More than six years after signing the $1.6 billion Commercial Resupply Services (CRS) agreement with NASA to deliver 12 Dragon cargo missions and a total of 44,000 pounds (20,000 kg) of payloads, experiments, and supplies to the International Space Station (ISS), SpaceX—the Hawthorne, Calif.-based launch operator—will hit 50-percent-complete on its initial contractual obligation next week, when it delivers its sixth dedicated mission toward the orbital outpost. Liftoff of the company’s homegrown Falcon 9 v1.1 booster and the CRS-6 Dragon is scheduled to occur from the storied Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla., during an “instantaneous” window which opens at 4:33 p.m. EDT Monday, 13 April. An on-time launch will produce a rendezvous, capture, and berthing at the space station Wednesday morning. If SpaceX is unable to meet this window, it has Eastern Range clearance to recycle 24 hours for a backup attempt at 4:10 p.m. EDT Tuesday, 14 April, which will in turn push back the berthing time to Thursday.
As described in a recent AmericaSpace article, this particular Dragon will fly with its unpressurized “Trunk” empty of payloads, but will transport about 4,390 pounds (1,990 kg) of provisions, payloads, tools, and scientific equipment to the station’s incumbent Expedition 43 crew in its pressurized segment. That cargo consists of 1,100 pounds (500 kg) of crew supplies, including care packages from home, food, and provisions, 1,140 pounds (518 kg) of miscellaneous items for the station’s Environmental Control and Life Support System (ECLSS) and Electrical Power System (EPS), 1,860 pounds (844 kg) of “Utilization” hardware—including U.S.-sponsored experiments and research payloads from the Canadian Space Agency (CSA), the Japan Aerospace Exploration Agency (JAXA), and the European Space Agency (ESA)—and about 79 pounds (36 kg) of command and data-handling equipment, TV and photographic gear, and EVA tools. According to NASA, the EVA tools include wire ties, one Fan Pump Separator (FPS), and a number of rechargeable battery assemblies for the U.S. Extravehicular Mobility Units (EMUs).
Further detail has also been shed on a cadre of experiments, provided by the Center for the Advancement of Science in Space (CASIS). As noted in AmericaSpace’s previous CRS-6 article, this includes the Rodent Research-2 investigation, which will transport mice to the ISS as part of ongoing studies of mammalian physiology in the microgravity environment. Led by Principal Investigator Samuel Cadena, the experiment’s specific foci are to monitor the musculoskeletal and neurological systems of the mice as model organisms of human health and disease. “Living in microgravity results in significant and rapid effects on the physiology of mice that mimic the process of aging and some diseases in humans on Earth,” it was explained, “including muscle atrophy and the loss of bone mineral density.” It is hoped that long-duration exposure—the mice will remain in orbit for at least five weeks—will “induce changes in gene expression, protein synthesis, metabolism and eye structure/morphology that will be identifiable as a series of assessable biomarkers for tracking the onset and progression of disease.”
In addition, other CASIS payloads aboard CRS-6 include Principal Investigator Paolo Divieti Pajevic’s OSTEO-4 experiment, which seeks to study the function of osteocytes—the most common cells in bone—as part of efforts to analyze changes in the physical appearance and genetic expression of the mouse bone cells in weightlessness. Meanwhile, Principal Investigator Paul Reichert’s Microgravity Growth of Crystalline Monoclonal Antibodies for Pharmaceutical Applications will utilize the Handheld High-Density Protein Crystal Growth (HDPCG) hardware and seeks to crystallize two human monoclonal antibodies. The latter are specialized proteins, formed by immune cells which “bind” to target cells, and the overall experiments seeks to test new pharmaceutical products for the treatment of human diseases. It is hoped that the crystal growth process will be of sufficiently high quality “to improve drug delivery and purification methods and to determine protein structure.” Additionally, Principal Investigator Lenore Rasmussen’s investigation will fly aboard CRS-6 to test radiation resistance of an electroactive polymer called “Synthetic Muscle.” Developed by Ras Labs, Synthetic Muscle can contract like real muscle, and also expand, carrying potentially useful applications for advanced robotics, realistic prosthetics, and human-like robots.
