It was a textbook liftoff – apart from two minor but worrying details.As the US shuttle Discovery blasted off from Florida’s Cape Canaveral launch pad on Tuesday, cameras showed a piece of debris falling away from the exterior fuel tank. They also revealed a nick in the protective tiles near the nose landing gear. No doubt controllers could not help thinking about the Columbia disaster in 2003 when foam falling from the fuel tank punched a hole in the wing’s protective heat shield at launch, leading to the shuttle’s disintegration on re-entry. Now, under safety rules introduced after the fiasco, the potential damage to Discovery during the launch will have to be carefully scrutinised. Astronauts have already unfolded and tested an extendable robot arm equipped with a laser. Later they will train in on the orbiter’s wings and nose cap to check for any problems.