Following Monday’s disappointing scrub of the third Commercial Resupply Services (CRS)-3 mission of the Dragon cargo craft to the International Space Station (ISS), SpaceX—the Hawthorne, Calif.-based launch services organization, headed by entrepreneur Elon Musk—has successfully ended a 13-month hiatus with a rousing liftoff at 3:25:22 p.m. EDT Friday, 18 April. In spite of a predicted 40-percent likelihood of acceptable weather at launch time, and ominous clouds and thunder prevalent in the Cape Canaveral area for much of the day, SpaceX’s upgraded Falcon 9 v1.1 roared aloft from Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla. Just 10 minutes after liftoff, Dragon had separated from the second stage of the rocket and was in the process of unfurling its solar arrays and communications and navigation appendages, preparatory to a rendezvous and berthing at the ISS in two days’ time.
As explained in AmericaSpace’s post-scrub article on Monday, the chances of a successful launch Friday seemed unlikely, with a 60-percent predicted likelihood of unacceptable weather conditions. Key concerns included thick cloud and risk of flight through lightning and precipitation. Although the AmericaSpace Launch Tracker highlighted that there remained a 40-percent chance that the weather would play ball today, the added challenge with the CRS-3 mission is that its ISS rendezvous commitment required an “instantaneous” launch at 3:25:22 p.m. EDT, leaving “no wiggle room to compensate for adverse conditions.”
It was always clear that, aside from another scrub early in the countdown, any attempt to launch CRS-3 on Friday was likely to go down to the wire. By 2:25 p.m. EDT, a storm cell which produced heavy showers over the Cape earlier in the day began to dissipate, and the next weather system was not expected to arrive until after launch time. Conditions remained cloudy, but at 2:30 p.m. EDT SpaceX declared that it had completed fueling of the upgraded Falcon 9 v1.1 rocket—which is flying its first Dragon mission and only its fourth voyage in total—with liquid oxygen and a refined form of rocket-grade kerosene, known as “RP-1.” During the latter stages of the countdown, explained the Launch Tracker, gases streamed from the vehicle, due to cryogenic oxygen boil-off, which was rapidly replenished to flight levels until close to launch time.
Against many odds, with one hour left before liftoff, the weather was classified as “Green,” with no conditions to immediately violate the Launch Commit Criteria and everything expected to remain that way through launch. Twenty minutes later, at 2:50 p.m. EDT, the Eastern Range—whose technical difficulties in recent weeks extensively delayed both CRS-3 and United Launch Alliance’s (ULA) Atlas V—declared itself ready to support the launch. Weather conditions, too, had improved slightly to about 60 percent favorable.
At 3:12 p.m. EDT, at T-13 minutes, the standard poll of all stations was conducted, producing a unanimous “Green” (“Go for Launch”), and the terminal countdown got underway at T-10 minutes. Now running on the autosequencer, the nine Merlin-1D engines of the Falcon 9 v1.1’s first stage were chilled down in order to provide pre-launch thermal conditioning. With all propellant tanks verified to be at their correct flight pressures, the launch pad’s “strongback” was completely retracted by T-4 minutes. The Flight Termination System (FTS)—tasked with destroying the vehicle in the event of a major accident during ascent—was placed onto internal power and armed, and by T-2 minutes and 15 seconds the first stage was confirmed to be at flight pressure.
“Range Green” came the final call from U.S. Air Force Range personnel. At T-1 minute, the flight computer was confirmed to be in control of the vehicle and the second-stage tanks reached flight pressures. SLC-40’s “Niagara” deluge system began to flood the pad surface with 30,000 gallons (113,500 liters) of water per minute to suppress acoustic waves radiating from the Merlin-1D engine exhausts. At T-45 seconds, all tanks were confirmed at flight pressure. Under gloomy skies, at T-3 seconds, the nine Merlin-1Ds roared perfectly to life, ramping up to their required parameters, and at 3:25:22 p.m. EDT the fourth mission of the Falcon 9 v1.1 and SpaceX’s first Dragon flight in 13 months was at last airborne.
