Third Time's a Charm as SpaceX Launches 10th Mission of 2017 with Intelsat 35e

SpaceX and Pad 39A established another record this evening (Wednesday, 5 July), as the personal-best-beating tenth Upgraded Falcon 9 of 2017 roared into space and the historic, Apollo-era complex saw its second launch in only 12 days. The 230-foot-tall (70-meter) booster lifted off at 7:38 p.m. EDT, right on the opening of a 58-minute “window” and successfully delivered the Intelsat 35e high-throughput communications satellite into Geostationary Transfer Orbit (GTO).

Wednesday’s successful launch came after a pair of disappointing scrubs on Sunday and Monday, both automatically commanded at T-9 seconds. Following the second scrub, SpaceX elected to return to Upgraded Falcon 9 to a horizontal configuration for attention, standing down for a couple of days to prepare for a third launch attempt. Due to the heavyweight nature of the payload—which tips the scales at around 14,770 pounds (6,700 kg)—no attempt to land the Upgraded Falcon 9’s first stage on either the Autonomous Spaceport Drone Ship (ASDS) or Landing Zone (LZ)-1 was made on this mission.

From the maiden voyage of the mighty Saturn V to the first manned lunar landing and from the ascent of Skylab to the first and last flights of the Space Shuttle, historic Pad 39A at the Kennedy Space Center (KSC) in Florida has seen dozens of launches since November 1967. Earlier this spring, after a multi-year hiatus, it returned to operational service, hosting SpaceX’s birds and has now conducted an impressive eight missions between February and tonight. These lofted 15 communications satellites into orbit, as well as a pair of Dragon cargo ships to the International Space Station (ISS) and saw Pad 39A’s first fully classified customer since the shuttle era.

Even in those few short months, the pad has established a number of new records, from the flight of a re-used Upgraded Falcon 9 first-stage “core” in March to an empirical turnaround record of just 14 days between two launches. But tonight, SpaceX added another feather to its cap by flying its tenth mission of the year and setting a new record of just 12 days between launches from Pad 39A. Moreover, when one counts a third Upgraded Falcon 9—which thundered out of Vandenberg Air Force Base, Calif., on 25 June—this year has seen a remarkable uplift in SpaceX’s launch cadence, as the Hawthorne, Calif.-based organization sets its sights on ticking-off up to 20 missions in 2017.

The payload for Monday’s flight was the heavyweight Intelsat 35e satellite, which will provide communications coverage over the Americas, the Caribbean, Europe and sub-Saharan Africa from its geostationary orbital “slot” at 325.5 degrees East longitude, positioned over the Atlantic Ocean, to the north-east of Brazil. Fabricated by Boeing, Intelsat 35e will replace the 2002-launched Intelsat 903 satellite, which is expected to be maneuvered to a new orbital location by year’s end.

Intelsat 35e is the fourth of Luxembourg-based Intelsat’s high-throughput “EpicNG” advanced digital platforms, the concept for which was first unveiled back in 2012. It is characterized by the capability of frequency re-use, afforded by a mix of frequency and polarization in small spot-beams. Previously, the Ka-band has been favored for high-throughput operations, but EpicNG extends the technique to the more reliable Ku-band and C-band. The first EpicNG bird, Intelsat 29e, was launched via Europe’s Ariane 5 booster in January 2016, followed by Intelsat 33e in August and Intelsat 32e in February 2017.

Contracts for the fabrication of Intelsat 35e were awarded to Boeing in July 2014, with the satellite based in design upon the highly-reliable 702MP main bus. This is a “medium-power” platform, capable of supporting a payload power of between six and 12 kilowatts. Its tailored payload module interfaces with the bus at four locations, and with just a handful of electrical connectors, for simplicity and cost efficiency. The 702 configuration was first flown in 1999 and several missions suffered problems with their solar array concentrators, which led to the implementation of a pair of six-paneled triple-junction gallium arsenide cells. At present, Intelsat is the main customer for the 702MP.

Original plans anticipated that a payload of Intelsat 35e’s size and mass would require the as-yet-untried Falcon Heavy booster, but incremental upgrades to the “barebones” Falcon 9 in recent years have allowed the heavyweight satellite to fit within its envelope. Following delivery from Boeing’s Satellite Development Center in El Segundo, Calif., to Florida, Intelsat 35e underwent final tests and fueling and was encapsulated into its bulbous payload fairing. Last Thursday, the Upgraded Falcon 9 concluded a customary Static Fire Test of the nine Merlin 1D+ engines of its first stage on Pad 39A, before being returned to the nearby horizontal integration facility for the installation of its payload.

