A new era for the Global Positioning System rocketed into orbit Thursday night, beginning a concerted effort to sharpen the precision capabilities beaming from the world's foremost space-based navigation network.

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Spaceflight Now's Stephen Clark has assembled this gallery of awesome launch photos.

Check out this collection of beautiful liftoff photos taken by Pat Corkery for United Launch Alliance.

"The 45th Space Wing, Space and Missile Systems Center, GPS Wing, Boeing and United Launch Alliance team are proud to launch the first installment of the GPS Block 2F," said Col. Andre Lovett, 45th Space Wing vice commander and Launch Decision Authority. "This mission proves our dedication to deliver space effects that benefit, protect and defend our nation."

"We've asked the proud men and women of the 5th to operate at its fastest tempo ever and they have answered the call without missing a single beat," said Lt. Col. Lance Jones, 5th Space Launch Squadron director of operations and the Air Force launch director. "With another successful launch, our government and industry team will carry the momentum from this year to next and continue to successfully deliver national assets on orbit."

The next launch of a Delta 4 will be a Heavy rocket from Cape Canaveral in October carrying a classified payload for the U.S. National Reconnaissance.

"We congratulate the Air Force and our mission partners on the successful launch of the first of the new generation of GPS satellites," said Jim Sponnick, United Launch Alliance vice president, Delta Product Line.

"Today's launch comes on the heels of the 50th anniversary of the first Delta launch and was the 13th mission success for the newest Delta launch vehicle, the Delta 4.

"The partnership between the Air Force and the Delta team has resulted in the successful launches of many national security missions directly supporting our troops on the battlefield. Launching the first of the next generation of GPS satellites is a great way to start our next 50 years."

T+plus 3 hours, 33 minutes, 15 seconds. SPACECRAFT SEPARATION! The first satellite for the Global Positioning System Block 2F program has been deployed into orbit from the United Launch Alliance Delta 4 rocket's upper stage, completing tonight's successful ascent.

The 3,400-pound spacecraft, built by The Boeing Company, is a next generation navigation satellite that will be bring new advancements to the orbiting constellation. It should be ready for use in a few months.

"On-orbit checkout and testing consists of two phases," the Air Force's GPS Wing says. "The first is a functional test focused on the nominal (satellite) launch activities, health status verification and (satellite) checkout. The second phase is designed to assess the command and control capabilities of the ground segment and assess the performance of the navigation payload. GPS 2F SV-1 is scheduled to be set healthy approximately 90-120 days after launch."

T+plus 3 hours, 32 minutes. Just one minute away from casting GPS 2F-1 free from its launcher.

T+plus 3 hours, 30 minutes. The rocket has achieved the correct roll rate as planned.

T+plus 3 hours, 29 minutes. Spin-up of the rocket stage has started in preparation for releasing GPS 2F-1 about four minutes from now.

T+plus 3 hours, 27 minutes. The upper stage has reoriented itself into the attitude for release of the satellite.

T+plus 3 hours, 25 minutes. That was a successful third burn for the upper stage, putting the rocket into a good orbit.

T+plus 3 hours, 22 minutes, 27 seconds. Final burn complete! The RL10B-2 motor fired back to life for the third of three burns to send the GPS 2F-1 spacecraft into the proper orbit for the navigation network.

T+plus 3 hours, 21 minutes, 40 seconds. Pitch and yaw controls look good.

T+plus 3 hours, 21 minutes, 10 seconds. Engine chamber pressure is right on the mark.

T+plus 3 hours, 20 minutes, 50 seconds. Ignition! The upper stage if firing once again. This burn will last just approximately 97 seconds in duration.

T+plus 3 hours, 19 minutes. The upper stage of the Delta 4 rocket is nearing the end of its long coast upward away from Earth. The motor is preparing to burn its engine one more time to propel GPS 2F-1 the rest of the way into orbit.

T+plus 3 hours, 10 minutes. The thermal conditioning roll program has been nulled out as scheduled.

T+plus 3 hours. Now 20 minutes away from engine re-start on the upper stage. In preparation for that event, the rocket will complete the BBQ thermal roll and begin maneuvering itself into the proper orientation for ignition. Then, the stage will start a system chilldown with cryogenic fuel and use its tiny thrusters to settle the propellants in the tanks before firing the engine.

