SpaceX kept up its impressive launch pace as the company reused its first Block 5 Falcon 9 booster in Tuesday’s launch of Merah Putih. Liftoff, from Space Launch Complex 40 at the Cape Canaveral Air Force Station, occurred at the opening of a two-hour window at 01:18 Eastern Time (05:18 UTC). This was the first Block 5 Falcon 9 to have been reflown and successfully landed on the drone ship to allow for an expected third flight.

Merah Putih, formerly known as Telkom 4, is a high-throughput C-band communications satellite that will be operated by Indonesia’s PT Telkom, or Telkom Indonesia. The satellite will restore communications capacity that were lost when the aging Telkom 1 satellite failed last August.

The Merah Putih satellite was constructed by Space Systems/Loral, based around the SSL-1300 platform. Equipped with sixty C-band transponders, the 5,800-kilogram (12,786 pound) spacecraft will provide communications services to Indonesia and India. Marah Putih will be located in geostationary orbit at Telkom 1’s old slot at 108 degrees East and is expected to provide at least fifteen years of service.

PT Telkom operates Indonesia’s largest fleet of communications satellites. Its fleet currently consists of the Telkom 2 and Telkom 3S satellites – launched in 2005 and 2017 respectively – the older Telkom 1 having failed unexpectedly last year. The company’s first satellite, Palapa A1, was launched aboard a Delta 2914 rocket in July 1976, with the identical Palapa A2 following it to orbit eight months later. Four second-generation Palapa B satellites were launched between 1983 and 1992 – the first, Palapa B1, was deployed from Space Shuttle Challenger during the STS-7 mission.

Palapa B2 is notable for having been launched twice. Following deployment from Space Shuttle Challenger during 1984’s STS-41B mission, the satellite’s Payload Assist Module D (PAM-D) kick motor failed to fire, leaving the spacecraft stranded in low Earth orbit. After deploying its own satellites, Space Shuttle Discovery collected Palapa B2 nine months later during STS-51A – along with the Westar 6 satellite that had also been deployed from STS-41B and suffered a kick motor failure. After refurbishment, Palapa B2 returned to orbit as Palapa B2R in April 1990, atop a Delta II 6925-8 rocket.

Palapa B3 – which was renamed Palapa B2P before launch – and Palapa B4 were both launched using expendable Delta rockets: Palapa B2P flying aboard a Delta 3920/PAM-D in Mach 1987 and Palapa B4 atop a Delta II 7925-8 in May 1992. Subsequent Palapa satellites would be operated by PT Indosat, following a reorganization of Indonesia’s state-owned telecommunications companies in the mid-1990s.

From the end of the 1990s, PT Telkom adopted the name Telkom for its satellites. Telkom 1 was launched on 12 August 1998 aboard an Ariane 4 rocket, which flew in the 42P H10-3 configuration. A replacement for Palapa B2R, which was designed to operate for fifteen years, Telkom 1 had just completed its eighteenth year in orbit when it stopped transmitting at the end of August last year. While PT Telkom initially announced that they were experiencing problems re-pointing one of the spacecraft’s communications antennae, it soon became clear to observers that the satellite had begun to disintegrate in orbit.

Once it became clear that they would not be able to return Telkom 1 to service, PT Telkom transferred customers to other satellites – including their own Telkom 2 and 3S and third-party spacecraft – which required customers to reorient their receiver antennae to point at the new satellites. Indonesia’s banking industry was particularly badly affected by the failure, which disrupted communications with thousands of ATMs across the country.

Merah Putih, which was to have replaced Telkom 1 even if it was still operational, will take over at Telkom 1’s position, fully restoring normal service and providing expanded capacity for the future.

Telkom 2 was launched in November 2005 aboard an Ariane 5ECA rocket, replacing the Palapa B4 satellite at 118 degrees East longitude. In August 2012 a second satellite – Telkom 3 – was launched to be co-located with Telkom 2, however the Proton-M/Briz-M rocket that was carrying the satellite left it, and Russia’s Ekspress-MD2 spacecraft, stranded in lower-than-planned orbits. An investigation found faults in both the third stage of the Proton – which did not affect the outcome of the mission – and in the Briz-M upper stage whose pressurization system had malfunctioned, causing an emergency shutdown a few seconds into the third of four planned burns.

