Making its eighth flight in less than 12 months, its sixth flight of the year, its fourth flight in just 10 weeks, and its second flight in a mere 14 days, SpaceX has triumphantly delivered its latest Dragon cargo mission toward the International Space Station (ISS). Liftoff of the CRS-4 flight—the fourth dedicated Dragon resupply mission under the language of the $1.6 billion Commercial Resupply Services contract, signed with NASA back in December 2008—took place at 1:52 a.m. EDT Sunday, 21 September, under crystal-clear and virtually cloudless skies, from Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla. Originally planned to fly at 2:16 a.m. Saturday, CRS-4 was kept on the ground for an additional 24 hours, due to adverse weather conditions. The Falcon 9 v1.1 launch vehicle performed admirably, inserting Dragon precisely into low-Earth orbit, ahead of the cargo ship’s rendezvous and berthing at the space station early Tuesday.
In fact, the Falcon 9 v1.1 has rebounded remarkably from a mixture of highs and lows in 2014. Following a frustrating summer, which saw the Orbcomm OG-2 mission delayed repeatedly, prior to a successful launch on 13 July, SpaceX—the Hawthorne, Calif.-based launch services organization, headed by entrepreneur Elon Musk—picked itself up and scored two “personal bests” with AsiaSat-8 on 5 August, delivering two payloads within three weeks and achieving a record fourth flight in a single calendar year. A personal-best-beating fifth mission, with AsiaSat-6 on 7 September, further cemented its reliability credentials. With CRS-4, SpaceX not only beat its personal bests yet again, but for the first time succeeded in flying two missions within the same calendar month. These achievements followed two earlier successes in 2014: the delivery of the Thaicom-6 geostationary satellite in January and the third dedicated Dragon (CRS-3) mission to the ISS in April.
Carrying about 5,000 pounds (2,270 kg) of equipment and supplies for the space station’s incumbent Expedition 41 crew, Dragon was hoisted atop its launch vehicle at SLC-40 shortly after Thursday’s successful rollout and “hot-fire” test of the nine Merlin-1D first stage engines. These hot fires are carried out shortly before each Falcon 9 v1.1 launch. SpaceX initially hoped to fly at 2:16 a.m. Saturday, 20 September, and was required to meet an “instantaneous” launch window in order to create the proper rendezvous conditions for its journey to the ISS. This offered no margin to accommodate delays caused by technical problems or an unacceptable weather outlook.
In support of this opening attempt, the countdown commenced late Friday, when the vehicle was powered-up on the pad, but it seemed obvious from an early stage that the weather would go down to the wire. With heavy rain lashing the Cape, multiple violations kept the weather classified as “Red” (“No-Go”) throughout the late evening. Hoping for a lucky break, SpaceX managers and engineers pushed ahead with fueling the Falcon 9 v1.1 with a mixture of liquid oxygen and a highly refined form of rocket-grade kerosene (known as “RP-1”) a little after 10 p.m. The cryogenic nature of the oxygen—whose liquid state exists within a temperature range from -221.54 degrees Celsius (-368.77 degrees Fahrenheit) to -182.96 degrees Celsius (-297.33 degrees Fahrenheit)—required the fuel lines of the Merlin-1D engines to be chilled, in order to avoid thermally shocking and fracturing them. Within the next hour, fueling was complete, after which the vehicle transitioned into a “Replenishment Mode,” whereby boiled-off cryogens were continuously topped-up until close to the launch time.
Alas, it was not to be. The weather proved increasingly stubborn, and shortly before midnight Friday conditions had deteriorated to less than 30 percent favorable. “The entire Central Florida coast,” noted AmericaSpace’s Launch Tracker, “has rain clouds with a band of rain moving slowly over the area.” The worst was yet to come. By 12:40 a.m. Saturday, just 90 minutes before the opening of the instantaneous window, two of the 10 weather-related Launch Commit Criteria—specifically Disturbed Weather and Thick Cloud—had declared themselves as “Red” (“No-Go”). All 10 weather rules must be “Green” (“Go”) in order for a mission to go ahead, making it increasingly likely that the launch would be scrubbed for the night and postponed by 24 hours. By 1:30 a.m., conditions had fallen to just 10 percent acceptable, with Thick Cloud and Flight Through Precipitation added to the list of woes. Finally, at 1:47 a.m., the Launch Director called a scrub.