Unlike several previous Dragons, including January’s long-delayed CRS-5, the CRS-6 mission has met with relatively little delay, with only a slight realignment of its target launch date from 10 April to 13 April, confirmed at the end of March. This impressive adherence to schedule is in spite of a recent juggling of flight priorities which has seen CRS-6 leapfrog Turkmenistan’s first national satellite, TurkmenAlem52E/MonacoSat—also internally known as “Thales,” in honor of its manufacturer, the Paris, France-headquartered Thales Group—whose original 21 March launch date has been postponed until No Earlier Than (NET) 24 April. As detailed in a recent AmericaSpace article, issues surrounding the problematic performance of helium pressurization bottles during testing raised sufficient concern that SpaceX replaced the bottles on Thales’ Falcon 9 v1.1 “out of an abundance of caution.” That replacement effort was reportedly “nearing completion” at the start of April.
Monday’s scheduled launch of CRS-6 will mark SpaceX’s second attempt to soft-land the first stage hardware of its Falcon 9 v1.1 on the Autonomous Spaceport Drone Ship (ASDS)—a 288-feet-long (87.8-meter) x 100-feet-wide (30.5-meter) Marmac 300 Freight Barge, equipped with diesel-powered azimuth thrusters, repurposed from oil rigs—several hundred miles out to sea, to the northeast of the Cape. This is part of SpaceX’s continuous effort to develop a fully reusable capability for its Falcon 9 v1.1 hardware. A previous attempt during the CRS-5 launch in January achieved partial success, for although the first stage reached the deck of the barge, a premature exhaustion of hydraulic fluid to the hypersonic grid fins caused it to impact at a 45-degree angle and exploded. Original plans for another attempt during the Deep Space Climate Observatory (DSCOVR) launch in February were called off due to rough sea conditions.
As described in a recent article by AmericaSpace’s Mike Killian, repairs were conducted and a planned series of upgrades to make the ASDS more stable in rough waters were announced as being underway by SpaceX founder Elon Musk. On Tuesday, 7 April, the two primary support vessels—the Elsbeth III, which draws the ASDS barge, and the Go Quest, which carries communications and tracking hardware—put to sea, heading a short distance off Port of Jacksonville to evaluate improvements made in advance of the CRS-6 landing attempt. Following these tests, the Elsbeth III was recorded as having returned to port at 6:36 a.m. EDT on Wednesday, 8 April, ahead of its deployment for dedicated CRS-6 mission operations. The tug was reported to have departed Port of Jacksonville at 3:37 a.m. EDT today (Saturday, 11 April), bound for a position in the Atlantic Ocean about 200 miles (320 km) to the northeast of Cape Canaveral.
CRS-6 will mark SpaceX’s fourth launch of the year, following hard on the heels of CRS-5 to low-Earth orbit on 10 January, DSCOVR toward the L2 Lagrange Point on 11 February, and, most recently, the Eutelsat 115 West B and ABS-3A communications satellites to Geostationary Transfer Orbit (GTO) on 1 March. If CRS-6 launches on time next week, this will make 2015 the first year in SpaceX’s history that it has delivered missions in as many as four consecutive months. Moreover, the mission fits into a manifest which should see as many as five Dragons flown in 2015, more than twice as many as has ever been achieved in any previous year. If these are executed according to schedule, CRS-6 will be followed by CRS-7 in June and CRS-9 in December, each of which will carry an International Docking Adapter (IDA) to support NASA’s Commercial Crew needs, whilst CRS-8 in September will deliver the Bigelow Expandable Activity Module (BEAM) to the station. To date, SpaceX has launched no more than two Dragons per year since its inaugural Commercial Orbital Transportation Services (COTS) test flight, back in May 2012, and if all goes well the company will complete 50 percent of its initial 12-flight CRS commitment to NASA when CRS-6 reaches the ISS and should reach 75-percent-complete by year’s end.
Following standard procedure, the Falcon 9 v1.1 was transported out to SLC-40 Saturday, where supported a brief Static Fire Test of the nine Merlin 1D engines on its first stage. It was then returned to its processing hangar for final preparations and the standard Launch Readiness Review (LRR) on Sunday, 12 April. Due to the nature of its destination—the ISS—the launch must occur precisely on time. Unlike several other missions, there exists no margin to accommodate last-minute technical issues or poor weather conditions. If the vehicle cannot launch on time Monday, the attempt will be scrubbed and the countdown clock recycled to track a second opportunity Tuesday afternoon. AmericaSpace understands that SpaceX’s launch campaign has been refined to meet this tight “window” and that the aim is to roll the Falcon 9 v1.1 out to the pad as close to launch as possible.