Ignition occurs at T+plus 3 hours, 20 minutes for a 97-second firing. Spacecraft separation happens at T+plus 3 hours, 33 minutes.

T+plus 2 hours, 45 minutes. The Delta 4 rocket is using a three-burn ascent profile. It is the seventh time in 13 missions of the Delta 4 family that the upper stage has performed three firings to boost payloads into high orbits.

T+plus 2 hours, 15 minutes. The rocket is soaring away from Earth in its current egg-shaped orbit. The upcoming engine firing at 2:20 a.m. EDT will occur as the rocket nears apogee. The burn lasts 97 seconds and puts the spacecraft into an 11,047 nautical mile circular orbit inclined 55 degrees to the equator.

Deployment of GPS 2F-1 from rocket to complete the launch is expected at 2:33 a.m. EDT.

T+plus 1 hour, 56 minutes. The upper stage has completed one passive roll program and just started another. This one will continue until it's almost time for the next burn.

T+plus 90 minutes. Unlike the previous generations that rode on smaller rocket Delta 2 rockets, the dozen next-generation GPS 2F craft will be delivered into orbit atop the Delta 4 and Atlas 5 fleets of boosters in the Air Force's Evolved Expendable Launch Vehicle program.

The Delta 2's, although highly reliable, weren't powerful enough to inject the GPS satellites directly into the orbiting constellation. The three-stage vehicles released the craft into a highly elliptical orbit stretching from 100 miles at its closest point with Earth to some 11,000 miles at its highest point, which is the altitude where the GPS network resides. The newly-launched satellites were themselves fitted with a solid-fuel kick motor that ignited a few days into flight and finished the job of propelling the craft into a circular orbit.

United Launch Alliance's powerful Delta 4 and Atlas 5 rockets will haul the GPS 2F satellites directly to their desired destinations, bypassing the circuitous route of the past. So instead of taking days to reach the GPS orbit, the new 2F-1 satellite will get there in three-and-a-half hours tonight.

T+plus 75 minutes. To recap, the Delta 4 rocket carrying the GPS 2F-1 navigation satellite launched from Cape Canaveral's Complex 37 at 11:00 p.m. EDT.

All appeared to go smoothly during the ascent and no problems were reported by the telemetry folks.

The rocket is now coasting toward a point about 11,000 nautical miles above the planet where the third and final burn is planned at T+plus 3 hours and 20 minutes.

T+plus 60 minutes. To see the track the rocket is following this evening, click here.

T+plus 40 minutes. The rocket has started the planned thermal-controlling roll program. It will continue in this roll for about 75 minutes.

T+plus 27 minutes, 30 seconds. The rocket is 214 miles in altitude, 5,460 miles downrange.

T+plus 27 minutes. The rocket has just entered a two-hour, 56-minute coast period before the final engine burn to deliver GPS 2F-1 into the desired orbit this evening.

T+plus 26 minutes, 5 seconds. Delta is 166 miles in altitude, 5,070 miles downrange from the launch pad and traveling 32,042 feet per second.

T+plus 24 minutes, 40 seconds. SECO 2. The second of three firings by the upper stage during tonight's launch has been completed.

T+plus 24 minutes. This burn injects the rocket into a highly elliptical orbit stretching about 11,000 nautical miles at its furthest point.

T+plus 23 minutes, 30 seconds. About one minute left in this burn by the Delta 4 rocket's upper stage.

T+plus 23 minutes, 15 seconds. The initial orbit achieved hit the expected targets.

T+plus 22 minutes, 40 seconds. Good engine chamber pressure reported.

T+plus 22 minutes. This burn will last just over three minutes in duration.

T+plus 21 minutes, 23 seconds. Ignition! The RL10B-2 engine, fed by liquid hydrogen liquid oxygen, has been reignited to propel GPS 2F-1 into an intermediate orbit.

T+plus 17 minutes. The vehicle is now in a coast mode before the next firing of the upper stage engine. Ignition of the RL10 engine is now four minutes away.

T+plus 13 minutes. Delta is 167 miles in altitude, 1,891 miles downrange from the launch pad.

