SpaceX Falcon 9 in flawless Inmarsat-5 F4 launch

by William Graham

SpaceX conducted its sixth launch of the year Monday, with a Falcon 9 rocket deploying the Inmarsat-5 F4 communications satellite. Liftoff, from the Kennedy Space Center, was on schedule at the opening of a 51-minute launch window at 19:20 local time (23:20 UTC). The booster Рas planned Рdid not return for a landing due to the performance requirements of the heavy satellite.

Falcon 9 Launch:

Inmarsat-5 F4 is the last in a series of four high-power communications spacecraft which Inmarsat will use to support its Global Xpress mobile satellite broadband product.

Inmarsat was founded in 1979 as the International Maritime Satellite Organization, an intergovernmental partnership to provide satellite communications for maritime users. Privatized in 1999, Inmarsat is based in London and provides global broadband and communications services in addition to maintaining public service operations for maritime and aeronautical users.

The four Inmarsat-5 satellites were built by Boeing. Based around the BSS-702HP satellite bus, each carries eighty-nine Ka-band transponders and is designed for a service life of fifteen years. Envisioned as a three-satellite constellation, the first three satellites were ordered in 2010.

The first of these – Inmarsat-5 F1 – launched in December 2013 aboard a Proton-M/Briz-M rocket contracted by International Launch Services (ILS). Proton rockets were again used to launch the F2 and F3 satellites, which followed in February and August 2015 respectively.

The Inmarsat-5 F4 satellite was ordered in 2013 as a backup satellite, providing Inmarsat with a replacement should one of the other three be lost in a launch failure or alternatively serving as an on-orbit spare. In 2014 Inmarsat signed a contract with SpaceX to launch its EuropaSat spacecraft, along with options for the launches of Inmarsat-5 F4 and an Inmarsat-6 satellite.

While delays in the development of the Falcon Heavy have led to Inmarsat moving EuropaSat to an Ariane 5 rocket – with launch now scheduled for the end of June – they have come to an agreement with SpaceX to use a Falcon 9 instead of Falcon Heavy for the Inmarsat-5 F4 launch.

With a mass of 6,070 kilograms (13,380 pounds), Inmarsat-5 F4 is close to the Falcon 9’s maximum payload capacity to geosynchronous transfer orbit. To accommodate the satellite, SpaceX launched the Falcon 9 in its fully expendable configuration, foregoing an attempt to recover the first stage in order to maximize the mass it can deliver into orbit.

The rocket flew without the landing legs and grid fins that have become a common sight on SpaceX launches, with the first stage using all of its propellant to thrust its payload towards orbit.

The potential to use Falcon 9, instead of Falcon Heavy, for the Inmarsat launches was foreseen when the original contract was agreed in 2014. However, only upgrades to the Falcon 9 introduced at the end of 2015 brought Inmarsat-5 F4 within its capabilities.

This upgraded version of the Falcon 9, which has become known as the Falcon 9 Full Thrust or Falcon 9 v1.2, is the third major revision of the Falcon 9. In its original form – retrospectively known as the Falcon 9 v1.0, the Falcon 9 first flew in June 2010 carrying a mockup of the Dragon spacecraft – the Dragon Spacecraft Qualification Unit (DSQU).

From the sixth launch onwards the Falcon 9 v1.1 configuration introduced stretched first and second stages over its predecessor, with its engines upgraded from the Merlin-1C to Merlin-1D and the first stage engines rearranged from a square grid to an octagonal – or OctaWeb – arrangement.

The increased performance of the Falcon 9 v1.1 allowed SpaceX to start experimenting with propulsive landings, leading up to their first attempt to recover Falcon 9’s first stage, which was made during January 2015’s launch of a Dragon spacecraft on the CRS-5 mission. Although the first stage made it to its target landing platform – an Autonomous Spaceport Drone Ship (ASDS) barge deployed in the Atlantic Ocean – the rocket ran out of hydraulic fluid during its final descent and could not complete a controlled landing.

In June of the same year the Falcon 9 suffered its first – and to date only – launch failure, when a second stage pressure vessel broke loose, overpressurizing the stage’s oxidiser tank and leading to the disintegration of the rocket.

Returning to flight in December 2015, the Falcon 9 flew for the first time in the Full Thrust – or Falcon 9 v1.2 – configuration with uprated engines, a further stretched second stage and denser, supercold, liquid oxygen allowing a greater amount of oxidiser to be stored for the volume of the rocket’s tanks.

On its first launch, the Falcon 9 v1.2 achieved the first successful landing of a first stage, which returned to Cape Canaveral’s Landing Zone 1, the former Launch Complex 13. Subsequent launches saw more first stages recovered, both at sea and on land, and March’s successful deployment of the SES-10 satellite marked the first time a recovered first stage was re-launched.

With the v1.2 configuration, the Falcon 9’s first stage can be recovered on most launches – either by returning to the launch site on low orbit or low mass launches, or using the Autonomous Spaceport Drone Ships for recovery at sea for missions where additional performance is required – such as most geosynchronous launches.

