Space station robotics shine in cargo transfer work
BY STEPHEN CLARK
Posted: February 4, 2011
Canadian robotics systems aboard the International Space Station retrieved two cargo platforms from the Japanese HTV resupply freighter this week, stockpiling the outpost with more spare parts and proving an adroit mechanized handyman can perform operational duties in space.
If you're a subscriber to our Spaceflight Now Plus video service, you can watch the fascinating robotics work in high-definition movies.
The operations started Tuesday, when astronauts at the controls of the station's 58-foot-long Canadian robot arm pulled a pallet from the belly of the HTV, handed it to a smaller Japanese arm, then attached the cargo-carrying cradle to the outdoor porch of the Kibo lab module.
Space station commander Scott Kelly and flight engineers Cady Coleman and Paolo Nespoli operated the robotic arms during the move.
On Wednesday, the Canadian arm moved to a mobile railcar on the space station's truss to pick up Dextre, an automated robot with human-like arms designed to accomplish precise tasks like a spacewalking astronaut.
The tips of Dextre's appendages include grippers with force moment sensors, giving the robot a sense of touch by determining how much pressure and torque to apply during maintenance jobs, much like a human.
Ground controllers in Houston sent hundreds of remote commands to Dextre Thursday to retrieve two spare parts payloads from the HTV pallet.
While the station crew slept, the robot grappled a flex hose rotary coupler and unbolted the apparatus from the exposed pallet. With its feet still attached to the robotic arm, Dextre pulled away from Kibo's porch and placed the spare cooling system component on its workbench.
Before Dextre, such work usually required direct interaction with the station crew.
"Having ground-based flight controllers perform these tasks while the crew sleeps helps enhance our productivity," said Tim Braithwaite, the Canadian Space Agency's representative in Houston. "The on-board crew's valuable time can therefore be saved for science and research instead of time-intensive maintenance spacewalks or robotics."
The robot arm next moved Dextre back to the pallet to grab a cargo transfer container, which holds fresh electrical circuit breakers and a video distribution unit.
Each of the replacement units is about the size of a kitchen stove.
Braithwaite said Dextre's arms are stable and responsive to controller inputs, but the ground-based operators were challenged when the robot's target was drifting through the field-of-view of an alignment camera.
Thanks to the ground team's hard work, Braithwaite said Dextre's performance was "flawless" Thursday night.
The lab's robot arm moved Dextre back to an attachment fixture on the Destiny module Friday, where it is expected to stay until at least March.
Dextre will hold onto the cargo transfer container with its arm, and the flex hose rotary coupler will remain on the robot's workbench. The payloads were supposed to go on a logistics carrier on the station's backbone truss, but the platform is stuck on the ground due to delays in launching the shuttle Discovery.
Officials decided to keep the spare parts on Dextre until the shuttle delivers another Express Logistics Carrier, the payloads' permanent home.
NASA calls the payloads Orbital Replacement Units, or ORUs, which are large spare parts placed on the exterior of the station to stand by until a primary component fails. The wisdom of such an arrangement was proved when a crucial ammonia cooling system pump module failed last year. Astronauts conducted three spacewalks to install a replacement already stored outside the space station.
Dextre will provide electrical power to the ORUs until after Discovery's visit.
Now empty, the HTV's exposed pallet will be snared by the station's two robot arms again Monday for a choreographed move back inside the barrel-shaped cargo freighter.
Astronauts will use a camera system to precisely align the pallet with the entry point into the HTV cargo bay. Guide rails will help slide the cradle back inside.
The vehicle blasted off Jan. 20 from southern Japan and arrived at the outpost Jan. 27. Astronauts have already transferred refrigerator-sized scientific racks from the ship's pressurized compartment into the station.
The unmanned spacecraft will be moved by the robotm arm from the bottom to the top of the station around Feb. 18 to make room for the docking of Discovery on Feb. 26. If it stayed in its current position, the 33-foot-long HTV would be too close to the shuttle's cargo bay while it is at the complex.
The space station crew will re-attach the Kounotori 2 resupply ship to the Earth-facing side of the complex in March for final cargo unloading and stowage of trash inside the craft.
The HTV is currently scheduled to leave the station March 28 and plunge back into the atmosphere a day later for a planned destructive re-entry.
Dextre will be called back into duty after Discovery's flight to place the HTV's exposed payloads on the cargo carrier delivered by the shuttle.