T+plus 12 minutes, 14 seconds. SECO 1. The upper stage engine has shut down after the first of three planned firings to inject the GPS spacecraft into navigation network tonight.

T+plus 11 minutes, 27 seconds. Delta is 172 miles in altitude, 1,544 miles downrange from the launch pad.

T+plus 10 minutes, 50 seconds. The upper stage's the RL10 engine working well, still firing as planned to reach a low-altitude parking orbit this evening.

T+plus 10 minutes, 5 seconds. The vehicle's steep climb leveled off as it gains speed toward orbital velocity.

T+plus 9 minutes, 50 seconds. Delta is 169 miles in altitude, 1,216 miles downrange from the launch pad.

T+plus 9 minutes, 20 seconds. About three minutes remain in this firing of the upper stage to place the vehicle into an initial parking orbit around Earth.

T+plus 9 minutes. The RL10 engine is burning a mixture of liquid oxygen and liquid hydrogen cryogenic propellants. Chamber pressures still look good.

T+plus 8 minutes, 25 seconds. First stage flight events occurred very close to planned times.

T+plus 8 minutes, 4 seconds. Delta is 155.7 miles in altitude, 873 miles downrange from the launch pad.

T+plus 7 minutes, 3 seconds. Delta is 141.7 miles in altitude, 689 miles east of the launch pad.

T+plus 6 minutes, 30 seconds. Good pitch and yaw controls on the upper stage engine.

T+plus 5 minutes, 50 seconds. Delta is 119 miles in altitude, 491 miles east of the launch pad.

T+plus 5 minutes, 27 seconds. Good chamber pressure data being reported from the RL10 engine as it thrusts to reach orbit.

T+plus 4 minutes, 45 seconds. The protective payload fairing enclosing the GPS satellite atop the rocket has separated.

T+plus 4 minutes, 32 seconds. The cryogenic RL10B-2 upper stage engine has ignited!

T+plus 4 minutes, 16 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, 9 seconds. MECO! Main engine cutoff confirmed as the RS-68 powerplant shuts down.

T+plus 4 minutes, 1 second. The main engine is throttling down to 57 percent thrust in preparation for shutdown.

T+plus 3 minutes, 35 seconds. Altitude 55 miles, 135 miles downrange.

T+plus 3 minutes, 25 seconds. Good pitch and yaw controls on the main engine.

T+plus 3 minutes, 15 seconds. The main engine continues to perform well, consuming its liquid hydrogen and liquid oxygen propellants.

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 2 minutes, 15 seconds. A beautiful nighttime launch to begin the GPS 2F-1 mission!

T+plus 2 minutes. Delta is 21.3 miles in altitude, 21.7 miles downrange from the launch pad.

T+plus 1 minute, 42 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, 37 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 the planet with its main engine firing at full throttle and the two strap-on boosters giving a powerful extra kick.

T-minus 10, 9, 8, sequencer now controlling, T-minus 6, 5, main engine start, 3, 2, 1, booster ignition and LIFTOFF! Liftoff of the Delta 4 rocket and a new era for the Global Positioning System!

T-minus 12 seconds. Ignitors are armed and the residual hydrogen burnoff sparklers have fired beneath the main engine.

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

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

T-minus 35 seconds. Upper stage liquid hydrogen tank is confirmed at flight level.

T-minus 1 minute and counting. The ignition conditions for the RS-68 main engine are "go." The terminal countdown sequencer will take control at T-minus 8.5 seconds. Ignition of the RS-68 powerplant will follow at T-minus 5.5 seconds. The engine powers up to the 102 percent level of thrust for a computer-controlled checkout before liftoff.

T-minus 70 seconds. The Air Force-controlled Eastern Range has given its "go" for launch.

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, 43 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, 35 seconds. The liquid oxygen tank in the first stage is confirmed at the proper level and pressure for flight.

T-minus 3 minutes, 15 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. Ordnance devices aboard the vehicle are being armed.

T-minus 4 minutes, 10 seconds. The systems of the first and upper stages of the Delta 4 rocket have switched from ground-fed power to internal batteries for launch.

T-minus 5 minutes and counting! The final phase of today's countdown has commenced for launch of the Delta 4 rocket carrying the GPS 2F-1 navigation satellite. Liftoff is set to occur at 11:00 p.m. EDT from pad 37B at Cape Canaveral Air Force Station.

