SpaceX brings home Dragon with 2,700 pounds of cargo
BY STEPHEN CLARK
Posted: March 26, 2013
A suite of refrigerated biomedical research samples and other equipment traveled from the International Space Station back to Earth on Tuesday, nestled inside a commercial Dragon spaceship completing a 25-day resupply flight to the orbiting scientific laboratory.
Designed, built and operated by SpaceX, the California-based space firm founded by Elon Musk, the capsule arrived on Earth less than six hours after departing the space station with nearly 2,668 pounds of cargo strapped inside the craft's shirtsleeve-environment cabin.
Recovery boats were on hand to retrieve the floating capsule and hoist the gumdrop-shaped spaceship on deck to sail to the Port of Los Angeles, where it was supposed to arrive as soon as Wednesday.
NASA plans to take charge of the most sensitive experiment samples in Los Angeles and fly the cargo back to laboratories in Houston. The rest of the equipment will be handed over to NASA once SpaceX transports the capsule to its facility in McGregor, Texas.
SpaceX has a $1.6 billion contract with NASA for at least 12 unmanned resupply missions to the space station. Tuesday's splashdown ended the second of the dozen contracted missions, coming five months after the first operational flight in October 2012.
Before the Dragon spacecraft left the space station, astronauts packed biological specimens, including bags of blood and urine, into freezers to preserve the samples for scientists on Earth. Researchers will use the samples from space station crews to study how the human body reacts to long-term spaceflight.
A SpaceX spokesperson said all the cargo was in good shape, including the refrigerated specimens, which were kept at cold temperatures throughout the descent, splashdown and recovery procedures. A freezer lost power on the Dragon's last flight in October, but no such problems occurred Tuesday, the spokesperson said.
Other science payloads returned inside the Dragon spacecraft focused on the growth of plants in space, solar power generation, the formation of crystals in metal alloys, medical diagnoses aboard the space station, and scores of other investigations.
The space station astronauts closed the hatch leading into the Dragon spacecraft Monday, and the lab's robotic arm removed the capsule from a berthing port on the complex early Tuesday. Controlled by ground controllers and then astronaut Tom Marshburn, the 58-foot arm let go of the resupply vehicle at 6:56 a.m. EDT (1056 GMT).
"Sad to see the Dragon go," Marshburn radioed mission control in Houston. "Performed her job beautifully heading back to her lair."
A deorbit burn beginning at about 11:42 a.m. EDT (1542 GMT) put the craft on course for re-entry. Shielded by an envelope of carbon ablator, the Dragon fell through the atmosphere about a half-hour later, encountering temperatures as hot as 3,000 degrees Fahrenheit as it streaked across the Pacific Ocean toward the splashdown zone southwest of San Diego.
Parachutes unfurled to stabilize the craft as the capsule plunged into the stratosphere, then three main chutes opened at an altitude of about 10,000 feet to slow the Dragon's descent to less than 15 mph.
Recovery teams spotted the capsule before it hit the water and were alongside the spacecraft within a half-hour to begin safing operations.
The Dragon cargo carrier launched March 1 on SpaceX's Falcon 9 rocket and almost immediately encountered trouble. Three-fourths of the spacecraft's thrusters failed to activate after deployment from the Falcon launcher, leaving SpaceX engineers scrambling to salvage the mission.
Working in a control center at SpaceX's headquarters in Hawthorne, Calif., engineers commanded the Dragon's propulsion system to open and close a series of pressurization valves, a procedure known as "pressure slamming," to resolve the problem, which Musk attributed to possible blockage in helium pressurant lines.
The Dragon spacecraft's propellant tanks were supposed to pressurize shortly after arriving in orbit, but with one of four thruster pods activated normally, the unmanned freighter was left drifting around Earth while controllers tried to fix the glitch.
SpaceX convinced NASA it had a handle on the problem, and the space agency cleared the Dragon spacecraft to approach the space station March 3, one day later than scheduled because the capsule missed a maneuver to catch up to the complex while SpaceX struggled with the propulsion system malfunction.
The Dragon delivered 1,869 pounds of supplies to the space station when it arrived March 3.
After the retirement of the space shuttle, the Dragon spacecraft is the only vehicle capable of returning large amounts of cargo from the space station to Earth. Russia's crewed Soyuz capsule can only accommodate limited cargo when landing with a three-person crew.
Space station managers value the capacity to return cargo to Earth. Some experiments require the hands-on attention and analysis of researchers on the ground, and broken components from the space station's extensive power, life support and other systems could be examined and refurbished for launch on a later mission, helping engineers understand failure modes and avoid unnecessary purchases of new hardware.
The space station's fleet of logistics vehicles also includes the Russian Progress freighter, the European Space Agency's Automated Transfer Vehicle, and Japan's H-2 Transfer Vehicle.
NASA partnered with SpaceX and Orbital Sciences Corp. to design and test commercial cargo spacecraft to pick up some of the station resupply duties of the space shuttle. The space agency provided technical support and funding to support the privately-led effort.
Orbital Sciences plans to start flying its Cygnus spacecraft to the space station as soon as this summer. The first test launch of Orbital's Antares rocket is scheduled for mid-April from the Mid-Atlantic Regional Spaceport at Wallops Island, Va.
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