• The 372nd Delta rocket launch since 1960
• The 30th Delta 4 rocket mission since 2002
• The 5th Medium+ 5,4 configuration to fly
• The 46th main engine from RS-68 family used
• The 4th RS-68A main engine flown
• The 44th-47th GEM-60 solid rocket motors flown
• The 460th production RL10 engine to be launched
• The 32nd RL10B-2 engine launched
• The 25th Delta 4 rocket launch from Cape Canaveral
• The 25th use of Delta 4 by the Air Force
• The 85th Evolved Expendable Launch Vehicle flight
• The 98th United Launch Alliance mission since 2006
• The 23rd Delta 4 under the ULA banner
• The 7th ULA launch this year
• The 3rd launch of the Delta family in 2015
• The 7th Wideband Global SATCOM satellite
• The 1st Block 2-Follow On WGS satellite
• The 5th WGS on Delta 4 /UL>

This pause is designed to give the launch team the opportunity to catch up on any work running behind schedule and verify all is in readiness for the final moments of the count. Also, a series of polls will be conducted during the hold to give approval to proceed with the launch.

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The rocket stands fueled and ready for launch at 8:07 p.m. EDT today. The countdown remains on schedule.

Complex 37 has two giant sphere-shaped fuel tanks to store the cryogenic liquid oxygen and liquid hydrogen. The LOX tank holds 250,000 gallons and LH2 sphere about 850,000 gallons.

The cryogenics are fed from the storage tanks through pipelines to the pad. For the Common Booster Core, the propellants are routed up to the launch table upon which the rocket sits. Tail service masts, the large box-like structures at the base of the vehicle, feed the oxygen and hydrogen to the booster via separate umbilicals.

The upper stage receives its cryos from the middle swing arm that extends from the Fixed Umbilical Tower to the front-side of the rocket.

Chilled to Minus-423 degrees Fahrenheit, the liquid hydrogen will be consumed by the RS-68A main engine along with liquid oxygen during the first four minutes of the launch.

At the launch pad, clearing of personnel is underway. Also, the powerup of the Delta 4 rocket's avionics is starting.

The wheeled structure moved along rail tracks to its launch position about the length of a football field away from the rocket. The 9-million pound tower shielded the Delta from the elements during the its stay on the pad, provided workers 360-degree access to the various areas on the vehicle and was used to attach the strap-on solid motors and the payload during the launch campaign. The tower is 90-feet wide and 40-feet deep.

Crews will spend the next couple of hours securing the complex for launch before leaving the danger area around the pad. All workers must be clear of the area for the start of hazardous operations in the countdown, which include fueling the Delta 4's Common Booster Core first stage and the second stage with supercold liquid oxygen and liquid hydrogen propellants.

Testing of communications links between the rocket and Air Force Eastern Range will occur after fueling is accomplished. Steering checks of the first stage RS-68A engine and second stage RL10B-2 powerplant are on tap in the last hour of the count.

A build-in hold is slated for T-minus 4 minutes, during which time teams will go through final polling to grant clearance to launch. The Delta 4 will transition to internal power as the count resumes, ordnance will be armed and the propellant tanks pressurized as clocks target the main engine ignition time at T-minus 5 seconds.

Liftoff remains scheduled for 8:07 p.m. EDT, the opening of an 39-minute window that extends to 8:46 p.m. EDT (0007-0046 GMT).

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Liftoff has been reset for tomorrow, Thursday, at 8:07 p.m. EDT.

The WGS 7 spacecraft is targeting an 8:07 p.m. EDT liftoff from Complex 37. A 39-minute launch opportunity extends to 8:46 p.m. EDT.

"This is the seventh installment of the WGS system. The satellites are an important element of a new, high-capacity comm system providing communications capability to our troops in the field," said Ron Fortson, United Launch Alliance's director of mission management.

Managers gathered this morning for the Launch Readiness Review, which culminated with the consensus to proceed with picking up the countdown Wednesday.

We will have complete live coverage of the count and launch on this page.

A reminder that if you will be away from your computer but would like to receive countdown updates, sign up for our Twitter feed to get text messages on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.) Forecasters are predicting a 60 percent chance of allowable weather, with the concerns being anvil clouds, cumulus clouds and lightning from leftover afternoon thunderstorms.

The satellite will join a constellation of WGS satellites already in orbit that provide global coverage to the U.S. military and allies.

"It provides the highest data-rate communications for the government," said Rico Attanasio, Boeing director of Military Satellite Communications.

Boeing is the builder of the WGS fleet and ULA has launched all of the craft to date.

The satellites supply communications such as maps and data to soldiers on the battlefield, relay video from unmanned aerial reconnaissance drones, route voice calls and data messaging, and even offer quality-of-life considerations like television broadcasts and email delivery to the troops.

The enhanced RS-68A main engine will power the medium-lift rocket off the pad at Cape Canaveral’s Complex 37 with the Wideband Global SATCOM satellite No. 7 bound for a super-synchronous transfer orbit.

The evening’s launch opportunity extends from 8:07 to 8:46 p.m. EDT.

Weather forecasters are projecting a 60 percent chance of favorable conditions for launch, with clouds and lightning the primary concerns.

Read our preview story.