Fifteen launches in a single calendar year is a remarkable accolade and earlier tonight (Wednesday, 11 October), SpaceX successfully delivered the heavyweight SES-11 communications satellite to Geostationary Transfer Orbit (GTO), atop its venerable Upgraded Falcon 9 booster. Originally scheduled to fly last Saturday from historic Pad 39A at the Kennedy Space Center (KSC) in Florida, the mission was postponed a few days and was “leapfrogged” by the third batch of Iridium NEXT satellites, which rode another Upgraded Falcon 9 out of Vandenberg Air Force Base, Calif., early Monday. Tonight’s flight also marked the third occasion that SpaceX has employed a “used” first-stage core, which returned safely to Earth and made a pinpoint touchdown on the Autonomous Spaceport Drone Ship (ASDS), “Of Course I Still Love You”, offshore in the Atlantic Ocean.
Already, 2017 has seen the long-awaited inauguration of Pad 39A for SpaceX operations, as well as its first classified payload for the National Reconnaissance Office (NRO), its first reused Upgraded Falcon 9 first stage and its first reused Dragon cargo vehicle. Including tonight’s mission, no less than 42 major payloads have been carried into orbit this year, six of which have headed towards a 22,300-mile-high (35,800 km) geostationary altitude. Thirty-five others—including 30 Iridium NEXT satellites, spread across launches in January, June and October—have headed for low-Earth orbit, with Taiwan’s Formosat-5 lofted into a near-polar, Sun-synchronous orbit in August for intensive observations of the Home Planet. Included in this figure have been three Dragon cargo missions to the International Space Station (ISS), the greatest number ever launched in a single calendar year.
With a relatively spacious, two-hour “launch window”, extending from 6:53 p.m. through 8:53 p.m. EDT, weather conditions along the Space Coast on Wednesday proved highly favorable. “Isolated coastal showers are possible this evening, but there is only a slight chance of one being enhanced enough to violate the Cumulus Cloud Rule,” noted the 45th Weather Squadron at Patrick Air Force Base in its briefing at noon today. With the Cumulus Cloud Rule declared as the only potentially violating factor, SpaceX worked against the backdrop of a 90-percent probability of acceptable conditions at T-0. In the event of a 24-hour scrub to Thursday, conditions were anticipated to deteriorate to 80-percent-favorable, with an expected shift of winds and an increased concern of coastal showers.
Primary payload for tonight’s launch was the SES-11 communications satellite, flying on behalf of Luxembourg-based operator SES. This marks the fourth SES bird to be delivered to orbit by SpaceX, following SES-8—its very first customer to geostationary orbit—way back in December 2013 and, more recently, SES-9 in March 2016 and SES-10 earlier this year. At least two more satellites, SES-12 and SES-16, are also slated to ride Upgraded Falcon 9s in the coming months. When it reaches its proper orbital position at 105 degrees West longitude, SES-11 will cover the Americas, including Mexico and the Caribbean Sea, with its transponders marketed as EchoStar-105.
Weighing about 11,500 pounds (5,200 kg), SES-11 is built on Airbus Defence and Space’s three-axis-stabilized EuroStar-3000 “bus”, equipped with frequency-agile remote-controlled Flexible Command Receivers to effect a more robust operations control link. Its twin solar arrays provide an electricity-generating capability of some 13 kilowatts and the EuroStar-3000 was the first commercial satellite family to employ lithium-ion batteries in place of older nickel-cadmium ones for power during orbital eclipse. The bus also benefits from a bi-propellant chemical thruster system for initial orbit-raising and maneuvers and an electric plasma propulsion system for station-keeping at GTO. It is anticipated that SES-11 will remain fully functional for about 15 years.