In its summary of the Static Fire Test, SpaceX announced that it was aiming for an opening launch attempt during a 58-minute “window” which extends from 7:36 p.m. EDT through 8:34 p.m. EDT Sunday. However, weather conditions in Florida were predicted to be marginal, with a 40-percent chance of acceptable conditions at T-0. “Another round of afternoon and evening storms are expected across Central Florida today, this time favoring the east side of the peninsula,” noted the 45th Weather Squadron at Patrick Air Force Base in their L-1 briefing on Saturday morning. “The main weather concerns for launch…are lingering cumulus clouds along the sea breeze and anvils from inland storms.” In the event of a 24-hour delay to the backup launch opportunity on Monday evening, conditions were anticipated to improve to 60-percent-favorable.

Such concerns were clearly on the mind of SpaceX CEO Elon Musk, too. “Another SpaceX launch today,” Mr. Musk tweeted his 9.7 million followers on Sunday morning, before adding cautiously: “If weather is good.”

Notwithstanding this grim outlook, SpaceX characteristically pressed ahead with its launch preparations. Fueling of the booster with a highly refined form of rocket-grade kerosene (known as “RP-1”) got underway about one hour before T-0. Shortly thereafter, at 35 minutes before launch, liquid oxygen began flowing into the tanks. At 7:26 p.m. EDT, with ten minutes remaining before T-0, the terminal countdown autosequencer was initiated. The nine Merlin 1D+ first-stage engines, arranged in a circle of eight, with a ninth at the centre, were chilled, ahead of ignition, and the Flight Termination System (FTS) was placed onto internal power and armed.

In the final minutes, the Upgraded Falcon 9 transitioned to internal power and the Intelsat 35e payload was powered-up, with the vehicle assuming primary command of all critical functions—entering “Startup”—at T-60 seconds. At the same time, the deluge system began to flood Pad 39A’s surface with water to reduce the reflected energy at liftoff.

However, Sunday’s countdown clock abruptly halted at 7:36 p.m. EDT, with the clock holding at T-9 seconds. The exact cause was not immediately apparent. “Currently awaiting details of what caused the abort,” noted AmericaSpace’s Launch Tracker at 7:42 p.m. “The engines were scheduled to be ignited at T-3 seconds.” However, even with a relatively spacious window, it was readily apparent that a 24-hour scrub would be called. “The rocket is currently being safed and the launch teams will be preparing for de-tanking,” our Tracker continued. “This launch attempt is now officially scrubbed and the launch teams will be shooting for a 24-hour turnaround.”

A few minutes later, at 7:55 p.m., the first official word emerged from SpaceX. “Guidance abort issued just before liftoff; standing down for today,” the organization tweeted. “Vehicle and payload are healthy.”

The meteorological outlook improved markedly in time for Monday’s launch attempt, with the 45th Weather Squadron noting a 70-percent likelihood of acceptable conditions. “The Bermuda high-pressure ridge axis remains over the southern portions of the Spaceport,” it was announced at 12:30 p.m. EDT. “This is creating light surface winds, which allows sea-breeze storms to progress inland over most of the Space Coast, but hindering the inland movement over northern areas of the country.” It was stressed that steering-level winds were also light, causing storms to remain on the sea-breeze as it slowly moved away from the launch site. “Main concern for launch is cumulus clouds developing from storm outflows,” it was noted.

As afternoon wore into evening, SpaceX showed its colors and determination to press ahead with the second attempt to get Intelsat 35e into orbit. “All systems go for launch of @Intelsat 35e,” it tweeted at 5:45 p.m. EDT. “Targeting liftoff at 7:37 p.m. EDT. Weather is 70% favorable.”

For the second time in two days, SpaceX teams headed into countdown operations. Approximately an hour before the opening of the launch window, it was revealed that T-0 had been moved 15 minutes to the right to 7:52 p.m. EDT, due to predicted weather conditions. “Weather is proving to be an issue for today’s launch,” noted AmericaSpace’s Launch Tracker. “The T-0 has been put back…in an effort to avoid a storm cell in the region.” This was subsequently pushed back yet further to 8:07 p.m., with an understanding the Launch Commit Criteria (LCC) rules pertaining to lightning may have been violated. By now, Monday’s launch window was rapidly ebbing towards its 8:35 p.m. closure point and another scrub seemed increasingly likely.

