SpaceX’s second Falcon 9 v1.1 rocket—and the first from Cape Canaveral Air Force Station’s storied Space Launch Complex (SLC)-40—must wait a little longer to fly, having been thwarted by first-stage technical issues. Originally scheduled to liftoff at 5:37 p.m. EST, about 11 minutes after local sunset, the countdown clock was stopped and recycled twice as engineers and managers scrambled to assemble and execute troubleshooting plans. Despite their sterling efforts, and increased hopes that the Falcon might yet fly before the 6:43 p.m. closure of the 66-minute “window,” it was not to be. With unacceptable weather conditions forecast for Tuesday, SpaceX expects to be in position for another launch attempt no earlier than Thursday, 28 November.
Coming less than two months after the 29 September inaugural voyage of the Falcon 9 v1.1 rocket from Vandenberg Air Force Base, Calif., this second flight has been described by SpaceX as its “First GEO Transfer Mission” to deliver the SES-8 communications satellite into a projected 180 x 50,000-mile (300 x 80,000 km), 20.75-degree-inclination geostationary transfer orbit. All previous SpaceX flights have carried payloads no higher than low-Earth orbit, marking out this mission as the first for the Hawthorne, Calif.-based launch services organization to venture to deliver a cargo to geostationary transfer orbit. When operational, the 7,100-pound (3,200 kg) SES-8 spacecraft will utilize Ku- and Ka-band transponders to provide bandwidth-growth capacity for the Asia-Pacific region.
In readiness for tonight’s planned liftoff, the 227-foot-tall (69.1 meter) booster was put through a smooth Wet Dress Rehearsal (WDR) and hot-fire test of its nine Merlin-1D first-stage engines on Thursday, 21 November. A Launch Readiness Review last weekend established Monday as the official launch target date. Late Sunday, the Falcon team rolled their vehicle out to SLC-40 and, early Monday afternoon, the process of loading liquid oxygen and rocket-grade kerosene (known as “RP-1”) aboard the tanks began a little under four hours ahead of liftoff and was concluded at T-3 hours and 15 minutes.
Unlike the Merlin-1C engines used by the earlier Falcon 9 v1.0, the newer Merlin-1D engines of the v1.1 generate about 56 percent increased thrust at sea level and are arranged in a so-called “Octaweb” layout. Whereas the v1.0 carried its engines in a “tic-tac-toe” configuration, the v1.1 features a circle of eight engines and a ninth in the center. This change increases the Falcon 9’s reliability, whilst also streamlining the manufacturing process. “The eight engines surrounding one center engine simplify the design and assembly of the engine section, reducing production time from about three months to a matter of weeks,” SpaceX explained. “The new layout also provides individual protection for each engine and further protects other engines in case of an engine failure. It significantly reduces both the length and weight of the Falcon 9 first stage.” Another benefit is that the Octaweb should enable the first stage to eventually become reusable, allowing it to survive a propulsive return-over-water maneuver and travel to a vertical touchdown at its launch site.
Ironically, Monday was probably the best day to attempt the SES-8 launch. According to meteorologists at Patrick Air Force Base, there was an 80-percent likelihood of acceptable conditions today, and, indeed, the weather remained “Green” throughout the latter stages of the countdown. However, it is expected to decrease to just 30 percent on Tuesday, with cumulus and thick clouds posing a key threat to Launch Commit Criteria. “On Tuesday, the Gulf system approaches Florida with widespread clouds, precipitation and isolated thunderstorms (some possibly severe) throughout Central Florida,” the Air Force noted. “There is a possibility that a fast transit of the boundary could bring in acceptable weather conditions towards the end of the launch window.” As a consequence, reducing its prediction of acceptable conditions on Tuesday, it was added that “primary concerns for a 24-hour delay are thick clouds, disturbed weather and liftoff winds.”
