NASA kept an eye on the weather in Florida and 4,000 miles away in Spain, hoping for a break that would allow the launch of the repaired space shuttle Endeavour tonight.
Endeavour's flight to the international space station has been delayed almost two weeks by a leaking oxygen line and a damaged robot arm. The damage was caused by workers who accidentally rammed a platform into the 50-foot arm.
The robot arm is needed to lift a 14-ton girder from the payload bay for installation on the space station.
Besides performing construction work, the shuttle astronauts will deliver a fresh three-man crew to the space station and bring back the American and two Russians who have been on board since early June.
On Thursday evening, NASA announced a launch time of 8:15 p.m. The space agency kept the time secret until about 24 hours in advance, under post-Sept. 11 security guidelines.
Forecasters said there was an 80 percent chance of good launch weather, with gusty wind the main concern. But the outlook was much worse at the two emergency landing sites in Spain, where rain, thick clouds and turbulence were expected throughout the weekend.
At least one overseas landing site must have acceptable weather for the launch to proceed.
A Moroccan air base that used to serve as an emergency landing site has not been considered for months because of security concerns.
NASA's last countdown was halted Nov. 10 at the two-hour mark because of a leak in the astronauts' oxygen supply. A cracked hose was replaced. The robot-arm damage occurred while workers were hunting for the leak.