Three months after the catastrophic loss of its Commercial Resupply Services (CRS)-7 Dragon cargo mission to the International Space Station (ISS)—which appeared to have fallen victim to a failed helium tank strut, provided by an external supplier—SpaceX stands ready to resume launches of its workhorse Falcon 9, albeit in a heavily modified form, perhaps as soon as mid-November. Last week, a successful 15-second static firing of the upgraded “Merlin 1D+” engines, destined for the Falcon 9 v1.2 (internally known as the “Falcon 9 v1.1 Full Thrust”) variant of the vehicle, shook the ground of the new Falcon Booster Test Stand at SpaceX’s facility in McGregor, Texas, for the first time. Although SpaceX previously stressed that no provisional date had been released for the Falcon 9’s Return to Flight (RTF) mission, recent comments by CEO Elon Musk in Berlin indicate that another launch might be attempted within six to eight weeks.
The flight—which will likely transport the SES-9 communications satellite into Geostationary Transfer Orbit (GTO) on behalf of the Luxembourg-headquartered SES satellite services provider and operator—is expected to use the v1.2, whose first-stage Merlin 1D+ and second-stage Merlin 1D+ Vacuum engines will run at their full, 100-percent power level. This is in contrast to the 80 percent of rated performance seen on previous v1.1 missions. A further 13 percent of additional performance will be accrued through a range of structural enhancements to the vehicle’s airframe and a process of “densifying” and thereby increasing the liquid oxygen propellant load. All told, this is expected to yield a performance “gain” of 33 percent over the earlier v1.1.
The loss of CRS-7 on 28 June broke a chain of 13 successful missions for the v1.1 between the launch of Canada’s CASSIOPE scientific satellite in September 2013 and the CRS-5 Dragon cargo flight in April 2015. During those 19 months, SpaceX delivered its first half-dozen payloads into GTO, together with one satellite into polar orbit, four ISS-bound Dragons into low-Earth orbit, and also accomplished its maiden foray to the L1 Lagrange Point, some 930,000 miles (1.5 million km) beyond Earth. Equipped with nine Merlin 1D engines on its first stage, the v1.1 offered a 200,000-pound (90,700-kg) increased propulsive yield over the 1.1-million-pound (503,000-kg) first-stage output of the Merlin 1C engines of its predecessor, the v1.0. Fueled by a mixture of liquid oxygen and a highly refined form of rocket-grade kerosene, known as “RP-1,” the Merlin 1D was extensively tested during the summer of 2012 and its 1.3-million-pound (590,000-kg) first-stage thrust significantly raised the bar for SpaceX, by enabling a 27-percent payload hike to low-Earth orbit and a somewhat smaller increase to GTO.
Also factored into the v1.1 and subsequent v1.2 designs was the much-publicized capability to soft-land its first-stage hardware on the deck of the Autonomous Spaceport Drone Ship (ASDS) in the Atlantic Ocean, as part of SpaceX’s ongoing effort to eventually confer reusability on its vehicles. This capability was afforded by three engine firings toward the end of first-stage flight: an initial “Boost-Back” to adjust its impact point, push it “upward” and redirect it towards its launch site, followed by a decelerating “Supersonic Retro-Propulsion” maneuver and finally a “Landing” burn to alight on the ASDS at a smooth 4.5 mph (7.2 km/h). In support of this goal, a series of “controlled oceanic touchdowns” in April, July, and September 2014 were followed with mixed fortune earlier this year, when two attempts were made to land on the ASDS. The first reached the deck, but impacted hard at a 45-degree angle and exploded, whilst the second landed with excessive lateral velocity and toppled over upon impact.
By this point, and even with only a relatively small number of v1.1 vehicles actually having flown, the effort to bring an enhanced Falcon—variously described as the “v1.2” or the “Full Thrust” (FT)—to operational status steadily gained momentum. It is understood that the v1.1 utilized the Merlin 1D engine at 80 percent of its rated capability, with 20 percent held in reserve, in order to afford maximum flexibility for the payload to achieve its correct orbital location. In contrast, the v1.2/FT centers around an upgraded “Merlin 1D+” engine, which reportedly generates 1.53 million pounds (694,000 kg) of thrust at liftoff, effectively operating at “full” (100-percent) capacity. This will increase to around 1.7 million pounds (771,100 kg) as the vehicle travels higher into the rarefied upper atmosphere. Similarly, the Merlin 1D Vacuum engine of the second stage will see a corresponding increase in propulsive yield from 180,000 pounds (81,600 kg) in the v1.1 to 210,000 pounds (95,250 kg) in the v1.2/FT. According to a source close to SpaceX, “FT” is the internal code name for calculating the Merlin 1D’s output at 100 percent, adding that “this improves the Falcon 9’s performance by 20 percent, although this “improvement” was not really new: it was always there, but never utilized.” At the time of the CRS-7 failure, it is understood that SpaceX intended to stage its first v1.2/FT launch in July 2015, delivering SES-9 to GTO.