At the instant of liftoff, the nine first-stage engines generated 1.3 million pounds (590,000 kg) of thrust, about 200,000 pounds (90,000 kg) greater than the earlier Falcon 9 v1.0, and pushed the vehicle uphill for 180 seconds. Their propulsive yield gradually rose to 1.5 million pounds (680,000 kg) in the rarefied high atmosphere. “Unlike airplanes, a rocket’s thrust actually increases with altitude,” noted SpaceX. “Falcon 9 generates 1.3 million pounds of thrust at sea level, but gets up to 1.5 million pounds of thrust in the vacuum of space. The first-stage engines are gradually throttled near the end of first-stage flight to limit launch vehicle acceleration as the rocket’s mass decelerates with the burning of fuel.”
With around 1,970 seconds of test time and a lengthy qualification program, SpaceX has expressed supreme confidence in the Merlin-1D. During a full-duration-mission firing in June 2012in McGregor, Texas, the engine operated at or above the power (147,000 pounds of thrust) and duration (185 seconds) required for a Falcon 9 launch. The Merlin-1D has a vacuum thrust-to-weight ratio in excess of 150:1, making it the most efficient liquid-fueled rocket engine in history. The ignition system for the v1.1’s first stage was tested in April 2013. The stage also includes four extendible landing legs, manufactured from carbon-fiber and aluminum honeycomb, to support a series of tests which SpaceX CEO Elon Musk hopes will lead to vertical-takeoff-vertical-landing (VTVL) capability by the latter half of the present decade. Although SpaceX intends to demonstrate the performance of the legs during ocean splashdown, it has repeatedly stressed that this system remains “experimental” and carries only a 40-percent chance of success in the early tests.
Immediately after clearing the SLC-40 tower, the Falcon 9 v1.1 executed a combined pitch, roll, and yaw program maneuver to establish itself onto the proper flight azimuth for the injection of the Dragon payload into low-Earth orbit. Eighty seconds into the ascent, the vehicle passed Mach 1 and experienced a period of maximum aerodynamic stress (known as “Max Q”) on its airframe. At 3:27:52 p.m., as planned, two of the nine engines shut down to reduce the rate of acceleration, ahead of Main Engine Cutoff (MECO) and separation of the first stage. The remaining seven Merlin-1Ds continued to burn hot and hard, finally shutting down at T+2 minutes and 58 seconds, and the first stage was jettisoned five seconds later. The turn then came for a single “burns” by the Falcon’s restartable second stage, which ignited for the first time at T+3 minutes and 10 seconds. Its single Merlin-1D Vacuum engine, with a maximum thrust of 180,000 pounds (81,600 kg), burned for six minutes and 43 seconds to deliver Dragon into a “parking” orbit. During this period, a protective nose cone covering the spacecraft’s berthing mechanism was jettisoned.
At 3:35:37 p.m. EDT, ten minutes after leaving the Cape, the fourth Dragon—which follows hard on the heels of the inaugural Commercial Orbital Transportation Services (COTS) Demo mission in May 2012 and the dedicated CRS-1 and CRS-2 missions in October 2012 and March 2013, respectively—was successfully separated from the second stage of the Falcon 9 v1.1 To resounding applause from the SpaceX team, a painful 13-month hiatus in flight operations was over, and the first of an anticipated three Dragon missions for 2014 was formally on its way to the ISS.
Within the language of the $1.6 billion Commercial Resupply Services (CRS) contract, signed between NASA and SpaceX in December 2008, the company is required to conduct 12 dedicated Dragon missions by 2016 and haul a total of 44,000 pounds (20,000 kg) of equipment and supplies to the ISS. The CRS-3 mission sports an upgraded power and cargo capability for Dragon, as well as demonstrating the ability of the Falcon 9 v1.1’s first stage to perform an ocean splashdown on extendible landing legs. In the immediate aftermath of the CRS-2 mission last March, it was anticipated that CRS-3 would fly in the September-November timeframe, although this quickly became December as the schedule of U.S. visiting vehicles morphed to accommodate changing conditions.
By August, both CRS-3 and the first dedicated Cygnus cargo flight by Orbital Sciences Corp. (ORB-1) were accommodated within the same December “launch window” and SpaceX accepted to postpone their mission until January 2014. By the end of the year, with ORB-1 itself delayed until January, this date had moved to no earlier than 22 February, which soon shifted to early March and finally settled on the 16th. A successful hot-fire test of the nine Merlin-1D first-stage engines on the Falcon 9 rocket was conducted at SLC-40 in the days preceding the opening launch attempt, but SpaceX notified NASA that it would postpone the mission for a further two weeks.
