SpaceX Falcon 9 launches with Intelsat 35e at the third attempt

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SpaceX successfully conducted the launch of an expendable Falcon 9 on Wednesday. In what was the third attempt to launch, the mission lofted the Intelsat 35e communications satellite from Florida’s 39A at the Kennedy Space Center at 19:38 Eastern. As pre-planned, the booster wasn’t recovered.

SpaceX Launch:

The launch was the tenth Falcon 9 mission of 2017 and the fourth to be flown in the last month – three of which have come in a two week period.

Unlike last weekend’s launches, which both saw Falcon’s first stage make successful landings aboard SpaceX’s Autonomous Spaceport Drone Ships (ASDS), this launch used the expendable version of the rocket.

This foregoes recovering the first stage in order to maximize the rocket’s performance for payload delivery. The removal of landing hardware – such as legs and grid fins – reduces the overall mass of the rocket, while the first stage can use up all of its fuel boosting Intelsat 35e towards orbit.

Intelsat 35e is a 6,761-kilogram (14,906 lb) communications satellite bound for geostationary orbit. Built by Boeing, Intelsat 35e is based on the BSS-702MP satellite bus, with an expected service life of at least fifteen years. A replacement for Intelsat 903, Intelsat 35e will be stationed over the Atlantic Ocean at a longitude of 34.5 degrees west.

The satellite carries high-bandwidth C- and Ku-band communications payloads, with equivalent capacity to 124 thirty-six-megahertz C-band transponders and 39 thirty-six-megahertz Ku-band transponders.

The C-band payload will provide telecommunications services to Europe, Central and Southern Africa, South America, the Caribbean and parts of North America, while the Ku-band transponders will be used for direct-to-home broadcasting to the Caribbean and support for mobile communications and government services in Europe and North Africa.

The spacecraft which Intelsat 35e will replace, Intelsat 903, was launched in February 2002 aboard a Proton-K rocket with a Blok DM3 upper stage – a commercial version of the Blok DM-2M. Intelsat 903 was the fourth of seven Intelsat-9 satellites. These spacecraft were manufactured by Space Systems/Loral, with a design life of thirteen years. Following its replacement by Intelsat 35e, the fifteen-year-old Intelsat 903 will be redeployed to a less critical slot in Intelsat’s constellation.

Intelsat was formed in 1964 as the International Telecommunications Satellite Organization, an intergovernmental organization tasked with operating a fleet of satellites to provide worldwide broadcasting and telecommunications services.

The organization’s first satellite, Intelsat I F-1, or Early Bird, was a 68-kilogram (150 lb) spacecraft built by Hughes for a design life of eighteen months. It was launched in April 1965 atop a Delta-D rocket from Cape Canaveral. Intelsat remained an intergovernmental organization until it was privatized in 2001.

Intelsat 35e is the fourth satellite to be launched as part of Intelsat’s next-generation EpicNG fleet, utilizing high-performance satellites to increase capacity. The first EpicNG satellite – Intelsat 29e – was launched in January 2016, Intelsat 33e launched in August 2016 and Intelsat 32e this February.

All three previous launches were conducted by Arianespace, using Ariane 5 ECA vehicles. Intelsat 32e is operated by Intelsat on behalf of DirecTV as SKY Brasil 1. The launch is the first that SpaceX has conducted for Intelsat.

The Intelsat launch marked the thirty-eighth flight of the Falcon 9 rocket, and the forty-third launch overall for SpaceX. A two-stage rocket, Falcon 9 first flew in June 2010 with a mockup of SpaceX’s Dragon spacecraft, the Dragon Spacecraft Qualification Unit.

The first five Falcon 9 launches used a configuration known retrospectively as the Falcon 9 v1.0. From the sixth flight – September 2013’s launch of Canada’s CASSIOPE satellite – an improved Falcon 9 v1.1 was used. A further enhanced version, the Falcon 9 v1.2, debuted in December 2015. SpaceX continues to make incremental upgrades to the rocket, progressing towards Block 4 and Block 5 versions of the rocket that will further improve performance and reduce the amount of work needed before a stage can be reflown.

The ability to recover and reuse the first stage is a unique feature of many of the Falcon 9’s missions. The rocket was designed to be partially reusable, with early flights attempting to achieve this by parachuting the first stage into the Atlantic Ocean.

When this proved unworkable, with no stages surviving descent, SpaceX switched instead to a propulsive recovery either via a floating platform – the Autonomous Spaceport Drone Ship (ASDS) – at sea, or by flying the first stage back to a landing pad at the launch site. To date, SpaceX has successfully recovered the first stage on thirteen Falcon 9 missions – five on land and eight at sea – including seven successful landings from seven attempts in 2017.

This mission, however, did not attempt to recover the first stage. The performance requirement to deliver the 6,761-kilogram (14,906 lb) Intelsat 35e spacecraft to geosynchronous transfer orbit meant that the first stage had to burn all of its propellant to push the satellite towards orbit, without reserving fuel to attempt a landing. Intelsat 35e is the heaviest satellite Falcon 9 to be carried on a geosynchronous mission to date.

