The space shuttle Atlantis has touched down in Florida's early morning darkness after a successful 12-day mission that saw the first building work carried out on the International Space Station in more than three years.

Tyres hissing and trailing a braking parachute, Atlantis returned to Earth at 6:21am local time (11:21 BST), when it landed at the Kennedy Space Center in Florida.

The shuttle's descent from orbit began just over an hour earlier, when Commander Brent Jett was cleared by mission control to fire the spacecraft's rockets for two minutes and 40 seconds and to begin positioning the shuttle for its rear-first re-entry to the Earth's atmosphere.

During its bumpy, super-heated descent, the skin of the shuttle reached temperatures of around 1,650C (3,000F) as the spacecraft hurtled downwards, slowing from its orbital speed of 29,000kph (18,000mph) in a wide loop across the Pacific Ocean, Mexico’s Yucatan Peninsula and Florida’s southwest coast.

The Atlantis mission, STS-115, was the third safely completed flight by a Nasa shuttle since the Columbia disaster in 2003, and the first since then to carry out meaningful work in space. The crew of six added a $372 million (£197 million) solar power unit to the space station.

The space station's solar arrays were unfurled last Thursday. Over the coming years, constantly adjusting to receive the sun's rays, they will double the energy output of the station. A further 15 shuttle flights are intended to finish the ISS by 2010, when the fleet is scheduled to retire.

Atlantis's return to Earth was delayed by a day because of bad weather and more important concerns surrrounding a small object seen floating next to the shuttle in space. The object, which kept the same orbit as the spacecraft, was never identified.

But a seven-hour inspection of the shuttle and its delicate heatshield — the source of $1 billion (£531 million) of Nasa concerns since the break-up of Columbia in 2003 —showed that it was safe to return. Further examination of footage of the outside of Atlantis showed two other harmless pieces of debris also floating nearby. One of these was recognised as a plastic bag.

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