As the day dawned at Cape Canaveral this morning, another Delta 2 rocket darted into the sky on a satellite deployment mission. But this successful launch was remarkably different. Instead of bringing joy, there was deep sadness from the finality bought by the flight.

Read our full launch story.

The launch photo gallery is posted here.

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"I am exceedingly pleased with today's launch, and elated to be a part of a mission that plays a critical component of our nation's infrastructure. Today's launch culminates the awesome team work and commitment of government and industry team of dedicated professionals. We achieved a major milestone in GPS history today, as we launch the last GPS 2R-M satellite and begin a new era of GPS services to modernize and sustain the GPS constellation. GPS has evolved to the status of global utility, vital to commercial users and the security of the world. The future technology for GPS lies ahead as we synchronize the development and deployment of the future GPS 2F and GPS 3 satellites, the Next Generation Control System, and the new M-Code User Equipment," said Col. Dave Madden, commander of the Global Positioning Systems Wing.

"This morning's successful launch of GPS 2R-21(M) was the direct result of a focused Delta 2 and GPS team executing a textbook launch campaign," said John Wagner, the mission director from the Launch and Range Systems Wing. "Congratulations to the United Launch Alliance, Lockheed Martin and our entire Air Force team on a job well done."

Stunning high-definition video of today launch is available for Spaceflight Now+Plus users here.

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"With this successful mission the 45th Space Wing is accomplishing another major milestone in our national quest to improve and maintain our space capabilities," said Brig. Gen. Edward L. Bolton Jr., commander of the 45 SW. "The GPS constellation has tremendous national security and economic importance and our Air Force team makes it happen. On its last Air Force mission, the Delta 2 once again lived up to its reputation as one of the most reliable boosters in our fleet."

"The successful launch of this final satellite in the GPS 2R-M program is a true testament to the dedication, skill and operational excellence of our joint government-industry team," said Col. Dave Madden, commander of the Air Force's Global Positioning Systems Wing. "We look forward to successfully executing a smooth and efficient on-orbit checkout and making this advanced satellite operational for the warfighter and civil users around the globe."

This is the 89th consecutive successful Delta 2 rocket launch dating back to May 1997. The Delta 2's overall history since debuting in 1989 has achieved 142 successes in 144 flights.

The next Delta 2 rocket launch will occur from Cape Canaveral's pad 17B on the evening of September 15 carrying the Space Tracking and Surveillance System (STSS) technology demonstration mission. NASA will lend its expertise to launch the two-satellite payload for the Missile Defense Agency.

Delta has delivered the GPS 2R-21 spacecraft into a highly elliptical transfer orbit as planned.

"Everything looks very nominal," says Dave Podlesney, a Lockheed Martin GPS executive. "Everything is working well."

The satellite will fire its own kick motor Wednesday to circularize the orbit. Deployment of the solar panels and antenna appendages is planned for Thursday. The satellite should be checked out and ready to join the navigation network within 30 days to replace the aging GPS 2A-26 craft deployed more than a decade ago.

Video of this morning's Delta 2 rocket launch is available for Spaceflight Now+Plus users here.

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T+plus 70 minutes, 35 seconds. Spacecraft separation confirmed! The U.S. Air Force's Global Positioning System Block 2R-21 spacecraft has been released from the Delta 2 rocket's third stage to complete this morning's launch sequence.

T+plus 69 minutes, 16 seconds. The spacecraft should be flying on its own. But the launch team is awaiting data from the downrange stations to confirm that.

T+plus 67 minutes, 15 seconds. A problem at the Guam tracking station is preventing live data from being received back at the Cape.

T+plus 66 minutes, 20 seconds. By this point, the third stage should be burned out of its solid fuel, ending the Delta 2 rocket's powered flight for the launch of the GPS 2R-21 spacecraft.

T+plus 65 minutes, 40 seconds. The third stage continues to burn.

T+plus 64 minutes, 55 seconds. Third stage ignition! The Thiokol Star 48B motor is firing to propel the GPS 2R-21 satellite into its targeted orbit for this launch.

T+plus 64 minutes, 20 seconds. The solid-fueled third stage has spun up.

