Nasa's first educator astronaut has held her inaugural lesson from orbit.

Barbara Morgan conducted a 25-minute lesson with students at the Discovery Center of Idaho while aboard the International Space Station.

Morgan and three fellow astronauts answered questions on everything from global warming to how fast it was possible to throw a baseball in space.

"Astronauts and teachers actually do the same thing. We explore. We discover, " she said.

"The great thing about being a teacher is that you get to do that with students. The great thing about being an astronaut is that you get to do that in space. Both are absolutely wonderful jobs."

Canadian astronaut Dave Williams said that the crew could see the effects of deforestation from space and the glow of forest fires. The team also discussed the effects of zero gravity.

Morgan, who has waited over 20 years to get into space, was the backup astronaut to Christa McAuliffe who died in the Challenger disaster of 1986.

Meanwhile, Nasa has delayed a decision on whether or not to make repairs on the Space Shuttle until today. A 5in hole was knocked out of the heat shield of Endeavour by a chunk of frozen foam 58 seconds after launch.

Nasa has said that it would be safe to land without repairs, since that area of the shield would not bear the full brunt of re-entry heating. The agancy will make a final decision later today.