SpaceX took a step into the future Thursday as it reused – for the first time – a recovered first stage of a previously-flown Falcon 9 rocket. Thursday’s mission, carrying the SES-10 communications satellite, lifted off from Pad 39A at Florida’s Kennedy Space Center at 18:27 local time (22:27 UTC) and once again landed the booster.
Thursday’s mission made use Falcon 9 the second orbit-capable rocket – after the Space Shuttle – to achieve partial reusability. The Falcon 9 flew from Launch Complex 39A at the Kennedy Space Center, the same pad from which the Shuttle began eighty-two of its missions, including its first and final flights.
Reusability has long been a key objective for SpaceX. Making the company’s first launch in March 2006, the small Falcon 1 vehicle carried a parachute system intended to bring its spent first stage back to Earth.
SpaceX attempted to recover the first stages of four Falcon 1 vehicles. However, the rocket’s first launch failed early in the mission and its third launch failed at stage separation, leaving the first stage unrecoverable. During the second and fourth launches, recovery attempts were unsuccessful.
Following three failures, SpaceX achieved its first successful launch in September 2008, with the fourth Falcon 1 successfully placing the demonstration payload RatSat into low Earth orbit. The rocket made its fifth and final flight in July 2009, successfully placing Malaysia’s RazakSAT satellite into orbit. For the RazakSAT launch, the Falcon flew without a recovery system.
SpaceX originally planned a family of Falcon rockets, with the smaller single Falcon 1, a five-engine Falcon 5 and a nine-engine Falcon 9. Two heavier vehicles, the Falcon 9S5 and 9S9, would have used two additional cores strapped to the first stage, with the 9S5 using Falcon 5 cores and the 9S9 Falcon 9 cores.
The Falcon 5 was abandoned before it ever flew, while the Falcon Heavy vehicle which SpaceX intends to introduce later this year is an evolution of the Falcon 9S9 concept. The Falcon 9 made its first flight in June 2010 with a mockup of SpaceX’s Dragon spacecraft, the Dragon Spacecraft Qualification Unit.
The first five Falcon 9 launches used a version of the rocket which has retrospectively become known as the Falcon 9 v1.0. Following the rocket’s original design the first stage was powered by nine Merlin-1C engines arranged in a square three-by-three grid. The second stage used a single Merlin Vacuum engine, derived from the Merlin-1C. Both stages of the two-stage vehicle are fuelled by RP-1 kerosene propellant, oxidized by liquid oxygen.
Following its maiden flight, the Falcon 9 v1.0 made four more launches, all carrying Dragon spacecraft. The first of these launches, in December 2010, carried Dragon C1. Dragon’s maiden flight, C1 completed two revolutions around the Earth before the capsule reentered the atmosphere and splashed down in the Pacific Ocean.
The final three launches of the original Falcon 9 carried Dragon missions to the International Space Station; the first the Dragon C2+ COTS demonstration mission, followed by the first two operational flights under the Commercial Resupply Services (CRS) program.
The earliest Falcon 9 launches carried parachutes which were to have been used to recover the first stage. However, this was abandoned due to the stage disintegrating during reentry, before the parachutes could be deployed. Instead, SpaceX began to investigate using the stage’s engines to make a powered descent and landing. Alongside this, an improved Falcon 9 vehicle, the Falcon 9 v1.1, was developed.
To help with the reusability development program, SpaceX constructed a test vehicle – Grasshopper – a single-engine Falcon 9 v1.0 first stage with fixed landing gear. In 2012 and 2013 Grasshopper made a series of test flights from SpaceX’s facility at McGregor, Texas.
After eight successful low-altitude flights, Grasshopper was replaced with a new three-engine development vehicle using the stretched first stage of the Falcon 9 v1.1. This new test vehicle introduced the retractable landing legs and later grid fins that would fly with operational Falcon 9 rockets, making four successful flights in 2014 before a sensor issue led to its failure during the fifth mission.
