Cape Canaveral, Fla. ? Thunderstorm clouds forced NASA to call off Thursday’s launch of space shuttle Endeavour on a mission to deliver a new crew to the international space station and fix the orbiting outpost’s robot arm.

Launch managers said they would try again this evening, even though the weather was expected to worsen.

A NASA security helicopter hovers over the astronaut transport van (not shown) as it heads to the pad for the scheduled launch of Endeavour. NASA scrapped Thursday's launch because of the nearby thunderstorm clouds. Endeavour will take a team of astronauts to the International Space Station.

The delay means yet another day in orbit and a record-breaking stay for Americans Daniel Bursch and Carl Walz. They have been living aboard the space station since December along with their Russian commander, Yuri Onufrienko.

Their mission, already at the 176-day mark, will reach at least 189 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.

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.

The 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 fleeting problem with one of Endeavour’s orbital-maneuvering systems that cropped up in the final 1 1/2 hours; that trouble, though, was quickly resolved.

The countdown was halted at the nine-minute mark. “We see no hope at all in our weather situation improving,” said launch commentator Bruce Buckingham.

Throughout the afternoon and evening, fighter jets enforced a no-fly zone around the launch pad, and the surrounding waters were off-limits. The crew departed for the pad in secrecy, as part of anti-terrorism precautions.