For the 10th time in a little over four years, SpaceX delivered a Dragon cargo ship on a journey toward the International Space Station (ISS) in the opening minutes of Monday morning. Liftoff of the CRS-9 mission—conducted under the language of the initial $1.6 billion Commercial Resupply Services (CRS) contract with NASA—occurred on-time at 12:45 a.m. EDT from Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla. In keeping with ISS-bound flights, the launch window was an “instantaneous” one, imposing additional restrictions upon the SpaceX team and leaving little margin for last-moment technical issues or changeable weather conditions.
About 10 minutes after rising from the Cape, Dragon separated from the second stage of its Upgraded Falcon 9 booster and was in the process of deploying its solar arrays and other hardware, ahead of a robotic capture and berthing by Expedition 48 Commander Jeff Williams and Flight Engineer Kate Rubins on Wednesday morning. Meanwhile, the first stage of the booster executed a smooth touchdown at Landing Zone (LZ)-1 at the Cape just 8 minutes and 17 seconds after launch, marking the second “land” landing of Upgraded Falcon 9 hardware, following last December’s historic opening attempt.
As outlined in AmericaSpace’s CRS-9 preview article, today’s mission is particularly significant for NASA, as the agency presses ahead with its plans to launch the first Commercial Crew vehicles—Boeing’s CST-100 Starliner and SpaceX’s Crew Dragon—to the space station at some stage in 2017. The first of two International Docking Adapters (IDAs) is housed aboard Dragon’s unpressurized “trunk” and in mid-August will be installed, via robotics and the gloved hands of spacewalkers Williams and Rubins, onto Pressurized Mating Adapter (PMA)-2 at the forward end of the Harmony node. This will provide the primary Commercial Crew docking interface, with a second IDA tentatively scheduled to follow aboard another Dragon in mid-2018. In addition to the IDA, today’s CRS-9 pressurized load also includes a wide range of research payloads in support of 280 new and ongoing science investigations for the incumbent Expedition 48 crew.
In readiness for the opening launch attempt, the two-stage Upgraded Falcon 9 conducted a customary Static Fire Test of the nine Merlin 1D+ first-stage engines on Friday evening. Configured in an octagonal pattern, with a circle of eight engines and a ninth in the center, the first stage generates 1.5 million pounds (680,000 kg) of propulsive yield at T-0. With the satisfactory conclusion of the test, SpaceX engineers pressed ahead with a smooth Launch Readiness Review (LRR).
According to the 45th Weather Squadron at Patrick Air Force Base, meteorological conditions for the wee hours of Monday morning were anticipated to be 90-percent favorable, tempered by the slight possibility of violating the Cumulus Cloud Rule and a chance of Flight Through Precipitation. Southeasterly low-level winds and isolated onshore morning showers were highlighted and expected to remain in place during the early part of the week, creating “moderate temperatures” and “any potential sea breeze storms to move inland.” A delay to the backup opportunity at 12:00 a.m. EDT Wednesday, 20 July, was expected to trigger markedly worse conditions of around 70-percent favorable, with the added risk of violating the Thick Cloud Rule.
The Upgraded Falcon 9 hardware arrived at the Cape in late June, with Monday’s launch representing the seventh flight of the new vehicle in as many months. Unveiled last year, the booster—which benefits from “full-thrust” engines, an upgraded airframe and a 33-percent performance hike over its predecessor, the Falcon 9 v1.1—stands about 230 feet (70 meters) tall and can deliver up to 50,300 pounds (22,800 kg) into low-Earth orbit. On its maiden voyage in December 2015, the Upgraded Falcon 9’s first stage alighted smoothly on LZ-1, with five successive attempts to touchdown on the Autonomous Spaceport Drone Ship (ASDS) in the Atlantic Ocean. Of these ASDS landing attempts, three met with full success and the others succumbed to failure. Hedging its bets, perhaps, SpaceX noted in its press kit that CRS-9’s landing attempt on LZ-1 would be “experimental” in nature.
The Upgraded Falcon 9 requires a far shorter period to load its liquid oxygen and rocket-grade kerosene (known as “RP-1”) propellants and does not commence tanking until T-35 minutes. Countdown operations reached their critical “Go/No-Go” polling point of all stations at T-13 minutes and the Terminal Count got underway at 12:35 a.m. EDT, with 10 minutes remaining until T-0. During these final minutes, the Merlin 1D+ engines were chilled, preparatory to their ignition sequence, and all external power utilities from the Ground Support Equipment (GSE) were disconnected. The “strongback” was retracted from the booster at T-5 minutes and the Flight Termination System (FTS) was placed onto internal power and armed.
