NASA adapted the former Saturn facilities at Complex 39 to service the Space Shuttle. LC-39A was converted first, with LC-39B undergoing modifications afterwards. Permanent Fixed and Rotating Service Structures (FSS and RSS) were constructed at each launch pad to provide access to the Shuttle – previously Saturn had used an umbilical tower built into the mobile launch platform, and a separate mobile service structure that was transported into position as required.
Space Shuttle Columbia made the first launch of the Space Shuttle program, STS-1, from LC-39A on 12 April 1981. Eighty-two of the Space Shuttle’s 135 missions began at LC-39A, with the other fifty-three launches taking place from LC-39B. The final Space Shuttle mission, STS-135, was flown from LC-39A by Atlantis in July 2011.
With the Space Shuttle retired, NASA and SpaceX signed a twenty-year lease agreement for LC-39A in 2014. SpaceX has modified the complex to suit their preferred method of assembling Falcon rockets – constructing a hangar at the base of the pad’s launch ramp so the rockets can be put together horizontally, rather than using the vertical integration atop a Mobile Launcher Platform (MLP) which NASA used for Saturn and the Shuttle.
The pad can support both Falcon 9 and Falcon Heavy rockets, with some reconfiguration work needed on the launch mount between launches of the two types of rocket.
SpaceX typically roll Falcon rockets out a few days before launch to perform a static fire test, starting up the first stage engines – including the boosters in the case of Falcon Heavy – to check that everything is working as expected. This test was conducted on Friday 5 April in preparation for this launch, after which Falcon Heavy was taken down and returned to its hangar for installation of the payload.
The Transporter/Erector (TE) or Strongback is used to move Falcon between its hangar and the launch pad, to raise the rocket to vertical and to provide umbilical connections to the vehicle prior to liftoff.
Booster mate inside SpaceX's hangar at LC-39A ahead of Falcon Heavy’s static fire yesterday pic.twitter.com/G7ZPhOBkyj
— SpaceX (@SpaceX) April 6, 2019
Fuelling of Falcon Heavy for this launch began fifty minutes ahead of its planned liftoff, when loading of RP-1 propellant into the three booster cores commenced. Liquid oxygen flowed into the first stage and booster oxidizer tanks five minutes later. The second stage fuel load began with propellant thirty-five minutes before launch, with oxidizer loading starting at the eighteen-and-a-half minute mark. With seven minutes to go, the Merlin-1D engines on all three boosters began chilldown in preparation for their startup.
About four minutes before launch the arms at the top of the Strongback opened and the structure rotated slightly away from Falcon Heavy. The Strongback remained angled at 88.5 degrees until Falcon lifts off, at which point it rapidly fell back to its fully-retracted position. The rocket transfered to internal power about 100 seconds before liftoff.
In the final ninety seconds of the countdown, Falcon Heavy entered self-alignment and the onboard computers conducted their final pre-launch checks of the vehicle. The rocket’s propellant tanks were pressurized, and with 45 seconds to go the Launch Director gave a final “go” for launch. Falcon Heavy’s ignition sequence began at T-2 seconds, with the twenty-seven Merlin-1D engines of three boosters roaring to life. At the zero mark in the countdown, Falcon Heavy lifted off to begin the deployment of Arabsat-6A.
After clearing the launch pad, Falcon maneuvered to an easterly trajectory out over the Atlantic Ocean. The rocket experienced maximum dynamic pressure (Max-Q) sixty-nine seconds after liftoff – this is the point in Falcon Heavy’s flight where it experiences the greatest aerodynamic forces, due to the combination of its increasing velocity and the decreasing density of the atmosphere that the rocket is passing through. Falcon Heavy reached Mach 1, the speed of sound, at around the same point in the flight.
Two and a half minutes after liftoff the two side boosters shut down. This event – designated booster engine cutoff (BECO) – was followed four seconds later by separation – with the two side boosters detaching from the center core and reorienting themselves for their recovery maneuvers. Seventeen seconds after separating the two side boosters performed near-simultaneous boostback burns, each firing three engines to change course and head back towards their launch site.