As the launch sequence continues with the third stage burn and subsequent deployment of the GPS 2R-21 satellite, the second stage will conduct one additional engine firing to deplete its remaining fuel supply and lower its orbital inclination. This is designed to minimize the amount of land that the stage flies over during its natural fall from orbit and future reentry.

T+plus 63 minutes, 23 seconds. The second stage has completed its second burn of this launch. In the next minute, tiny thrusters on the side of the rocket will be fired to spin up the vehicle in preparation for jettison of the second stage.

T+plus 62 minutes, 40 seconds. The Delta 2 rocket's second stage is firing again. The burn is in progress to boost the vehicle into a higher orbit.

T+plus 62 minutes, 17 seconds. The Guam tracking site is receiving data from the rocket and relaying that telemetry back to Cape Canaveral.

T+plus 60 minutes. The rocket is soaring over the western Pacific Ocean, and restart of the second stage engine is just a couple of minutes away.

T+plus 53 minutes. The Delta 2 rocket should be coming within the Guam tracking station's coverage zone in about 10 minutes, restoring a live telemetry link from the vehicle.

T+plus 45 minutes. According to the launch sequence, the thermal conditioning roll of the rocket will end in about 11 minutes. Ignition of the second stage is coming up in 17 minutes.

T+plus 35 minutes. Restart of second stage engine is expected at about T+plus 62 minutes, 29 seconds. The stage will fire for approximately 42 seconds to raise the orbit's high point, or apogee. That will be followed by separation between the second and third stages. The upper stage will burn to inject GPS into the intended transfer orbit. Deployment of the payload to complete the launch is expected at T+plus 68 minutes.

T+plus 26 minutes, 23 seconds. The vehicle just passed out of range from the Ascension Island tracking site in the central Atlantic Ocean. The next station to acquire the rocket's signal will be Guam a half-hour from now.

As this coast phase of the launch continues, you can see a map of the rocket's planned track here.

T+plus 21 minutes, 20 seconds. The vehicle is 99 miles in altitude, 4,035 miles downrange from the launch pad and traveling at 16,682 mph.

T+plus 20 minutes, 45 seconds. Ascension Island is relaying data from the rocket to engineers at Cape Canaveral.

T+plus 19 minutes. As the rocket coasts in this parking orbit, it performs a "BBQ roll" maneuver to keep the thermal conditions on the vehicle equal. This maneuver was scheduled to start at about T+plus 17 minutes, 20 seconds and conclude at T+plus 56 minutes, 25 seconds.

T+plus 16 minutes. The official liftoff time was 6:35:00.231 a.m. EDT.

T+plus 13 minutes. The rocket is flying out of range from the Antigua tracking station. The next site to acquire signal will be Ascension Island in about seven minutes.

T+plus 11 minutes, 30 seconds. The vehicle is 97.4 miles in altitude, 1,728 miles downrange from the launch pad and traveling at 16,686 mph.

T+plus 11 minutes, 4 seconds. SECO 1. The second stage engine cutoff has occurred, completing the motor's first firing of the day. The Delta 2 rocket with GPS 2R-21 has arrived in a preliminary orbit around Earth following launch today from Cape Canaveral. The vehicle will coast for about 52 minutes before the second stage is re-ignited.

T+plus 10 minutes, 40 seconds. The vehicle is 97.3 miles in altitude, 1,527 miles downrange from the launch pad and traveling at 16,354 mph.

T+plus 10 minutes. About a minute left in this initial firing of the second stage.

T+plus 9 minutes, 57 seconds. The vehicle is 97 miles in altitude, 1,362 miles downrange from the launch pad and traveling at 15,773 mph.

T+plus 9 minutes, 10 seconds. The vehicle is 96.8 miles in altitude, 1,210 miles downrange from the launch pad and traveling at 15,209 mph.

T+plus 9 minutes. The second stage engine is still firing, consuming a hydrazine propellant mixture and nitrogen tetroxide oxidizer. This burn is needed to achieve a parking orbit around Earth.

T+plus 7 minutes, 58 seconds. The vehicle is 94 miles in altitude, 952 miles downrange from the launch pad and traveling 14,309 mph.

