A replacement Global Positioning System spacecraft for the world's best-known satellite constellation ascended into orbit Friday night aboard a Delta 4 rocket in a spectacular sendoff at sunset.

Read our full story.

"ULA is honored to work with this world-class U.S. government and contractor mission team, and we are proud to contribute to the GPS capabilities that were delivered to orbit today," said Jim Sponnick, ULA vice president, Atlas and Delta Programs. "Congratulations to the entire team on tonight’s successful launch of the GPS 2F-6 satellite and the continued one-launch-at-a-time focus."

SPACECRAFT SEPARATION! The GPS satellite has been deployed by the Delta 4 rocket, completing tonight's launch!

To recap, a United Launch Alliance Delta 4 rocket was launched at 8:03 p.m. EDT carrying a new Global Positioning System spacecraft to advance the navigation network with every launch.

We will post confirmation of spacecraft separation and mission success when announced.

T+plus 20 minutes. The rocket has just entered a two-hour, 47-minute coast period before the final engine burn to deliver GPS 2F-6 into the desired circular orbit to join the navigation network.

T+plus 17 minutes. Delta has flown into a good transfer orbit.

T+plus 15 minutes, 31 seconds. SECO 1. The upper stage engine has shut down after the first of two planned firings to inject the GPS spacecraft into navigation network today.

T+plus 13 minutes, 30 seconds. Second stage performance still looks good.

T+plus 12 minutes. Delta is now in orbit.

T+plus 11 minutes, 45 seconds. Speed now 16,450 mph.

T+plus 11 minutes. The RL10 engine is burning a mixture of liquid oxygen and liquid hydrogen cryogenic propellants.

T+plus 13 minutes, 30 seconds. Delta is 177 miles in altitude, 1,870 miles northeast of the launch pad, traveling over 15,200 miles per hour.

T+plus 9 minutes. Delta is 170 miles in altitude, 1,380 miles northeast of the launch pad, traveling over 13,000 miles per hour.

T+plus 8 minutes. Rock steady controls on the upper stage engine.

T+plus 7 minutes. Still looking good as Delta arcs over the Atlantic.

T+plus 6 minutes. Delta is 143 miles in altitude, 760 miles northeast of the launch pad and traveling 12,000 mph.

T+plus 4 minutes, 51 seconds. The protective payload fairing enclosing the GPS satellite atop the rocket has separated.

T+plus 4 minutes, 35 seconds. The cryogenic RL10B-2 upper stage engine has ignited!

T+plus 4 minutes, 21 seconds. The Common Booster Core first stage and the attached interstage have been separated in one piece from the Delta 4's upper stage. The upper stage engine's extendible nozzle is dropping into position.

T+plus 4 minutes, 14 seconds. MECO! Main engine cutoff confirmed as the RS-68 powerplant shuts down.

T+plus 4 minutes, 5 seconds. The main engine is throttling down to its minimum power setting in preparation for shutdown.

T+plus 3 minutes, 5 seconds. Passing Mach 10.

T+plus 3 minutes. The main engine continues to perform well, consuming its liquid hydrogen and liquid oxygen propellants.

T+plus 2 minutes, 35 seconds. Passing Mach 5.

T+plus 2 minutes, 30 seconds. The RS-68 is consuming nearly a ton of propellants per second as the powerplant pushes the Delta 4 rocket closer to the edge of space.

T+plus 1 minute, 44 seconds. Solid motor separation! The spent boosters have been shed from the first stage. Delta 4 continues powering its way toward space on the thrust generated by the RS-68 main engine.

T+plus 1 minute, 35 seconds. The twin solid rocket boosters have burned out of their propellant. Standing by for jettison.

T+plus 60 seconds. Now passing through the region of maximum aerodynamic pressure as the vehicle accelerates through the lower atmosphere.

T+plus 50 seconds. The launcher has broken through the sound barrier.

T+plus 30 seconds. The Delta 4 rocket is climbing away from Cape Canaveral with its main engine firing at full throttle and the two strap-on boosters giving a powerful extra kick.

LIFTOFF! Liftoff of the Delta 4 rocket with another Global Positioning System spacecraft for the world's best-known satellite constellation. And the vehicle has cleared the tower!

T-minus 12 seconds. Residual hydrogen burnoff ignitors have been fired beneath the main engine.

T-minus 22 seconds. The steering system for the solid rocket motor nozzles has been activated.

T-minus 30 seconds. Green board. All systems remain "go" for launch.

T-minus 40 seconds. Upper stage liquid hydrogen tank is confirmed at flight level.

