The Ku-band dish is shown extended and then retracted aboard sistership Endeavour during pre-launch preparations for the last shuttle mission. Photos: NASA

A communications and radar antenna aboard space shuttle Atlantis was damaged by workers inside the ship's Florida hangar on Sunday evening, NASA said today.

The incident occurred during routine pre-flight preparations for Atlantis' planned mid-April launch to the International Space Station.

The 3-foot-diameter graphite-epoxy dish was being rotated inside the shuttle's payload bay when it struck a "cherry-picker" bridge crane used by workers for access.

At the time of the incident, the bridge was unmanned and stationary, NASA spokesman Joel Wells said.

Officials say it is not yet know how the incident occurred. NASA's prime shuttle contractor -- United Space Alliance -- was responsible for stowing the antenna for launch.

"(USA has) as an internal investigation going on now to determine how it happened and prevent it from happening again," Wells said.

The dish is part of the shuttle's Ku-band communications system used to beam back television signals and data to Earth from space. The dish also will be used as a rendezvous radar during Atlantis' approach and departure from the International Space Station. The Ku-band assembly was being stowed so the 60-foot long payload bay doors could be closed.

Managers decided late Monday afternoon to repair the dish while Atlantis sits in its hangar. Other options passed up included making repairs later at the launch pad or simply replacing the dish.

The extra work will delay Atlantis' scheduled departure from the hangar next Monday. How long the delay will last is unclear.

When the shuttle does leave, it will be rolled to the nearby Vehicle Assembly Building for attachment to an external fuel tank and twin solid rocket boosters atop a mobile launching platform. The completed shuttle stack then will be transported to a seaside launch pad.

The space agency had hoped to launch Atlantis on April 14 at 0041 GMT (13th at 8:41 p.m. EDT) to begin a 10-day mission to outfit and repair the International Space Station. However, other launch activity at Cape Canaveral is expected to push the earliest Atlantis launch attempt to around April 17 at 2302 GMT (7:02 p.m. EDT).

Veteran shuttle commander Jim Halsell will lead the STS-101 mission, also known as ISS flight 2A.2a. The other crewmembers include pilot Scott Horowitz and mission specialists Mary Ellen Weber, Jeff Williams, Jim Voss, Susan Helms and Russian cosmonaut Yuri Usachev.

The main purpose of STS-101 will be servicing the Russian Zarya module -- the first ISS element launched in November 1998. The work will extend Zarya's certified life to the end of 2000. The astronauts will also replace a failed battery and install electronics to fix a second battery to restore Zarya's power system to proper working order.

Williams and Voss plan one spacewalk for STS-101. The excursion will prepare the station for arrival of Zvezda and attach the rest of the Strela crane to ISS. The first part was taken to the station during the last shuttle visit last May.

The other time docked to the station will be spent transferring equipment and supplies from the shuttle to ISS.