A replacement for Telkom 3, Telkom 3S, was successfully launched by an Ariane 5 ECA in February 2017. After it entered service, Telkom 2 was relocated to 157 degrees East to support a partnership between PT Telkom and Intelsat – the satellite operating alongside the twenty-year-old Intelsat 5 spacecraft.

SpaceX undertook the launch of Merah Putih, using a Falcon 9 vehicle. The launch marked the first time a previously-flown, or “flight-proven” Block 5 first stage has been used.

The Block 5 version of Falcon 9, designed to meet NASA’s requirements for human-rating the vehicle while also providing for rapid and repeated reuse of the first stage booster without major refurbishment, first flew in May with the successful launch of Bangladesh’s Bangabandhu-1 satellite.

Merah Putih is set to lift off tomorrow morning at 1:18am Eastern with a window extending to 3:18am Eastern. This flight will be the first reflight of the Block 5 Falcon 9 booster B1046 that originally flew Bangabandhu-1 back in May. pic.twitter.com/fn3S9aZKTl — Brady Kenniston (@TheFavoritist) August 6, 2018

Block 5 replaces earlier Block 3 and Block 4 versions of the Falcon 9, also unofficially known collectively as Falcon 9 Full Thrust or Falcon 9 v1.2.

Falcon 9 is the only rocket currently flying that re-uses stages from previous missions for subsequent launches.

Where mission requirements allow, and the first stage has not reached the end of its useful life, a series of engine burns are made after the stage separates from the rest of the rocket, guiding it to a powered landing either at a land-based Landing Zone, or at sea aboard an Autonomous Spaceport Drone Ship (ASDS) – a converted barge that is towed out into the Atlantic or Pacific Ocean to provide a landing platform for stages that do not have enough fuel to make it back to land.

The Falcon 9 is a two-stage rocket, with the rocket’s payload sitting atop the rocket’s second stage enclosed within a payload fairing (except for SpaceX’s own Dragon spacecraft, which does not use a fairing). Currently only the rocket’s first stage is reusable. However, SpaceX is actively working on recovering the payload fairing for future reuse and has expressed an interest in making the second stage reusable going forwards.

The first stage used for the Merah Putih launch was Core 1046 (B1046.2), the same booster that was used for the Bangabandhu mission. After playing its role in that mission, Core 1046 performed a successful landing aboard the drone ship Of Course I Still Love You in the Atlantic Ocean, downrange from Cape Canaveral. Following Tuesday’s launch, the booster will again attempt to land on Of Course I Still Love You.

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Tuesday’s launch was the sixtieth flight of SpaceX’s Falcon 9 vehicle, not including February’s launch of the closely-related Falcon Heavy rocket. This number also excludes the attempt to launch Israel’s Amos 6 satellite in September 2016 – which saw the Falcon 9 explode during fuelling ahead of a static fire test a few days before the planned launch, with the loss of rocket and payload – and thirteen atmospheric test flights with the Grasshopper and Falcon 9R Dev-1 development vehicles which were used to practise landing before the first successful attempt at first-stage recovery.

Falcon 9 first flew in June 2010, with initial versions of the rocket – now retrospectively known as Falcon 9 v1.0, although this name was not used when the rocket was in service – having its nine first stage Merlin 1C engines arranged in a square grid. From the sixth flight onwards, this was replaced with the stretched Falcon 9 v1.1, which also incorporated Merlin-1D engines arranged in the now-familiar octagonal, or OctaWeb, layout. A further upgrade, Falcon 9 Full Thrust – more commonly but unofficially known as Falcon 9 v1.2 – was introduced in December 2015 and achieved the first successful first stage recovery on its maiden flight. This further stretched the rocket’s second stage, uprated the first stage engines and began the use of subcooled liquid oxygen – which is stored more densely at cooler temperatures, allowing the rocket to carry a greater mass of oxidizer. The subsequent Block 4 and Block 5 vehicles have been incremental enhancements on the Full Thrust design.

