For the 30th time in under seven years, the roar of Merlin rocket engines heralded another mission for SpaceX earlier today, as the Hawthorne, Calif.-headquartered launch services company delivered its latest payload to orbit, earlier today (Sunday). Flying for the tenth time in its “Upgraded” configuration—and its maiden launch from historic Pad 39A at the Kennedy Space Center (KSC) in Florida—the workhorse Falcon 9 booster behaved flawlessly, as it delivered the CRS-10 Dragon cargo ship into low-Earth orbit, bound for the International Space Station (ISS).
After yesterday’s launch attempt was scrubbed at T-13 seconds, due to a Thrust Vector Control (TVC) issue, Sunday proved charmed and the Upgraded Falcon 9 roared aloft at 9:38 a.m. EST. In doing so, SpaceX fulfilled another requirement under its Commercial Resupply Services contract with NASA. Current plans call for Dragon to be robotically captured and berthed at the space station on Monday, where it will remain for about four weeks.
Despite being classified as a secondary mission objective, attention was inevitably drawn to today’s triumphant touchdown of the upgraded Falcon 9 first stage on Landing Zone (LZ)-1 at neighboring Cape Canaveral Air Force Station. Formerly part of the Cape’s Launch Complex (LC)-13—utilized extensively by Atlas boosters between 1958 and 1978, most notably launching NASA’s Lunar Orbiter program—the complex was out of service for more than three decades, before SpaceX leased it from the Air Force in February 2015 as its first rocket landing site. Less than a year later, on 21 December 2015, the returning first stage of the first Upgraded Falcon 9 powered itself back to Earth and alighted precisely, close to the center of the 282-foot-wide (86-meter) landing pad. The feat was repeated at the end of last July’s CRS-9 Dragon mission.
Last Sunday, as is customary before each mission, the Upgraded Falcon 9 underwent a Static Fire Test of the nine Merlin 1D+ first-stage engines, which raised a thunderous roar, a cloud of smoke and yielded 1.5 million pounds (680,000 kg) of propulsive yield. Customary as it may be, the event was notable in that it marked the first occasion that rocket engines had been fired at Pad 39A since the final voyage of the Space Shuttle, back in July 2011. And if the 230-foot-tall (70-meter) Upgraded Falcon 9 itself looked peculiar, it certainly was, for the loss of Amos-6 in a launch pad explosion last 1 September led to new rules, precluding primary payloads from being mounted atop the vehicle during its test-firings.
With the successful completion of last weekend’s Static Fire Test, the CRS-10 Dragon was installed atop the Upgraded Falcon 9, as SpaceX moved towards an opening launch attempt at 10:01 a.m. EST Saturday, 18 February. The weather outlook at the Cape was predicted to be iffy, with a paltry 50-percent likelihood of acceptable conditions at T-0. The arrival of a strengthening upper-level trough over the Gulf of Mexico on Friday was expected to usher in widespread clouds and rain, migrating over the Florida peninsula and risking entrenchment over KSC by mid-morning Saturday. Nor did Sunday’s backup launch attempt at 9:38 a.m. offer a significantly better alternative; its 70-percent-favorable forecast was tempered by the possibility of violating the Cumulus Cloud Rule.
In spite of the gloomy outlook, SpaceX pressed ahead with the final stages of the countdown. The Upgraded Falcon 9 benefits from “full-thrust” engines, an upgraded airframe and can deliver up to 50,300 pounds (22,800 kg) into low-Earth orbit. It requires a far shorter timeframe to load its liquid oxygen and rocket-grade kerosene (known as “RP-1”) propellants and, before last September’s anomaly, tanking typically did not commence until T-35 minutes. “Following the completion of our investigation,” SpaceX told AmericaSpace, “we indicated we were adjusting our fueling procedures. That’s temporary until we roll out the new [Falcon 9] design.” When the Upgraded Falcon 9 returned to flight in January, RP-1 tanking began more than an hour ahead of T-0, followed by liquid oxygen loading about 45 minutes before launch. A similar protocol was followed with CRS-10, with RP-1 beginning to enter the Upgraded Falcon 9’s tanks at 8:51 a.m. and liquid oxygen shortly thereafter at 9:19 a.m.
As circumstances transpired, the weather outlook for Saturday improved to 70-percent favourable, with a potential violation of the Thick Cloud Rule identified by the 45th Weather Squadron as the key obstacle. Passing T-10 minutes, the terminal countdown autosequencer was initiated and the nine Merlin 1D+ first-stage engines—arranged in a circle of eight, with the ninth at the center—were chilled-down, ahead of ignition. All external Ground Support Equipment (GSE) utilities were disconnected. The “strongback” was retracted and the Flight Termination System (FTS) was placed onto internal power and armed. In the final minutes before 10:01 a.m. EST, the Upgraded Falcon 9 transitioned to internal power and assumed primary command of all critical functions, going into “Startup”, at T-60 seconds. 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”.