All events for the Monday launch attempt ran like clockwork until the final quarter-hour ahead of the 5:37 p.m. EST opening of the window, just 11 minutes after local sunset. A technical issue then arose with a first-stage liquid oxygen vent valve, prompting the SpaceX launch team to hold the countdown clock at T-13 minutes. At length, an update confirmed that an unanticipated “signature” on the vent valve was being addressed and that engineers were closing in on a troubleshooting plan, with hopes remaining high that the team would press on with the countdown. Soon afterward, the clock was recycled to T-19 minutes, tracking a revised liftoff time of 5:54 p.m.
In readiness for this new T-0, the SES-8 spacecraft was confirmed to be on internal power and “Go for Launch” at 5:38 p.m. Three minutes later, at T-13 minutes, all stations were polled and confirmed their state of readiness as “Go” to proceed with the Terminal Count at T-10 minutes. As planned, the Terminal Count got underway at 5:44 p.m. and ticked down to T-6 minutes and 11 seconds—just prior to Autosequence Start—before halting again, apparently due to an issue with the transfer to first-stage internal power. SpaceX’s live webcast highlighted that the hold was called as preparations were underway for the transition to internal power and that the Falcon 9 was being safed.
Fears of an abort were allayed by the lengthy nature of the launch window, and at 5:59 p.m. the countdown clock again recycled to T-13 minutes—the normal recycling point from which the Terminal Count may begin again—and held there as managers analysed the data and considered their options for another attempt. Finally, at 6:12 p.m., a revised T-0 of 6:30 p.m. was announced and the clock correspondingly recycled to T-18 minutes in support of this new launch time. All stations were again polled and, again, returned a unanimous “Go” for launch at 6:17 p.m., after which the countdown passed T-13 minutes and continued counting into the Terminal Count. At T-9 minutes and 43 seconds, the flight control system was enabled and the nine Merlin-1D engines on the first stage began a “chill-down” sequence as part of launch conditioning. Autosequence Start occurred at T-6 minutes, with the Falcon’s propellant tanks verified to be at the proper flight pressures, and the launch pad’s “strongback” was retracted from the vehicle.
At T-4 minutes and 30 seconds, the Falcon transitioned to internal power and the Launch Vehicle Release System commenced its own autosequence. However, at 6:27 p.m.—at around the time that the vehicle was scheduled to activate its ignition system and transfer the Flight Termination System (FTS) to internal power—the clock stopped again at T-3 minutes and 40 seconds as the team worked a first-stage issue. Since the window closed at 6:43 p.m., there remained insufficient time to recycle back out to T-13 minutes for another attempt, and at 6:35 p.m. SpaceX officially scrubbed today’s effort to get SES-8 into orbit.
Moving ahead, Thursday, 28 November—Thanksgiving Day—is shaping up as the next possible opportunity to launch the mission. Assuming a Thursday attempt goes ahead, Autosequence Start will occur at T-6 minutes, after which the SpaceX Launch Director and the Air Force Range Control Officer will verify that all stations are “Go” for launch. At T-60 seconds, SLC-40’s “Niagara” deluge system will flood the pad surface with 30,000 gallons (113,500 liters) of water per minute to suppress acoustic waves radiating from the Merlin-1D exhaust plumes. The vehicle’s propellant tanks will be pressurized, and at T-3 seconds the nine engines will roar to life. Under computer control, their start-up sequence will be tightly monitored and, assuming the ignition protocol is normal, hold-down clamps will be commanded to release the vehicle at T-0.
At the instant of liftoff, the first stage engines will generate 1.3 million pounds (590,000 kg) of thrust, about 200,000 pounds (90,000 kg) greater than the Falcon 9 v1.0, and will push the vehicle uphill for 180 seconds. Their propulsive yield will gradually rise to 1.5 million pounds (680,000 kg) in the rarefied high atmosphere. “Unlike airplanes, a rocket’s thrust actually increases with altitude,” noted SpaceX. “Falcon 9 generates 1.3 million pounds of thrust at sea level, but gets up to 1.5 million pounds of thrust in the vacuum of space. The first-stage engines are gradually throttled near the end of first-stage flight to limit launch vehicle acceleration as the rocket’s mass decelerates with the burning of fuel.”