The Falcon 9 v1.1 itself first flew in September 2013, delivering a cluster of payloads including Canada’s CASSIOPE satellite into orbit. The Falcon 9 v1.1 stretched both the first and second stages of the rocket and upgraded from Merlin 1C to Merlin 1D engines.
The first stage engines were rearranged into the octagonal – or OctaWeb – configuration that is now familiar. The upgrades increased the rocket’s payload capacity, giving it sufficient margin on some missions for powered recovery tests following first stage separation.
The first few Falcon 9 v1.1 launches tested restarting the first stage engines after separation, attempting to achieve a controlled descent into the ocean. The rocket first flew with legs in April 2014, and grid fins to provide additional control were added ahead of January 2015’s launch of the CRS-5 Dragon mission.
During the CRS-5 launch, SpaceX deployed its first Autonomous Spaceport Drone Ship (ASDS) – Just Read the Instructions – into the Atlantic Ocean to provide the returning stage with a landing platform. A converted barge, the ASDS was positioned downrange and left unmanned for the landing attempt. Although the first stage reached the drone ship, it depleted its hydraulic fluid during descent resulting in a hard and uncontrolled landing and explosion.
The next Dragon launch, CRS-6, made another landing attempt using Just Read the Instructions three months later. The stage toppled over on touchdown, before again exploding.
The final mission for which Just Read the Instructions was deployed was the CRS-7 launch in June 2015. Towards the end of first stage flight, a composite-overwrapped pressure vessel (COPV) broke loose inside the second stage oxidizer tank. The tank overpressurised, resulting in structural failure and the disintegration of the Falcon.
Just Read the Instructions was subsequently converted back to a regular barge; however her name was reused for a new drone ship commissioned for launches out of Vandenberg Air Force Base. A replacement East Coast ASDS was also introduced, named Of Course I Still Love You. The two vessels are named after ships in the works of science fiction author Iain M. Banks.
When Falcon returned to flight after the CRS-7 failure, it was in a new configuration which has become known informally as the Falcon 9 v1.2 or Falcon 9 Full Thrust.
This version of the Falcon 9 has uprated engines and uses supercold liquid oxygen to increase oxidizer density, allowing a greater mass to be carried relative to the volume of its tanks. The second stage was further stretched compared to the Falcon 9 v1.1.
The Full Thrust configuration’s improved performance allows for recovery attempts on a greater range of missions, including geosynchronous launches such as Thursday’s. On missions that do not require the rocket’s full performance the first stage can now return to the launch site for a touchdown on dry land.
In December 2015, the first flight of the Falcon 9 v1.2 carried eleven Orbcomm communications satellites into low Earth orbit, with the first stage making its first attempt to fly back to Cape Canaveral.
A landing pad – Landing Zone 1 (LZ-1) – was constructed on the site of Launch Complex 13, a former Atlas launch pad which was used between 1958 and 1978. While the second stage continued to orbit, successfully deploying its payload, the first stage achieved a flawless landing at Landing Zone 1 marking the first time SpaceX had successfully brought the stage back to Earth.
The Falcon 9 v1.1 made its final flight in January 2016 with an unsuccessful attempt to land on the new Just Read the Instructions after lifting off from Vandenberg Air Force Base with the Jason 3 satellite.
One of the first stage’s legs failed to lock into position and the stage toppled over on landing. In March 2016 SpaceX made its first recovery attempt with Of Course I Still Love You, during the launch of the SES-9 satellite. The first attempt to recover the first stage from a geosynchronous mission, the first stage returned to the drone ship but did not have sufficient fuel remaining to achieve a survivable landing.
The next launch, the CRS-8 Dragon mission, achieved the first successful landing at sea.
Launched on 8 April 2016, the twenty-third flight of the Falcon 9 and the third of the v1.2 configuration lifted off from Space Launch Complex 40 at the Cape Canaveral Air Force Station to send Dragon on its way to the International Space Station.