Monday’s launch will be only the second time SpaceX will not attempt to recover the rocket’s first stage since the v1.2 was introduced, following March’s launch of EchoStar XXIII which – like Inmarsat-5 F4 – was too heavy to allow the rocket sufficient leftover performance to attempt a landing.

With the expendable first stage freeing up additional performance, Falcon 9 will be targeting a supersynchronous transfer orbit, with a higher apogee than a typical geosynchronous mission. This reduces the amount of its own fuel the satellite will need to burn in order to complete its insertion into a geostationary orbit above Earth’s equator.

The two-stage Falcon 9 took a little over half an hour to carry Inmarsat-5 F4 into orbit. Ahead of Monday’s launch, the rocket underwent a static fire test on Thursday before returning to its hangar for the payload to be installed. The vehicle was rolled back out to the launch pad on Sunday morning.

Monday’s launch took place from Launch Complex 39A (LC-39A) at the Kennedy Space Center, one of two SpaceX-operated launch pads on Florida’s Space Coast. The other pad, Cape Canaveral Air Force Station’s Space Launch Complex 40 (SLC-40) is currently out of action following last September’s explosion of a Falcon 9 during fuelling ahead of its static fire – days before the scheduled launch of the Amos 6 satellite which was destroyed in the accident.

SLC-40 is expected to return to service later this year, taking over launch operations as LC-39A is prepared for the debut launch of the Falcon Heavy.

Launch Complex 39A is part of the Kennedy Space Center’s historic Launch Complex 39, which was built in the 1960s for the Apollo program’s Saturn V rocket. Pad 39A was used for twelve of the Saturn V’s thirteen launches, including Apollo 8 and Apollo 11, and was the point of departure for every manned mission to land on the Moon. The final Saturn launch from LC-39A was the unmanned deployment of the Skylab space station in May 1973.

Following the end of the Apollo program, Launch Complex 39 was rebuilt for the Space Shuttle, which made its first flight from LC-39A in April 1981. Eighty-two of the Shuttle’s 135 missions lifted off from pad A, with the rest flying from nearby LC-39B. The Space Shuttle’s final flight, Atlantis’ STS-135 mission, lifted off from LC-39A in July 2011.

In 2014, SpaceX reached an agreement to lease pad 39A from NASA for a term of twenty years. Monday’s launch is the fifth time a Falcon 9 has flown from the launch pad, with all of these flights occurring in 2017.

Fuelling of the Falcon 9 began sixty minutes before the scheduled launch – 10 minutes later than advertised – with a poll approximately three minutes beforehand confirming that controllers were happy to proceed into propellant tanking. The RP-1 fuel was loaded first into the two stages of the rocket, with liquid oxygen – the oxidiser for both stages – beginning to flow into the vehicle around 45 minutes before liftoff.

In the final few minutes of the countdown, the rocket underwent final readiness checks and pre-launch operations. Seven minutes before the countdown reached zero, the first stage engines were chilled in preparation for ignition. Shortly afterwards the strongback – a structure used to transport the rocket to the launch pad, erect it and provide umbilical connections up until liftoff – rotated a few degrees away from Falcon 9.

The United States Air Force’s Range Control Officer (RCO) gave final launch approval on behalf of the Eastern Range at the two-minute mark in the countdown. SpaceX’s own Launch Director confirmed a final ‘go’ for launch half a minute later. In the final minute of the countdown onboard computers ran final checks over the vehicle, propellant tanks were brought up to flight pressures and the launch pad’s water deluge system was activated.

Three seconds before the end of the countdown, Falcon 9’s nine Merlin-1D first stage engines ignited. At the zero mark in the count Falcon was released to begin her climb towards orbit. Seventy-seven seconds after liftoff the rocket passed through the area of maximum dynamic pressure, or Max-Q.

The Falcon 9’s first stage, core 1034, burned for the first 165 seconds of Monday’s mission, providing the initial boost to carry Inmarsat-5 F4 out of the densest regions of Earth’s atmosphere. Four seconds after ending its burn, the spent stage separated. With no recovery planned for Monday’s launch, core 1034 continued on a ballistic trajectory, reentering and falling into the Atlantic Ocean.

The second stage ignited seven seconds after stage separation, beginning the first of two burns for its single vacuum-optimised Merlin-1D engine. This first burn lasted five minutes and 46 seconds, with the rocket’s payload fairing being jettisoned thirty-nine seconds into the burn.

At the end of the second stage’s first burn, the launch entered an eighteen-minute, twenty-one-second coast phase. The second burn, beginning at the end of the coast, saw the upper stage engine fire for another fifty-five seconds to reach a planned supersynchronous transfer orbit.

Inmarsat-5 F4 separated from the Falcon 9 three minutes and fifty-three seconds after the end of the second burn.

Monday’s launch was the second of the month for SpaceX, following the NROL-76 mission which flew successfully to low Earth orbit on 1 May. The next Falcon 9 launch is scheduled for 1 June, carrying the CRS-11 Dragon resupply mission for the International Space Station. Inmarsat’s next satellite, EuropaSat, is slated for launch aboard an Ariane 5 rocket on 28 June.

(Images via SpaceX and Inmarsat).

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