NASA, in preparation for a spacewalk on Saturday, has devised makeshift snorkels that would allow an astronaut in a spacesuit to continue breathing even if a sudden water leak should fill the helmet, as happened to an Italian astronaut who almost drowned in July.
Two astronauts, Col. Michael S. Hopkins of the Air Force and Richard A. Mastracchio, are to step out of an air lock on the International Space Station at 7:10 a.m. Eastern time in the first of at least two spacewalks aimed at replacing a malfunctioning pump module that is part of the space station's cooling system.
Koichi Wakata, a Japanese astronaut, will be operating a robotic arm from inside the station to assist with the repairs.
Colonel Hopkins will be wearing the same spacesuit — No. 3011 — that leaked in July. During that spacewalk, water partly filled the helmet. The astronaut in the suit then, Luca Parmitano, was able to hurry back to safety, but not before water covered his eyes and blocked his nostrils.
Engineers found that contamination had clogged one of the suit's filters, causing water from the suit's cooling system to back up. Those parts have been replaced, and tests have indicated no lingering problems.
Officials admit to some uneasiness, however, because the source and cause of the contamination remain unknown.
NASA had planned to send a replacement spacesuit to the station. But on Dec. 11, a valve controlling one of two loops of circulating ammonia that cool equipment on the space station malfunctioned. When attempts to control the ammonia flow using a different valve proved inadequate, space station managers decided to send the astronauts out on the spacewalks.
Engineers have devised low-tech countermeasures in case water again floods into a helmet.
An absorbent pad installed in the back of the helmet can hold 20 to 27 ounces, or about 600 to 800 grams, of water. The astronauts will periodically tilt their heads back to check if the pads have become "squishy."
In addition, station crew members made improvised snorkels out of available materials: plastic tubing and Velcro. The tubes will extend from the helmet down into the chest area of the spacesuit. If water is encroaching on the astronaut's face, "this is your last resort," said Allison Bolinger, the lead spacewalk officer. "The crew member can lean down and use this to breathe, to receive fresh oxygen down near his midsection."
During Saturday's spacewalk, which is expected to last about six and a half hours, Colonel Hopkins and Mr. Mastracchio will disconnect cables to the pump module and open up the insulation that covers it.
The ammonia pump itself is operating normally, but the ammonia has been too cold because of the problem with the valve, which controls the temperature. That led to the shutdown of an internal cooling loop of circulating water, to stop the cold ammonia from freezing the water.There is no immediate danger to the station's six crew members, but the station would be in more serious trouble if the other ammonia loop malfunctioned.
On the second spacewalk, planned for Monday, the astronauts will replace the 780-pound pump module with a spare one. If necessary, a third spacewalk would take place on Wednesday.
This article has been revised to reflect the following correction:
Correction: December 21, 2013
An earlier version of this article misidentified the astronaut who is wearing a spacesuit that once leaked. It is Col. Michael S. Hopkins, not Richard A. Mastracchio.
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