Immediately, SpaceX teams initiated their post-scrub protocols, safing the Falcon 9 v1.1 on the pad, draining propellants from the tanks, and beginning to reconfigure systems in anticipation of a second launch attempt early Sunday morning. The Eastern Range had granted approval for two back-to-back attempts, with Sunday’s instantaneous window timed to open at 1:52 a.m. Late Saturday afternoon, the countdown commenced again, under much more benign skies. The previous night’s persistent rain had cleared, with light showers and thunderstorms predicted to change to cloudy and overcast and expected to clear further to partly cloudy by the time the countdown reached T-0.
Fueling was complete by 10:35 p.m. and the weather had improved markedly. “What a difference a day makes,” exulted AmericaSpace’s Launch Tracker. “Yesterday, at this time, it was raining with heavy clouds covering the Cape Canaveral area. Now, 24 hours later, there is some light scattered clouds to the south and stars shining overhead and the air is still. If the weather continues to hold like this, it will be fantastic conditions for an on-time launch.”
Indeed it was. With meteorological conditions having risen to 70 percent favorable, and only Heavy Cloud and Disturbed Weather threatening the Falcon 9 v1.1’s climb to space, these quickly moved to 90 percent favorable by 12:50 a.m. Across the press site at the Cape, the cloudless skies glowed with almost crystal clarity. Launch teams pressed crisply through the standard “Go-No Go” polling of all stations and at 1:39 a.m., at T-13 minutes, the Launch Director authorized a formal “Go for Launch.” This cleared the way for the beginning of the Terminal Countdown at 1:42:36 a.m., at T-10 minutes, under whose auspices the Merlin-1D engines were chilled, preparatory to their ignition sequence. All external power utilities from the Ground Support Equipment (GSE) were disconnected, and at 1:47 a.m. the approximately 90-second process of retracting the “strongback” away from the Falcon 9 v1.1 began. The Flight Termination System (FTS), which would allow the Range Safety Officer to remotely destroy the rocket in the event of a major accident during ascent, was placed onto internal power and armed.
By T-2 minutes and 15 seconds, the first stage’s propellant tanks had reached their proper flight pressures. “Range Green” came the welcome call, as all of the chess pieces fell into place under perfect skies. The Merlin-1D engines were purged with gaseous nitrogen, and, at T-60 seconds, SLC-40’s “Niagara” deluge system of 53 nozzles was 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 Merlin-1Ds roared to life, ramping up to a combined thrust of 1.3 million pounds (590,000 kg). Following computer-commanded health checks, the vehicle was released from SLC-40 at 1:52:00 a.m. to commence SpaceX’s sixth mission of the year and its second mission within just two weeks.
Immediately after clearing the tower, the Falcon 9 v1.1 executed a combined pitch, roll, and yaw program maneuver to establish itself onto the proper flight azimuth to inject the CRS-4 Dragon spacecraft into low-Earth orbit. Eighty seconds into the ascent, the vehicle surpassed the speed of sound and experienced a period of maximum aerodynamic stress (known as “Max Q”) upon its airframe. At about the same time, the Merlin-1D Vacuum engine of the second stage underwent a chill-down protocol, ahead of its own ignition later in the ascent phase. At 1:54 a.m., 130 seconds after liftoff, two of the first-stage engines throttled back, under computer control, in order to reduce the rate of acceleration at the point of Main Engine Cutoff (MECO).
Finally, the seven remaining first-stage engines shut down, and, a few seconds later, at 1:54:46 a.m., the lower component of the Falcon 9 v1.1 separated from the rapidly ascending stack. Although this vehicle was not equipped with extendible landing legs, it was hoped that it would still be able to attempt a controlled oceanic landing as part of SpaceX’s ongoing campaign to develop a fully reusable capability for the Falcon 9 family.
With the first stage gone, the turn then came for the restartable second stage, whose single Merlin-1D Vacuum engine—with a maximum thrust of 180,000 pounds (81,600 kg)—roared to life at 1:54:55 a.m. and burned for six minutes and 45 seconds to continue the boost to deliver Dragon into an initial “parking” orbit. During this period, a protective nose cone, covering the spacecraft’s berthing mechanism, was jettisoned. About 35 seconds after the second stage engine fell silent, at 2:02:15 a.m., the cargo ship separated from the stack. Almost immediately, Dragon’s twin solar array “wings” were unfurled, to begin providing electrical power for its systems, and the Guidance and Navigation Control (GNC) Bay Door was deployed to expose critical rendezvous sensors which will be needed for the two-day rendezvous profile to reach the ISS.
