Astronaut Jim Newman during a space station assembly spacewalk in December 1998. Photo: NASA

Backup oxygen supplies in the pressure suits worn by shuttle spacewalkers are being inspected and cleaned to remove any traces of potentially flammable contamination found in all of NASA's spacesuits.

In the meantime, extensive testing shows the lower pressure primary oxygen systems in the $2 million spacesuits are free of similar contamination and would operate safely even if flammable contamination was present but hidden from view.

As a result, NASA plans to press ahead with plans to launch the shuttle Atlantis to the international space station in early September, a flight that features a spacewalk by astronaut Edward Lu and Russian cosmonaut Yuri Malenchenko.

While no spacewalker has ever had to use a secondary oxygen pack, or SOP, NASA is leaving no stone unturned to make sure the protective spacesuits are safe for use in any scenario, including unlikely mishaps that might knock a suits primary oxygen system out of action.

"The likelihood of any such scenario is extremely remote," said Gregory Harbaugh, a veteran shuttle spacewalker who now oversees spacewalk planning at the Johnson Space Center in Houston.

"Nevertheless, my concern is and has always been to ensure the safety of the crew. And hydrocarbon contamination in the environment of 6,000 psi oxygen is not a good mixture. It is something that has the potential of creating a fire if the right conditions are satisfied."

The contamination was discovered in June when technicians were repairing a leaking regulator in a spacesuit's secondary oxygen pack. The SOPs, which operate at much higher pressures than the primary system, can provide about 30 minutes of air in an emergency.

Analysis showed the oily residue was made up of hydrocarbons, which can burn in the presence of oxygen. Technicians quickly inspected the rest of NASA's shuttle spacesuits and found similar contamination in every SOP.

Harbaugh said the regulators in all 12 of NASA's spacesuits will be thoroughly cleaned before the next shuttle flight. In addition, so-called "cold traps" will be used in the oxygen lines used to load the high pressure SOPs that will cause any contamination to condense out of the flow.

Astronaut Mark Lee wears his spacewalking suit during the second Hubble Space Telescope servicing mission. Photo: NASA

"Every one of these 12 regulators is going to be cleaned before we use them for flight," Harbaugh said. "In parallel, we've gone off and looked at the primary (oxygen) system. ... The data to date shows that the primary system is actually quite clean.

"However, I'm not in a position to say today that we know definitively that every nook and cranny of the primary system is clean," he said. "And we may not be in that posture before we fly. So given that possibility, we undertook testing and analysis to make sure we understood what the implications of that might be."

To make sure the suits Lu and Malenchenko will use in September are safe, engineers carried out a battery of tests at a NASA facility in White Sands, N.M., in which generic spacesuit oxygen systems were subjected to extreme conditions and contamination levels far higher than anyone ever expects to see.

"In every instance, we found no indication of any potential for ignition," Harbaugh said. "We contaminated these regulators at roughly twice the level of contamination that we'd seen on the secondary side, which is almost 1,000 times what we've seen so far on the primary side. All results were negative.

Outside experts were called into to examine the results and all were in agreement "that that analysis and the testing is valid," Harbaugh said. "And therefore we're OK to proceed (with flights) with the primary side being in the condition we now know it to be."

Asked if any previous spacewalkers were in danger or if NASA dodged a bullet by discovering the contamination issue in June, Harbaugh said "there's no way to know how far we could go without having a problem."

"It is conceivable we could do the next five years and 165 EVAs (spacewalks) and not have any problem at all," he said. "But that's not the approach we're going to take. I'm going to make certain there's no problem."