CAPE CANAVERAL, Fla. – Stormy weather prevented NASA from launching Discovery for the second day in a row Sunday, extending a yearlong grounding of the space shuttle prompted by persistent trouble with fuel-tank foam.

Launch officials said they would try again Tuesday, on the Fourth of July, after giving the work force a day of rest and a chance to replenish the shuttle’s on-board fuel. The weather was expected to improve by Tuesday, although rain was still in the forecast.

“We’ve concluded that we’re not going to have a chance to launch today,” launch director Mike Leinbach announced to his team.

Replying from the cockpit, shuttle commander Steven Lindsey said: “Looking out the window it doesn’t look good today, and we think that’s a great plan.”

He noted that July Fourth would be “a good day to launch.”

Lindsey and the six other astronauts had boarded the fueled spaceship just an hour earlier for what would have been only the second shuttle flight since the 2003 Columbia disaster. The countdown was halted with more than an hour remaining, much earlier than Saturday’s postponement.

The afternoon sky was considerably darker than on Saturday and left NASA with little choice but to call off the launch to the international space station. Thunderstorms were moving in quickly from the west, and lightning was detected within a few miles of the launch pad. The astronauts rode back to crew quarters in the rain.

The back-to-back delays cost NASA an estimated $2 million in overtime pay and fuel costs.

Among the invited guests who stuck around for try No. 2 were family members of the perished Columbia astronauts. Vice President Dick Cheney was back in Washington, after a brief visit to the space center Saturday.

NASA Administrator Michael Griffin approved launching the shuttle for the 12-day mission despite the concerns of two top agency managers who wanted additional foam repairs. Columbia was brought down by a chunk of flyaway fuel-tank foam insulation, and a piece broke off Discovery’s tank last July, barely missing the shuttle.

A lot of other people thought approving the mission was a good idea, Griffin said Sunday in an interview on CNN’s “Late Edition with Wolf Blitzer.”

“I judged the odds to be very low that we’re risking a vehicle,” Griffin said, according to a CNN transcript. “I’ve kind of steeped myself in this problem over the last month, and I am quite confident that we’ve got a very good chance of flying and flying safely.”

“We think we’re in good shape; we’re in solid shape to go,” Griffin said.

Sen. Bill Nelson, D-Fla., who flew on a space shuttle in 1986 right before the Challenger disaster, defended Griffin’s decision and said it was an acceptable risk.

Griffin said any risk would be only to the shuttle and not the crew, since the astronauts could take refuge in the international space station until a rescue vehicle is sent up.

Bryan O’Connor, the top safety officer, and chief engineer Christopher Scolese recommended at a flight readiness review meeting two weeks ago that the shuttle remain grounded until design changes were made to 34 areas on the fuel tank known as ice-frost ramps. These wedge-shaped pieces of foam insulate brackets on the tank that hold long pressurization lines in place. The intent is to keep ice or frost from forming on the metal brackets once the tank is filled with super-cold fuel.

NASA engineers redesigned the external fuel tank after the Columbia accident, and again after a 1-pound piece of foam insulation came off the tank during the launch of Discovery last summer. The last foam loss caused Griffin to ground the shuttle fleet for almost a year while engineers worked on design changes.

Once in orbit, Discovery’s seven-member crew will test shuttle inspection and repair techniques.