Coming on the heels of the inaugural Commercial Orbital Transportation Services (COTS) Demo in May 2012 and the dedicated CRS-1 in October 2012, CRS-2 in March 2013, and CRS-3 in April-May 2014, the current flight is the fifth overall Dragon to rise into orbit and the fourth to be conducted under the $1.6 billion Commercial Resupply Services contract between SpaceX and NASA. This contract was signed in December 2008 and requires SpaceX to conduct 12 dedicated Dragon flights to the ISS and haul upwards of 44,000 pounds (20,000 kg) of equipment and supplies to the international outpost. Current plans envisage the CRS-5 Dragon to launch in December 2014, followed by as many as four more in February, June, August, and December 2015.
In charge of Dragon’s successful arrival are the Expedition 41 crew, which is currently staffed by Russian cosmonaut Maksim Surayev, U.S. astronaut Reid Wiseman, and Germany’s Alexander Gerst. Last week, Wiseman installed the Centerline Berthing Camera System (CBCS) inside the Earth-facing (or “nadir”) hatch of the station’s Harmony node, then routed video equipment to permit imagery to be obtained by the Robotics Workstation (RWS) in the cupola and by Mission Control in Houston, Texas. Meanwhile, Gerst worked to pre-pack items which will be returned to Earth aboard the CRS-4 mission in mid-October. Unlike all other operational unpiloted Visiting Vehicles—including Russia’s Progress, Europe’s Automated Transfer Vehicle (ATV), Japan’s H-II Transfer Vehicle (HTV), and Orbital Sciences’ Cygnus—SpaceX’s Dragon has the capability to survive re-entry at the end of each mission and return payloads and experiments safely back to Earth.
As with earlier Dragons, the CRS-4 mission will approach the station along the so-called “R-Bar” (or “Earth Radius Vector”), which provides an imaginary line from the center of Earth toward the ISS, effectively approaching its quarry from “below.” In so doing, Dragon will take advantage of natural gravitational forces to provide braking for its final approach and reduce the overall number of thruster “burns” it needs to make. By the morning of Tuesday, 23 September, it will have reached the vicinity of the station.
A carefully orchestrated symphony of maneuvers will bring Dragon to a “Hold Point” about 1.5 miles (2.4 km) from the ISS, 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 the spacecraft will creep toward the station at less than 3 inches (7.6 cm) per second. Critically, at 650 feet (200 meters), it will enter the so-called “Keep Out Sphere” (KOS), which provides a collision-avoidance exclusion zone around the ISS, and its rate of closure will slow to a little under 2 inches (5 cm) per second. After clearance has been given, Dragon will advance to the 30-foot (10-meter) “Capture Point,” within range of the 57.7-foot (17.4-meter) Canadarm2 robotic arm.
Following the capture of the cargo ship, it will be maneuvered to its berthing port on the nadir interface of the Harmony node. The physical berthing will occur in two stages, with the Expedition 41 crew overseeing “First Stage Capture”—in which hooks from Harmony’s nadir Common Berthing Mechanism (CBM) will extend and snare Dragon to pull their respective CBMs into a mechanized embrace—and finally “Second Stage Capture,” when 16 bolts will be driven to rigidize the two vehicles. With CRS-4 now a part of the ISS for the next four weeks, the crew will be given a “Go” to pressurize the vestibule leading from the Harmony nadir hatch into Dragon, and this will allow them to access the craft, which is loaded with about 5,000 pounds (2,270 kg) of supplies.
Among the CRS-4 payload are 1,644 pounds (746 kg) of scientific experiments and materials to support 255 research investigations which will take place during the current Expedition 41 and forthcoming Expedition 42 missions, through the spring of 2015. Its science experiments will enable model organism research, using rodents, fruit flies, and plants, whilst several new technology demonstrations will permit studies of astronauts’ bone density, the movement and positioning of small satellites with state-of-the-art thrusters, and the first 3-D printer in space for additive manufacturing. It was also intended that up to four replacement Long Life Batteries (LLBs) for the U.S. Extravehicular Mobility Unit (EMU) space suits would be carried, but a recent AmericaSpace article highlighted that two will be carried aboard CRS-4 and two others aboard the Soyuz TMA-14M mission, scheduled for launch on 25 September. An issue with the LLBs currently aboard the ISS caused a pair of U.S. EVAs in August to be deferred, and they are now expected to take place on 7 and 15 October, involving U.S. Orbital Segment (USOS) crewmen Reid Wiseman, Alexander Gerst, and Barry “Butch” Wilmore.