Assuming that NASA and SpaceX press ahead with the opening launch attempt—a decision which is expected to be announced in a press briefing at the Kennedy Space Center (KSC) on Sunday, 12 April—the Patrick Air Force Base weather forecast anticipates mostly cloudy conditions, with a 30 percent likelihood of rain and a 10 percent probability of lightning. Temperatures range between 19.4 degrees Celsius (67 degrees Fahrenheit) and 28.9 degrees Celsius (84 degrees Fahrenheit). Current estimates predict a 60 percent chance of acceptable weather, with potential violations of the Anvil Cloud Rule and the Thick Cloud Rule being the primary risk factors. “A cold frontal system makes its way south through the weekend, gradually increasing moisture and instability in Central Florida,” it was noted by the 45th Weather Squadron. “As the front stalls over Florida, clouds, showers and thunderstorms become more likely each day through Sunday.” Although the frontal boundary is expected to begin to dissipate over Central Florida early Monday, the risk of rain, thick cloud, and anvils are expected to drift toward the coast from inland storms. “Maximum upper-level winds are from the north-west at 55 knots near 45,000 feet (13,700 meters),” it was explained.
In the event of a 24-hour delay, conditions are expected to improve to 70 percent favourable. “On Tuesday, the front continues to slowly disintegrate,” it was pointed out by the 45th Weather Squadron, “decreasing the cloudiness and inland thunderstorm coverage.” Maximum upper-level winds from the west are expected to be somewhat calmer at 40 knots.
Following rollout to SLC-40, probably Sunday, depending upon the results of today’s Static Fire Test, the Falcon 9 v1.1 will be fueled with liquid oxygen and a highly refined form of rocket-grade kerosene, known as “RP-1.” The cryogenic nature of the oxygen—whose liquid state exists within a range from -221.54 degrees Celsius (-368.77 degrees Fahrenheit) to -182.96 degrees Celsius (-297.33 degrees Fahrenheit)—requires the fuel lines of the engines to be chilled, in order to avoid thermally shocking and potentially fracturing them. All propellants should be fully loaded within one hour, and at 4:20 p.m. EDT Monday, the countdown will reach its final “Go/No-Go” polling point of all stations at T-13 minutes. Assuming it passes through the poll of flight controllers, the Terminal Countdown will get underway at T-10 minutes.
During this phase, the Merlin 1D engines will be chilled, ahead of their ignition sequence. All external power utilities from the Ground Support Equipment (GSE) will be disconnected and at 4:28 p.m., the roughly 90-second process of retracting the “strongback” from the vehicle will get underway. The Flight Termination System (FTS)—which is tasked with destroying the Falcon 9 v1.1 in the event of a major accident during ascent—will be placed onto internal power and armed. By T-2 minutes and 15 seconds, the first stage’s propellant tanks will attain flight pressure. The Merlin 1Ds will be purged with gaseous nitrogen, and, at T-60 seconds, the SLC-40 complex’s “Niagara” deluge system of 53 nozzles will be activated, flooding the pad surface and flame trench with 30,000 gallons (113,500 liters) of water, per minute, to suppress acoustic energy radiating from the engine exhausts.
At T-3 seconds, the nine Merlins will roar to life, ramping up to a combined thrust of 1.3 million pounds (590,000 kg). Following computer-commanded health checks, the stack will be released from SLC-40 at 4:33 p.m. EDT. Immediately after clearing the tower, the booster will execute a combined pitch, roll, and yaw program maneuver, which is designed to establish it onto the proper flight azimuth to inject the CRS-6 Dragon into low-Earth orbit. Eighty seconds into the uphill climb, the vehicle will exceed the speed of sound and experience a period of maximum aerodynamic duress—colloquially dubbed “Max Q”—on its airframe. At about this time, the Merlin 1D Vacuum engine of the second stage will undergo a chill-down protocol, ahead of its own ignition later in the ascent. At 4:35 p.m., 130 seconds after liftoff, two of the first-stage engines will throttle back, under computer command, in order to reduce the rate of acceleration at the point of Main Engine Cutoff (MECO).
Finally, at T+2 minutes and 58 seconds, the seven remaining engines will shut down, and, a few seconds later, the first stage will separate from the rapidly ascending stack. The turn will then come for the restartable second stage, whose Merlin 1D Vacuum engine—with a maximum thrust of 180,000 pounds (81,600 kg)—will come to life to continue the boost into orbit. Based upon previous Dragon missions, it will burn for about six minutes and 45 seconds to inject the cargo ship into a “parking orbit.” During this period, the protective nose fairing, which covers Dragon’s berthing mechanism, will be jettisoned. Ten minutes after departing the Cape, the sixth overall ISS-bound Dragon will separate from the second stage and unfurl its two electricity-generating solar arrays, deploy its Guidance and Navigation Control (GNC) Bay Door to expose critical rendezvous sensors, and begin the intricate sequence of maneuvers to reach the ISS on Wednesday, 15 April.
