Astronauts Barry "Butch" Wilmore and Terry Virts floated back outside the International Space Station Wednesday for the second of three spacewalks to help ready the lab complex for dockings by commercial crew capsules being built by Boeing and SpaceX. Back inside the station's airlock, Virts reported a small amount of water in his space helmet, but officials said he was not in any danger.

Even so, given a near-catastrophic helmet leak less than two years ago, engineers will need to troubleshoot the latest issue to make sure the suit's internal systems are healthy enough for Virts and Wilmore to carry out a third planned spacewalk Sunday.

On July 16, 2013, European Space Agency astronaut Luca Parmitano's helmet flooded with water during a spacewalk. He made it back to the safety of the station's airlock in the nick of time, assisted by fellow spacewalker Christopher Cassidy - but the event easily could have turned fatal.

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Last week NASA space station managers delayed the the first two of the series of three planned spacewalks after exhaustive troubleshooting to verify the health of critical internal spacesuit components.

The problem with Virts' suit Wednesday was not noticed until he and Wilmore had returned to the station's airlock at the end of a successful six-hour 43-minute excursion. Along with a small blob of cold water floating in his helmet, Virts reported a water absorption pad at the back of the helmet, one of several safety measures implemented in the wake of the 2013 incident, was wet.

"Terry was saying he's got some water in his helmet, he just noticed it a minute ago," European Space Agency astronaut Samantha Cristoforetti told flight controllers in Houston. "It's about 3 inches in diameter, it's kind of pooling on the front side of the helmet above his eye level, and he does feel a little bit of squishiness in the back of the HAP (helmet absorption pad)."

A few minutes later, she said the pad was moist, but not saturated, possibly indicating the water flow did not begin until very late in the spacewalk. The frightening 2013 water intrusion was caused by clogged pores in an internal filter, but it was not immediately known what might have caused the problem Wednesday.

"It's not drink bag water," Virts reported after his helmet was off. "The drink bag bite valve was dry the whole time, that whole area of the helmet was dry and if you taste the water, it has a chemical taste, not exactly like chlorine but something like that. So it's some type of technical water, it's not drink bag water."

Virts' suit, serial number 3005, experienced a similar water intrusion after a spacewalk in December 2013, one of two that followed the much more serious incident the previous July. The December incident occurred at about the same time as the one Wednesday, when the airlock's pressure was holding at 5 pounds per square inch for routine post-spacewalk leak checks. How that timing might play into the troubleshooting was not known.

"At first, I saw just a little bit of water pooled in my helmet and it seemed normal because I was face down and that's where water pools," Virts said. "Except for when there's no gravity, so that's not normal."

The issue will be reviewed during an already planned space station Mission Management Team meeting Friday.