From SpaceX’s headquarters in Hawthorne, Calif., came the unique blend of humor from the company’s director of Crew Operations, former shuttle and ISS astronaut Garrett Reisman. “Just another typical late Sunday night at work in Hawthorne,” he tweeted. “Launching rockets and spacecraft. Woooodoggies!”
Fueling concluded and the first stage propellant tanks attained their proper flight pressures. At T-60 seconds, the “Niagara” water deluge system at SLC-40 was activated, flooding the launch pad and flame trench with 30,000 gallons (113,500 liters) of water per minute to suppress acoustic energy at the instant of engine ignition. The nine Merlins roared to life at T-3 seconds and ramped perfectly up to a combined 1.5 million pounds (680,000 kg). After computer checks validated their health, the vehicle departed SLC-40 at 12:45 a.m. EDT, turning night into day across the marshy Florida landscape. 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 deliver the CRS-9 Dragon into low-Earth orbit at an inclination of 51.6 degrees.
Passing through the speed of sound at 80 seconds into the ascent, the Upgraded Falcon 9 experienced maximum aerodynamic stress (colloquially known as “Max Q”) on its airframe. Later, two of the first-stage Merlins were throttled back to reduce the rate of acceleration at Main Engine Cutoff (MECO). Two-and-a-half minutes after leaving the Cape, the seven remaining Merlins were shut down and the first stage separated from the stack.
In the meantime, the first stage commenced its second mission of the morning: to return to LZ-1 for a soft landing. Two minutes and 42 seconds after departing SLC-40, the stage executed the first of three “burns” of its Merlin 1D+ engines—the so-called “Boost-Back”—which served to adjust the impact point, pushing it “upward” and directing it back towards LZ-1. “Falcon 9 first-stage entry burn underway,” SpaceX tweeted at 12:52 a.m. EDT. “Second stage and Dragon continuing nominally.”
Assisted by on-board nitrogen thrusters, the first stage “flipped” over and an “Entry” burn slowed it down to about 560 mph (900 km/h). A final “Landing” burn reduced this yet further to just 4.5 mph (7.2 km/h). The first stage utilized compressed helium to deploy its four extendable landing legs and a quartet of lattice-like hypersonic grid fins—configured in an “X-wing” layout—were unfurled to control the lift vector. Landing occurred at approximately 8 minutes and 17 seconds after launch. “First stage landing at LZ-1,” SpaceX tweeted at 12:55 p.m. EDT. “Second stage and Dragon continuing to orbit.”
Unsurprisingly, the congratulations flooded in. “Anyone in the market for a pre-owned boost-stage rocket?” Garrett Reisman rhetorically asked. “Ask about our group purchase discounts.” Elsewhere, Kennedy Space Center (KSC) Director and former shuttle astronaut Bob Cabana added: “Awesome launch and return of Falcon 9.”
With the first stage gone, the turn came for the restartable second stage, whose single Merlin 1D+ Vacuum engine—capable of 210,000 pounds (92,250 kg) of thrust—ignited to continue the boost toward 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 about nine minutes and 37 seconds into the mission. Around two minutes later, its pair of power-producing solar arrays were deployed. And two hours and 19 minutes after launch, the Guidance and Navigation Control (GNC) Bay Door was opened to expose critical rendezvous sensors. An intricate series of maneuvers to reach the vicinity of the ISS on Wednesday morning also got underway.
As with previous Dragons, CRS-9 will approach the space station along the “R-Bar” (or “Earth Radius Vector”), which provides an imaginary line from Earth’s center toward the ISS, effectively approaching its quarry 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 burns. 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 Canadarm2 and capture by Expedition 48 Commander Jeff Williams and Flight Engineer Kate Rubins, based in the multi-windowed cupola.
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 48 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 48 crew will be given a “Go” to pressurize the vestibule leading from the Harmony nadir hatch into the cargo ship.
Although today’s launch was the tenth mission sent toward the space station, it is actually the ninth ISS-bound Dragon to actually achieve orbit, when one counts last June’s loss of CRS-7 during first-stage ascent. Under the terms of its original CRS contract with NASA, SpaceX executed a Commercial Orbital Transportation Services (COTS) “Demo” flight in May 2012, followed by six “operational” Dragons between October 2012 and April 2015. The failure of CRS-7 in June 2015 brought operations grinding to a halt for several months, but Dragon returned to the ISS in April 2016 with CRS-8. According to Novosti Kosmonavtiki, another Dragon—CRS-10—is targeted for November 2016, carrying the Department of Defense’s Space Test Program (STP)-H5 with the Lightning Imaging Sensor (LIS) and the Stratospheric Aerosol and Gas Experiment (SAGE)-III to enhance the station’s capability as a research platform.
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