Bad weather has for two days running forced the US military to delay the first full flight test of its national missile defence system in two years.
Eight previous missile tests have had mixed success
Friday's postponement was caused by heavy rain over the central Pacific Ocean, said a spokesman for the Pentagon's Missile Defence Agency.
The missile defence system, being built in Alaska, is designed to track and intercept long range missiles.
The Pentagon is spending $10bn a year on the project.
The goal, announced by US President George W Bush in 2002, was to have a basic ground-based shield in place by the end of this year.
When the test does go ahead, a target missile will be launched from Kodiak Island, Alaska. Within minutes, an interceptor missile will fire from the central Pacific Kwajalein atoll in the Marshall Islands.
The last test was in December 2002. It failed when the interceptor missile failed to separate from its booster rocket.
Out of the eight tests carried out so far, five interceptor missiles hit their target.