Space station astronauts unbolted a commercial cargo ship early Thursday, used the lab's robot arm to pull it away and released it into open space to set the stage for re-entry and splashdown off the Baja California peninsula to close out a successful test flight and set the stage for the start of routine cargo delivery missions later this year.
With the space station's Canadian-built robot arm locked onto the Dragon cargo craft, four gangs of motorized bolts holding the capsule in place were driven out, releasing the spacecraft from Harmony's Earth-facing port at 4:07 a.m. EDT (GMT-4).
Flight engineer Joseph Acaba, operating the robot arm from a computer work station inside the lab's multi-window cupola compartment, pulled the Dragon capsule away, moving it to a pre-determined release point well away from station structure.
One orbit later, Acaba and flight engineer Donald Pettit released the spacecraft, opening snares in the arm's latching end effector at 5:49 a.m. as the space station sailed 250 miles above the southern Indian Ocean. SpaceX flight controllers in Hawthorne, Calif., working in concert with NASA's flight control team at the Johnson Space Center in Houston, then monitored three quick rocket firings to begin Dragon's departure and eventual descent to Earth.
Within 11 minutes or so, the capsule was outside a pre-defined safety zone around the space station and SpaceX assumed full responsibility for the remainder of the mission.
"The departure sequence is fairly quick, it's a three-burn series, two small burns then one big burn," said NASA Flight Director Holly Ridings. "The Dragon will head away from the space station outside the integrated space and that'll be the end of our integrated activity with the SpaceX/Dragon team. That process is 10 or 11 minutes after the release time."
"So again, very quick, very different from rendezvous day when we spent a lot of time in integrated space. The Dragon will head on out and be on its own in terms of the Dragon team controlling and managing the rest of the activities through the day."
Once outside the safety zone, the SpaceX team planned to close a protective door over navigation sensors and the grapple fixture used by the robot arm.
"We'll be closing that up, performing some checkouts and then performing our large re-entry burn, which till take about 10 minutes," said SpaceX mission director John Couluris. "And with that, about five-and-a-half hours after release from the arm, we should be in the water."
Deorbit ignition, the rocket firing designed to drop the far side of the capsule's orbit into the atmosphere, was targeted for 10:51 a.m. Stabilizing drogue parachutes were expected to deploy at an altitude of 45,000 feet around 11:35 a.m. with three main parachutes opening one minute later at an altitude of 10,000 feet. Splashdown was targeted for 11:44 a.m.
The Dragon capsule, making only its second test flight -- the first to the International Space Station -- was launched atop a SpaceX Falcon 9 rocket on May 22 from the Cape Canaveral Air Force Station. The solar powered spacecraft chalked up a near flawless performance and on May 25, the capsule maneuvered to within about 30 feet of the space station, turned off its thrusters and stood by while Pettit, operating the lab's robot arm, locked on and pulled it in for berthing.
SpaceX and NASA originally planned three test flights before beginning routine space station resupply missions under a $1.6 billion contract calling for at least 12 missions. After the initial 2010 test flight, the first time a commercial entity had successfully recovered a spacecraft from orbit, SpaceX lobbied to combine the objectives of the second and third planned test flights into a single mission.
NASA managers ultimately agreed. The objectives of the second test flight were accomplished with a series of navigation and abort tests the day before berthing and the goals of the third flight were accomplished with the space station linkup.
The capsule carried a relatively light load of low-priority supplies and equipment for the test flight and the astronauts off-loaded the bulk of the 1,100 pounds of gear in a single day. That left re-entry and splashdown as the final objectives of the mission.
The SpaceX team successfully brought a Dragon capsule back to Earth at the end of the 2010 test flight and Couluris said he was not expecting trouble Thursday.
"We're really looking forward to it," he said. "We've done it once (before), but it's still a very challenging phase of flight. Only a few countries have done this before, so we're not taking this lightly at all. But the crew looks good and we should be ready for it."
The splashdown zone is roughly 575 miles southwest of southern California. American Marine of Los Angeles, under contract to SpaceX, is providing a 185-foot crane-equipped barge to recover the capsule, along with an 80-foot crew boat and two rigid hull inflatables. The SpaceX recovery team consists of about a dozen engineers and technicians and four divers.
If all goes well, the spaceraft will be hauled onto the deck of the primary recovery ship and taken to the Port of Los Angeles for shipment to SpaceX's McGregor, Texas, facility for post-flight processing.
The Dragon vehicle is the only space station cargo craft designed to return to Earth, giving NASA the ability to send home experiment samples and hardware for the first time since the space shuttle's retirement last year. During routine resupply missions, SpaceX plans to get high-priority items off the craft within 48 hours of splashdown with the remainder going to NASA within 14 days.
For the test flight, environmental samples will be turned over to NASA in the Port of Los Angeles in a run through of the early access protocols. The remainder of the 1,455 pounds of return cargo will be off-loaded in McGregor and turned over to NASA.