Cape Canaveral, Fla. ? A pair of space station astronauts had to hammer loose a stuck connector during an urgent spacewalk to restore a crucial cooling system Saturday, then an ammonia leak erupted and hampered the entire repair effort.

Despite making one of the longest spacewalks ever, Douglas Wheelock and Tracy Caldwell Dyson had to give up trying to remove a broken ammonia pump and retreat inside.

Disappointed managers said two more spacewalks now will be needed to replace the pump and get the International Space Station’s cooling system operating normally again. The original plan called for two spacewalks.

Another spacewalk won’t be attempted until Wednesday at the earliest. Engineers huddled following Saturday’s eight-hour, three-minute effort — the sixth longest spacewalk ever — to consider their options.

“We will get through this problem,” said space station program manager Mike Suffredini. “The challenge is to get through this problem before the next problem hits the other cooling system.”

The pump failure knocked out half of the space station’s cooling system last weekend, leaving the orbiting lab with only one good cooling loop. Another breakdown could leave the station in a precarious situation.

From the start, NASA described the repair work as some of the most challenging ever attempted at the 220-mile-high complex.

The latest trouble struck halfway through Saturday’s spacewalk. Wheelock and Caldwell Dyson could not get one of the four pressurized ammonia hoses to come off the disabled pump.

A bit of ammonia coolant leaked out as the spacewalkers struggled with the connections.

Lagging well behind by this point, the spacewalkers managed to remove three of the four hoses. Wheelock tried once more to disconnect the balky line, banging the jammed button with a special tool. It worked.

Mission Control erupted in applause. “Awesome,” Mission Control radioed.

But the exuberance was dampened by a stream of escaping ammonia.

The astronauts managed to stop the leak when they plugged the troublesome connector back in.