T-minus 55 seconds. The Air Force-controlled Eastern Range has given its "go" for launch.

T-minus 1 minute and counting. The ignition conditions for the RS-68 main engine are "go." Ignition of the RS-68 powerplant will follow at T-minus 5 seconds. The engine powers up to the 102 percent level of thrust for a computer-controlled checkout before liftoff.

T-minus 75 seconds. The liquid hydrogen fuel tank on the upper stage is being secured for launch.

T-minus 80 seconds. Upper stage liquid oxygen tank has been secured at flight level.

T-minus 1 minute, 50 seconds. The first stage liquid hydrogen tank has reached flight level and pressure.

T-minus 2 minutes. The rocket's upper stage liquid oxygen tank is being secured.

T-minus 2 minutes, 30 seconds. The liquid oxygen tank in the first stage is confirmed at the proper level and pressure for flight.

T-minus 3 minutes and counting. Ordnance devices aboard the vehicle are being armed.

T-minus 3 minutes, 25 seconds. The systems of the first and second stages of the Delta 4 rocket have switched from ground-fed power to internal batteries for launch.

T-minus 3 minutes, 30 seconds. Replenishment of liquid hydrogen and liquid oxygen to the Common Booster Core first stage is being secured in preparation to pressurize the tanks for launch.

T-minus 4 minutes and counting! Now into the final phase of the countdown for liftoff at 8:03 p.m. by the Delta 4 rocket carrying the GPS 2F-6 spacecraft from pad 37B at Cape Canaveral Air Force Station.

Permission to launch has been granted by the ULA launch director.

The final readiness polls of the launch team and mission managers have been completed. No technical problems are being worked and all rocket, spacecraft and ground systems are "go" for liftoff at 8:03 p.m.

Standing by for the launch team readiness check for continuing the countdown.

Now 15 minutes to launch! The launch team will be polled in the next few minutes to confirm all systems are "go" to press onward for 8:03 p.m. liftoff.

The GPS 2F-6 spacecraft atop the Delta 4 is switching from ground-fed power to its internal batteries for launch.

Weather is observed GO and forecast GO for launch.

Launch minus 30 minutes!

The ULA launch team and management are guiding the countdown from the Delta Operations Center, located about 9,200 feet from the pad. The engineers overseeing the rocket and ground systems are located on the third floor and the Mission Directors Center room is on the fourth floor. Both rooms have a view of pad 37B and the Delta 4 rocket out their windows. Other rooms are also set up for engineering support.

The DOC was formerly built to support the Titan-Centaur program but was refurbished to support Delta 4.

The countdown is entering the final 45 minutes until the Delta 4 rocket launch from Cape Canaveral at 8:03 p.m. EDT. Here's a look at some stats about today's mission. This will be:

• The 366th Delta rocket launch since 1960
• The 26th Delta 4 rocket mission since 2002
• The 11th Medium+ 4,2 configuration to fly
• The 40th main engine from RS-68 family used
• The 39th-40th GEM-60 solid rocket motors flown
• The 447th production RL10 engine to be launched
• The 29th RL10B-2 engine launched
• The 21st Delta 4 rocket launch from Cape Canaveral
• The 22nd use of Delta 4 by the Air Force
• The 70th Evolved Expendable Launch Vehicle flight
• The 82nd United Launch Alliance mission since 2006
• The 19th Delta 4 under the ULA banner
• The 5th ULA launch this year
• The 2nd launch of the Delta family in 2014
• The 66th GPS satellite to launch
• The 54th GPS launch on a Delta rocket
• The 6th GPS Block 2F satellite
• The 5th Block 2F launch on Delta /UL>

T-minus 4 minutes and holding. The countdown has entered the planned 45-minute hold leading toward the 8:03 p.m. EDT liftoff of the Delta 4 rocket.

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. A series of management polls will be conducted during the hold to give approval to proceed with the launch.

One hour till launch!

And a reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text message updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

The flight slews and commanding tests for the vehicle steering systems are complete. The first stage Common Booster Core, the strap-on solid rocket motors and upper stage engine steering checks were run through a pre-launch test pattern.

First stage liquid hydrogen conditioning for flight is complete.

Now entering into the final 90 minutes of the countdown to launch of Delta 366 and the sixth Block 2F satellite for the GPS constellation.

The rocket stands fueled and ready for launch at 8:03 p.m. EDT today. The launch team is not reporting any significant issues, weather conditions are green and the countdown remains on schedule.

The flight hazard area has been established.

Upper stage fuel and oxidizer conditioning for flight iscomplete.

