Spacewalking NASA astronauts Rick Mastracchio and Mike Hopkins charged through the challenging first steps of a three phase International Space Station cooling system repair campaign on Saturday, accomplishing all they set out to do and more during a 5 1/2 hour spacewalk.
One major concern among the NASA Mission Control team that planned the three-spacewalk, five-day repair strategy was a possible repeat of the water leak in the helmet of the NASA space suit worn by Italian astronaut Luca Parmitano during the most recent U.S.-orchestrated excursion on July 16. Another was the possible leak of toxic ammonia coolant at the work site, where the two men are replacing a cumbersome pump module.
Spacewalker Rick Mastracchio, center and suspended head down from the tip of the International Space Station's robot arm, removes a boxy cooling system pump module from the six person orbiting science laboratory. Photo Credit:NASA TV
The first concern never materialized. A few snowlike flakes of frozen ammonia emerged as the two astronauts disconnected coolant lines. The quantities, however, were not sufficient enough to pose a hazard. The spacewalk’s task list was extended for the removal of the old pump module from its perch and temporary stowage at the work site to ease the task of installing a replacement on the second spacewalk, which was moved from Monday to Tuesday following Saturday's excursion for an unrelated spacesuit issue.
Saturday's momentum in dealing with the ISS cooling issue was tempered by a new space suit issue that emerged at the end of the spacewalk -- an inadvertent activation of the sublimator in Mastracchio's space suit, a device that regulates internal temperatures.
The activation may have exposed the sublimator to water, though post spacewalk inspections by the ISS crew did not reveal any moisture.
Nonetheless, NASA elected to submit Mastracchio's suit to a drying protocol, and there were other suits aboard the ISS that could be assigned to the spacewalkers.
If the two men are as productive Tuesday as they were on Saturday, Mastracchio and Hopkins may complete the repairs without a third excursion tentatively planned for Wednesday, or Christmas Day.
"We are thinking we may be down to the two (spacewalk) case now," NASA's Mission Control told the spacewalkers several hours after the spacewalk came to a productive end at 12:29 p.m., EST.
Saturday's aggressive pace came with some discomfort for Mastracchio, who received permission from Mission Control to warm up his suit to deal with cold toes. Hopkins made an airlock pit stop to top off his breathing oxygen supply. Mastracchio urged ground controllers to refrain from the opportunity to do even more.
Loop A of a dual loop ISS cooling system that circulates liquid ammonia through external radiators shutdown on Dec. 11. The difficulty was traced to the electrical circuitry in a flow control valve housed within the three-year-old pump module.
The circulation of ammonia through Loops A and B provides thermal control to internal as well as external ISS electrical components, including life support and scientific hardware. The Loop A ammonia draws heat from internal electronic equipment through heat exchangers in the U.S. segment Harmony and Destiny lab modules. The Dec. 11 shutdown occurred when ammonia at temperatures too low for the water loops that remove heat from the habitable crew modules threatened to reach the heat exchangers. While external cooling continued through Loop A, non-essential internal electronics in the European Columbus and Japanese Kibo science modules as well as Harmony were deactivated. Loop B took on some of the thermal control duties.
Much of the station's U. S. segment research activities have been interrupted as a consequence.
On Saturday, Mastracchio and Hopkins worked as much as 90 minutes ahead of schedule to:
**Deactivate the old pump module with the faulty flow control valve. The task involved deftly disconnecting four pressurized ammonia coolant lines and temporarily reconnecting them to a cooling system jumper box that will maintain the external ammonia flow until the replacement pump module is installed.
**Remove five electrical connectors.
**Loosen four bolts securing the pump module to the station's power truss.
**Take on the removal of the old pump module from its platform on the truss, a task initially planned for Monday. The 780-pound module was temporarily stowed near the work site, clearing the way for the installation of a spare on Monday. The spare pump module is stowed close to the right side solar power truss.
Japanese astronaut Koichi Wakata, working from an internal control post, served as the Irobot arm operator, providing the spacewalkers with a 58-foot-long mobile work platform.
In response to the worrisome July 16 helmet flooding incident, whose root cause remains under investigation, NASA made changes to the spacesuits worn by the two men.
Hopkins donned the same suit worn by Parmitano. However, a fan pump separator in the personal life support system backpack of the protective NASA garment was replaced as was a secondary oxygen supply, some water filters and a valve.
The old fan pump separator from Parmitano's suit was returned to Earth aboard a Russian Soyuz crew transport in November as part of NASA's inquiry into the July 16th incident in which 1 to 1 1/2 liters of water pushed along by the fan pump entered the spacewalker's helmet. It appears that particulates from the water that circulates through the NASA space suits to cool the astronauts clogged small water ports in the fan pump separator. The device circulates breathing air in the spacesuit and extracts moisture.
When the fan pump separator filled with water on July 16, it did not trip off as intended. Instead, the fan kept running and directed water into an air flow channel at the back of Parmitano's helmet. The flow channel extended over the top of his head.
The planned six to seven hour July 16th spacewalk was halted a little more than 90 minutes into the outing. Parmitano and his partner, NASA astronaut Chris Cassidy, made their way back to the safety of the U.S. airlock with water flowing into Parmitano's helmet and massing around his eyes, ears and nose. Both men subsequently completed their tours of duty on the ISS as scheduled and returned to Earth.
The source, or sources, of the particulate as well as the water chemistry behind the formation of the contaminants remain an active focus of NASA's investigation into the worrisome incident.
The spacesuits for Saturday's excursion were equipped with absorbent pads in the helmets to soak up as much as 800 milliliters of leaking water and makeshift snorkels fashioned from plastic water tubes and positioned close to the mouths of the spacewalkers. Mastracchio and Hopkins repeatedly checked for "squishiness" in the pads atop their heads at the request of NASA Mission Control, with the first check coming at 30 minutes into the excursion.
No leaky water was reported, and the snorkels were not needed.
During Tueday's spacewalk, Mastracchio and Hopkins will return to the worksite to physically swap out the old pump module with one of three spares stored outside the station. The primary task assigned to the third spacewalk, if needed, is to move the old pump module to a permanent external storage slot. Engineers are hopeful it could be equipped with a new flow control valve at some point in the future.
NASA astronauts Doug Wheelock and Tracy Caldwell Dyson carried out a similar swap out in August 2010, when the pump motor in an older pump module failed.
"The challenge is to keep it slow and steady," said Caldwell Dyson of working with the unwieldy module.
Meanwhile, the Orbital Sciences Corp. "ORB-1" re-supply mission to the ISS that was postponed by the cooling system problems has been re-scheduled for lift off from the Mid-Atlantic Regional Spaceport in Virginia on Jan. 7 at 1:55 p.m., EST. Previously scheduled for Dec. 19, the mission is the first to be flown under a $1.9 billion, eight flight agreement between the Dulles, Va., company and NASA.