Space station snags Dragon capsule

The robotic arm of the International Space Station captures the Dragon capsule. In a moment of high drama on the high frontier, flight engineer Donald Pettit, operating the International Space Station's robot arm, this morning reached out and locked onto SpaceX's Dragon capsule. That capture of the commercial cargo ship came after a complex rendezvous, a final sequence of approach-and-retreat test maneuvers and quick work to adjust critical sensors that were getting fooled by reflections from a Japanese research module.
The last-minute hiccups were just that, relatively minor adjustments to correct for the real-world performance of complex laser and infrared imagers used to compute the Dragon cargo ship's velocity and distance from the station.
But like everything in the world of manned spaceflight, where the stakes are high and the margins for error small, flight controllers in Houston and at SpaceX's Hawthorne, Calif., control center took their time, inserting additional checks to make sure everything was working properly.
Now running well behind schedule, flight controllers left it up to Pettit as to whether he felt comfortable grappling the spacecraft in orbital darkness or would prefer delaying to the next daylight pass depending on lighting conditions. When all was said and done, the crew was about two hours behind schedule when the Dragon completed its approach, halting at a designated capture point 30 feet directly below the lab complex.
As the huge space station and the diminutive cargo craft flew in tandem at 5 miles per second, Pettit, working inside the lab's multi-window cupola module, decided to press ahead in orbital darkness, guiding the arm's latching end effector onto a grapple fixture on the side of the cargo ship at 9:56 a.m. EDT (GMT-4). Internal snares were tightened to secure the spacecraft to the arm, completing a rendezvous that began with Dragon's launch Tuesday from the Cape Canaveral Air Force Station.
"Capture is confirmed!" NASA's mission control commentator, Josh Byerly, said as flight controllers burst into applause.
"Congratulations on a wonderful capture, you've made a lot of folks happy down here, over in Hawthorne and right here in Houston," astronaut Megan Behnken radioed from Houston. "Great job, guys.
"Houston, station, it looks like we've got us a dragon by the tail," Pettit radioed, then joked: "We're thinking this sim went really well, we're ready to turn it around and do it for real."
Pettit, the European Space Agency's Andre Kuipers and NASA flight engineer Joseph Acaba, along with Russian crewmates Oleg Kononenko, Gennady Padalka and Sergei Revin, planned to berth the Dragon capsule at the Earth-facing port of the station's forward Harmony module before going to bed.
The flight plan called for Kuipers to operate the robot arm while Pettit focused on inspecting the common berthing mechanism components on the Dragon and the Harmony module to make sure there were no problems that would prevent an airtight seal when the spacecraft was locked into place. Using binoculars, Pettit reported the mating surfaces appeared to be in good condition, although additional inspections were planned to make sure while the arm moved Dragon into position.
Going commercial
The rendezvous and capture marked a moment of high drama for SpaceX, the 10-year-old California startup spearheading NASA's attempt to put transportation to and from low-Earth orbit on a more commercial footing.
SpaceX plans to begin regularly scheduled logistics flights to the space station later this year under a $1.6 billion contract with NASA that calls for at least 12 missions and the delivery of 44,000 pounds of cargo and supplies. A second company, Orbital Sciences, holds a $1.9 billion contract for eight missions to deliver the same amount of cargo.
The goal is to replace the cargo delivery capability that was lost with the space shuttle's retirement. To save money, the agency implemented a more commercial approach to contracting, giving the companies more say in engineering decisions and flight control. As a result, this week's mission is being billed as the first commercial space flight to the station.
Three test flights were initially envisioned by NASA and SpaceX under a separate contract valued at up to $396 million. After the maiden two-orbit flight of a Dragon capsule in 2010, SpaceX lobbied to combine the second and third test flights into a single mission, with a close approach Thursday to test guidance and control systems and the final rendezvous today.
"This is pretty tricky," SpaceX founder Elon Musk said before launch. "The space station is zooming around the Earth every 90 minutes and it's going 17,000 miles an hour. So you've got to launch up there, you've got to rendezvous and be tracking space station to within inches, really, and this is a thing that's going 12 times faster than the bullet from an assault rifle. So it's hard."
But the NASA-SpaceX team made it look easy, with a flawless launch Tuesday, a smooth approach to the space station Wednesday and a successful series of tests Thursday during a close-approach "fly under" to verify the performance of the cargo ship's flight control system.
The rendezvous Friday required a stepwise approach to hold points 1.5 miles and .9 miles directly below the station. The capsule then moved up to a point just 820 feet below the lab for another series of controllability tests, advancing, retreating and holding in place on command.
With the Dragon stationkeeping about 720 feet below the space station, NASA cleared SpaceX to continue the approach up the "r-bar," or radius vector, an imaginary line between the station and the center of the Earth. The original flight plan called for a brief stop at 100 feet before a final push to the robot arm capture point just 30 feet below the lab complex.
But flight controllers wanted additional time to monitor the output of an infrared video system used in concert with a LIDAR laser ranging system to help the Dragon's flight computers calculate its distance from the station and its closure rate. Additional holds were ordered to make sure everything was working properly and to give Pettit a daylight grapple.
Finally poised at the capture point, the cargo ship's rocket thrusters were disabled, clearing the way for Pettit to drive the station's robot arm in for grapple. Assuming the berthing procedure goes smoothly, the crew plans to open hatches and enter the Dragon spacecraft early Saturday.
For its initial visit, the Dragon capsule is carrying nearly 1,150 pounds of cargo: 674 pounds of food and crew provisions; 46 pounds of science hardware and equipment; 271 pounds of cargo bags needed for future flights; and 22 pounds of computer equipment.
As it now stands, Dragon will remained docked until May 31. At that point, the station's robot arm will unberth the capsule and then release it. Unlike all other Russian, European and Japanese cargo ships servicing the International Space Station, the Dragon is equipped with a heat shield and parachutes for an ocean splashdown off the coast of California.