The launch director has given approval to resume the count for liftoff at 11:00 p.m. EDT.

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 appear to be "go" for liftoff at 11:00 p.m. EDT.

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

The GPS 2F-1 spacecraft atop the Delta 4 has switched from ground-fed power to its internal batteries for launch.

A load relief file based on the upper level winds is being transmitted to the Delta 4 rocket's flight computer. This program informs the rocket on the wind conditions it can expect to see during ascent.

T-minus 5 minutes and holding. The countdown has entered a planned 15-minute hold. 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.

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Now 25 minutes away from blastoff of the Delta 4 rocket and GPS 2F-1 spacecraft launch. The team is not working any technical issues and activities are running on the planned schedule.

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 Air Force launch weather officer has given his final planned briefing to mission managers in the countdown. "We are sitting in real good shape."

None of the rules are being violated and the chance of clouds interfering tonight has dropped to only 10 percent.

Winds are very light and the temperature at launch time will be 75 degrees F.

T-minus 30 minutes and counting. The countdown is headed to the T-minus 5 minute point where a 15-minute hold is planned. Liftoff is targeted for 11:00 p.m., which is the opening of today's 19-minute launch window.

About three-and-a-half hours after launch, the Delta 4 rocket will deliver its satellite payload directly to the GPS constellation's altitude 11,000 miles high. Ground controllers expect to have the new bird checked out and ready for use in 90 to 120 days, the Air Force says.

The new GPS 2F-1 spacecraft will take over the Plane B, Slot 2 location of the network, considered one of the primary positions in the constellation that is divided into six orbital groupings with multiple satellites flying in each.

The craft assumes the current home of the GPS 2A-27 satellite, which was launched in September 1996 and has exceeded its expected lifetime. It will be relocated as part of the Air Force's efforts to spread out the available satellites and increase coverage.

That particular slot was supposed to be occupied by the GPS 2R-20 satellite after it launched in March 2009. But an interference problem with a test payload aboard the craft prevented it from entering service as scheduled.

The RS-68 first stage main engine spin start pressurization operation is starting.

Safety checks have been completed successfully.

The safety system checks are underway at this point in the countdown.

The propellant conditioning has been completed on all four cryogenic tanks. The Delta 4 rocket is fueled up and ready for today's launch.

No issues are being worked in the countdown. All remains on target for liftoff at 11 p.m.

The thermal insulation inspections have been completed following fueling and there were no problems reported tonight.

The countdown is entering the final 90 minutes until the Delta 4 rocket launch from Cape Canaveral at 11:00 p.m. EDT. Here's a look at some stats about today's mission. This will be:

• The 349th Delta rocket launch since 1960
• The 13th Delta 4 rocket mission since 2002
• The 11th Delta 4 rocket launch from Cape Canaveral
• The 6th Medium+ 4,2 configuration to fly
• The 6th Delta 4 under the ULA banner
• The 2nd Delta 4 launch this year
• The 61st GPS satellite to launch
• The 50th GPS launch on a Delta rocket
• The 1st GPS Block 2F satellite

Radio frequency link checks between tracking facilities at the Cape and the launch vehicle are underway.

The flight slews and commanding tests for the vehicle steering systems are complete and satisfactory.

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

The launch team is kicking off the steering checks for the RS-68 main engine and RL10 upper stage engine, plus commanding tests with the solid rocket motors.

Upper stage liquid oxygen topping has commenced. That puts all four cryogenic fuel tanks aboard the Delta 4 rocket in topping mode.

There are no Collision Avoidance, or COLA, periods during today's launch window. A COLA is a moment in which liftoff cannot occur because the rocket's trajectory would take it too close another object already in space. The overall launch window extends from 11:00 to 11:19 p.m. EDT.

The topping mode is starting for the upper stage's liquid hydrogen tank. The first stage's LOX and LH2 tanks are in topping as well.

The upper stage liquid oxygen filling has been completed. That means the Delta 4 rocket now stands fueled with all four of the vehicle's cryogenic tanks loaded.

The first stage liquid hydrogen tank is now entering the topping phase after the post-fueling valve tests wrapped up.

