File image of Atlas 2A rocket sitting on the pad ready to launch GOES-L last May. Photo: NASA

Sunday's launch of the next U.S. weather satellite is being postponed one week so technicians can make repairs to part of the Lockheed Martin Atlas rocket's guidance system.

Liftoff of the Geostationary Operational Environmental Satellite-M (GOES-M) spacecraft from Cape Canaveral Air Force Station is now targeted for Sunday, July 22.

A cracked diode was discovered during recent testing of the Remote Control Unit at its BAE Systems manufacturing plant in San Diego.

"The RCU unit was being tested over at BAE. After they finished the testing they go through a normal inspection just to make sure all the testing went correctly. When they inspected they thought we had a crack in one of the diodes on the box," Adrian Laffitte, Lockheed Martin's Atlas director, said in an interview Tuesday.

The circuit board with the suspect diode has been removed from the unit for fixing. Officials have also decided to install protective sleeves on similar diodes in the unit's power supply system.

Once that work is done the unit will have to undergo significant retesting, as well as verification that the sleeves don't create any additional trouble.

The box is slated for shipment to Cape Canaveral on Sunday for installation onto the Centaur upper stage Monday.

Final pre-flight preparations will then resume with routine testing of the vehicle.

The box had been scheduled for attachment to the rocket on Monday for a launch attempt this coming Sunday, but the diode problem simply shifted the game plan one week, Laffitte said.

The launch window on July 22 will extend from 3:01 to 4:25 a.m. EDT.

Laffitte said officials are working with the Air Force-controlled Eastern Range to secure a backup launch opportunity on July 23, with liftoff coming just two hours after shuttle Atlantis is scheduled to land at nearby Kennedy Space Center.

The only conflict is expected to be a set of Range radars, which are used to track the shuttle as well as monitor weather balloons dispatched to gather information of conditions aloft for the Atlas rocket. Since the radars aren't a mandatory requirement for the shuttle, the issue is not expected to be an obstacle for the extraordinary double-header landing and launch from Florida's Space Coast.

GOES-M is the fifth and final satellite in the current series of Space Systems/Loral-built weather spacecraft for NASA and NOAA.

The craft will be placed an orbital storage 22,300 miles above the equator where it will wait to replace one of the nation's two GOES satellites. When one of the aging spacecraft fails, GOES-M is supposed to be ready to take over on short notice, providing meteorologists with the data they need to generate weather forecasts and track hurricanes.