However, the clock was halted at T-13 seconds, necessitating a scrub, in view of the instantaneous requirement of the CRS-10 mission. A couple of technical issues on the Upgraded Falcon 9’s second stage had arisen during the terminal countdown; namely the Thrust Vector Control (TVC) and the FTS. Launch was rescheduled for 9:38:59 a.m. EST Sunday. “Standing down to take a closer look at positioning of the second-stage engine nozzle,” SpaceX tweeted at 10:05 a.m. SpaceX CEO Elon Musk later added: “If this is the only issue, flight would be fine, but need to make sure that it isn’t symptomatic of a more significant upstream root cause.” He expanded upon this by pointing out that the glitch would be “99% likely to be fine”, overcome by a closed-loop TVC, but SpaceX erred on the side of caution and elected to scrub.
Sunday’s backup attempt was also expected to feature 70-percent-favorable weather and SpaceX moved into a 24-hour turnaround of their vehicle. This time, the countdown proceeded without incident. Three seconds before T-0, the new Merlins roared to life, pumping out a combined thrust of 1.5 million pounds (680,000 kg). Liftoff occurred precisely on time at 9:38 a.m. This was SpaceX’s 11th cargo delivery run to the space station, counting the Commercial Orbital Transportation Services (COTS) Demo mission in May 2012 and ten “dedicated” CRS flights between October 2012 and July 2016. However, this is actually the tenth ISS-bound Dragon to achieve orbit, following the high-altitude breakup of a Falcon 9 v1.1 and the loss of CRS-9 back in June 2015.
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-10 Dragon into low-Earth orbit at an inclination of 51.66 degrees. 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 becoming the first rocket in almost six years to depart Pad 39A, the seven remaining Merlins fell silent and the first stage separated from the stack.
It was now the turn of the second stage, equipped with a single, restartable Merlin 1D+ Vacuum engine, capable of 210,000 pounds (92,250 kg). This now picked up the baton to deliver its payload into low-Earth orbit. During its burn, the protective nose fairing—covering Dragon’s berthing mechanism—was jettisoned and the spacecraft separated from the second stage a little under ten minutes after launch. Shortly thereafter, its pair of power-generating solar arrays were deployed. By 2.5 hours into the flight, Dragon’s Guidance and Navigation Control (GNC) Bay Door was opened to expose critical rendezvous sensors, ahead of the two-day journey to the ISS.
As with its predecessors, CRS-10 will approach the space station along the “R-Bar” (or “Earth Radius Vector”), which provides an imaginary line from Earth’s center towards its quarry, 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 Monday 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 50 Flight Engineer Thomas Pesquet, backed-up by Commander Shane Kimbrough. Both men will be based in the multi-windowed cupola for the operation.
The Robotics Officer (ROBO) in the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas, will then command the physical berthing of the cargo ship to the nadir CBM of the Harmony node. Berthing will occur in two stages, with the Expedition 50 crew overseeing “First Stage Capture”, in which hooks from the node’s nadir CBM will extend to snare the cargo ship and pull their respective CBMs into a tight mechanized embrace. “Second Stage Capture” will then rigidize the two connected vehicles, by driving 16 bolts, effectively establishing Dragon as part of the ISS for the next month. Shortly afterwards, the Expedition 50 crew will be given a “Go” to pressurize the vestibule leading from the Harmony nadir hatch into the cargo ship.
Although the primary focus of today’s launch was to deliver the CRS-10 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. The provision of landing legs and hypersonic grid fins on the Falcon 9 v1.1 allowed for four “controlled oceanic touchdowns” of first stages in April, July and September 2014, followed by four mixed-success attempts to physically land on the deck of the Autonomous Spaceport Drone Ship (ASDS) in the Atlantic Ocean.
Only on the maiden flight of the Upgraded Falcon 9 in December 2015 was a perfect controlled touchdown achieved; a success sweetened yet further by the fact that it did so on solid ground, at LZ-1. Since then, with the exception of three ASDS landing failures in January, March and June 2016, four returning Falcon first stages have touched down perfectly on the drone ship—the most recent instance being last month’s Iridium NEXT mission—and another has alighted on 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. “Baby came back!” tweeted Mr. Musk.
With Dragon now safely en-route to the ISS, the focus can turn to the next missions. On Wednesday, Iridium announced that its second batch of NEXT satellites—previously due to be launched by SpaceX in April—will now not launch until mid-June. The delay comes in response to a backlog of missions still on SpaceX’s books, after the September on-pad failure. “After such a successful first launch, we are eager to maintain the momentum until our network is completed,” noted Iridium CEO Matt Desch. “Even with this eight-week shift, SpaceX’s targeted schedule completes our constellation in mid-2018.” The announcement came as Iridium successfully connected the first NEXT satellite via its crosslinks into its existing global low-Earth orbit constellation.
As is customary, SpaceX has remained tight-lipped on its future manifest, stating only that its next mission from Pad 39A will deliver the heavyweight EchoStar-XXIII communications satellite to Geostationary Transfer Orbit (GTO). No launch date has been officially announced, but 28 February has been suggested. If EchoStar-XXIII does fly before month’s end, it will mark the shortest-ever interval between two launches from Pad 39A, eclipsing the 17 days betwist a pair of Space Shuttle missions in April 1985.
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