Contracts to build SES-11 were signed between SES and Airbus Defence and Space in September 2014, with launch initially targeted for the fourth quarter of 2016. However, as SpaceX’s flight backlog stacked up in the wake of last year’s Amos-6 explosion, SES-11 found itself slipping steadily to the right. Last month, the satellite was shipped from Airbus’ facility in Toulouse, France, to Cape Canaveral, where it underwent final testing and fueling. In the meantime, the Upgraded Falcon 9 pressed smoothly through a customary Static Fire Test of the nine Merlin 1D+ engines on its first stage on 2 October. The booster was then returned to a horizontal configuration and transferred to the nearby Horizontal Integration Facility (HIF) for the installation of the bullet-like payload shroud housing SES-11. The 230-foot-tall (70-meter) Upgraded Falcon 9 was then returned to Pad 39A and raised to the vertical on Tuesday evening. As highlighted last month by SpaceX, this represents the third occasion in which an Upgraded Falcon 9 first stage has been used for a second launch. It was previously used to deliver the CRS-10 Dragon to orbit, back in February 2017.
Loading of the Upgraded Falcon 9 with liquid oxygen and a highly-refined form of rocket-grade kerosene (known as “RP-1”) got underway at 5:45 a.m. EDT, about an hour before T-0. Since the Amos-6 failure, boosters have been put through a slightly longer and more conservative fueling regime. Liquid oxygen tanking got underway at T-35 minutes, visually manifesting itself through periodic bursts of vapor from the rocket. Passing T-10 minutes at 6:43 p.m., the terminal autosequencer was initiated and the nine Merlin 1D+ engines of the first stage—configured in a circle of eight, with a ninth at the center—were chilled down, preparatory to the ignition sequence. By this stage, dusk was rapidly approaching, with sunset expected at 6:57 p.m., just four minutes after liftoff. The stage was set for a truly spectacular cusp-of-sunset climb to orbit.
At T-2 minutes, the Air Force Range Safety Officer declared all ground assets to be “Go for Launch” and the booster transferred to Internal Power and assumed primary control of all critical functions. The Niagara deluge system flooded Pad 39A with 30,000 gallons (113,500 liters) of water, per minute, to suppress the acoustic energy. The Eastern Range declared its readiness to support the launch as “Green”. Three seconds before liftoff, the nine Merlins roared to life, ramping up to a combined thrust of 1.5 million pounds (680,000 kg).
Liftoff occurred on-time at 6:53 p.m. EDT and the vehicle followed a perfect ascent trajectory, its first stage providing the muscle for the first 2.5 minutes, before separating. It then commenced a six-minute descent back to Earth, guided by its hypersonic grid-fins and propulsive “Entry” burn. “First-stage entry burn complete,” SpaceX tweeted at 7 p.m. “Second stage continuing nominally to geostationary transfer orbit.” In spite of some agonizing video dropouts, the first stage alighted smoothly on the Autonomous Spaceport Drone Ship (ASDS), “Of Course I Still Love You”, situated about 420 miles (680 km) off the coast of Cape Canaveral.
“Falcon 9 keeps rolling along, baby!” exulted former NASA astronaut Garrett Reisman, who currently serves as SpaceX’s director of crew operations. Today’s landing was the 11th successful touchdown of a Falcon 9 first stage on either the East or West Coast drone ships, since April 2016. All told, counting seven other landings on solid ground at Cape Canaveral’s Landing Zone (LZ-1), SpaceX has brought Upgraded Falcon 9 first stages back to Earth safely on 18 occasions in just 22 months.
Described as a “hybrid” satellite, with 24 transponders operating in the Ku-band and 24 transponders in the C-band, it will replace the Ku-band capability of the 2004-launched AMC-15 satellite and the C-band capacity of the 2006-launched AMC-18 satellite, both of which are entering the twilight of their 15-year operational lifetimes. During its time at 105 degrees West, it is expected that SES-11 will “accelerate the development of the U.S. video neighborhood and the delivery of HD and UHD channels”. Optimized for digital television delivery, it promises to cover 100 million homes and will comprehensively cover North America, including Hawaii, Mexico and Caribbean.