Dragon cargo ship reaches destination after shaky start
BY STEPHEN CLARK
Posted: March 3, 2013
SpaceX's Dragon spacecraft, packed with 2,300 pounds of supplies, approached the International Space Station on Sunday, holding steady a few feet below 450-ton complex as astronaut Kevin Ford carefully snagged the capsule with a robotic arm.
The astronauts handed over control of the lab's 58-foot robotic arm, nicknamed Canadarm 2, for engineers in Houston and Canada to maneuver the Dragon spacecraft into position on the Earth-facing port of the space station's Harmony module.
It was the first time controllers on the ground used the arm to install a newly-arrived craft on the space station, but the remote control operation went smoothly, and the Dragon spacecraft was firmly bolted to the complex at 8:56 a.m. EST (1356 GMT).
"What a fantastic day," Ford radioed to mission control shortly after capturing Dragon. "The vehicle's beautiful, the station's beautiful, the Canadarm 2 is beautiful, too, and it flew fantastic."
Sunday's smooth rendezvous consistently ran ahead of schedule, and the Dragon spacecraft flew toward the space station from behind, arriving more than 1,000 feet below the complex at about 3:40 a.m. EST (0840 GMT).
Ford, Tom Marshburn and Chris Hadfield monitored Dragon's glacial approach from below. The craft paused three times at predetermined hold points, allowing engineers on the ground to verify Dragon's laser and thermal sensors had a good lock on the space station.
The logistics craft pulled within reach of the space station's robot arm at 5:22 a.m. EST (1022 GMT). After Dragon disabled its rocket thrusters, the privately-owned spaceship held steady while Ford guided the arm to snare the craft an hour earlier than advertised.
Unlike Russia's crewed Soyuz capsules or Progress servicing vehicles, which come in for a docking with the space station, Dragon flies on autopilot to an imaginary box directly below the outpost, close enough for astronauts to grab it with the robot arm.
"I remember exactly where I was the very first time I ever heard of this scheme ... when I was a young astronaut," Ford said. "I said, 'We're going to do what?' That was when it was an idea, and now it's starting to become routine. So great job to everybody who dreamed it up and who made it all work. It's really something to see."
The glitch in the capsule's thruster system appeared to put the mission in jeopardy moments after launch Friday, but quick thinking by SpaceX's control team resolved the problem, which engineers say could be attributed to blockage in the spacecraft's oxidizer pressurization lines.
Three-fourths of the spacecraft's thrusters were inoperable after launch, and the capsule's power-generating solar panels did not extend as programmed. Engineers sent manual commands to unfurl the Dragon freighter's solar arrays, and coaxed all of the craft's thrusters back online several hours after liftoff.
SpaceX convinced NASA on Saturday the problem was history, and the space agency agreed to permit the truck-sized delivery spaceship to approach the huge orbiting laboratory.
"As they say, it's not where you start but where you finish that counts," Ford said. "You guys really finished this one on the mark. You're aboard, and we've got lots of science on there to bring aboard and get done, so congratulations to all of you."
Among Dragon's cargo: 767 pounds of research equipment, 601 pounds of external hardware, and 178 pounds of crew provisions.
Check out a list of cargo inside Dragon.
SpaceX promised a surprise for the crew inside the Dragon spacecraft, and workers packed fresh fruit and other goodies for the astronauts.
The astronauts plan to open Dragon's hatch late Sunday or early Monday and begin unpacking payloads stowed inside the capsule's pressurized compartment.
Later this week, possibly as soon as Tuesday, ground controllers will guide the robot arm into Dragon's unpressurized trunk section to retrieve two grapple bars launched aboard the SpaceX mission to help astronauts replace one of the space station's cooling radiators.
This is the first Dragon flight to deliver hardware to the space station inside its trunk. In the future, NASA plans to fly large experiment packages and other vital spare parts to the outpost using Dragon's unpressurized cargo capacity.
After the retirement of the space shuttle, the Dragon spaceship and Japan's HTV resupply freighter are the only two spacecraft capable of carrying large payloads for mounting outside the space station.
And Dragon is the only servicing platform with the ability to return significant amounts of cargo from the space station to Earth.
Astronauts will pack some 3,000 pounds of equipment into Dragon's pressurized module over the next three weeks, including experimental blood samples and broken or used components from the space station's life support, electrical and health monitoring systems.
Departure of the Dragon spacecraft is set for March 25, and the capsule will parachute to a splashdown in the Pacific Ocean west of Baja California.
The mission is SpaceX's second of 12 planned resupply flights to the space station under a $1.6 billion contract with NASA. It is the third Dragon mission to the station, including a demonstration flight in May 2012.