With around 1,970 seconds of test time and a lengthy qualification program, SpaceX has expressed supreme confidence in the Merlin-1D. During a full-duration-mission firing in June 2012 in McGregor, Texas, the engine operated at or above the power (147,000 pounds of thrust) and duration (185 seconds) required for a Falcon 9 launch. The Merlin-1D has a vacuum thrust-to-weight ratio in excess of 150:1, making it the most efficient liquid-fueled rocket engine in history. The ignition system for the v1.1’s first stage was tested in April 2013. The stage also includes four extendible landing legs, manufactured from carbon-fiber and aluminum honeycomb, to support a series of tests which SpaceX CEO Elon Musk hopes will lead to vertical-takeoff-vertical-landing (VTVL) capability by the latter half of the present decade.
Immediately after clearing the SLC-40 tower, the Falcon 9 will execute a combined pitch, roll, and yaw program maneuver to establish itself onto the proper flight azimuth for the injection of the SES-8 communications satellite into geostationary transfer orbit. Eighty seconds into the ascent, the vehicle will pass Mach 1 and experience a period of maximum aerodynamic stress (known as “Max Q”) on its airframe. The Merlin-1Ds will continue to burn hot and hard, finally shutting down at T+2 minutes and 58 seconds, and the first stage will be jettisoned five seconds later. The turn will then come for two “burns” by the Falcon’s restartable second stage, which will ignite for the first time at T+3 minutes and 10 seconds. Its single Merlin-1D Vacuum engine, with a maximum thrust of 180,000 pounds (81,600 kg), will burn for 320 seconds to establish the vehicle and SES-8 payload into a “parking” orbit.
A minute into the second-stage flight, the two-piece Payload Fairing (PLF)—a 43-foot-long (13.1-meter) protective cover which encapsulates the SES-8 satellite—will separate from the vehicle. “Like the inter-stage between the first and second stages,” explained AmericaSpace’s Launch Tracker in its notes for the inaugural Falcon 9 v1.1 launch on 29 September, “a pneumatic system is used to separate the two halves, rather than the traditional pyrotechnics.” Fabricated from carbon-fiber and aluminum-honeycomb, the PLF was extensively tested by SpaceX in April 2013 within the confines of the Reverberant Acoustic Test Facility at NASA’s Plum Brook Station in Sandusky, Ohio, part of the Cleveland-based Glenn Research Center.
The first shutdown of the second-stage engine is scheduled to occur at T+8 minutes and 30 seconds, after which the vehicle will coast for 18 minutes, ahead of a second “burn”—lasting about one minute—to carry SES-8 into geostationary transfer orbit. And five minutes after the Merlin-1D Vacuum shuts down for the second time, at 32 minutes and 53 seconds after liftoff, the satellite will be released into its 180 x 50,000-mile (300 x 80,000 km), 20.75-degree-inclination transfer orbit. This process will be monitored closely, for SpaceX was unsuccessful in restarting the Merlin-1D Vacuum during the 29 September maiden flight of the Falcon 9 v1.1. A propulsive-return-over-water test is not planned to occur on the SES-8 flight, or on next month’s launch of the Thaicom-6 communications satellite, but will be attempted on the February 2014 flight of the third dedicated Dragon mission (SpX-3) to the International Space Station.
Described by SpaceX as its “First GEO Transfer Mission,” SES-8 has been built by Orbital Sciences Corp. and will be co-located with the 2002-launched NSS-6 communications satellite at 95 degrees East longitude. Its primary purpose is to utilize its high-performance beams to support bandwidth-growth capability in the Asia-Pacific region, with specific focus upon emerging markets in South Asia and Indochina. Equipped with 33 Ku-band and Ka-band transponders, SES-8 will also provide expansion capacity for direct-to-home, very-small-aperture terminals and government applications. Operated by Dutch-based operator SES World Skies, the satellite should remain operational in geostationary orbit for about 15 years.Missions » Commercial Space » SES » SES-8 »