Spacewalkers finish part of their Saturday to-do list
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: March 21, 2009
Engineers are studying options for freeing a jammed locking pin, part of a clamp that apparently was installed backwards by a spacewalker today in the topsy-turvy world of microgravity. The backward clamp prevented a stowed space station cargo carrier from fully deploying and locking into place.
The spacewalkers also ran into familiar problems re-configuring a wiring panel because of a stuck connector that has defied repeated disconnection attempts.
The patch panel, located near the station's vertical zenith 1, or Z1, truss, routes power to and from the lab's four stabilizing gyroscopes. One gyro was tied into a circuit breaker used by another stabilizer during an earlier mission because of a circuit failure. The circuit breaker was replaced, but attempts to disconnect the cable in question so it could be hooked back up to its own circuit breaker were unsuccessful during an earlier mission and astronaut Steven Swanson was unsuccessful making another attempt today.
Lead flight director Kwatsi Alibaruho said Swanson was trained to simply re-wire the panel from the back, but he ran out of time during today's spacewalk. The work may be added to a third and final spacewalk Monday or deferred to a later assembly mission. The gyros operate normally in the current configuration, but a single worst-case failure in the circuitry could disable two gyros at the same time and NASA managers want to restore normal redundancy as soon as possible.
"We had certainly another exciting day in space today," Alibaruho said. "We didn't accomplish everything we wanted to accomplish on this EVA, but just know we did accomplish all the critical-path items that were scheduled."
Inside the space station, meanwhile, the astronauts carried out a critical test of a new urine processor distillation assembly centrifuge that was carried up by Discovery.
The station's water recycling system is designed to convert sweat, condensate and urine into pure water for drinking, personal hygiene and oxygen generation. But the original distillation assembly malfunctioned shortly after it was installed late last year, victim of some sort of internal vibration or interference issue.
The water recycling system is crucial to NASA's plans for eventually supporting a full-time crew of six aboard the station.
The replacement distillation assembly was installed Friday and today, the crew fired up the new centrifuge for a test run.
"That activation and checkout went very well," Alibaruho said. "What we did was, we pointed a high definition camera and microphone at the unit. That unit is like a big centrifuge, kind of similar to a washing machine. So the vibrations and the sounds that it makes tells us quite a bit about its health.
"Basically, that unit functioned normally. We spun it up for about five or so minutes without any fluid in it, just to make sure that the motor was spinning properly and the rpm and the currents and the voltages on the motor looked normal. All of that looked very normal and in fact, we did get feedback from the ISS crew that that new distillation assembly actually sounded much quieter than the original. So, just based on qualitative feedback from the crew, we know there's certainly a difference in performance of this unit versus the original that was installed on the last mission.
"So tomorrow (Sunday), what's on the plate is to actually fill the urine processor with urine and attempt to do a full process cycle on that and shunt that processed urine to the water recovery system to then allow us to take an end-of-mission sample. So that work is going very well."
As for today's spacewalk, Alibaruho said Swanson and Joseph Acaba accomplished the highest-priority objectives: breaking torque on a solar array battery pack that will be replaced in June; installing a GPS antenna on a Japanese module; and photographing radiator panels to help engineers assess an area of damage and any other possible problems.
But the astronauts were unable to unstow and deploy an unpressurized cargo carrier attachment system, or UCCAS, on the lower side of the port 3, or P3, solar array truss segment. The UCCAS was built into the truss segment and has been stowed since launch. During today's deployment, Swanson and Acaba removed clamps and locking pins and attempted to rotate the mechanism outward.
As it turns out, one variable-diameter locking pin, part of a clamp-like device, was reinstalled in the wrong orientation, causing the pin to physically interfere with the deployment. The spacewalkers struggled to free the jammed pin, even using a tool as an impromptu lever. But they were unsuccessful.
"One of the first things they do when they come out to prep the UCCAS for its deploy is to pull the adjustable-diameter pin out of the hinge line where it's holding it from deploying inadvertently, and move it over to the stow location," said lead spacewalk officer Glenda Laws-Brown.
"As you know, when you get to the international space station there is no up and down. And my guess is they thought they had it in the right configuration, but because up is down and down is up, it was actually 180 degrees out from where it should have been."
Spacewalk planners are evaluation options for freeing the jammed pin and an attempt may be added to the crew's third spacewalk Monday. In the meantime, Swanson tied down the UCCAS mechanism with tethers before today's spacewalk ended to make sure the system cannot inadvertently move.
"All in all, it was a successful EVA in that the highest priority tasks were completed and as far as the tasks we had difficulty with, tasks that we had problems with, these are things where there will be no long term programmatic impact," Alibaruho said.
"However, we do want to take a much closer look at that UCCAS mechanism that was not fully deployed today. We had the crew attach some tethers to that, we had the crew essentially put it in a safe configuration to where it can sustain all of the planned structural loading of events from thruster-driven attitude control or gyroscope-driven attitude control. So the station is in a perfectly safe configuration right now. But we will be looking at that in more detail and we probably attempt some remediation on EVA 3."