Sunday's spacewalk is the 187th in the history of the space station, and one of many planned for the coming year to prepare the space station for a new era in human spaceflight

MIAMI, USA Two US astronauts on Sunday, March 1, made speedy work of their third spacewalk to get the International Space Station ready for the arrival of more commercial spacecraft in the coming years.

Tethered to the outside of the orbiting outpost, space station commander Barry Wilmore and flight engineer Terry Virts reported no problems with their spacesuits during the outing, but Virts discovered a small amount of water building up in his helmet after he re-entered the space station.

A similar problem occurred after Wednesday's (February 25) spacewalk, when about three inches of water collected in Virts' headpiece, but NASA said the problem did not put the astronauts in danger.

Still, the US space agency has expressed concern about repeated technical failures in the American spacesuits, all linked to the same cooling system and a 2013 emergency water leak that nearly drowned Italian spacewalker, Luca Parmitano.

This time, Virts described the water as appearing like condensation, and he said there was about the same amount he had seen on the prior spacewalk, when about 15 milliliters was collected.

"Virts's suit, suit number 3005, has a history of what is called sublimator water carryover," said a NASA commentator on the space agency's live broadcast.

"Essentially a small amount of residual water forms in the sublimator cooling component, that condenses once the suit is re-introduced to a repressurized environment after being exposed to vacuum... resulting in a small amount of water pushing into the helmet."

He added it was "not an issue" for the astronauts' safety.

Fast workers

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US astronauts speed through ISS spacewalk