(AP) -- Astronauts climbed aboard space shuttle Atlantis on Monday for an afternoon liftoff to the space station, as the sky over the launching site gradually cleared.
Forecasters put the odds of acceptable weather at an improved 80 percent. Low clouds were the sole concern for the 2:28 p.m. liftoff.
The six astronauts grinned and waved as they headed to the launch pad late Monday morning. Commander Charles Hobaugh was the first one into the shuttle.
With a couple hours remaining before liftoff, NASA detected an electrical issue that seemed to be associated with the cabin lighting. Launch commentator George Diller said engineers saw the same thing on a previous flight and might wait until the shuttle is in orbit to deal with it.
Atlantis is loaded with big spare parts for the International Space Station. NASA wants to stockpile as much equipment there as possible before the shuttle fleet is retired next year.
The 11-day flight will keep the astronauts in orbit through Thanksgiving. They will unload nearly 30,000 pounds of pumps, tanks and other spare parts, as well as science experiments. Three spacewalks will be conducted to carry out the work.
It is NASA's last shuttle flight of the year and among only six remaining.
Gathering for the launch were about 100 Twittering space fans who won invitations from NASA. They were among the first to sign up online last month for this first-ever launch "tweetup."
NASA put up a white circus-like tent at the press site of Kennedy Space Center, expressly for the Twitter crowd. The long rows of tables covered with laptops were briefly vacated as the crowd walked over to the main road to the launch pad to watch the crew drive by in the so-called astrovan. The crowd cheered and waved to the astronauts, and immediately posted Twitter updates.
"100 nerds against the road waving at the astrovan," one wrote.
"I was begging the astronauts to take me with them as they stopped and waved at us," another tweeted.
NASA estimates the 100 tweeters have a following of more than 150,000. The space agency sees it as a beneficial outreach program.
On the Net:
©2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
Explore further: Europe postpones launch of first 'space plane'