Cape Canaveral, Fla. ? Two astronauts who stepped out of the international space station Thursday for an unusually risky spacewalk were quickly ordered back in when Mission Control spotted a pressure drop in one of the men’s oxygen tanks.

NASA stressed that the spacemen were never in any danger. They were safely in the pressurized confines of the orbiting complex within minutes, and said they were feeling fine.

The spacewalk — a critical repair effort to replace a fizzled circuit breaker — was put off until Tuesday at least. Controllers said they needed to understand what went wrong before sending astronaut Mike Fincke and cosmonaut Gennady Padalka back outside.

Fincke had just popped open the hatch and floated outside when the frightening words came from Russian Mission Control: “You need to return. Something is not right.”

Mission Control informed the spacemen that the pressure in Fincke’s prime oxygen bottle was falling rapidly. They needed to get back inside, fast, and close the hatch.

They sealed the hatch 14 minutes and 22 seconds after opening it and repressurized the Russian air lock.

Fincke and Padalka were using an odd mishmash of U.S. and Russian gear, and carrying out a spare circuit breaker. The new breaker is needed to restore power to one of the gyroscopes that help keep the station stable and pointed in the right direction.

The mission was fraught with risk, even before Thursday night’s suit trouble. NASA had to leave the space station empty during a spacewalk for only the second time ever, forcing flight controllers on the ground to keep an eye on the outpost’s systems.

NASA has been bending its own rules to keep the space station operating since the grounding of the shuttle fleet after last year’s Columbia catastrophe. The grounding has all but stopped the delivery of replacement parts and reduced the size of the station crew from three to two.

Backdropped by a blue and white Earth, the international space station is seen June 15, 2002. Two astronauts who stepped out of the international space station Thursday for an unusually risky spacewalk were quickly ordered back in when Mission Control spotted a pressure drop in one of the men's oxygen tanks.

The announcement that the spacewalk was officially over came soon after both crewmen were instructed to take off their spacesuits, nearly an hour after the spacewalk began.

It was a disappointing moment in space.

“Have some tea, coffee,” Mission Control kindly told the crew.