T+plus 7 minutes, 25 seconds. Second stage engine chamber pressure continues to look good.

T+plus 7 minutes, 10 seconds. The vehicle is 90 miles in altitude, 787 miles downrange from the launch pad and traveling 13,817 mph.

T+plus 6 minutes, 5 seconds. The vehicle is 80 miles in altitude, 572 miles downrange from the launch pad and traveling over 13,000 mph.

T+plus 5 minutes, 16 seconds. The rocket's nose cone enclosing the spacecraft has been jettisoned.

T+plus 4 minutes, 43 seconds. The spent first stage has been jettisoned and the Delta's second stage engine has ignited!

T+plus 4 minutes, 29 seconds. MECO. The first stage main engine cutoff is confirmed.

T+plus 4 minutes. A half-minute remaining in the first stage burn. Everything is reported normal aboard the vehicle.

T+plus 3 minutes, 50 seconds. The vehicle is 47 nautical miles in altitude, 204 miles downrange from the launch pad, traveling at 9,175 mph.

T+plus 3 minutes, 20 seconds. The main engine is still firing normally, burning a mixture of highly refined kerosene fuel and supercold liquid oxygen.

T+plus 2 minutes, 55 seconds. The vehicle is 34.8 nautical miles in altitude, 111 miles downrange from the launch pad, traveling at 6,296 mph.

T+plus 2 minutes, 30 seconds. The vehicle is 28 nautical miles in altitude, 76 miles downrange from the launch pad, traveling at 5,300 mph.

T+plus 2 minutes, 15 seconds. The three air-ignited solid rocket boosters have burned out and separated. The rocket is now flying solely on the power generated by the liquid-fueled first stage main engine.

T+plus 1 minute, 30 seconds. The Delta 2 rocket now weighs half of what it did at liftoff 90 seconds ago.

T+plus 1 minute, 9 seconds. All six ground-start solid rocket boosters have burned out of propellant and separated from the Delta 2's first stage. A moment before the jettison occurred, the three remaining motors strapped to rocket ignited to continue assisting the rocket's RS-27A main engine on the push to space.

T+plus 56 seconds. The Delta 2 rocket has passed through the region of maximum aerodynamic pressure during its atmospheric ascent.

T+plus 35 seconds. Now traveling faster than the speed of sound, the vehicle is soaring into the sky at sunrise carrying the last of the Global Positioning System 2R replenishment satellites.

T+plus 30 seconds. The six solid rocket motors ignited on the launch pad have surpassed their period of maximum thrust. Each of the Alliant Techsystems-made boosters generate roughly 100,000 pounds of thrust.

T+plus 10 seconds. The vehicle has cleared the tower at Complex 17A as the venerable Delta 2 makes its final launch from this historic pad at Cape Canaveral.

Ignitors are armed, T-minus 10, 9, 8, all systems remain go across the board, 5, 4, 3, 2, 1, engine start, and LIFTOFF! Liftoff of the Delta 2 rocket on one last mission for the United States Air Force.

T-minus 30 seconds. The launch ignition sequence will begin in the final two seconds of the countdown when a United Launch Alliance engineer pushes the engine start switch. The process begins with ignition of the two vernier engines and first stage main engine start. The six ground-lit solid rocket motors then light at T-0 for liftoff.

T-minus 1 minute. Sixty seconds from launch. The vehicle's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable.

T-minus 100 seconds. First stage LOX topping to 100 percent is underway.

T-minus 2 minutes. Pressurization of the first stage liquid oxygen is now beginning. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

T-minus 2 minutes, 30 seconds. The GPS spacecraft has been declared "go" for launch.

T-minus 3 minutes and counting. The rocket's third stage safe and arm devices are being armed.

T-minus 3 minutes, 45 seconds. The Delta 2 rocket's systems are now transferring to internal power for launch.

T-minus 4 minutes and counting! The Delta 2 rocket is ready to launch the GPS 2R-21 military navigation satellite at 6:35 a.m. EDT from pad 17A at Cape Canaveral Air Force Station in Florida.

