NASA disclosed today that an investigation earlier this week that found multiple dings in the space shuttle Atlantis' heat shield must be restarted because about 40 tiles were missed.

The crew of the Atlantis had spent nine hours inspecting the heat shields on Tuesday. Using the shuttle's robotic arm, astronauts collected data and images of critical areas of the shuttle's thermal protection system, especially on the craft's nose and the edges of its wings. Part of a routine checkup after any shuttle launch, the inspection took up most of the crew's first full day in space.

A few hours after the inspection began, NASA announced that dings or scratches were found in some of the shuttle's outer tiles.

Scratches were found on the forward part of the shuttle's right wing, close to where it connects to the fuselage, according to NASA spokeswoman Katherine Trinidad. The damage, found on four different heat shield tiles, looks minor, but NASA will continue to investigate it.

The damage seems to be related to a debris impact that occurred about 104 seconds after the Atlantis lifted off Monday afternoon.

After today's spacewalk wrapped up late this afternoon, NASA announced that they have discovered that an area of the shuttle's heat shield had not been inspected at all. The area is below the forward thrusters on the vehicle's port nose.

The NASA astronauts will again use the robotic arm and sensors attached to it to run another inspection before the scheduled spacewalk begins Friday morning.

NASA has been especially diligent about studying the heat shields since the space shuttle Columbia broke apart upon re-entry on Feb. 1, 2003. According to NASA, an investigation found that the disaster was caused by a hole in the heat-resistant panels that protected the wing from the high temperatures of re-entry. The hole allowed superheated air into the wing, which was destroyed, sending the shuttle spinning out of control before it broke apart.

Atlantis blasted off from the Kennedy Space Center on Monday afternoon. The crew is on an 11-day mission to repair and upgrade the Hubble Space Telescope.