A Boeing Delta 4 Heavy rocket lifts off on its maiden voyage from the Cape Canaveral Air Force Station in Cape Canaveral, Florida December 21, 2004 on a demonstration mission for the U.S. Air Force. [Photo: Reuters.com]

Damage to a Florida launch pad from a fuel leak during a preflight rocket test will delay next month's flight of a U.S. government missile-warning satellite and possibly other key military spacecraft, the Air Force said on Thursday.

Following a test launch in 2004, a Boeing-built Delta 4 Heavy rocket was scheduled for its first satellite-delivery mission on April 1 from Cape Canaveral Air Force Station in Florida.

However, during a dress rehearsal for launch two weeks ago, some of the rocket's intensely cold liquid oxygen fuel leaked out and cracked the metal structure beneath the booster, the Air Force's Space and Missile Systems Center said.

The rocket fuel is minus 300 degrees Fahrenheit (minus 184 Celsius).

The payload, a $250 million Defense Support Program missile-warning satellite built by Northrop Grumman, had not yet been loaded aboard the booster. It will remain in its processing facility until the rocket is about three weeks away from launch.

The flight likely will be delayed until the summer, said Air Force spokesman Joe Davidson.

The Delta 4 Heavy is the largest unmanned booster currently available in the United States. It made a partly successful debut flight with a dummy payload in November 2004 but a fuel flow problem left the satellite in a lower orbit than planned.