Boeing conducted its first countdown rehearsal with the Delta 4 rocket at Cape Canaveral's Complex 37 on Monday evening, fueling the new expendable booster in a simulation of launch day activities.

The first Delta 4 rocket at launch pad 37B. Photo: Boeing

The countdown started in the late afternoon and workers rolled the mobile service tower away from the vehicle shortly after 7 p.m. for the Wet Dress Rehearsal, or WDR.

Officials concluded the test prior to the T-minus 5 minute mark due to a problem with the ground computer system encountered during the countdown, which resulted in the loss of insight into telemetry from the rocket, Boeing spokesman Robert Villanueva said.

With unfavorable weather conditions looming, the decision was made to safe the rocket for the night, allowing the mobile tower to be rolled back around the vehicle for protection.

"Monday's (Wet Dress Rehearsal) succeeded in proving out countdown timelines and procedures, even though the testing was secured early," Villanueva said.

In order to accomplish the rest of the rehearsal's objectives -- counting down the final five minutes to ensure activities are timed properly -- Boeing is planning another WDR on Friday.

A third and final rehearsal is expected in a couple weeks. That countdown will conclude with a brief firing of the rocket's main engine.

The countdown tests are designed to give engineers the chance to find any problems so they can be resolved before the real launch day arrives. The launch team members also get vital practice.