Shuttle launches 'disco ball'

The 48cm ball is covered with 900 highly-polished mirrors which are intended to reflect the sun's rays to be observed from the ground.

"Essentially it's a disco ball", said Linda Ham, a Nasa flight director.

Around 25,000 schools around the world are expected to follow the Starshine satellites orbit as part of a global Internet science project.

Starshine's path will be measured by students observing the twinkling of sunlight on its mirrors at dusk and dawn.

Students will use the data to measure the density of the atmosphere.

Inspired by Sputnik

The satellite will stay in orbit for the next eight months, before burning up as it re-enters the atmosphere.

The satellite's designer, Gil Moore, said he got the idea from his own observations of early satellites like Russia's Sputnik.

He said: "Back then I thought it would be a cool thing to have students run their own network instead of always having the professionals run the show.

"Now kids have access to personal computers, and the Internet allows them to take data anywhere in the world free."

Light reflected from the satellite will be visible as far north as Scotland and Canada, and as far south as the New Zealand and the southern tip of South America.

Discovery has now reached the end of its latest 10-day mission, preparing the International Space Station for its first long-term occupants next year.

Nasa plans to bring the shuttle down earlier than planned in order to avoid forecast rain in the Cape Canaveral landing area.