Engineers have conducted the standard evaluation of the Delta 4 rocket's thermal insulation following the loading of supercold propellants into the vehicle.

If you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

The first stage liquid oxygen tank is conditioned for flight.

The first stage liquid hydrogen tank is going into topping.

The vehicle is fully fueled! Loading of the upper stage liquid oxygen tank has been accomplished.

Post-filling tests on the hydrogen side of the upper stage are complete. The tank will be entering topping mode.

Loading of the upper stage liquid hydrogen tank has been accomplished as fueling proceeds this afternoon at Complex 37.

The first stage liquid oxygen loading just finished. The tank has been loaded with its supercold oxidizer that is chilled to Minus-298 degrees F. Topping will be completed as the count rolls on.

Fast-filling of the first stage liquid hydrogen tank is complete. After post-filling checks and valve tests, the tank will be placed in topping mode. The launch team will confirm the propellant is conditioned for flight.

After chilldown of the upper stage liquid hydrogen system, the was clear for loading the rocket's tank. The launch team is actively filling the upper stage's liquid hydrogen tank with propellant for the RL10 engine.

The Delta 4 rocket's Common Booster Core first stage and upper stage are being loaded with supercold liquid oxygen and liquid hydrogen.

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.

Chilldown of the upper stage liquid oxygen system is complete for loading the rocket's tank.

The "go" has been given for the upper stage liquid oxygen chilldown in advance of filling that tank.

First stage liquid oxygen tanking operation is switching from "slow-fill" to "fast-fill" mode. The rocket will be loaded with 40,000 gallons of supercold LOX.

With today's countdown going very smoothly, the launch team is preparing to start fueling the Delta 4 rocket's upper stage. The "go" has been given to start the chilldown conditioning of the upper stage liquid hydrogen system.

The first stage liquid oxygen chilldown is complete. "Slow-fill" mode is beginning to load a small percentage of the tank. The process then speeds up to the "fast-fill" mode until the tank is nearly full.

First stage liquid hydrogen tanking operation is switching from "slow-fill" to "fast-fill" mode.

And now the chilldown of Delta's first stage liquid oxygen system is starting. This preps the tank and pumping to guard against shock when the supercold oxidizer begins flowing into the rocket a short time from now.

Liquid hydrogen flow to the first stage is confirmed. Some 110,000 gallons of LH2 will fill the rocket's tank.

The cold gas chilldown conditioning of the liquid hydrogen system has been accomplished. Liquid hydrogen propellant will begin to flow into the first stage in "slow-fill" mode. That is sped up to "fast-fill" after a small portion of the tank is loaded.

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

And fueling operations have begun. The hydrogen system's cold gas chilldown conditioning is underway.

A "go" has been given to start the cold gas chilldown conditioning of the first stage liquid hydrogen system. This is the precursor to filling the vehicle with propellant.

T-minus 4 hours, 15 minutes and counting! The team is ready for cryogenic fueling as the countdown is underway for today's opportunity to launch the Delta 4 rocket with the GPS 2F-6 navigation satellite.

The launch team is manning stations for the start of fueling operations.

A check of the current weather shows everything is green.

T-minus 4 hours, 15 minutes and holding. The countdown has entered a 15-minute built-in hold, a pre-planned pause designed to give the team time to catch up on any work that could be running behind schedule. Once the clocks resume ticking, the Countdown for today's launch operation will begin.

A dramatic turnaround with the weather is predicted for tomorrow night's launch opportunity.

"The front is now moving through the area and will clear Central Florida overnight, bringing in drier and slightly cooler air Friday. Weather is looking great for a Friday launch with partly cloudy skies," the Air Force weather officer says.

The outlook calls for scattered high cirrus, good visibility, northerly winds 12 to 18 knots and a temperature of 76 degrees F.

Liftoff is planned to occur three minutes before sunset.

Tomorrow's launch time is 8:03 p.m. EDT. The weather forecast is 90 percent favorable.

To recap, the launch team was unable to send up weather balloons to measure high-altitude winds due to the lightning around the Cape tonight. A number of weather rules remained red as well. So the launch has been delayed 24 hours when much more favorable conditions are predicted.

SCRUB! The weather is not going to cooperate with a launch of the Delta 4 rocket from Cape Canaveral tonight. The launch team will begin a 24-hour recycle of the countdown and try again Friday evening at 8:03 p.m. EDT.

First stage fuel conditioning for flight is complete.

Steering checks that normally occur at this point in the countdown are on hold due to the lightning advisory in place for the launch pad.