Standing by to resume the countdown in one minute. A "go" to continue the count has been announced. Clocks will be ticking down from the T-minus 4 minute mark for launch at 6:35 a.m. EDT.

At liftoff, the six ground-lit solid boosters and the first stage main engine will fire to power the Delta away from pad 17A and begin the 68-minute ascent to deploy the GPS 2R-21 satellite.

Two minutes remain in the built-in hold.

The Air Force status check was just conducted with no problems voiced.

Final instructions are being given the launch team before the countdown resumes.

No problems were reported during the readiness poll of the launch team. Liftoff continues to be targeted for 6:35 a.m. EDT.

Launch team readiness polling is beginning.

Liftoff of an enhanced spacecraft for the Global Positioning System is just ten minutes away.

"The current GPS constellation has the most satellites and the greatest capability ever. GPS is the preeminent military space-based position, navigation and timing service supporting the warfighter and the growing needs of our global economy. We are committed to maintaining the current level of service while striving to improve the GPS system as it we sustain it and as we modernize it into the future," said Col. Dave Madden, commander of the Air Force's Global Positioning Systems Wing.

T-minus 4 minutes and holding. The countdown has entered the final planned hold point for today's launch. During this planned 10-minute hold, officials will poll the team members in the various control centers to ensure all systems are "go" to proceed with the countdown for liftoff at 6:35 a.m. EDT.

The launch weather officer confirms the current conditions are acceptable for liftoff of the Delta 2 rocket this morning.

The first stage kerosene fuel tank is being pressurized for flight.

The Lockheed Martin-built GPS spacecraft payload is now confirmed to be on internal battery power for flight.

T-minus 15 minutes and counting. Countdown clocks are running again following the planned 20-minute hold. The count will continue to the T-minus 4 minute mark where another planned hold is scheduled. Launch remains set to occur at 6:35 a.m. EDT (1035 GMT).

The GPS 2R-21 spacecraft cargo atop the Delta 2 rocket is now switching to internal power for launch.

Now 30 minutes from liftoff. During a poll of the launch team a moment ago, all of the members voiced a "ready" status to resume the countdown at the end of the hold as scheduled.

GPS 2R-21 will become the 218th primary payload put into space by the venerable Delta 2 rocket over the past 20 years. Here's a look at some other stats about today's mission. This will be:

• The 343rd Delta rocket launch since 1960
• The seventh Delta of 2009
• The 144th Delta 2 rocket mission since 1989
• The 69th Delta 2 rocket fly in the 7925 configuration
• The 60th GPS satellite to launch
• The 49th time a Delta 2 has launched with a GPS satellite
• The 21st GPS Block 2R satellite and 8th modernized
• The 108th Delta 2 rocket to fly from Cape Canaveral
• The 62nd Delta 2 launch from pad 17A

T-minus 15 minutes and holding. Clocks have entered the first of two planned hold periods during the final portion of the Terminal Countdown. This pause will last 20 minutes in duration.

These holds are designed to give the launch team a chance to deal with any problems and catch up on work that could be running behind schedule.

The first stage engine steering checks just finished. Technicians will take the next few minutes to review the data from the tests.

The second stage engine slews are complete. First stage tests have begun.

The launch team is beginning the "slew" or steering checks of the first and second stage engines. These are gimbal tests of the nozzles on the first stage main engine and twin vernier engines and second stage engine to ensure the rocket will be able to steer itself during launch.

The launch weather officer has revised the forecast and removed the chance of showers in the vicinity at liftoff time. The odds of acceptable conditions for today's launch opportunity have gone up to 90 percent.

The Delta 2 rocket stands in the predawn darkness on the east-central coast of Florida as the countdown enters the final 60 minutes until blastoff.

Today marks the 60th Global Positioning System satellite to fly, when you count the early test craft as well as the satellites that comprise the precision navigation network known across the globe.

The first experimental GPS craft was launched in February 1978 aboard an Atlas booster from Vandenberg Air Force Base, California. Ten additional launches followed through 1985 as the U.S. military tested the space-based navigation concept using the so-called Block 1 GPS satellite design.

