SpaceX has triumphantly reached the halfway mark in its initial $1.6 billion Commercial Resupply Services (CRS) contract with NASA, by successfully bringing its CRS-6 Dragon cargo ship away from the International Space Station (ISS) and guiding it toward a perfect, parachute-assisted splashdown in the Pacific Ocean at 9:42 a.m. PDT (12:42 p.m. EDT) Thursday, 21 May. Aboard the Dragon—which rose to orbit on 14 April, atop SpaceX’s Falcon 9 v1.1 booster from Space Launch Complex (SLC)-40 at Cape Canaveral Air Force Station, Fla.—for the return journey was almost 3,100 pounds (1,400 kg) of NASA cargo and experiment results, including research on how spaceflight and the microgravity environment affect the aging process and bone health. Thus concludes the second of what SpaceX hopes will be a personal-best-beating total of five Dragon missions to be flown in 2015.
As described in AmericaSpace’s CRS-6 launch report, this was the sixth of 12 flights under the inaugural contract with NASA and ferried 4,390 pounds (1,990 kg) of payloads, provisions, tools, and scientific experiments to the incumbent Expedition 43 crew, which presently consists of Commander Terry Virts of NASA, Italy’s first woman in space, Samantha Cristoforetti, Russian cosmonauts Anton Shkaplerov and Gennadi Padalka, and One-Year crewmen Scott Kelly and Mikhail Kornienko. Following its departure on 14 April, the Dragon followed a 65-hour rendezvous regime, before it was captured by the space station’s 57.7-foot-long (17.6-meter) Canadarm2 robotic arm on 17 April and subsequently berthed at the Harmony nadir interface. In doing so, it represented the 14th capture of an unpiloted cargo ship by the “Big Arm,” which has grappled four H-II Transfer Vehicles (HTVs) on behalf of the Japan Aerospace Exploration Agency (JAXA), seven Dragons—including the Commercial Orbital Transportation Services (COTS) Demo in May 2012 and the six dedicated CRS missions—and three Cygnuses for Orbital Sciences Corp.
Following the capture and berthing of CRS-6, the Expedition 43 crew pressurized the vestibule leading from the Harmony nadir hatch into Dragon, and after the opening of hatches the lengthy process of unloading the cargo got underway. As described in AmericaSpace’s CRS-6 preview article, that cargo consisted of 1,100 pounds (500 kg) of crew supplies, 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 payloads from the Canadian, Japanese, and European space agencies—and about 79 pounds (36 kg) of command and data-handling equipment, television and photographic gear, and EVA tools. CRS-6 was clearly one of the most science-heavy Dragons ever launched into orbit, with payloads sponsored by NASA and the Japanese, Canadian, and European space agencies.
According to the original manifest, the planned departure of Virts, Shkaplerov, and Cristoforetti aboard Soyuz TMA-15M on 14 May would have meant that Scott Kelly would have been the only U.S. Orbital Segment (USOS) crew member aboard the ISS for the complex CRS-6 unberthing operation. All previous Dragon unberthings have featured at least two USOS crew members. However, the reshuffling of the ISS manifest in the aftermath of last month’s Progress M-27M failure meant that the return of Soyuz TMA-15M is now expected to occur on 11 June, and, as a result, a full USOS complement of three—Virts, Cristoforetti, and Kelly—were aboard the station today for the CRS-6 departure.
The cargo ship was closed out and the final payload results were loaded yesterday (Wednesday), and Virts and Kelly grappled Dragon with Canadarm2, ahead of today’s unberthing “Early start today,” tweeted Cristoforetti, early Thursday morning. “@AstroTerry and I began #Dragon final prep at 4:30! #Canadarm2 had already grappled it yesterday.” Virts and Kelly released Dragon into free flight at 7:04 a.m. EDT, whereupon it executed a trio of separation maneuvers to commence its return to Earth. Unlike Japan’s HTV, Russia’s Progress, Europe’s now-retired Automated Transfer Vehicle (ATV), and Orbital Sciences’ Cygnus, the Dragon is the only unpiloted cargo ship which can return large quantities of payloads back to Earth. Commanded by SpaceX flight controllers, Dragon’s Guidance, Navigation and Control (GNC) Bay Door was closed to protect its navigation sensors and the spacecraft performed a 600-second deorbit “burn” at 11:49 a.m. EDT. Its unpressurized “trunk”—which is not intended to survive re-entry—was jettisoned and the pressurized segment plunged into the sensible atmosphere, experiencing peak temperatures of 1,600 degrees Celsius (2,900 degrees Fahrenheit) across its Phenolic Impregnated Carbon Ablator (PICA-X) heat shield.
After passing through the furnace of re-entry, at an altitude of 8.5 miles (13.7 km), Dragon’s twin drogue parachutes were deployed to stabilize the rapidly descending spacecraft. Shortly thereafter, at 1.8 miles (3 km), the trio of red-and-white main canopies unfurled to guide SpaceX’s sixth dedicated Dragon—and its seventh overall, counting the COTS Demo—to a smooth splashdown at 9:42 a.m. PDT (12:42 p.m. EDT), about 155 miles (250 km) off the California coastline. After recovery, it was to be transported by ship to Long Beach, Calif., where its NASA cargo would be unloaded, and the spacecraft itself returned to SpaceX’s test facility in McGregor, Texas, for processing.
CRS-6 marks the only mission of SpaceX’s five-Dragon manifest not to include a major unpressurized payload in its trunk. During January’s CRS-5 flight, the large Cloud Aerosol Transport System (CATS) was delivered and later installed on the Exposed Facility (EF) of Japan’s Kibo laboratory, whilst June’s CRS-7 and December’s CRS-9 are expected to deliver a pair of International Docking Adapters (IDAs 1 and 2) for NASA and September’s CRS-8 will bring the Bigelow Expandable Activity Module (BEAM) to the space station. To date, SpaceX has launched no more than two Dragons per year since its COTS Demo, back in May 2012, and if it accomplishes five flights in 2015 it will have reached 75 percent complete on its original 12-flight CRS commitment to NASA by year’s end. According to SpaceX, launch of the CRS-7 mission is anticipated No Earlier Than (NET) 26 June, with an “instantaneous” window which opens at 11:09 a.m. EDT. This will produce conditions for a rendezvous and berthing at the space station, about two days later.
The CRS-6 mission has also set a new record for SpaceX for the longest-duration Dragon flight to date and the longest berthed period for a Dragon at the ISS. From the moment of its berthing at the Earth-facing (or “nadir”) port of the Harmony node at 9:29 a.m. EDT on Friday, 17 April, through to its unberthing by Expedition 43 Commander Terry Virts, One-Year crewman Scott Kelly, and Italy’s first woman in space, Samantha Cristoforetti, at 7:04 a.m. EDT on Thursday, 21 May, it had spent 33 days, 21 hours, and 35 minutes attached to the multi-national orbital outpost. This neatly eclipses SpaceX’s previous berth-to-unberth personal best of 31 days, 22 hours, and 41 minutes, set during the CRS-4 mission, last fall. Moreover, today’s CRS-6 return to Earth brought to an end a flight which totaled 36 days, 20 hours, and 32 minutes from launch through splashdown, which also surpasses the previous CRS-4 record of 34 days, 13 hours, and 46 minutes. Although this represents an incremental record, and perhaps hardly worthy of notice as each Dragon flies successfully to and from the ISS, it is a potent indicator of the maturity of SpaceX’s Commercial Cargo capability.
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