A check of the current weather shows five of the weather rules are red for electrical potential in the air, lightning, cumulus clouds, attached anvil clouds and disturbed weather.

The flight hazard area has been established.

Engineers have conducted the standard evaluation of the Delta 4 rocket's thermal insulation following the loading of supercold propellants into the vehicle.

The first stage liquid oxygen tank is conditioned for flight.

NEW LAUNCH TIME. Liftoff has been adjusted slightly to 8:09 p.m. EDT due to a COLA, or collision avoidance cutout in the first minute of the window.

And a reminder that if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text message updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

If you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

The vehicle is fully fueled! Loading of the upper stage liquid oxygen tank has been accomplished.

A check of the current weather shows five of the weather rules are red for electrical potential in the air, lightning, cumulus clouds, attached anvil clouds and disturbed weather.

Post-filling tests on the hydrogen side of the upper stage are complete. The tank will be entering topping mode.

The first stage liquid oxygen loading just finished. The tank has been loaded with its supercold oxidizer that is chilled to Minus-298 degrees F. Topping will be completed as the count rolls on.

Loading of the upper stage liquid hydrogen tank has been accomplished as fueling proceeds this afternoon at Complex 37.

The Delta 4 rocket's Common Booster Core first stage and upper stage are being loaded with supercold liquid oxygen and liquid hydrogen.

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.

Fast-filling of the first stage liquid hydrogen tank is complete. After post-filling checks and valve tests, the tank will be placed in topping mode. The launch team will confirm the propellant is conditioned for flight.

Chilldown of the upper stage liquid oxygen system is complete for loading the rocket's tank. This is the last of the rocket's four cryogenic supplies to be filled in today's countdown to launch.

After chilldown of the upper stage liquid hydrogen system, the was clear for loading the rocket's tank. The launch team is actively filling the upper stage's liquid hydrogen tank with propellant for the RL10 engine.

First stage liquid oxygen tanking operation is switching from "slow-fill" to "fast-fill" mode. The rocket will be loaded with 40,000 gallons of supercold LOX.

The first stage liquid oxygen chilldown is complete. "Slow-fill" mode is beginning to load a small percentage of the tank. The process then speeds up to the "fast-fill" mode until the tank is nearly full.

A check of the current weather shows five of the weather rules are red for electrical potential in the air, lightning, cumulus clouds, attached anvil clouds and disturbed weather.

With today's countdown going very smoothly, the launch team is preparing to start fueling the Delta 4 rocket's upper stage. The "go" has been given to start the chilldown conditioning of the upper stage liquid hydrogen system.

First stage liquid hydrogen tanking operation is switching from "slow-fill" to "fast-fill" mode.

And now the chilldown of Delta's first stage liquid oxygen system is starting. This preps the tank and pumping to guard against shock when the supercold oxidizer begins flowing into the rocket a short time from now.

Liquid hydrogen flow to the first stage is confirmed. Some 110,000 gallons of LH2 will fill the rocket's tank.

The cold gas chilldown conditioning of the liquid hydrogen system has been accomplished. Liquid hydrogen propellant will begin to flow into the first stage in "slow-fill" mode. That is sped up to "fast-fill" after a small portion of the tank is loaded.

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

And fueling operations have begun. The hydrogen system's cold gas chilldown conditioning is underway.

A "go" has been given to start the cold gas chilldown conditioning of the first stage liquid hydrogen system. This is the precursor to filling the vehicle with propellant.

T-minus 4 hours, 15 minutes and counting! The team is ready for cryogenic fueling!

The launch team is manning stations for the start of fueling operations.

T-minus 4 hours, 15 minutes and holding. The countdown has entered a 15-minute built-in hold, a pre-planned pause designed to give the team time to catch up on any work that could be running behind schedule. Once the clocks resume ticking, the Countdown for today's launch operation will begin.

The GO has been given to start liquid oxygen and liquid hydrogen fueling preparations.

A check of the current weather shows four of the weather rules are currently red for electrical potential in the air, lightning, cumulus clouds and attached anvil clouds.

Check out photos of the Delta 4 rocket during rollback of the launch pad's mobile gantry this morning.

The Delta 4 rocket's RIFCA flight computer is powered up for flight and alignment is stable. And interrogation checks are being performed on the C-band beacon used for tracking the vehicle during its flight downrange.

T-minus 5 hours, 15 minutes and counting! The countdown has commenced for this evening's scheduled launch of the Delta 4 rocket to deliver a new GPS navigation satellite into orbit for the United States military and civil users.

