For the ninth time this year, the roar of nine Merlin 1D+ engines pummeled Pad 39A at the Kennedy Space Center (KSC) in Florida earlier today (Monday, 14 August), as SpaceX successfully delivered its third Dragon cargo mission of 2017 onto a course for the International Space Station (ISS). Liftoff of the Upgraded Falcon 9 booster occurred on-time at 12:31 p.m. EDT Monday and within minutes the Dragon had entered low-Earth orbit and was in the process of deploying its electricity-generating solar arrays and Guidance, Navigation and Control (GNC) Bay Door. Capture and berthing at the ISS is scheduled to occur on Wednesday, 16 August.
2017 has already taken shape as the most spectacular and launch-heavy year in the history of Hawthorne, Calif.-headquartered SpaceX. Including today’s flight, 11 Upgraded Falcon 9 vehicles have rocketed away from Earth, with nine from KSC in the last six months alone and the other pair from Space Launch Complex (SLC)-4E at Vandenberg Air Force Base, Calif. Twenty-nine major payloads have flown, including three ISS-bound Dragons, SpaceX’s first customer for the National Reconnaissance Office (NRO) and five “high-energy” missions to Geostationary Transfer Orbit (GTO). Eleven missions—and counting—within a single calendar year represents an ongoing “personal best” for SpaceX, which previously attained a peak of eight successful launches in 2016.
Today’s mission was the twelfth ISS-bound Dragon to be flown under the language of the $1.9 billion Commercial Resupply Services (CRS) contract, signed between NASA and SpaceX in December 2008. Including an initial Commercial Orbital Transportation Services (COTS) “demo” flight in May 2012, no fewer than 13 Dragons have been launched, although only 12 have actually reached orbit, following the high-altitude breakup of CRS-7 in June 2015. With SpaceX having averaged no more than two Dragons per year, today’s flight of CRS-12 is the first time that the organization has despatched as many as three cargo ships to the space station in a single calendar year. CRS-12 follows hard on the heels of CRS-10 in February and CRS-11 in June.
In readiness for today’s launch, SpaceX conducted a customary static firing of the 230-foot-tall (70-meter) Upgraded Falcon 9’s Merlin 1D+ first-stage engines late last week. “Static fire test of Falcon 9 complete,” SpaceX tweeted Thursday. “Targeting August 14 launch from Pad 39A for Dragon’s next resupply mission to the @Space_Station.”
Weather conditions for both the primary (Monday) and backup (Tuesday) launch opportunities were expected to be broadly favorable, with the 45th Weather Squadron at Patrick Air Force Base predicting a 70-percent likelihood of good weather. Afternoon thunderstorms over the weekend were expected to pose a risk of violating the Cumulus Cloud Rule and Flight Through Precipitation Rule. There also remained the possibility on Monday that the chance of storms could hamper the securing of the Upgraded Falcon 9’s first stage, after it had touched-down on Landing Zone (LZ)-1 at the Cape.
As is customary for launches bound for the ISS, today’s T-0 was an “instantaneous” one, with no wiggle-room for pauses in the countdown, due to hardware or weather issues. Loading of the Upgraded Falcon 9 with liquid oxygen and a highly refined form of rocket-grade kerosene (known as “RP-1”) got underway about an hour before launch. Since last September’s on-the-pad explosion of the Amos-6 mission, the booster has been put through a slightly longer fueling regime.
Passing T-10 minutes, the terminal countdown 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, ahead of the ignition sequence. At T-2 minutes, the Air Force Range Safety Officer declared all ground assets as “Go for Launch” and the Upgraded Falcon 9 transitioned to Internal Power and assumed primary command of all critical functions, going into “Startup” at T-1 minute. At this stage, the Niagara deluge system began flooding the pad surface with 30,000 gallons (113,500 liters) of water, per minute, to suppress the acoustic energy. The Eastern Range declared its readiness as “Green”.