After propelling the Falcon 9 for the first two and a half minutes of her mission the first stage – Core 1021 – separated. Six minutes later, following boostback, reentry and landing burns, the stage touched down atop the drone ship. A year later, following refurbishment and testing, the same first stage was ready to fly again.
For Thursday’s launch Core 1021 was joined by a new second stage, as this part of the rocket is still expendable. In the time that has passed since its previous launch, Falcon 9 has completed eight successful launches and recovered six first stages from seven attempts.
Although all of its launches in the last year have been successful, a Falcon 9 exploded during fuelling ahead of a static fire test in September. The explosion destroyed the Amos 6 satellite which had already been mated to the rocket ready for launch and damaged the launch pad at Space Launch Complex 40 (SLC-40).
An investigation determined the cause of the anomaly to be the structural failure of a second stage COPV caused by the build-up and solidification of oxygen bubbles between the outer casing and inner lining of the pressure vessel. Falcon returned to flight in January with the deployment of ten Iridium satellites from Vandenberg. East coast launches have switched to the Kennedy Space Center and Launch Complex 39A (LC-39A) while SLC-40 is repaired.
Built in the 1960s to support the Apollo program, LC-39A is one of two original pads at Launch Complex 39. It was the site of twelve of the Saturn V rocket’s thirteen launches, including all of the missions which landed astronauts on the Moon.
The final Saturn launch from the pad placed America’s first space station, Skylab, into orbit. The complex’s second pad, LC-39B, was used for the launch of Apollo 10 atop a Saturn V and four low Earth orbit flights with the Saturn IB rocket and Apollo spacecraft – three visits to Skylab and the Apollo-Soyuz mission.
After Apollo, Complex 39 was converted for the Space Shuttle. Columbia made her maiden flight from LC-39A in April 1981. Eighty-two of the 135 Space Shuttle missions were launched from pad A, with the remainder flying from LC-39B. The Shuttle’s final flight, Atlantis’ STS-135, lifted off from Launch Complex 39A on 8 July 2011.
Prior to Thursday’s mission, the Space Shuttle was the only orbital launch system to achieve partial reusability. The five Space Shuttle orbiters were designed to glide back to Earth at the end of their missions – landing on runways at the Kennedy Space Center’s Shuttle Landing Facility, Edwards Air Force Base and the White Sands Space Harbor – before being refurbished and relaunched.
During their careers, Discovery, Atlantis and Endeavour completed thirty-nine, thirty-three and twenty-five missions into low-Earth orbit respectively. Challenger was lost, along with her crew, during launch of her tenth mission – and the twenty-fifth of the Space Shuttle program – STS-51-L, on 28 January 1986. Columbia broke apart during reentry at the end of her twenty-eighth mission, STS-107, on 1 February 2003 claiming the lives of her seven astronauts.
As well as the orbiters, the Space Shuttle’s twin solid rocket boosters were recovered and reused following their separation during the Shuttle’s ascent to orbit. The boosters were recovered successfully after all of the Shuttle’s launches except STS-3 and STS-51-L. The Shuttle stack’s large external tank was not recovered.
Parts of other rockets have been recovered from time to time; Arianespace has occasionally fitted parachutes to Ariane 5 boosters and recovered the casings from the Atlantic Ocean. However, this is for research and the boosters are not refurbished or reused.
The Soviet Union developed Buran, a spaceplane similar in design to the Space Shuttle and launched by the Energia rocket. Although Buran itself was recovered, Energia was expendable and the program was canceled for political reasons before Buran could fly again.
The preparations for SES-10 were impressive, coming so soon after the previous launch. Following the successful Static Fire test, the rocket and payload underwent an integration that allowed for rollout to occur overnight ahead of Thursday’s launch.
With a multi-hour pad flow that included testing the satellite, the key countdown events began over one hour ahead of T-0, with readiness polling for fuel loading.