Today's operational GPS system began launching in February 1989 on Delta 2 rockets from the Cape. The flights deployed 9 of the Block 2 and 19 Block 2A satellites made by Boeing. The Lockheed Martin-built Block 2R spacecraft started flying in 1997 to replenish the constellation.

"When we were in the Block 1 era, our accuracies were in in the orders of four to five meters. Right now, our accuracy is sub-meter, which enables us to utilize smart bombs and GPS-guided bombs, which have significantly decreased collateral damage on the battlefield as well as given us a higher probability of success of actually hitting the target we intend to hit. So it has made a huge difference," said Col. Dave Madden, commander of the Air Force's Global Positioning Systems Wing.

The checks of the rocket's safety systems are underway. That will be followed a short time from now by engine steering tests.

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Countdown clocks are continuing to the T-minus 15 minute mark where a 20-minute built-in hold is planned. A final 10-minute hold at T-minus 4 minutes will lead to the target liftoff time of 6:35 a.m. EDT.

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been accomplished. The filling process took 23 minutes and 45 seconds, ending at 5:15 a.m. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket now stands fully fueled for liftoff. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel along with the liquid oxygen over the past hour-and-a-half. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels last week. The nine strap-on booster rockets and third stage use solid propellants.

The first stage liquid oxygen tank just reached the 95 percent full level. The "rapid load" valve was closed, with the slower "fine load" phase continuing to fill the tank.

A bright white plume of vapors have begun streaming from a vent on the rocket and the bottom of the vehicle is icing over as the super-cold liquid oxygen continues to flow into the first stage.

The countdown is progressing on schedule, fueling is continuing and the weather is looking promising for liftoff of the Delta rocket some 90 minutes from now at 6:35 a.m. EDT.

"As others have pointed out, this is the end of an era and United Launch Alliance is very proud of its 20-year history supporting the Air Force," said John Gerlitz, Air Force Delta 2 program manager at ULA.

"The people of ULA realize that every GPS satellite is important to warfighter. Particularly, our Delta 2 team (is) extremely proud to have played such an important part of what can be argued as one of the most successful launch programs in our nation's history."

The launch team has completed work to turn on and configure the Delta's onboard guidance computer.

Now 10 minutes into this approximate 25-minute process to fill the first stage liquid oxygen tank.

LOX loading begins! Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from the storage reservoir at Complex 17, through plumbing and into the bottom of the Delta 2 rocket. The LOX will be consumed by the first stage main engine during the first four-and-a-half minutes of flight along with the 10,000 gallons of RP-1 kerosene already loaded aboard the vehicle.

The official "go" has been given by the launch director to start filling the rocket's first stage with liquid oxygen.

The launch team has received approval to begin preparations for loading the rocket's first stage liquid oxygen tank as planned.

The cumulus cloud rule is back in a "go for launch" status. The clouds around the Cape are clearing as the countdown proceeds toward the 6:35 a.m. EDT liftoff.

We're now two hours away from witnessing the final launch of a Delta 2 rocket with a Global Positioning System satellite aboard.

"Lockheed Martin and the Delta 2 program have provided a vital role in ensuring improved accuracy and signal availability to our users worldwide. This is a significant milestone in GPS history as we bring to an end the launch of the last GPS 2R-M satellite and we also bring the beginning of the new era of GPS technology," said Col. Dave Madden, commander of the Air Force's Global Positioning Systems Wing.

Future launches of the next generation GPS satellites will begin in 2010 using the bigger Delta 4 and Atlas 5 rockets.

The weather team is monitoring widely scattered showers that have been moving through the area and cumulus clouds over the launch site. The radar shows the situation is improving and the current "no go" cloud coverage should clear shortly.

The launch time forecast includes some scattered clouds at 3,000 feet, a broken deck of clouds at 30,000 feet, a chance of showers in the area, good visibility, easterly winds of 10 gusting to 15 knots and a temperature around 78-80 degrees F.

The next milestone in the count will be loading super-cold cryogenic liquid oxygen into the first stage starting about 30 minutes from now.

The kerosene and liquid oxygen will be consumed by the stage's Pratt & Whitney Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

The first stage fuel tank of the Delta 2 rocket has been fully loaded for today's planned 6:35 a.m. EDT launch. The tank was filled with a highly refined kerosene, called RP-1, during a 19-minute, 15-second process that concluded at 4:19 a.m.

