Spacewalkers Unable To Deploy Cargo Carriers
Frank Morring, Jr./Johnson Space Center, Houston 
More mission updates can be followed at the On Space blog.
Astronauts Joe Acaba and Richard Arnold weren't able to open a cargo attachment device to its full extension on the second try of the STS-119/15A International Space Station mission, leaving undone a pair of extravehicular activity (EVA) tasks that were intended to set the station up for the day when the space shuttle fleet stops flying.
The two spacewalkers used a hammer, their bodies and a lot of elbow grease to try to open the unpressurized cargo carrier attachment system - a foldout rack designed to hold large spare parts for future use after the space shuttle retires next year - to its full extension. Ultimately controllers here ordered a halt to the work, and directed the EVA crew to tie the cargo-attach rack into a secure position with tethers designed for long-term exposure to the space environment.
With the lack of success on the port side of the station truss, engineers here decided not to attempt to attach a similar device on the starboard side. Both of the attach points were designed to hold spare parts NASA hopes to preposition on the station truss before shuttle retirement, because they are too large to deliver to the ISS with other vehicles that will be flying after that.
The port-side job also went unfinished on the second EVA March 21, when Acaba and astronaut Steve Swanson weren't able to unfold the cargo carrier because it was catching on a clamp held in place with an adjustable diameter pin. Controllers rewrote the time line for the third spacewalk in the hope they would be able to finish the job, but lead ISS flight director Kwatsi Alabaruho conceded engineers didn't understand the root cause of the hang-up.
The workaround, which essentially involved applying more force to the deployment mechanism, was developed after study of electronic engineering drawings and a trial run in the neutral buoyancy lab here.
Once the job was abandoned, and the loose cargo carrier tied down, the EVA crew moved on to other tasks. Arnold lubricated the end effecter on the station's main robotic arm to prepare it for the arrival of Japan's H-II Transfer Vehicle in September on its inaugural mission. The HTV flies to a close rendezvous with the station, and the station crew will use the arm to grapple the unpiloted spacecraft and berth it for unloading.
Meanwhile, on March 22 shuttle commander Lee Archambault used Discovery's thrusters to maneuver the station 180 degrees from its normal attitude when an orbiter is docked to it, adding drag to the two big spacecraft to lower their orbit out of the way of a threatening piece of Chinese space debris that passed by March 23.
Astronaut Joe Acaba is shown attached to end of cargo arm, carrying cart, in photo from NASA TV