RP-1 loading was followed by LOX loading, as the Falcon 9 team pushed towards the ignition of the nine Merlin 1D engines.
First stage flight lasted for two minutes and 38 seconds ahead of staging three seconds later. Second stage ignition was timed at T+ 2 minutes and 49 seconds.
While the second stage continued towards orbit, with fairing separation – followed by the first-ever fairing recovery test success (objective met, fairings not actually recovered) – core 1021 prepared for its second date with Of Course I still Love You.
The stage fired a subset of its engines to slow itself as it reentered the atmosphere before making a landing burn as it approached the drone ship downrange.
Despite SpaceX’s recent success and the stage’s previous form, the landing attempts remain experimental and are particularly difficult on geosynchronous launches where much of the vehicle’s performance must go into getting the satellite to orbit.
Falcon’s three successful landings after geosynchronous launches all came on missions with significantly lighter payloads. The success or failure of Thursday’s landing attempt would not impact the overall success of the mission. However, it was still successful, marking the historic first for SpaceX.
The mission hit SECO-1 at 8 minutes and 34 seconds, prior to a coast phase until the second firing of the Upper Stage at 26 minutes and 29 seconds into the mission. SECO-2 occurred at T+27 minutes and 22 seconds, prior to a short coast to SES-10 S/C Sep at 32 minutes and 3 seconds into the mission.
SES-10 was the third satellite SpaceX have launched for Luxembourg-based SES, who operate one of the world’s largest fleets of geostationary communications satellites. The company’s SES-8 satellite was the payload for SpaceX’s first geosynchronous launch in December 2013, aboard a Falcon 9 v1.1. SES-9 was carried to orbit aboard a Falcon 9 Full Thrust last March.
The SES-10 satellite was built by Airbus Defence and Space, based on the Eurostar 3000 satellite bus. The 5,282-kilogram (11,645 lb) satellite is designed for an operational lifespan of at least fifteen years. The spacecraft will be positioned at a longitude of 67 degrees west. Its fifty-five Ku-band transponders will allow it to replace the AMC-3 and AMC-4 satellites, which have both been in orbit since the 1990s.
AMC-3 and AMC-4 are former GE Americom satellites which were originally named GE-3 and GE-4. GE-3 was launched atop an Atlas IIAS rocket in September 1997, while GE-4 lifted off atop an Ariane 44LP in November 1999. The satellites were renamed when SES acquired GE Americom and named it SES Americom in 2001. When SES Americom and SES New Skies were reorganized into SES World Skies in 2009 the two satellites were transferred to the new company, which was subsequently merged back into the SES parent company in 2011.
In early January, SES announced that in-flight entertainment services company Global Eagle had agreed to purchase all capacity on the AMC-3 satellite, now four and a half years past the end of its design life, to provide internet connectivity to aircraft over the Americas. SES will continue to operate the satellite, under the name Eagle 1. AMC-4 remains on-orbit at 67 degrees West, providing direct-to-home broadcasting and broadband internet services to the Southern United States, Central America, northwest South America and the Caribbean.
SES-10 will take over coverage of these areas, providing additional transponders and allowing the expansion of services to the rest of South America.
Thursday’s launch is the fourth of the year for SpaceX and the Falcon 9, following January’s Iridium launch, the CRS-10 Dragon launch in February and EchoStar XXIII in mid-March. The next Falcon launch is currently scheduled for 16 April, carrying the NROL-76 payload for the US National Reconnaissance Office.
The SES-10 launch is the first of a busy year for SES, who have five more launches scheduled before the end of 2017. Next up is SES-15, which had been scheduled to ride a Soyuz-STA/Fregat-M to orbit from Kourou at the start of April. This launch has now been delayed until around the middle of the month due to a general strike in French Guiana.
Three more SES satellites are scheduled for launch aboard Falcon 9 and one aboard an Ariane 5, later in the year.
(Images via SpaceX, SES and NASA).