Rapid-loading of the RP-1 tank has concluded with 9,800 gallons having been pumped into the rocket. Fine load is continuing.

Now 9,000 gallons aboard the rocket.

The launch team has computed that the full load for the first stage fuel tank will be 9,990 gallons.

Once the tank is filled to the 98 percent level, the "rapid load" valve will be closed and the slower "fine load" phase will continue to top off the tank.

At the present time, the current weather conditions would be "no go" for launch due to violation of the cumulus cloud rule. The forecast continues to indicate a 70 percent chance of acceptable weather during today's launch window.

The rocket's RP-1 tank is half-full already.

First stage propellant loading has passed the 3,000-gallon mark. This process to load the kerosene fuel takes about 20 minutes.

Fueling begins! About 10,000 gallons of the kerosene propellant, called RP-1, are pumping into the base of the rocket from storage tanks at pad 17A as fueling of the Delta 2's first stage begins for today's launch.

Preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank are beginning. After verifying valves, sensors, flow meters and equipment are ready, the highly refined kerosene fuel will start flowing into the vehicle a few minutes from now.

The first stage helium and nitrogen systems have been pressurized. And the "go" has been given for the start of fueling operations.

A small shower has moved ashore, bringing a light rain to pad 17A. Weather forecasters have predicted for several days that coastal showers could be expected during the countdown.

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The rocket's guidance system is being turned on.

And the launch team is starting the steps to pressurize the first and second stage helium and nitrogen systems and the second stage fuel and oxidizer tanks.

BEGIN COUNT. The Terminal Countdown has been initiated for today's launch of the Global Positioning System 2R-21 satellite aboard the Delta 2 rocket.

The next three hours will be spent fueling the rocket, activating systems and performing final testing before liftoff at 6:35 a.m. EDT from pad 17A at Cape Canaveral Air Force Station in Florida.

Workers have cleared the Complex 17 area in advance of the hazardous portion in today's launch operation. But a warning horn is now being sounded three times at the seaside complex as a precaution to alert any remaining personnel in the vicinity that they should leave immediately.

The pad clear status will allow the start of activities such as pressurizing the helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

The countdown clocks currently stand at T-minus 150 minutes and counting. Two planned holds -- at the T-minus 15 minute and the T-minus 4 minute points -- will give the launch team some time to catch up on any work running behind. The first hold will last 20 minutes in duration, the second extends 10 minutes.

The launch team has been polled to ensure all stations are manned and systems are set for the Terminal Countdown. There are no constraints standing in the way of beginning the count.

T-minus 150 minutes and holding. The countdown is entering the first of three planned holds that will occur over the course of the night. This first pause is 60 minutes long.

The two later holds -- at the T-minus 15 minute and the T-minus 4 minute points -- will give the launch team some time to deal with issues and catch up on any work running behind. Those two holds combined add up to a half-hour in duration.

The Delta 2 rocket stands poised on the launch pad with the Global Positioning System 2R-21 satellite tucked inside its nose cone for liftoff at 6:35 a.m. EDT.

"The United States Air Force and Air Force Space Command have been diligent stewards of GPS since its conception in the 1970s, and we continue this commitment to the critical component to our national infrastructure due to a culmination of many years of outstanding teamwork and commitment to mission success between the Air Force, which includes really the operations and the acquisition side, Lockheed Martin and ULA," said Col. Dave Madden, commander of the Space and Missile Systems Center's Global Positioning Systems Wing.

A picture taken a little while ago showing the Delta 2 rocket poised on the launch pad can be viewed here.

"We're very excited to be supporting the final launch of the modernized GPS 2R series -- GPS 2R-21. It's the third Delta 2 and the second GPS satellite we've launched this year. But it'll also be final launch for the 1st Space Launch Squadron here at Cape Canaveral," said Lt. Col. Erik Bowman, the Air Force launch director and the commander of the 1st SLS.