Citing its desire for “the highest possible level of mission assurance and allow additional time to resolve remaining open issues,” the Hawthorne, Calif.-based company explained that it was now tracking 30 March as its next available launch date. In the aftermath of the delay, SpaceX President and Chief Operating Officer Gwynne Shotwell explained that the company was working up to four issues. “We were struggling on some buffering data-transfer with Houston,” Shotwell stated, as explained in an article by AmericaSpace’s Emily Carney. “We wanted a little more time to work with the range on trajectory. We are going to try to do some re-entry and landing burns on the first stage. My operations crew was in a time crunch for Dragon, which is a very new Dragon. Finally, we did notice stains on the impact shielding.” This staining was caused by “oil contamination from the manufacturing process,” which left “regular patterns” on beta-cloth shields within Dragon’s unpressurized Trunk. “It didn’t show up right away when the blankets were manufactured,” Shotwell continued. “Luckily, our pre-encapsulation checks caught it.” After assessments, it was decided that the level of contamination was acceptable.
A launch on 30 March also became untenable, when Eastern Range—which monitors all missions originating from the East Coast—suffered an electrical short and a fire in a critical radar tracking asset which impacted the TEL-4 Telemetry Processing Facility, part of the Eastern Space and Missile Center (ESMC). “Inspections conducted by the U.S. Air Force that operates the Eastern Range and all of its assets revealed that extensive equipment replacements were needed to bring the radar station back online,” explained Spaceflight101, “a process that would take weeks, because there no backup components were available and had to be ordered to the Cape before being installed.”
With United Launch Alliance (ULA) also scheduled to fly its Atlas V rocket from the Cape’s SLC-40 complex on a mission to deliver the classified NROL-67 payload into orbit for the National Reconnaissance Office, both missions were put on hold as a solution was identified. At length, with the problem rectified, it was decided that since NROL-67 was on the Range first, it would be granted the next available launch opportunity, and the Atlas V successfully rocketed its top-secret cargo into orbit on Thursday, 10 April. Meanwhile, SpaceX accepted a “window” between 14-18 April in order to achievable favorable phasing for Dragon’s rendezvous profile with the ISS. A helium leak on the Falcon 9 v1.1’s first stage led to an unfortunate scrub of the opening launch attempt on the 14th, forcing SpaceX teams to reconfigure systems for a second attempt today.
This it the first Dragon mission to fly in more than 13 months, a longer-than-desirable period, which has for the most part been outside of SpaceX’s control. According to NASASpaceflight.com, three Dragons (CRS-3, 4, and 5) are scheduled for launch this year, in April, August, and November, followed by as many as four in 2015 and the final flights in 2016. However, judging from the delays to which CRS-3 has fallen victim, it seems likely that there will be some slippage to these targets. Nevertheless, SpaceX has continued to move from strength to strength, not only with Dragon itself, but also with the upgraded Falcon 9 v1.1 launch vehicle, which undertook its maiden voyage in September 2013 and has since delivered its first two geostationary payloads into orbit: the SES-8 communications satellite in December and the Thaicom-6 communications satellite in January.
All previous Dragon missions were launched by the earlier Falcon 9 v1.0 vehicle, and Monday’s mission will mark the first occasion on which an ISS cargo craft has been lofted atop the Falcon 9 v1.1. The new rocket’s enhanced performance means that CRS-3 has the capability to transport a record-sized payload of almost 5,000 pounds (2,270 kg) to the station. “Dragon got a few upgrades since its last trip to station,” explained SpaceX on its Facebook page. “To support the more critical science payloads for the ISS, the spacecraft … has nearly quadrupled its previous powered cargo capability. Dragon will carry additional freezers in its pressurized section and, for the first time ever, powered cargo inside its unpressurized Trunk … The spacecraft is also sporting redesigned cargo racks to accommodate the additional payloads.”
One of the freezers is a powered General Laboratory Active Cryogenic ISS Experiment Refrigerator (GLACIER), which provides for the transportation and preservation of biological and other samples at temperatures between -160 degrees Celsius (-301 degrees Fahrenheit) and 4 degrees Celsius (39 degrees Fahrenheit). Dragon will also carry a pair of Microgravity Experiment Research Locker Incubators (MERLINs), both of which will supply a refrigerator/incubator at temperatures from -20 degrees Celsius (-4 degrees Fahrenheit) to 48.5 degrees Celsius (119 degrees Fahrenheit).