Three seconds before liftoff, the Merlins roared to life, pumping out a combined thrust of 1.5 million pounds (680,000 kg) of thrust. Liftoff occurred on-time at 12:31 p.m. EDT. Immediately after clearing the tower, the Upgraded Falcon 9 executed a combined pitch, roll and yaw program maneuver to establish itself onto the proper flight azimuth to inject the CRS-12 Dragon into orbit at an inclination of 51.66 degrees to the equator. Passing the point of maximum aerodynamic turbulence (colloquially dubbed “Max Q”) at 70 seconds into the flight, the booster later throttled back two of the Merlins to reduce the rate of acceleration at Main Engine Cutoff (MECO). Two and a half minutes after launch, the seven remaining Merlins fell silent and the first stage separated from the stack.
As with its predecessors, CRS-12 will approach the space station along the “R-Bar” (or “Earth Radius Vector”), which provides an imaginary line from Earth’s center, effectively approaching from “below”. In so doing, Dragon will take advantage of natural gravitational forces to brake its final approach and reduce the need to perform excessive numbers of thruster firings. By Wednesday morning, it will reach a “Hold Point” about 1.5 miles (2.4 km) from the station, whereupon it must pass a “Go/No-Go” poll of flight controllers in order to draw nearer.
Further polls and holds will be made at distances of 3,700 feet (1,130 meters) and 820 feet (250 meters), after which Dragon will creep toward its target at less than 3 inches (7.6 cm) per second. Critically, at 650 feet (200 meters), it will enter the “Keep-Out Sphere” (KOS), which provides a collision avoidance exclusion zone, and its rate of closure will be slowed yet further to just under 2 inches (5 cm) per second.
After clearance has been granted for the robotic visitor to advance to the 30-foot (10-meter) “Capture Point”, the final stage of the rendezvous will get underway, bringing Dragon within range of the station’s 57.7-foot-long (17.6-meter) Canadarm2 and capture by Expedition 52 Flight Engineer Jack Fischer, backed-up by Italian astronaut Paolo Nespoli. Both crew members will be based in the multi-windowed cupola for the operation. Capture is currently targeted for 7 a.m. EDT Wednesday, with ground commanding to berth Dragon at the Earth-facing (or “nadir”) port of the Harmony node at 9 a.m.
It is expected that CRS-12 will remain attached to the space station until 10 September, returning to Earth shortly before the launch of Soyuz MS-06 and three new crew members for Expedition 53. As outlined previously by AmericaSpace, CRS-12 is laden with 6,415 pounds (2,910 kg) of equipment, experiments and supplies to support 250 ongoing and upcoming research investigations, as well as the Cosmic Ray Energetics and Mass (CREAM) payload for installation onto the Exposed Facility (EF) of Japan’s Kibo laboratory.
Although the primary focus of today’s launch was to deliver the CRS-12 Dragon into orbit, the discarded first stage was assigned the secondary objective of returning to a soft landing on the LZ-1 pad at Cape Canaveral Air Force Station. SpaceX’s record of bringing its Falcon hardware back through the “sensible” atmosphere has evolved considerably over the last three years. To date, eight Falcon 9 first stages have successfully landed on the Autonomous Spaceport Drone Ship (ASDS) in either the Atlantic or Pacific Oceans and—including today’s mission—six have alighted on solid ground at LZ-1.
Less than three minutes after leaving Pad 39A, the Upgraded Falcon 9’s first stage executed the first “burn” of its Merlin 1D+ engines—the so-called “Boost-Back”—which adjusted the impact point, pushing it upward and directly it towards LZ-1. Assisted by on-board nitrogen-fed thrusters, the first stage “flipped” over and performed Entry and Landing burns to incrementally slow it down, initially to about 560 mph (900 km/h) and eventually a touchdown velocity of 4.5 mph (7.2 km/h). Controlling the first stage’s lift vector were four lattice-like hypersonic grid fins, configured in an “X-wing” layout, and the Falcon touched down perfectly on LZ-1, less than nine minutes after departing Pad 39A.
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