"With this mission, the 45th Space Wing is accomplishing another major milestone in our national quest to improve and maintain our space capabilities. The GPS constellation has tremendous national security and economic importance. This launch is one of the many ways space operators, and the 45th Space Wing specially, contribute to ongoing combat operations overseas."

The 1st Space Launch Squadron has been responsible for overseeing Cape Canaveral's Complex 17 and facilities supporting Delta 2 rocket flights. But once this final Air Force Delta 2 mission occurs, the squadron will be disbanded and its remaining personnel moved to other groups.

"We are planning on inactivating the 1st Space Launch Squadron the day after the GPS 2R-21 launch," Bowman said. "After that, we'll be permitting many of our facilities over to NASA to support its Delta 2 missions."

NASA has two remaining Delta 2 missions on the Cape Canaveral manifest -- deployment of a space tracking demonstration on September 15 and the GRAIL lunar launch in 2011.

The gantry is arriving at its launch position where the tower will be secured to allow the Delta 2 rocket's sunrise liftoff carrying the Global Positioning System 2R-21 satellite. Now, workers will turn their attention to configuring the pad and putting the final touches on equipment before clearing Complex 17 overnight.

The Terminal Countdown commences at 3:35 a.m. EDT, followed shortly thereafter by loading kerosene fuel and then super-cold liquid oxygen into the first stage.

Liftoff remains scheduled for 6:35 a.m. EDT.

For what could be the final time in history, the mobile service gantry at Cape Canaveral's pad 17A is slowly rolling away from a Delta 2 rocket for launch.

The tower was used to stack the multi-stage vehicle atop the pad's launch mount, attach the nine strap-on solid motors and hoist the payload aboard the rocket. This cocoon-like structure wraps around the Delta to offer weather protection and full access for workers during the pre-launch flow.

Work has been underway this afternoon and evening at Complex 17, as ground crews retracted access platforms and stowed gear in the tower in advance of the structure wheeling away from the rocket.

The GPS spacecraft launching in the morning was delivered to the pad two weeks ago, then hoisted into the cleanroom and bolted to its Delta for the ride to orbit. The rocket's two-piece nose cone to shroud the satellite during ascent through the atmosphere was installed around the GPS craft last week.

Complex 17 has been around since the late 1950s and seen 160 launches by Thor and Delta vehicles. NASA will take over the site from the Air Force following tomorrow's flight. The space agency has two remaining Delta 2 missions scheduled from the Cape in September and in 2011, but those will use pad 17B.

The tower rollback process has begun.

At Cape Canaveral's pad 17A, the sun is setting and the powerful spotlights are being turned on. Ground crews are busy at work preparing the mobile service tower for retraction from around the Delta 2 rocket tonight.

The sliding doors on the backside of the tower just opened up to reveal the full vehicle standing tall. The doors enclose the cleanroom area where Delta payloads get attached to the rockets during the campaigns leading up to launch.

A few more access platforms still have to be folded up, then the tower will be free to roll back.

Final pre-flight preparations will get underway this afternoon as the Delta team and U.S. Air Force target a 6:35 a.m. EDT launch on Monday morning from Cape Canaveral, Florida.

The weather outlook continues to predict a 70 percent chance of acceptable conditions during the 14-minute launch window. Coastal rain showers over the launch pad or in the rocket's flight path are the primary concern.

The launch time forecast includes scattered cumulus clouds at 3,000 feet, scattered cirrus at 25,000 feet, showers in the vicinity, good visibility, easterly winds of 12 gusting to 20 knots and a temperature around 78-80 degrees F.

Watch this page for live reports throughout the countdown and launch!

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The Launch Readiness Review occurred today and resulted in officials giving formal approval to begin the countdown for Monday's planned 6:35 a.m. EDT liftoff of the Global Positioning System 2R-21 spacecraft.

"We will not launch until it is ready, but we anticipate a very good and clean launch. So Go Delta," said John Wagner, the Air Force's mission director from the Space and Missile System Center's Launch and Range Systems Wing.

The 12-story Delta 2 rocket will be propelled off the launch pad with its main engine and six strap-on solid-propellant boosters firing to generate over 700,000 pounds of thrust.

