Following a successful static test firing last weekend at Cape Canaveral Air Force Station’s Space Launch Complex (SLC)-40, SpaceX stands ready for its second commercial mission to geostationary transfer orbit. Liftoff of the Thaicom 6 communications satellite, aboard the third uprated Falcon 9 v1.1 rocket, is officially targeted to occur within an 87-minute “window,” which opens at 5:50 p.m. EST Friday, 3 January. When operational in a 22,240-mile (35,780-km) orbit, Thaicom 6 will provide communications services across Asia, Europe, Australia, and Africa, in addition to offering direct-to-home television coverage to Thailand, Laos, Cambodia, and Myanmar.
Friday’s launch attempt will be the first by any nation in 2014 and comes hard on the heels of the standard static test on Saturday, 28 December. According to NASASpaceflight.com, the test put the Falcon 9 v1.1 and SpaceX’s launch team through their countdown protocols and culminated in a short firing of the nine Merlin-1D engines on the rocket’s first stage. Early indications from SpaceX are that the test ran as expected, clearing the way for this week’s Launch Readiness Review, ahead of liftoff.
Built by Orbital Sciences Corp. at its Dulles, Va., manufacturing facility, the 7,330-pound (3,325-kg) Thaicom 6 satellite carries a hybrid C-band and Ku-band communications payload, with 18 C-band and eight Ku-band transponders. Operated by the Thaicom Public Company Limited, headquartered in Bangkok, it will be positioned in geostationary orbit at 78.5 degrees East, co-located with the 2006-launched Thaicom 5. When fully operational, it is expected that Thaicom 6 will remain active for about 15 years.
“The Thaicom 6 satellite design is based on Orbital’s highly successful, flight-proven GEOStar-2 satellite platform,” noted Orbital Sciences. “The company’s GEOStar product line includes the GEOStar-2 design, which is optimized for smaller satellite missions that can support up to 5.0 kilowatts of payload power.” Thaicom 6’s gallium arsenide solar arrays will produce up to 3.7 kW of electrical power for the three-axis-stabilized satellite, with maneuvering capability for station-keeping provided by hydrazine thrusters. Last week, Thaicom Public Company Limited—the Bangkok-headquartered subsidiary of Shin Corporation and principal operator of the new satellite—announced that it had acquired a 66-percent booking on Thaicom 6’s capacity. It was also noted that the satellite would provide “higher quality of the digital TV and more high-definition channels.”
Originally targeted for launch on 20 December, the final preparations for the Thaicom 6 launch were pushed to the right as a result of the delayed SES-8 mission, which suffered two scrubbed attempts in late November. This will be the third launch of the uprated Falcon 9 v1.1 rocket, which first flew last September, carrying Canada’s CASSIOPE scientitic payload into low-Earth orbit. This success was followed by SpaceX’s first mission to geostationary transfer orbit on 3 December, which delivered the SES-8 communications satellite. The new booster is powered by nine Merlin-1D engines on its first stage and a single Merlin-1D Vacuum engine on its second stage.
Tracking an early evening liftoff Friday, SpaceX will poll all stations for their “Go-No Go” status at T-13 minutes, after which the Terminal Count will commence at T-10 minutes. The Falcon 9’s flight control system will be enabled and the nine Merlin-1D engines on the first stage will begin a “chill-down” protocol as part of pre-launch conditioning. Autosequence Start will occur at T-6 minutes, with the rocket’s propellant tanks verified to be at their proper flight pressures, and SLC-40’s “strongback” will be completed retracted by T-4 minutes. The Flight Termination System (FTS)—tasked with destroying the Falcon in the event of a major accident during ascent—will be placed onto internal power and armed, and by T-2 minutes and 15 seconds the first stage will reach flight pressure.
At T-1 minute, the flight computer will assume primary control of the vehicle, with the second-stage tanks pressing to flight pressures. SLC-40’s “Niagara” deluge system will begin to 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. At T-45 seconds, all tanks will be confirmed at flight pressure. With propellant tanks fully pressurized, at T-3 seconds the nine Merlin-1D engines will roar to life, gradually ramping up to full power and producing a liftoff at 5:50 p.m. EST. The criticality of these final few seconds were highlighted on 28 November—Thanksgiving evening—when the SES-8 countdown was dramatically aborted after engine ignition due to a slower than intended thrust ramp.
At the instant of liftoff the nine first-stage engines will generate 1.3 million pounds (590,000 kg) of thrust, about 200,000 pounds (90,000 kg) greater than the earlier 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 great 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 v1.1 will execute a combined pitch, roll, and yaw program maneuver to establish itself onto the proper flight azimuth for the injection of Thaicom 6 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 about 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 about 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 five minutes to establish the vehicle and Thaicom 6 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 Thaicom 6—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 will 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 Thaicom 6 into geostationary transfer orbit. About 35 minutes after launch, the satellite should be released into orbit. Assuming a success on Friday, this launch will kick off an ambitious 2014 manifest for SpaceX, which is presently gearing up to stage at least three Dragon cargo delivery missions to the International Space Station (ISS), with the first targeted for mid-February.
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