That issue in the Delta 4 rocket's countdown has been resolved, the launch team just announced. Work to finish fueling the vehicle before tonight's 11:00 p.m. EDT liftoff is underway.

The launch team has run into some sort of issue during the first stage liquid hydrogen post-fueling vent and relief checks. Engineers are assessing it.

The first stage liquid oxygen tank has been loaded and the upper stage's LOX tank is being filled currently. The upper stage liquid hydrogen has been tanked as well.

Weather remain favorable and there's an 80 percent chance of "go" conditions at launch time tonight.

The Delta 4 rocket carrying the first satellite in a new generation for the Global Positioning System is scheduled for liftoff time at 11:00 p.m. EDT.

Boeing developed this satellite and 11 more coming down the pike to sustain and further upgrade the Global Positioning System for the U.S. Air Force.

"These next-generation satellites provide improved accuracy through advanced atomic clocks; a more jam-resistant military signal and a longer design life than earlier GPS satellites; and a new civil signal that benefits aviation safety and search-and-rescue efforts," said Craig Cooning, vice president and general manager at Boeing Space and Intelligence Systems. "GPS 2F is the culmination of our deep experience with 39 successful satellites from previous missions, representing more than 30 years of teamwork with the Air Force."

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The chilldown of the upper stage liquid oxygen system is reported complete, clearing the way for loading the rocket's tank with 4,500 gallons. This is the last of the rocket's four cryogenic supplies to be filled in today's countdown to launch.

The launch team is actively loading the upper stage's liquid hydrogen tank with 10,000 gallons of propellant for the RL10 engine.

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

Fast-fill loading of the first stage liquid hydrogen tank has been completed. Vent and relief checks will be performed shortly.

Now four-and-a-half hours till launch. 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. 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.

The chilldown of the upper stage liquid hydrogen system is reported complete, clearing the way for loading the rocket's tank.

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.

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

The launch team also has gotten the approval to start chilldown conditioning of the upper stage liquid hydrogen system.

And 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 start of liquid hydrogen fueling of the first stage is now 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.

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

And on the first stage liquid hydrogen side, the cold gas chilldown conditioning has begun now, too.

Fueling has officially begun with chilldown of the first stage liquid oxygen system. This preps the tank and pumping to guard against shock when the supercold oxidizer begins flowing into the rocket a short time from now.

ULA's launch director has given the formal "go" to begin fueling the Delta 4 rocket for tonight's flight to the GPS constellation.

T-minus 6 hours, 15 minutes and counting! The Terminal Countdown begins now for today's flight of the United Launch Alliance Delta 4 rocket with the Global Positioning System 2F-1 satellite.

The countdown has one planned built-in hold at T-minus 5 minutes lasting some 15 minutes, leading to liftoff at 11:00 p.m. EDT (0300 GMT).

The launch pad has been verified evacuated of all 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 launch team has been polled to verify all consoles are manned and ready to begin the Terminal Countdown when this hold ends at 4:30 p.m. No technical issues are being worked and the weather is forecast to be acceptable tonight.

The call to "man stations for Terminal Count" has gone out to the launch team.

T-minus 6 hours, 15 minutes and holding. The countdown has just entered a planned 60-minute built-in hold, giving the team time to catch up on any work that could be running behind schedule. Once the clocks resume ticking at 4:30 p.m. EDT, the Terminal Countdown phase of today's launch operation will begin.

Now that the space shuttle Atlantis mission has successfully concluded, full attention turns to Cape Canaveral's Complex 37 launch pad where a Delta 4 rocket will try again tonight to get into orbit and deploy an advanced Global Positioning System satellite. Liftoff time is 11:00 p.m. EDT (0300 GMT).

The United Launch Alliance ground team just rolled back the 33-story mobile service to reveal the Delta for today's countdown. The structure had been put back around the rocket after Monday night's scrub.

The wheeled gantry moves along rail tracks to its launch position about the length of a football field from the rocket. The 9-million pound tower shields the Delta from the elements during the its stay on the pad, provides workers 360-degree access to the various areas on the vehicle and is 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 vehicle later this afternoon.

The Terminal Countdown will begin ticking at 4:30 p.m. EDT, leading to the multi-hour process of loading the Delta 4's Common Booster Core first stage and the upper stage with supercold liquid oxygen and liquid hydrogen propellants.

