Artist's concept of Endeavour and the Shuttle Radar Topography Mission payload working in orbit. Photo: NASA

Space shuttle Endeavour has been cleared for launch following a last-minute check of heat resistant tiles installed on the craft.

NASA officials said Monday that a review of paperwork indicated only two of 30 suspect tiles on the shuttle needed to be replaced before Endeavour could lift off January 31, beginning an 11-day mission to produce a 3-D map of the Earth's surface.

The tile concern was raised following sistership Discovery's mission to the Hubble Space Telescope last month. After the shuttle landed, engineers found a thermal protection tile was missing from the shuttle's right inboard elevon.

An investigation into Discovery's problem revealed workers had not properly attached the tile to the shuttle. The padding put between the shuttle's skin and tile was not the appropriate thickness, allowing the tile to de-bond and fall off sometime between entry and landing.

The tile that fell off was a so-called "complex tile" because it is more difficult to manufacture and install than the 25,000 others that cover each shuttle.

To make sure Endeavour was safe, NASA ordered a review of paperwork to check records of tile installation work on the space agency's youngest spaceplane.

NASA determined only two tiles on Endeavour's nose may not have been attached properly. As such, those tiles have been removed and replacement work is wrapping up.

The SRTM radar cargo fills Endeavour's payload bay. Photo: NASA

"Through work record evaluation, engineering analysis and manual tile inspection, engineers are confident that Endeavour's thermal protection system is in excellent shape for launch," NASA spokesman Joel Wells said.

At launch pad 39A, technicians are preparing to reopen Endeavour's two 60-foot long payload bay doors for other unplanned work. Engineers have determined that fixtures which hold the shuttle's video cameras need to be strengthened. That work will not delay the launch.

Standard work to close the shuttle's engine compartment should be completed on Wednesday. Installation of ordnance devices also continues.

Endeavour's six international astronauts, led by commander Kevin Kregel, is due to arrive at Kennedy Space Center at 12 noon EST (1700 GMT) on Thursday. The three-day launch countdown will begin at 5:30 p.m. EST (2230 GMT) on Friday.

"We are in as good of a position as we normally are at this point, getting ready to pick up the countdown," Wells said.