From its fifty-nine launches to date, Falcon 9 has achieved complete success on fifty-seven missions. One early launch suffered an engine failure during first stage flight, which resulted in the rocket being able to deploy its primary payload, a Dragon resupply mission to the International Space Station, but not an Orbcomm communications satellite that was also aboard the rocket. Falcon 9’s only outright launch failure came in June 2015 when a second stage helium tank support broke loose, venting helium into the second stage oxidizer tank which caused the tank to rupture – destroying the vehicle. The failure resulted in the loss of a Dragon spacecraft that had been flying the CRS-7 mission to the International Space Station.

For Tuesday’s mission, Falcon 9 will fly from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Air Force Station.

SLC-40 is one of two East Coast launch pads used by SpaceX for Falcon 9 operations – alongside Launch Complex 39A (LC-39A) at the nearby Kennedy Space Center. Falcon 9 can also fly from Space Launch Complex 4E (SLC-4E) at Vandenberg Air Force Base in California, on the West Coast of the United States.

SLC-40 was the first launch pad to be built for Falcon 9 – constructed on the site of a former Titan III and IV launch complex dating back to the 1960s. Originally constructed as part of the Titan IIIC’s Integrate-Transfer-Launch (ITL) complex – alongside nearby Launch Complex 41 and a Vertical Integration Building – Launch Complex 40 entered service in June 1965 with the maiden flight of the Titan IIIC. A total of 55 Titan launches were made from Launch Complex 40 between 1965 and 2005 – with the launch pad being redesignated Space Launch Complex 40 in 1997.

Tuesday’s launch marks the thirty-sixth Falcon 9 mission from SLC-40 and the ninety-second launch from the pad overall – a number that also includes an atmospheric test of the launch abort system for SpaceX’s Dragon spacecraft in May 2015.

Falcon 9 vehicles are prepared for launch horizontally in a hangar that SpaceX constructed close to the launch pad. Following integration of the first and second stages, the rocket was brought to the pad for a static fire test, igniting the first stage engines in a brief burn to confirm they were ready for flight. This was conducted successfully last Thursday, with the rocket returning to its hangar for mating with its payload. SpaceX uses a transporter-erector, known as the Strongback, to transport Falcon 9 between its hangar and launch pad. The Strongback provides umbilical connections to the vehicle and is used to rotate the rocket between the horizontal and vertical positions.

Both the first and second stages of the Falcon 9 rocket burn RP-1 fuel – a refined petroleum product commonly known as rocket-grade kerosene – while liquid oxygen (LOX) is used as an oxidizer. Ahead of Tuesday’s launch, the launch director will poll flight controllers for a “go” to proceed with fuelling of the rocket about 38 minutes before the planned liftoff. Loading of RP-1 into both stages of the rocket and of liquid oxygen into the first stage will begin at the T-35 minute mark in the countdown. Second stage oxidizer loading will begin sixteen minutes before liftoff. Once the oxidizer tanks are full, they will continue to be topped off until the final minutes of the countdown to replace oxygen that boils off and is vented from the tanks.

Chilldown of the first stage engines will begin seven minutes before liftoff, preparing the fuel lines and engines for the cryogenic temperatures of the liquid oxygen. About four and a quarter minutes before liftoff the arms holding Falcon 9 to the Strongback will be opened, with the Strongback rotating away from the rocket about half a minute later. Initially, the Strongback is only retracted a few degrees – it then falls away from the rocket to its fully-retracted position at liftoff.

The final minute of the countdown will see the rocket’s propellant tanks brought up to flight pressure, the launch pad water deluge system activated, the flight termination system armed and the onboard computer conducting final pre-launch checks. The launch director will give the final “go” for launch at the 45-second mark.