Tonight's launch opportunity extends 19 minutes from 11:00 to 11:19 p.m. EDT.

The officials have not announced how the solid rocket booster steering issue that caused Monday's countdown abort was resolved. But preparations are underway for this next launch attempt.

Tower rollback has begun for tonight's launch of the Delta 4 rocket.

The Delta 4 rocket was just moments away from roaring to life and launching from Cape Canaveral's pad 37B on Monday, but a dramatic last-second abort stopped the countdown.

It was the third attempt to launch the mission carrying the first in a new generation of satellites for the Global Positioning System, and clocks were heading toward liftoff at 11:13 p.m. EDT after a smooth countdown throughout the evening.

"T-minus 15 seconds," the timer said.

"Ignitors armed," a launch team member called.

"ROFI ignition," said another engineer, referring to the radial outward firing ignitors that burn hydrogen beneath the main engine.

"T-minus 10, 9, 8, 7," the timer continued.

"Hold, hold, hold," a voice sounded.

The countdown sequencer script had aborted, automatically stopping the Delta 4 rocket from lighting its main engine and solid rocket boosters.

Well-rehearsed safing procedures began immediately to put the launch vehicle, the Complex 37 facility and GPS spacecraft into a secure configuration.

The Terminal Countdown Sequencer Rack, or TCSR, takes control at T-minus 8.5 seconds and guides activities through liftoff. Ignition of the RS-68 powerplant follows at T-minus 5.5 seconds. The engine begins to produce thrust at T-minus 3.3 seconds and then powers up to the 102 percent throttle at T-minus 1 second for a computer-controlled checkout before liftoff. The solid rocket boosters are lit at T-minus 20 milliseconds.

But Monday's attempt never actually got down to ignition. Computers detected a possible problem with the steering system on one of the twin solid rocket boosters.

The strap-on motors, which burn for 94 seconds to give the Delta a powerful kick toward space, use hydraulics to swivel their nozzles and steer the rocket during flight.

A joint statement to the press from the Air Force and United Launch Alliance said "an anomalous data signature" from the steering system triggered the countdown's abort.

"Mission managers are currently studying the situation to determine a corrective action plan," the statement says.

The earliest that launch could be attempted again is Thursday night. That day's window would extend from 11:00 to 11:19 p.m. EDT.

A video clip of tonight's countdown abort is posted here.

Draining of the propellants from the Delta rocket has begun.

The way the Delta 4 rocket's countdown works, the terminal sequencer takes control at T-minus 8.5 seconds. Ignition of the RS-68 powerplant follows at T-minus 5.5 seconds. The engine begins to produce thrust at T-minus 3.3 seconds and then powers up to the 102 percent throttle at T-minus 1 second for a computer-controlled checkout before liftoff. The solid rocket boosters are lit at T-minus 20 milliseconds.

The announcer had called T-minus 7 seconds right when another team member called the hold tonight.

Since the hydrogen burnoff sparklers had fired, that was the only shot at launching tonight. The solid rocket boosters' hydraulic systems will have to be reset during the scrub turnaround as well.

Exactly when the next launch attempt will be made is not known as this time.

This was the last date available on the Eastern Range for the launch to occur before to Wednesday morning's scheduled landing of the space shuttle Atlantis. The Range requires time in between events to reconfigure its tracking and communications equipment. So the next try, based purely on the Range, wouldn't be possible until late in the week.

The Delta 4 rocket and the GPS 2F-1 spacecraft have completed their switch back to external power.

Safing of the launch vehicle and pad systems is underway. There's no immediate word on what caused the hold.

An abort occurred inside the final seconds of the countdown when the sequencer was taking control of events leading up to liftoff. The hold was triggered just prior to main engine start.

HOLD! Countdown has been halted just before ignition!

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

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

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

T-minus 35 seconds. Upper stage liquid hydrogen tank is confirmed at flight level.

T-minus 1 minute and counting. The ignition conditions for the RS-68 main engine are "go." The terminal countdown sequencer will take control at T-minus 8.5 seconds. Ignition of the RS-68 powerplant will follow at T-minus 5.5 seconds. The engine powers up to the 102 percent level of thrust for a computer-controlled checkout before liftoff.