The count has a planned built-in hold at T-minus 4 minutes, leading to liftoff at 8:08 p.m. EDT (0008 GMT).

Technicians have finished all hands-on work at the launch pad and Complex 37 has been cleared of personnel in advance of fueling the rocket's two stages this afternoon. Pad systems and equipment stand ready for fueling activities, which should kick off shortly.

The 330-foot tall mobile service tower has been retracted from the Delta 4 rocket at Cape Canaveral's pad 37B for tonight's launch that will place the GPS 2F-6 satellite into Earth orbit.

The wheeled structure just 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-68 engine and second stage RL10 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 8:08 p.m. EDT, the opening of an 18-minute window that extends to 8:26 p.m. EDT (0008-0026 GMT).

"The GPS constellation is reliably serving global users with the most accurate and robust signals ever, and the navigation, timing accuracy and availability will improve as the GPS modernization efforts continue," said Col. Bill Cooley, director of the Space and Missile Systems Center's Global Positioning Systems Directorate.

"GPS is the most widely used and accepted system of its kind in the world today, and we stand ready to launch GPS 2F-6," he said.

If you will be away from your computer but would like to receive occasional updates, sign up for our Twitter feed to get text message updates sent to your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

And check out Spaceflight Now's Facebook page!

The Mobile Service Tower at Cape Canaveral's launch complex 37 is rolling away from the Delta 4 rocket that is scheduled to carry a Global Positioning System satellite into orbit at 8:08 p.m. EDT this evening (0008 GMT, Friday).

The sixth new-generation satellite for the Global Positioning System and its Delta 4 rocket booster have been cleared for blastoff into the navigation network Thursday from Cape Canaveral.

The GPS 2F-6 spacecraft is targeting an 8:08 p.m. EDT launch from Complex 37. An 18-minute window extending to 8:26 p.m. EDT will be available if conditions prevent an on-time liftoff.

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

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

And if you will be away from your computer but would like to receive occasional updates, sign up for our Twitter feed to get text message updates sent to your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

Boeing developed a dozen Block 2F satellites to sustain and further upgrade the Global Positioning System for the U.S. Air Force. The first was launched in May 2010, the second went up in July 2011, the third in October 2012, the fourth in May 2013 and the most recent in February to replace aging craft in the constellation.

They feature improved accuracy, enhanced internal atomic clocks, better anti-jam resistance, a civil signal for commercial aviation, a longer design life and reprogrammable onboard processors to evolve with future needs.

About three-and-a-quarter hours after liftoff Thursday, the Delta 4 rocket will deliver the satellite directly to the GPS constellation's altitude 11,047 nautical miles high.

Their services have permeated daily lives for countless millions of people, and now the latest Global Positioning System satellite is awaiting blastoff Thursday to bolster the navigation network.

Read our preview story.

The weather could be a challenge for launching the Delta 4 rocket on Thursday evening from Cape Canaveral. Forecasters are giving only a 30 percent chance of meeting the launch rules.

"There are two systems being monitored that could impact the launch. The first is a frontal system moving into the Southeast U.S. that will move into Central Florida on Thursday and clear the area by Friday morning," the Air Force weather team reports.

"The second is a weak tropical wave moving through the Bahamas. This wave will bring increased low-level moisture into the area overnight Tuesday through Thursday before the front pushes through overnight Thursday.

"On launch day, as the front moves through, scattered thunderstorms could cause multiple launch commit criteria violations.

"As for solar activity, several sunspots could cause solar flares this week, and a strong M-Class or X-Class flare could cause a proton flux concern. There is a 50% chance of an M-Class flare for the next 48 hours, and solar activity will be monitored and updated as we approach launch day.

"The primary concern for launch is anvil clouds, cumulus clouds and lightning.

"For a 24-hour delay, weather improves with cumulus clouds and solar activity being the primary concern."

The final reviews will be completed this week for the Delta 4 rocket launch carrying a replacement satellite for the Global Positioning System.

Liftoff is planned for Thursday night at 8:08 p.m. EDT.

Built by Boeing, the new satellite will become a modernized member of the orbiting GPS constellation. It features greater accuracy, better anti-jam characteristics and a new civilan signal for commercial aviation.

At launch complex 37, the payload has been attached to the rocket and the integrated checks were successfully completed. Last week, the attitude control system hydrazine fuel was loaded aboard the second stage. Now, activities to close out the vehicle compartments for flight are in work.

The Flight Readiness Review has been completed. Upcoming this week are the System Certification Review in which engineers report out their systems for the mission and the Launch Readiness Review occurs to grant approval to enter the countdown.