As Dragon begins its journey to the space station, the first stage hardware of the Falcon 9 v1.1 will begin making its way back to Earth. After it separates from the main body of the stack, about three minutes into the flight, the 150-foot-tall (46-meter) first stage will be traveling at a velocity of 2,900 mph (4,670 km/h) and maintaining stabilization has been likened to someone balancing a rubber broomstick on their hand, in the middle of a fierce windstorm. Three Merlin 1D engine firings will be executed in order to steadily reduce this velocity and stabilize the first stage. An initial “Boost-Back” burn will adjust the vehicle’s impact point, pushing it upward and directing it back toward the Cape. Assisted by nitrogen thrusters, the stage will flip over and a “Supersonic Retro-Propulsion” burn will slow it to about 560 mph (900 km/h). A final “Landing” burn will bring this down still further to just 4.5 mph (7.2 km/h). The first stage will utilize compressed helium to deploy its four extendable landing legs and a quartet of lattice-like hypersonic grid fins—configured in an “X-wing” layout—will be unfurled to control the lift vector. Coupled with engine gimbaling, these will enable a precision touchdown on the ASDS surface. During January’s partial successful attempt to soft-land Falcon 9 v1.1 first-stage hardware, an exhaustion of hydraulic fluid to the grid fins was initially blamed for the “hard” touchdown.
In charge of the successful arrival of CRS-6 are the incumbent Expedition 43 crew, which comprises Commander Terry Virts of NASA, together with Russian cosmonauts Anton Shkaplerov, Gennadi Padalka, and Mikhail Kornienko, U.S. astronaut Scott Kelly, and and Italy’s first woman in space, Samantha Cristoforetti. As part of their preparations, the crew will install the Centerline Berthing Camera System (CBCS) inside the Earth-facing (or “nadir”) hatch of the station’s Harmony node and route video equipment to permit imagery to be obtained for the Robotics Workstation (RWS) in the multi-windowed cupola and for Mission Control at the Johnson Space Center (JSC) in Houston, Texas.
As with previous Dragons, CRS-6 will approach the ISS along the “R-Bar” (or “Earth Radius Vector”), which provides an imagery line from Earth’s center toward the station, effectively approaching its quarry from “below.” In doing so, Dragon will take advantage of natural gravitational forces to provide braking for its final approach and reduce the overall number of thruster firings it needs to perform. By Wednesday morning, it will reach the vicinity of the ISS. A carefully orchestrated symphony of maneuvers will bring the cargo ship to a “Hold Point” about 1.5 miles (2.4 km) from the space station, whereupon it must pass a “Go/No-Go” poll of flight controllers in order to draw closer. 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 57.7-foot-long (17.6-meter) Canadarm2 mechanical arm. Cristoforetti will be at the controls for the capture and berthing, with Virts backing her up. Both astronauts will be stationed within the cupola. Following the initial capture of Dragon—an event anticipated to take place at about 7:14 a.m. EDT Wednesday—it will be maneuvered by Mission Control to its berthing interface on the nadir port of the Harmony node.
Physical berthing will occur in two stages, with the Expedition 43 crew overseeing “First Stage Capture,” in which hooks from the node’s nadir Common Berthing Mechanism (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. Shortly afterwards, the crew will be given a “Go” to pressurize the vestibule leading from the Harmony nadir hatch into the cargo ship.
Present plans envisage the CRS-6 Dragon remaining berthed at the ISS for about five weeks, with its robotic unberthing, departure, and return to Earth anticipated in mid-May. It will be loaded with about 3,000 pounds (1,360 kg) of supplies, hardware, and computer equipment, as well as experiment results, which it will transport back through the atmosphere to a parachute-assisted splashdown off the coast of Baja California. At present, Dragon is the only unpiloted cargo craft capable of returning payloads safely to Earth; by contrast, its partners—Europe’s Automated Transfer Vehicle (ATV), Japan’s H-II Transfer Vehicle (HTV), Russia’s Progress, and Orbital Sciences’ Cygnus—are loaded with trash and intentionally incinerated in the dense upper atmosphere.