T-minus 70 seconds. The Air Force-controlled Eastern Range has given its "go" for launch.

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, 40 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, 35 seconds. The liquid oxygen tank in the first stage is confirmed at the proper level and pressure for flight.

T-minus 3 minutes, 15 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. Ordnance devices aboard the vehicle are being armed.

T-minus 4 minutes, 10 seconds. The systems of the first and upper stages of the Delta 4 rocket have switched from ground-fed power to internal batteries for launch.

T-minus 5 minutes and counting! The final phase of today's countdown has commenced for launch of the Delta 4 rocket carrying the GPS 2F-1 navigation satellite. Liftoff is set to occur at 11:13 p.m. EDT from pad 37B at Cape Canaveral Air Force Station.

The launch director has given approval to resume the count for liftoff at 11:13 p.m. EDT.

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 appear to be "go" for liftoff at 11:13 p.m. EDT.

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

The GPS 2F-1 spacecraft atop the Delta 4 has switched from ground-fed power to its internal batteries for launch.

The launch director says everything is looking good right now.

T-minus 5 minutes and holding. The countdown has entered a planned 15-minute hold. 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.

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A load relief file based on the upper level winds is being transmitted to the Delta 4 rocket's flight computer. This program informs the rocket on the wind conditions it can expect to see during ascent.

The Air Force launch weather officer has given his final planned briefing to mission managers in the countdown. Conditions at Cape Canaveral are "go" for the Delta rocket tonight.

There is a coastal shower about 15 miles to the east and northeast of the launch site, but meteorologists aren't too concerned about that being an issue at liftoff time. They put the odds of weather delaying the launch at just 10 percent.

T-minus 30 minutes and counting. The countdown is headed to the T-minus 5 minute point where a 15-minute hold is planned. Liftoff is targeted for 11:13 p.m., which is the opening of today's 18-minute launch window.

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 RS-68 first stage main engine spin start pressurization operation is starting.

A little more than an hour and counting to the Delta 4 rocket and GPS 2F-1 spacecraft launch. The team is not working any technical issues and activities are running on the prescribed schedule.

Safety checks have been completed as intended.

The safety system checks are beginning at this point in the countdown.

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The launch team is entering the last 90 minutes of the countdown. With fueling of the Delta 4 rocket completed, this phase of the count is fairly quiet. Engineers are monitoring systems while the clocks tick down.

In the immediate future, the rocket's safety system will be checked.

Everything continues to proceed on schedule at Cape Canaveral for liftoff at 11:13 p.m. EDT.

The radio frequency link checks between the rocket and ground have been performed successfully.

There is one Collision Avoidance, or COLA, period during today's launch window. A COLA is a moment in which liftoff cannot occur because the rocket's trajectory would take it too close another object already in space. That "no go" minute tonight will be 11:17 p.m. EDT.

The overall launch window extends from 11:13 to 11:31 p.m. EDT.

The propellant conditioning has been completed on all four cryogenic tanks. The Delta 4 rocket is fueled up and ready for today's launch.

The countdown is entering the final two hours until the Delta 4 rocket launch from Cape Canaveral at 11:13 p.m. EDT. Here's a look at some stats about today's mission. This will be:

• The 349th Delta rocket launch since 1960
• The 13th Delta 4 rocket mission since 2002
• The 11th Delta 4 rocket launch from Cape Canaveral
• The 6th Medium+ 4,2 configuration to fly
• The 6th Delta 4 under the ULA banner
• The 2nd Delta 4 launch this year
• The 61st GPS satellite to launch
• The 50th GPS launch on a Delta rocket
• The 1st GPS Block 2F satellite

The thermal insulation inspections have been completed following fueling and there were no problems reported tonight.

The flight slews and commanding tests for the vehicle steering systems are complete and satisfactory.

The launch team is kicking off the steering checks for the RS-68 main engine and RL10 upper stage engine, plus commanding tests with the solid rocket motors.

Upper stage liquid oxygen topping has commenced. That puts all four cryogenic fuel tanks aboard the Delta 4 rocket in topping mode.

