For the second day in a row, thunderstorms forced NASA on Friday to call off space shuttle Endeavour's launch on a mission to the international space station.

Mission managers postponed the launch until Monday because of storms forecast throughout the weekend.

The delay in delivering a fresh crew to the international space station means at least four more days in orbit -- and a record-breaking stay -- for Americans Daniel Bursch and Carl Walz. They have been living aboard the orbiting outpost since December along with their Russian commander, Yuri Onufrienko.

Their mission, at the 177-day mark Friday, will reach at least 192 days by the time they return to Earth. The U.S. space endurance record stands at 188 days; Shannon Lucid posted that aboard Russia's Mir space station in 1996.

"I'm sure that Dr. Shannon Lucid will congratulate them on that particular feat when they finally do return home," said NASA Administrator Sean O'Keefe. Mission Control radioed up its own congratulations Thursday night.

Onufrienko has an even longer mission to his credit: a 193-day Mir flight in 1996. That's still far short of the 438-day world record held by his fellow countryman, Valery Polyakov.

Thursday evening's delay came as no surprise to the seven astronauts and cosmonauts aboard Endeavour. Approaching thunderstorms had threatened to postpone the flight all day. The launch team also had to deal with a last-minute problem with one of Endeavour's orbital-maneuvering systems.

The scrub on Thursday cost NASA just over $600,000, most of it in fuel. No money was lost on Friday's postponement because it came so early in the day.

Endeavour will take up a new space station crew: American Peggy Whitson and Russians Valery Korzun and Sergei Treschev, who will spend 4 months aboard.

During the eight days that Endeavour is docked to the space station, the shuttle astronauts will conduct three spacewalks to fix the robot arm and do other exterior work.

The 58-foot arm -- Canada's main space station contribution -- requires wrist surgery because of a problem that caused one of its joints to seize up. Engineers have managed to work around the problem but want to fix it before the arm is needed for major construction later this year.