However, the 20-percent performance hike achieved by throttling the engines from their 80-percent to 100-percent power levels has been expanded yet further to reach an overall 33-percent “performance gain” over the v1.1. This gain has been met in part through structural enhancements to the vehicle’s airframe, including a 10-percent increase in propellant tank volumes, a lengthened second stage with extended Merlin 1D Vacuum engine, upgraded landing legs and grid fins, an improved “Octaweb” support structure for the first-stage engine suite, a strengthened “interstage” between the two stages, and a central “pusher” to ensure a smooth stage-separation process. All told, these enhancements increase the height of the v1.2/FT vehicle to 229.6 feet (70 meters), about 5.6 feet (1.6 meters) taller than the v1.1.
Additionally, the 33-percent performance gain has been met through “super-cooling” the liquid oxygen load—in what Musk described as “deep cryo oxygen”—below its normal saturation condition, in order to increase its density and permit the carriage of a larger load of propellants in the Falcon 9’s tanks. “Propellant densification,” noted engineers Ke Nguyen and Timothy Knowles in an American Institute for Aeronautics and Astronautics (AIAA) paper, “is one of the key technologies needed to meet the challenges of future reusable launch vehicles.” The densification process, AmericaSpace understands, has required the installation of specialized cooling stations at SpaceX’s dedicated Falcon 9 pads of Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla., and Space Launch Complex (SLC)-4E at Vandenberg Air Force Base, Calif.
The additional performance gained from the structural modifications and the liquid oxygen densification is expected to be of assistance to SpaceX at it aims to deliver larger and heavier communications satellites to GTO and seeks lucrative Department of Defense contracts for major classified payloads. However, this stance has caused a measure of consternation and serious doubts have been raised over the frequency of major enhancements to SpaceX’s vehicles in a relatively short span of time. “The launch industry tends to be very conservative,” a Parabolic Arc article highlighted last July. “Changes are made very carefully and only after thorough testing. Experience has shown that while upgrades can improve a rocket’s performance, they can also cause problems.” The article quoted Gen. William Shelton, former commander of Air Force Space Command, who expressed concern that the upcoming v1.2/FT—which is believed to be the vehicle that SpaceX will use to bid for Department of Defense contracts—has yet to complete a single mission, much less pass through a full certification process. “In other words, the Air Force will be launching on yet another version of the Falcon 9, with an even shorter launch history than the one that just failed,” Parabolic Arc noted. “That can be handled with some additional certification work. However, it’s an unnerving prospect for an organization whose primary focus is on mission assurance, not cost.”
Notwithstanding these concerns, Musk expects that the v1.2/FT improvements will allow SpaceX to soft-land its first-stage hardware on the ASDS, even during high-energy launches to the 22,300-mile (35,900-km) altitude of GTO. Previously, only comparatively low-energy launches to Low-Earth Orbit (LEO) had seen soft-landing attempts, although SpaceX originally intended to bring the first stage from NASA’s L1-bound Deep Space Climate Observatory (DSCOVR) back to the ASDS in February 2015, but was ultimately thwarted by rough seas. “It’s always a trade-off between height and payload weight when the capacity is fixed,” AmericaSpace was told by a source close to SpaceX. “The higher the orbit, the less weight could get up there, with any given thrust capacity. LEO is relatively close, compared to GTO, so SpaceX was able to save some of the liquid oxygen for the landing attempts. With GTO, they needed to launch as high as possible and did not want to risk trying to save liquid oxygen for the landing attempts, as that could jeopardize their ability to get a client’s satellite as high as it needed to get.”
The weeks ahead are expected to see significant progress as SpaceX readies for an upcoming salvo of launches. The original CRS contract with NASA, signed back in December 2008, calls for 12 dedicated ISS cargo missions, of which six have been satisfactorily completed, and major payloads destined to fly aboard future Dragons include the Bigelow Expandable Activity Module (BEAM) and the second International Docking Adapter (IDA-2). There also exists a backlog of commercial payloads—including 11 Orbcomm OG-2 satellites—and NASA’s Jason-3 ocean surface topography mission, with the latter expected to ride an old-style v1.1, due to its LEO destination.
VIDEO: First static fire of the upgraded Falcon 9’s first stage
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