Falcon 9 flew without landing gear or grid fins, with the spent first stage falling into the Atlantic at the end of her mission. The first stage used on this mission was Core 1037.

The launch used the new fast fuelling process that SpaceXhase devised. Following a poll around the sixty-three-minute mark in the countdown, loading of RP-1 propellant aboard the rocket began an hour before launch.

The oxidiser, liquid oxygen, was loaded from the thirty-five minute mark onwards. Since the introduction of the v1.2 configuration, Falcon 9 uses supercold liquid oxygen. This is denser than the liquid oxygen previously used, allowing a greater mass to be loaded relative to the size of the vehicle’s tanks.

On Sunday, the launch was held via a launch abort called by an issue with the GNC criteria. The attempt on Monday suffered a hold at the same point in the countdown. However, the second issue was not with the rocket but with ground computers.

There were no such issues on the next attempt, which proceeded to engine start up.

Three seconds before liftoff, Falcon’s nine first-stage Merlin-1D engines ignited. With no problems detected at startup, the rocket lifted off once the countdown reached zero. After clearing the launch pad, Falcon maneuvered to an easterly trajectory taking it out over the Atlantic Ocean. Seventy-eight seconds after liftoff the vehicle passed through Max-Q, the area of maximum dynamic pressure.

The first stage burned for the first two minutes and forty-two seconds of the flight, after which it reached main engine cutoff, or MECO. Shutting down its engines, the spent first stage was jettisoned four seconds later with second stage ignition occurring seven seconds after separation.

Falcon 9’s second stage is powered by a single Merlin-1D engine, optimised to operate in a vacuum. The second stage conducted two burns to deliver Intelsat 35e into geosynchronous transfer orbit – the first of which lasted five minutes and 44 seconds, placing the stage and its payload into an initial parking orbit.

Forty-six seconds into the first burn, the payload fairing separated from around Intelsat 35e at the nose of the rocket.

Following the end of the second stage’s first burn – an event designated SECO-1 – Falcon 9 coasted for seventeen minutes and 41 seconds. A second burn of fifty-two seconds’ duration then injected the payload into its planned transfer orbit. Spacecraft separation occurred four minutes and 51 seconds later. Intelsat 35e will use its own propulsion system – an IHI Corporation BT-4 apogee motor – to circularise its orbit before performing on-orbit testing and preparing for entry into service.

The tenth Falcon 9 launch of 2017, the launch comes just over a week after the rocket’s previous launch, a successful mission flown from Vandenberg Air Force Base in California to deliver ten Iridium communications satellites into low Earth orbit.

That launch was two days after a partially-reused Falcon 9 launched BulgariaSat-1 from the Kennedy Space Center (KSC). The initial launch window – based on the first attempt on Sunday – opened nine days, four hours and 26 minutes after the BulgariaSat launch – flying from the same launch pad at KSC’s Launch Complex 39A.

This would have been the shortest time between two launches from the Kennedy Space Center, surpassing the ten days and 19 and a half hours between the May 1973 launches of Skylab atop the last Saturn V from LC-39A and its first crew, aboard Skylab 2 atop a Saturn IB, from LC-39B. At the time of Skylab’s launch, Skylab 2 was scheduled to lift off the following day, however this was delayed after the space station sustained damage during its ascent to orbit.

The previous fastest turnaround for a single pad at KSC was a little over twenty-seven days, between the STS-51-D and STS-51-B missions flown by Space Shuttles Discovery and Challenger, from LC-39A in April 1985.

Pad 39A was built in the 1960s for the Apollo program, supporting the Saturn V rocket for twelve of its thirteen flights. It was the launch pad from which Apollo 8 launched to become the first manned mission to orbit the moon, and from where all six missions that landed men on the moon lifted off. The launch pad was later reused by the Space Shuttle, which flew eighty-two missions from the pad including its first and last launches.

The launch was the last before the US Air Force’s Eastern Range enters a three-week downtime period to conduct maintenance, during which time no rockets will be able to launch from either the Kennedy Space Center, nor the adjacent Cape Canaveral Air Force Station.

The range will return to operations in time to support a United Launch Alliance Atlas V mission, scheduled for 3 August, which will deploy NASA’s TDRS-M communications satellite. SpaceX has its next launch scheduled for 10 August, with a Falcon 9 carrying the CRS-12 Dragon spacecraft, a resupply flight to the International Space Station.

Intelsat 35e was the second satellite to be launched this year for Intelsat, following February’s launch of Intelsat 32e aboard an Ariane 5 ECA rocket. Another Ariane 5 will be used to launch Intelsat 37e at the end of August.

(Images: SpaceX, Intelsat and L2 SpaceX – including a large collection of photos from this launch campaign via Sam Sun and Brady Kennison for NASASpaceFlight.com)

(To join L2, click here: https://www.nasaspaceflight.com/l2/)

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