While the side boosters made their initial post-separation maneuvers, Falcon’s center core continued to power Arabsat-6A towards orbit. It burned for 61 seconds longer than the outboard cores, with main engine cutoff (MECO) occurring at three minutes and 31 seconds mission elapsed time. The first and second stages separated four seconds after MECO, with second stage ignition coming seven seconds after staging.
Because recovery of the center core was attempted at sea, it did not make a boostback burn. Instead, the Autonomous Spaceport Drone Ship (ASDS) – a converted barge that SpaceX use to recover Falcon 9 and Falcon Heavy boosters when mission requirements preclude a return to the launch site – was positioned along the booster’s anticipated trajectory.
Falcon Heavy’s second stage is powered by a single Merlin Vacuum (MVac) engine, a version of the Merlin-1D which is optimized to operate in the vacuum of space. This can make multiple burns to inject Falcon’s payloads into precise orbits – during the launch the Merlin Vacuum made two burns, with the first lasting five minutes and six seconds. Twenty-five seconds after second stage ignition, Falcon’s payload fairing separated from around Arabsat-6A at the nose of the rocket.
The fairing, which protects the satellite from Earth’s atmosphere during ascent and ensures the rocket has a clean aerodynamic profile, was no longer needed once Falcon reaches space and was discarded to reduce weight. The fairing separates into two halves – SpaceX has been conducting experiments to try and recover the payload fairing for future re-use, and it is expected that one or both halves of the fairing from the mission will descend under parachute into the Atlantic Ocean as part of these trials.
While Falcon’s second stage was making its first burn, all three cores re-entered Earth’s atmosphere. The cores deployed grid fins to help guide their descent, and each core restarted a subset of its engines for a short entry burn to limit heating as it passes back into the denser layers of the atmosphere. The side boosters began their entry burns at about six minutes and eleven seconds mission elapsed time, with the center core making its burn seven minutes into the flight.
Falcon’s side boosters landed about seven minutes and 51 seconds after liftoff, performing synchronized touchdowns at Landing Zone 1 (LZ-1) and Landing Zone 2 (LZ-2) of the Cape Canaveral Air Force Station. The landing zones, built on the site of the former Atlas-Agena launch pad at Launch Complex 13 (LC-13), allow the two cores to be recovered simultaneously. Each core restarts its center engine shortly before touchdown to slow itself to a gentle landing, with landing gear being deployed during the final stages of descent.
LANDED IT!! pic.twitter.com/TklpGEWd2I
— Chris Bergin – NSF (@NASASpaceflight) April 11, 2019
The first engine burn of Falcon’s second stage ended at eight minutes and 48 seconds mission elapsed time – a point in the flight designated SECO-1. One minute later the first stage center core made its landing aboard the drone ship, Of Course I Still Love You. This will follow a similar sequence to the side booster landings – with either a single-engine or three-engine burn slowing the stage to a graceful touchdown aboard the ship.
During last year’s Falcon Heavy test flight recovery of the center core was unsuccessful as the rocket only had sufficient igniter fluid to restart one engine for what was planned to be a three-engine burn.
This time, SpaceX recovered all three boosters from this launch. Recovery of the center core was particularly difficult because of its higher velocity.
The coast between the first and second burns of Falcon Heavy’s second stage lasted 23 minutes and 27 seconds, beginning with SECO-1 and ending with the MVac engine restarting for its second burn. This was a one-minute, 26-second firing that raised Arabsat-6A into geosynchronous transfer orbit. Five minutes and two seconds after SECO-2 – the end of the second burn – Arabsat-6A separated from Falcon Heavy to begin its own journey.
The launch was the fourth of the year for SpaceX, following three successful Falcon 9 missions including the launch of a Crew Dragon demonstration mission last month. The next SpaceX mission, using a Falcon 9 to deploy a cargo version of the Dragon spacecraft, is currently slated to fly no earlier than 26 April. The next Falcon Heavy launch is currently targeting a liftoff in June with a multi-satellite mission for the US Air Force’s Space Test Program.