Less than two weeks since the spectacular launch of the AsiaSat-6 geostationary communications satellite, SpaceX stands ready to deliver its sixth Falcon 9 v1.1 mission of 2014 and its second Dragon cargo ship of the year toward the International Space Station (ISS). Current plans call for the two-stage vehicle to fly from Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla., at 2:16 a.m. EDT Saturday, 20 September. Assuming an on-time liftoff, Dragon will rendezvous and be berthed at the Earth-facing (or “nadir”) port of the space station’s Harmony node on Monday, 22 September, where it will remain for the next four weeks. It will deliver about 5,000 pounds (2,270 kg) of equipment and supplies for the incumbent Expedition 41 crew. This will be the fourth of 12 dedicated Dragon missions (CRS-4) under SpaceX’s $1.6 billion Commercial Resupply Services contract with NASA.
Making its eighth flight in under 12 months, its sixth of 2014 and its fourth in just 10 weeks, the Falcon 9 v1.1 is more than proving its worth as a launch provider for geostationary commercial passengers and for U.S. Government customers, most notably NASA. Since SpaceX signed the CRS contract with the space agency in December 2008—under which it will execute 12 unpiloted Dragon cargo flights to the ISS and deliver a total of 44,000 pounds (20,000 kg) of payloads and supplies to the ISS—the Hawthorne, Calif.-based launch services organization also won a $2.6 billion slice of the Commercial Crew transportation Capability (CCtCap) pie on Tuesday, 16 September. This positions SpaceX alongside Boeing as one of two commercial entities which will deliver U.S. astronauts into low-Earth orbit from U.S. soil by 2017.
However, the Falcon 9 v1.1 has experienced 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 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-record-beating fifth mission, with AsiaSat-6 on 7 September, further cemented its reliability credentials. If the SpX-4 mission launches on time, SpaceX stands poised to beat its own personal bests yet again. These achievements followed on the heels of two earlier successes in 2014: the delivery of the Thaicom-6 geostationary satellite in January and the launch of the third dedicated Dragon (CRS-3) to the ISS in April.
The Falcon 9 v1.1 was transferred to SLC-40 yesterday (Wednesday, 17 September) and underwent a standard “hot fire” test of the nine Merlin-1D first stage engines. Late tomorrow evening (Friday), 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 temperature 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 nine Merlin-1D first-stage engines to be chilled down, in order to avoid thermally shocking and fracturing them. All propellants should be fully loaded within one hour. At 2:03 a.m. Saturday, the countdown will reach its final “Go-No Go” polling point of all stations at T-13 minutes. Due to the nature of its destination, the ISS, this launch window will be an “instantaneous” one, with no margin to accommodate technical issues or unacceptable weather conditions. If the Falcon 9 v1.1 cannot launch at 2:16 a.m., the attempt will be scrubbed and the clock recycled to target a backup opportunity at 1:53 a.m. on Sunday, 21 September.
Assuming that the mission passes through the polls at T-13 minutes, the Terminal Countdown will get underway at T-10 minutes. During this phase, the Merlin-1D engines will be chilled, preparatory to their ignition sequence. All external power utilities from the Ground Support Equipment (GSE) will be disconnected, and at 2:11 a.m. the approximately 90-second process of retracting the “strongback” away from the Falcon 9 v1.1 will get underway. The Flight Termination System (FTS), which is tasked with destroying the rocket 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 reach flight pressure. The Merlin-1D engines will be purged with gaseous nitrogen, and, at T-60 seconds, SLC-40’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 vehicle will be released from SLC-40 to commence SpaceX’s sixth mission of 2014, its second Dragon of the year, and its fourth flight in less than 10 weeks, as well as marking a new “personal best” as the organization launches two of its rockets within just 13 days of one another.
Immediately after clearing the tower, the Falcon 9 v1.1 will execute a combined pitch, roll, and yaw program maneuver to establish itself onto the proper flight azimuth to inject the SpX-4 Dragon spacecraft into low-Earth orbit. Eighty seconds into the ascent, the vehicle will exceed the speed of sound and experience 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 will undergo a chill-down protocol, ahead of its own ignition later in the ascent phase. At 2:18 a.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 first-stage engines will shut down, and, a few seconds later, the lower component of the Falcon 9 v1.1 will separate from the rapidly ascending stack. The turn will then come for the restartable second stage, whose single Merlin-1D Vacuum engine—with a maximum thrust of 180,000 pounds (81,600 kg)—will roar to life at about 2:19:10 a.m. to continue the boost to deliver Dragon into orbit. Based upon previous Dragon missions, it will burn for about six minutes and 45 seconds to insert the cargo ship into a “parking orbit.” During this period, a protective nose cone, covering the spacecraft’s berthing mechanism, will be jettisoned.
Ten minutes after leaving the Cape, the fifth ISS-bound Dragon—which comes hard on the heels of the inaugural Commercial Orbital Transportation Services (COTS) Demo mission in May 2012 and the dedicated CRS-1 in October 2012, CRS-2 in March 2013, and, most recently, CRS-3 in April-May 2014—will separate from the second stage of the launch vehicle. It will unfurl its electricity-generating solar arrays, deploy its Guidance and Navigation Control (GNC) Bay Door to expose critical rendezvous sensors, and begin a complex sequence of maneuvers to reach the ISS.
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. Earlier this week, Wiseman installed the Centerline Berthing Camera System (CBCS) inside the nadir hatch of the 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 its 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 Monday, 22 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, and its rate of closure will slow to a little under 2 inches (5 cm) per second. After clearance has been given for Dragon to advance to the 30-foot (10-meter) “Capture Point,” with 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 6/8 October 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.
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