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

The upper stage liquid oxygen filling has been completed. That means the Delta 4 rocket now stands fueled with all four of the vehicle's cryogenic tanks loaded.

Now just three hours away from the launch of the GPS 2F-1 spacecraft aboard a Delta 4 rocket from Cape Canaveral, Florida. This is the first of a dozen next-generation satellites for the Global Positioning System.

"The 12 GPS 2F satellites will provide improved signals that will enhance the precise global positioning, navigation and timing services supporting both the warfighter and the growing civilian needs of our global economy," said Col. Dave Madden, commander of the Global Positioning Systems Wing at the Space and Missile Systems Center.

"The next-generation satellites will provide improved accuracy through advanced atomic clocks, a longer design life than the previous GPS satellites and a new operational civil signal that benefits aviation safety and search-and-rescue efforts, known as the L5 signal.

"It will also continue to deploy the modernized capabilities that began with the eight modernized GPS 2R satellites, including a more robust and higher power military signal to improve performance and anti-jam resistance.

"GPS has led the charge to improve military and civil navigation capabilities to ensure GPS remains the gold standard for position, navigation and timing service worldwide."

No issues are being tracked in tonight's work to fuel the Delta 4 rocket and launch remains on target for 11:13 p.m. EDT.

The topping mode is starting for the upper stage's liquid hydrogen tank. The first stage's LOX and LH2 tanks are in topping as well.

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The first stage liquid hydrogen tank is now entering the topping phase after standard valve tests.

Upper stage liquid hydrogen tank in fast-fill mode has finished as well. Checks will performed before topping commences.

Now four hours away from the planned liftoff time for the Delta 4 rocket carrying the first satellite in a new generation for the Global Positioning System. Launch remains on schedule for 11:13 p.m. EDT.

The Delta 4 rocket's Common Booster Core first stage has been loaded with supercold liquid oxygen and liquid hydrogen. The upper stage filling remains in work.

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. 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.

The chilldown of the upper stage liquid oxygen system is reported complete, clearing the way for loading the rocket's tank with 4,500 gallons. This is the last of the rocket's four cryogenic supplies to be filled in today's countdown to launch.

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

Fast-fill loading of the first stage liquid hydrogen tank has been completed. Vent and relief checks will be performed shortly.

The chilldown of the upper stage liquid hydrogen system is reported complete, clearing the way for loading the rocket's tank with 10,000 gallons of propellant for the RL10 engine.

Now five hours away from launch time. 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 continues.

And the launch team has been directed to start chilldown conditioning of the upper stage liquid hydrogen system. This will be the third tank aboard the rocket to be filled today.

First stage liquid oxygen and liquid hydrogen loading continues in progress at Pad B of Cape Canaveral's Complex 37. Both commodities are in the "fast-fill" mode now. The rocket will be loaded with 40,000 gallons of supercold LOX and 110,000 gallons of LH2.

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

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.

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

The hydrogen system's cold gas chilldown conditioning is officially underway.

Approval has been given to start the cold gas chilldown conditioning of the first stage liquid hydrogen system.

Chilldown of the first stage liquid oxygen system has begun. This preps the tank and pumping to guard against shock when the supercold oxidizer begins flowing into the rocket a short time from now.

The launch director has given his "go" to begin fueling the Delta 4 rocket with supercold liquid oxygen and liquid hydrogen as scheduled.

It's time to begin the third Terminal Countdown for the GPS 2F-1 spacecraft and the Delta 4 rocket at Cape Canaveral's Complex 37. Clocks are starting to tick toward the planned 11:13 p.m. EDT liftoff tonight from the Florida spaceport.

This is the last shot available on the Eastern Range for the launch to occur prior to Wednesday morning's scheduled landing of the space shuttle Atlantis. The Range requires time in between events to reconfigure its tracking and communications equipment. If the Delta doesn't fly tonight, the next attempt wouldn't be possible until late in the week.

Out at the launch pad, the complex has been cleared of all personnel and the facility is configured for liftoff. The mobile service tower has remained retracted in its launch position since Friday morning.

The team is not tracking any constraints that would delay the start of fueling around 5 p.m. EDT.

"Man stations for Terminal Count." The call is going out to the launch team to ensure all consoles are staffed and ready to support today's countdown.


Read our earlier status center coverage.