The U.S. space agency NASA has again postponed the launch of the space shuttle Endeavour, because of storms near the Kennedy Space Center in Florida.
Officials said they will now try to launch the shuttle Monday evening.
This is the fourth failed attempt to launch Endeavor on what was to be a 16-day mission to the International Space Station.
Saturday, the launch was canceled after a series of lightning strikes. Last month, two tries were canceled because of hydrogen gas leaks.
The shuttle is expected to transport astronaut Timothy Kopra to the International Space Station to take the place of Japan's Koichi Wakata, who will return home on the shuttle. Wakata has been on the space station since March.
The seven-member shuttle crew is also scheduled to install a Japanese-built porch on the International Space Station, in a series of five spacewalks.
The porch is the final component of a Japanese space module, known as Kibo, and will be used to expose certain experiments to the vacuum of space.
NASA faces a September 2010 deadline to complete construction of the Japanese lab section before the shuttle fleet is retired. Eight shuttle flights are dedicated to that construction effort.
Some information for this report was provided by AFP, AP and Reuters.