Of specific note will be NASA’s $26 million Rapid Scatterometer (RapidScat), which will be one of two powered payloads stored in Dragon’s unpressurized “Trunk” for the journey to the ISS. This 1,300-pound (590-kg) experiment will be robotically removed from the Trunk, by means of Canadarm2, and installed onto the exterior of Europe’s Columbus laboratory. Using low-energy microwave emissions, RapidScat will monitor the velocity and direction of oceanic winds and is expected to yield valuable data to complement three other operational satellite scatterometers. The European MetOp-A and MetOp-B missions, launched in October 2006 and September 2012, together with India’s OceanSat-2, which was delivered into orbit in September 2009, have all made significant inroads into an international effort to understand the ways in which interactions between the oceans and the atmosphere influence Earth’s climate. When it is operational, RapidScat’s position aboard the ISS—which operates in a high-inclination orbit of 51.6 degrees to the equator—will allow it to cross the orbital tracks of its three sister satellites, thus providing a valuable calibration source.
The urgent need for such a mission has become particularly acute in the last few years. Back in June 1978, NASA launched its short-lived Seasat mission, which offered great insights into oceanic behavior from a space-based instrument, and in June 1999 the agency lofted its Quick Scatterometer (QuikScat) spacecraft. The latter included a scatterometer called “SeaWinds,” whose 3.3-foot (1-meter) rotating antenna functioned for more than a decade, until it suffered a bearing failure on its motor in November 2009. This significantly impaired its ability to perform ocean wind measurements.
Last year, NASA announced its intention to launch a replacement instrument, assembled from spare parts left over from the development of QuikScat and the Advanced Earth Observing Satellite (ADEOS)-II, a joint U.S., Japanese, and French mission, launched in December 2002. “The ability for NASA to quickly reuse this hardware and launch it to the space station is a great example of a low-cost approach that will have high benefits to science and life here on Earth,” said ISS Program Manager Mike Suffredini. His praise was echoed by RapidScat Project Manager Howard Eisen: “RapidScat represents a low cost approach to acquiring valuable wind vector data for improving global monitoring of hurricanes and other high intensity storms. By leveraging the capabilities of the International Space Station and recycling left over hardware, we will acquire good science data at a fraction of the investment needed to launch a new satellite.”
Remarkably, RapidScat rose from planning to reality in barely 18 months, with Suffredini having offered Eisen’s team a mounting location on the Columbus module and a “free ride” aboard Dragon. “This accelerated timeline,” noted a NASA news release, “is a blink of an eye for NASA, where the typical project is years or decades in the making.” Much of the progress is attributable to the instrument’s use of commercial, off-the-shelf computer hardware, but has met with difficulties, not least the procurement of connectors which will enable RapidScat to physically attach itself to the ISS. “They’re special robotically-mated connectors that haven’t been made in years,” Eisen said. “We’re having to convince the company that produces these connectors to make us a small run in time for the mission and it hasn’t been easy.”
With MetOp-A and B and OceanSat-2 operating in polar orbits, the course of the space station’s 51.6-degree orbit will carry RapidScat over Earth’s surface at constantly changing times of day. Since oceanic winds are greatly affected by solar radiation—which also varies with the time of day—trends which currently escape the notice of the European and Indian scatterometers should be detectable by RapidScat. “We’ll be able to see how wind speed changes with the time of day,” said Project Scientist Ernesto Rodríguez. “RapidScat will link together all previous and current scatterometer missions, providing us with a more complete picture of how ocean winds change. Combined with data from the European ASCAT scatterometer mission, we’ll be able to observe 90 percent of Earth’s surface at least once a day, and in many places, several times a day.”
Present plans envisage Dragon remaining berthed at the ISS for about four weeks. It will then be loaded with supplies, hardware, and computer equipment, experiment results, and four powered payloads for its return to Earth. In total, about 3,800 pounds (1,720 kg) of payloads are expected to be brought back home when the CRS-4 spacecraft performs a parachute-assisted splashdown off the coast of Baja California in mid-October.
BELOW: More photos from our guys covering the CRS-4 launch, all rights reserved, unauthorized use is prohibited.
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