As always, SpaceX remained upbeat, noting the weather issue, but stressing that its bird and Intelsat payload were both healthy and ready to go. Then, at 7:04 p.m., SpaceX confirmed that it would move the T-0 time right to the end of Monday’s window. “Pushing T-0 to 8:35 p.m. EDT…for weather,” it tweeted. “Vehicle and payload remain in good health in advance of the @Intelsat 35e launch.” The 45th Space Wing at nearby Patrick Air Force Base also confirmed that it was “monitoring the weather for a time that will allow us to go”.

Polls to begin fueling were completed at 7:32 p.m. and, a couple of minutes later, some 341,700 pounds (155,000 kg) of RP-1 began flowing into the tanks of the Upgraded Falcon 9. As the countdown reached T-35 minutes, at 8 p.m., the process to load 793,670 pounds (360,000 kg) of liquid oxygen aboard the booster got underway. The countdown entered its terminal phase at T-10 minutes, with the Sun setting over the marshy Florida landscape. According to the 45th Weather Squadron, Monday’s sunset was at 8:24 p.m. EDT, about 11 minutes before T-0, placing this mission on the cusp of being classified as a “night launch”.

Passing “Startup”, the Launch Director verified that the vehicle and payload were “Go for Launch”, but—agonizingly—the countdown was again automatically halted at T-9 seconds. Earlier, SpaceX had confirmed that the cause of Sunday’s abort had been due to out-of-family guidance data, and ultimately a ground-side problem, which was thought to have been rectified. In the minutes after Monday evening’s scrub, it was not immediately clear if the cause was related.

SpaceX explained that it was “Standing down today due to a violation of abort criteria” and suggested that a third attempt might be made as soon as Tuesday, 4 July. However, Mr. Musk later confirmed that a longer delay would be effected. “We’re going to spend the 4th doing a full review of rocket & pad systems,” he tweeted. “Launch no earlier than 5th/6th. Only one chance to get it right.” During the course of Tuesday, the Upgraded Falcon 9 was lowered to the horizontal and transferred back to the integration building for more detailed inspections and analysis.

At length, a decision was reached to head for a third launch attempt on Wednesday, 5 July. “Following a complete review of all criteria, @SpaceX has confirmed we are ‘Go’ for #launch tonight,” Intelsat tweeted on Wednesday morning. Launch was targeted for 7:38 p.m. EDT, at the opening of a 58-minute window. Weather conditions stood at 90-percent-favorable, with the possibility of cumulus clouds forming along outflows from inland storms posing a slight risk. A similarly favorable outlook was predicted for Thursday.

As SpaceX controllers prepared for the critical poll, ahead of fueling, Elon Musk tweeted that the team had “reviewed all systems” and “done our best to ensure all is good”. At the time, it was not confirmed if the scrubs on Sunday and Monday—which both occurred at T-9 seconds—were related. At 6:38 p.m. EDT, an hour before the opening of Wednesday’s launch window, RP-1 began flowing aboard the Upgraded Falcon 9 for the third time in four days. This was followed by the onset of liquid oxygen fueling at 7:03 p.m.

As the milestones proceeded through the final minutes and seconds, the T-9-second ogre from Sunday and Monday remained present. On this occasion, however, the flight was charmed as the countdown progressed smoothly through the point at which it had twice previously stalled. Three seconds before launch, the nine Merlin 1D+ engines roared to life, kicking out a combined thrust of 1.5 million pounds (680,000 kg).

The vehicle departed Earth precisely on the opening of Wednesday’s window, on the stroke of 7:38 p.m. EDT. Climbing smoothly into the Californian sky, the booster performed with characteristic perfection, passing maximum aerodynamic turbulence (“Max Q”) at 70 seconds. Two-and-a-half minutes into ascent, the first stage was jettisoned, heading for a destructive—or “expendable”—dive back through the atmosphere. Due to the high-energy demands associated with heaving the mass of Intelsat 35e to orbit, insufficient propellant reserves existed to comfortably achieve an ASDS or LZ-1 landing on this mission.

With the first stage gone, the Merlin 1D+ Vacuum engine of the Upgraded Falcon 9’s second stage roared to life, a little under three minutes into the mission. Burning with 210,000 pounds (92,250 kg) of thrust, the engine glowed red-hot for almost six minutes, before shutting down and entering a protracted, 18-minute “coasting” phase. During the course of the burn, the payload shroud was jettisoned, exposing Intelsat 35e to the harsh environment of space for the first time. At 8:04 p.m. EDT, some 26 minutes after leaving KSC, the Merlin 1D+ Vacuum was re-lit for a short second burn and at 32 minutes into the flight Intelsat 35e separated to begin its 15-year mission.

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