The crew of Discovery have begun their first day in orbit with a painstaking, delicate search of the exterior of the shuttle to investigate whether the spacecraft was damaged during blast-off.

In an eerie reminder of the troubled take-off of the space shuttle Columbia, which broke up on its return to the Earth's atmosphere in 2003, video footage from yesterday's launch showed two pieces of debris falling away from Discovery.

A 4cm (1.5in) piece of thermal tile appeared to break off from the Discovery’s belly during lift-off, as well as a larger piece of foam, according to Nasa flight operations manager John Shannon. Neither object struck the space craft as they fell.

"Engineers on the ground are using the imagery and data from today’s inspections and from Tuesday's launch videos to determine the health of Discovery’s heat shield. The engineers continue to evaluate two debris events that were captured by video as Discovery climbed into space," the agency said on its website today.

Although Nasa officials have said that it is unlikely that the damage is serious, the crew of Discovery will spend seven hours today guiding a special pole equipped with laser sensors across the fragile thermal shield of the craft to look for damage.

The 15m (50ft) extension of the standard shuttle arm was installed on Discovery as one of many safety improvements recommended in the aftermath of the Columbia tragedy. Today's inspection is the first of its type.

The astronauts of Discovery will bring the pole to within 1.5 metres (5ft) of the surface of the craft but must not touch it because they run the risk of causing more damage to the tiles that protect the shuttle as it re-enters the atmosphere.

After using the laser to inspect the nose and wings of the shuttle, the areas that heat up the most on re-entry, the crew will carry out a visual inspection of the tail and crew quarters of Discovery.

Nasa officials stressed that damage to the shuttle's thermal tiles is not unusual, but that reforms put in place after the Columbia disaster demand that every "ding", as minor bumps to the craft are known, is investigated.

A piece of foam the size of a suitcase damaged several tiles on the wing of Columbia during its lift-off in January 2003. The shuttle then broke up 200,000ft above Texas after hot gases penetrated the craft as it returned to Earth.

Today's inspection is one of a series of tasks the crew of Discovery must perform as they prepare to dock with the International Space Station and practice a range of maneouvres designed to allow them fix the spacecraft in case something goes wrong.

Two astronauts, Stephen Robinson and Soichi Noguchi, will use today to test their equipment for a series of spacewalks they are planning to take during the mission. The astronauts are expected to test repair techniques on Discovery and install new equipment on the International Space Station.

This morning Discovery was 8,850km (5,500 miles) away from the space station. The shuttle is scheduled to arrive and dock at there at 0218 BST tomorrow.

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