Powered cargoes inside the unpressurized Trunk include the Optical Payload for Lasercomm Science (OPALS) to demonstrate high-bandwidth space-to-ground laser communications and the High-Definition Earth Viewing (HDEV) quartet of commercial HD video cameras to film Earth from multiple angles. Both of these payloads will be robotically installed onto the exterior of the ISS. Also aboard the vehicle will be a new Extravehicular Mobility Unit (EMU) space suit to replace the unit which malfunctioned and allowed water seepage into the helmet area during Luca Parmitano’s ill-fated EVA-23 in July 2013. The problematic suit will be returned to Earth aboard Dragon.
Today’s launch is indicative of the steady maturity of SpaceX technology, as it strives to develop a fully reusable Falcon 9, whose two stages will ultimately be able to complete their respective boost phases, propulsively return over water, and touch down on extendable landing legs, back at their launch site. The system was trialed, with mixed results, during the inaugural flight of the Falcon 9 v1.1, last 29 September, but it experienced an uncontrollable roll during its descent. This caused the final burn of the center Merlin-1D engine to be shortened, due to the centrifuging effect on propellant against the tank walls, which damaged the baffles and allowed debris to enter the engines. Landing legs were not flown aboard the second Falcon 9 v1.1 mission, which launched the SES-8 communications satellite in December, or aboard the third mission, which launched Thaicom-6 in January.
The Falcon 9 assigned to the CRS-3 mission boasted four fold-out landing legs, made from carbon-fiber and aluminum honeycomb, on its first stage, which will be deployed during the controlled descent. Although a touchdown on land is not yet planned, SpaceX hopes to touch down on water. Shortly after the burn-out and separation of the first stage, it will execute a maneuver with its cold-gas attitude-control system to establish an “engine-forward” orientation.
Three of the nine Merlin-1Ds will briefly fire to effect braking during the re-entry process and the four landing legs will be deployed using high-pressure helium once in atmospheric flight. The legs span 60 feet (18 meters) when fully deployed and the entire assembly weighs about 4,400 pounds (2,000 kg). Assuming that the vehicle does not again fall victim to excessive roll motions, the center Merlin-1D will ignite shortly before it makes a gentle impact with the Pacific Ocean. Elon Musk has stressed that although an attempt will be made to retrieve the first stage from the ocean, the system remains experimental in nature and he does not anticipate success for at least the first several attempts. Meanwhile, with the first stage gone, the turn will come for the Falcon 9 v1.1’s restartable second stage, whose single Merlin-1D Vacuum engine—with a thrust of 180,000 pounds (81,600 kg)—will fire to deliver Dragon into low-Earth orbit, at an altitude of 202 x 202 miles (325 x 325 km), inclined 51.54 degrees to the equator.
Following separation from the vehicle, Dragon was in the process of unfurling its electricity-generating solar arrays at the time of writing. It will also deploy its Guidance and Navigation Control (GNC) Bay Door to expose critical rendezvous sensors and begin a complex series of maneuvers to reach the ISS. It 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 perform.
By the third day of autonomous operations, it will have drawn into the vicinity of the space station and several “Go/No-Go” polls of flight controllers will permit it to gradually reduce its distance to about 30 feet (10 meters), placing it within range of the 57.7-foot (17.4-meter) Canadarm2 robotic arm. The spacecraft will then be captured by the Expedition 39 crew and berthed onto the Earth-facing (or “nadir”) port of the Harmony node. Berthing is anticipated early Sunday, about 38 hours after liftoff, and will be supported by Expedition 39 Commander Koichi Wakata and Flight Engineers Rick Mastracchio and Steve Swanson.
Following berthing, it is expected that Dragon will remain attached to the ISS for about a month. Orbital Sciences Corp.—NASA’s other Commercial Resupply Services partner—recently noted that Dragon “has a minimum 28-day stay requirement.” This almost certainly means that Orbital’s second dedicated Cygnus cargo mission (ORB-2), previously scheduled for launch on 6 May, will be delayed, because both spacecraft utilize the Harmony nadir interface. How long remains to be seen, for Soyuz TMA-11M is scheduled to depart on 14 May and a new crew will arrive aboard Soyuz TMA-12M on the 28th. Coupled with a subsequent solar beta angle cut-out, the next available date proposed by NASA for Orbital would be sometime after 9 June. “In the meantime,” Orbital stressed, “as a risk-reduction effort for our NASA customer, the ORB-2 team continues to work to be able to meet the 6 May launch capability, if needed.”
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