Live at the Cape: Launch Countdown Continues

A huge Delta IV Heavy rocket is gassed up and almost ready to go at Cape Canaveral Air Force Station tonight as countdown clocks tick toward launch of a top-secret national security mission.

The 24-story rocket and its classified National Reconnaissance Office payload are still scheduled to blast off at 7:33 p.m. tonight -- the opening of a four-hour launch window.

The fueling of the first and second stages of the rocket went without significant trouble.

Engineers ran into trouble during checkouts of telemetry streams between the rocket and the Tel-4 ground tracking station near the south end of Kennedy Space Center. But subsequent checks confirmed that data was flowing properly between the rocket and the ground station.

The communications links play a key role in public safety. Rocket systems beam back performance data to a network of ground stations during ascent into orbit. And if the rocket were to careen out of control, then safety officers could beam up signals to deliberately destroy the rocket before it could threaten populated areas.

Air Force meteorologists say there is a 90 percent chance conditions will be acceptable for launch. The prime concern is a chance of high winds or thick clouds over the launch complex.

You can check out the official forecast issued by the Air Force 45th Space Wing Weather Squadron here: Launch Forecast.

We'll have updates here in The Flame Trench throughout the day, so make sure to refresh this page for the latest news. We'll also webcast live United Launch Alliance television coverage of the terminal countdown and launch starting 25 minutes prior to liftoff. At that time, you'll see a video player embedded in the top item in the blog. Simply click it to launch live coverage.

We'll also send text message alerts on the status of the launch. Sign up here to receive those alerts on your cell phone.

Flying onboard will be a classified payload owned by the National Reconnaissance Office, the super-secret operates the nation's fleet of spy satellites. The launch attempt will be the fourth since Tuesday.