The U.S. space shuttle Atlantis entered Earth's orbit Friday on a mission to the International Space Station — the 135th and final flight of the 30-year-old shuttle program.

After days of rainy forecasts and cloudy weather, an estimated crowd of 1 million people watched the historic lift-off in and around the Kennedy Space Center in Florida.

NASA officials said they expect the shuttle to dock with the ISS Sunday on what they called a “pretty busy mission.” The shuttle's four-member crew is delivering supplies, spare parts and science experiments during its 12 days in space.

The cargo is expected to bridge the gap in supply shipments for the space station until commercial enterprises take over delivery by the end of this year at the earliest.

The space shuttles have served as the complex workhorses of the U.S. manned space program for the last 30 years, playing a key role in the building and operation of the International Space Station and performing other important missions. The end of the shuttle program leaves the United States without its own manned spacecraft.

NASA is ending the shuttle program to concentrate resources on deep-space exploration. The agency is working with several commercial U.S. aerospace companies to develop vehicles to replace the shuttles. Until then, Russia's Soyuz spacecraft will ferry U.S. astronauts to and from the ISS, while Russian, European and Japanese cargo rockets will continue their resupply and waste disposal missions to the station.

There were four astronauts on Atlantis for Friday's launch – Commander Chris Ferguson, Pilot Doug Hurley, Mission Specialist Rex Walheim and Mission Specialist Sandra Magnus. All four have flown on previous shuttle missions.