About three seconds before liftoff, the nine Merlin-1D engines on the first stage will begin their ignition sequence, building up thrust for a liftoff at T-0. The rocket will take a few seconds to clear the launch pad’s lightning towers, after which it will begin pitching downrange. Flying to the East, out over the Atlantic Ocean, Falcon will pass through the sound barrier about one minute after launch, before reaching Max-Q – the period of maximum dynamic pressure – about 79 seconds into flight.

Falcon 9’s first stage will power the ascent for the first two minutes and thirty seconds of flight. Once the first stage engines have shut down, the two stages will separate and the second stage will ignite its engine to continue Merah Putih’s powered ascent to orbit. These events will occur in quick succession, with stage separation coming four seconds after first stage main engine cutoff (MECO), and the second stage igniting two seconds after staging.

The second stage of Falcon 9 is powered by a single Merlin Vacuum (MVac) engine, a modified Merlin-1D optimized to give its peak performance in the vacuum of space. This engine will make two burns to inject Merah Putih into geostationary transfer orbit. The first of these will shut down at T+8:06, establishing an initial parking orbit. It is during this burn that Falcon’s payload fairing will separate, exposing the satellite to space for the first time.

The fairing will fall back to Earth, but may deploy parachutes to gather data and help SpaceX practice for future fairing recovery operations. SpaceX does not yet have a fairing recovery boat on the East Coast, so the company will not be able to catch the fairing before it hits the water, but they may be able to achieve a controlled ocean landing and subsequently fish the payload fairing out of the water. Due to contamination from the salt water, SpaceX needs to intercept the fairing before splashdown in order to make reuse practical.

While the second stage is powering Merah Putih towards orbit, the first stage will make a series of maneuvers as it attempts to return to Earth. After reorienting itself, the stage will deploy grid fins to help stabilize its descent before making an entry burn about six minutes and 13 seconds after liftoff: using a subset of its engines to slow down as it passes back into Earth’s atmosphere. By reducing the speed of reentry, heating of the vehicle is reduced improving its chances of surviving the process.

Once the engines shut down again, the stage will fall through the atmosphere towards the waiting drone ship, with a landing burn beginning shortly before the planned touchdown at eight minutes, eight seconds mission elapsed time.

Falcon 9 B1046.2 LANDS on OCISLY – and is now set to be the first booster to gain a .3! pic.twitter.com/4FqlC5weWy — Chris B – NSF (@NASASpaceflight) August 7, 2018

Tuesday’s launch marked the first time SpaceX has attempted to recover a previously-flown core since the Falcon Heavy demonstration flight when the two flight-proven side boosters made near-simultaneous touchdowns on landing pads at Cape Canaveral.

Core 1046 is the first Block 5 core to make multiple flights, and SpaceX has chosen not to recover earlier versions of the booster on recent launches as these cannot fly more than twice, and are of little further value to the company. In contrast, Block 5 vehicles are expected to be able to fly up to ten times without major refurbishment, and many more times after an overhaul.

Recovering the first stage – while intended to increase Falcon’s flight rate and decrease the cost of launches – is a secondary objective to getting Merah Putih into orbit. The second stage concluded its first burn at around the same time the first stage landed, entering a coast phase. The coast lasted around eighteen minutes, after which the second stage made a 58 second burn. This injected the payload into its planned geostationary transfer orbit, with spacecraft separation occurring just under five minutes after the second burn is complete.

After being deployed into an elliptical geostationary transfer orbit, Merah Putih will make several burns with its own apogee motor over the coming days to raise itself to geostationary orbit. Following commissioning and checkout, the satellite will become operational at a longitude of 108 degrees East over the equator.

Tuesday’s launch was SpaceX’s fifteenth mission of 2018, including the Falcon Heavy demonstration. The Merah Putih launch comes less than two weeks after Falcon 9’s previous mission, which successfully deployed ten Iridium-NEXT satellites after lifting off from California’s Vandenberg Air Force Base. Falcon’s next launch is currently expected to be another East Coast mission with the Telstar 18V communications satellite, slated for no earlier than (NET) 18 August.

Before then, a United Launch Alliance Delta IV Heavy will deploy NASA’s Parker Solar Probe mission to study the Sun.