A minute into the ascent, the rocket will already be 10 miles up as those six solid motors extinguish and separate. Three remaining solids are ignited for their minute-long firing.

The slender blue first stage keeps its RS-27A engine roaring through the initial four-and-a-half-minutes, climbing about 60 miles over the Atlantic Ocean before being jettisoned. That allows the hypergolic second stage engine to ignite and push the vehicle into a preliminary orbit stretching 111 miles at its high point and 94 miles at its lowest.

The second stage will settle into the parking orbit about 11 minutes after liftoff and begin a quiet coast to the other side of the planet where the launch sequence resumes about 50 minutes later over the western Pacific Ocean.

Another firing of the second stage, this time lasting just 42 seconds, begins the process of shaping the orbit for the GPS satellite cargo. The end result of this burn will be an orbit 670 miles at apogee and 103 miles at perigee.

Tiny thrusters then ignite to rapidly "spin up" the third stage and attached satellite to 55 rpm. The second stage separates from the spinning duo some 64 minutes after liftoff.

The solid-fuel third stage is lit moments later, delivering a minute-and-a-half of thrust to propel the satellite into a highly elliptical orbit reaching 11,000 miles at the high point, 104 miles at the lowest and inclined 40 degrees to the equator.

The Lockheed Martin-built satellite is cast free from the spent rocket 68 minutes into the ascent, completing the Delta 2 vehicle's job.

If all goes well, another solid-propellant kick motor on the satellite itself will fire in a few days to circularize its orbit at 11,000 miles and increase the inclination to 55 degrees where the GPS constellation flies.

Controllers will maneuver the craft into the Plane E, Slot 3 position of the constellation to take the place of GPS 2A-26. That aging satellite was launched in July 1996 with a seven-year design life.

"Speaking for Lockheed Martin, we have great confidence that this upcoming satellite is ready for flight and will meet our customer's expectations once on orbit," said Don DeGryse, the company's vice president of Navigation Systems.

After 20 years and over 50 launches for the U.S. military, the respected Delta 2 rocket will make one last flight for the Air Force at dawn Monday carrying the final spacecraft in the current generation of Global Positioning System satellites.

Liftoff from Cape Canaveral is planned during a brief window extending from 6:35 to 6:49 a.m. EDT (1035-1049 GMT).

The long-range weather outlook puts the odds of acceptable conditions at 70 percent. Coastal rain showers could pose a small threat for delaying the launch.

The launch weather team reported today: "Currently, a tropical wave over the western Atlantic will travel across southern Florida on Friday and Saturday. Afterwards, deep layered high pressure will build in from the east and be the dominant weather feature with the ridge axis located well to the north of central Florida. As a result, onshore flow will occur during the countdown. Typically under this regime widely scattered showers develop over the coastal waters during the early morning hours and move towards the coast. The primary concern during the countdown and launch window will be for one of these showers moving over the pad and flight path."

The launch time forecast includes scattered cumulus clouds, showers in the vicinity, good visibility, easterly winds of 10 to 18 knots and a temperature around 77 degrees F.

If the launch is delayed to Tuesday for some reason, the odds and forecast remain unchanged.

Riding atop the three-stage rocket is GPS 2R-21, the last satellite in the series built by Lockheed Martin to sustain the orbiting constellation for users worldwide. The Block 2R spacecraft began flying in 1997 to replenish the network and replace the older generations.

"Since the first successful launch in 1997, GPS 2R spacecraft have demonstrated unmatched capability, achieving exceptional on-orbit performance for military and civil users around the globe," said Don DeGryse, Lockheed Martin's vice president of Navigation Systems. "We are extremely proud of our partnership with the Air Force on this important program and look forward to providing increased GPS accuracy and reliability with the launch of the final GPS 2R-M satellite."

The final eight craft in the 21-satellite GPS Block 2R family were "modernized" to transmit additional signals and provide improvements aimed at greater accuracy, tougher resistance to interference and enhanced performance.

"Through effective collaboration and a joint commitment to successful execution, the GPS 2R program has significantly improved our nation's position, navigation and timing capabilities, and we look forward to enhancing the GPS constellation with this last 2R-M satellite," said Col. Dave Madden, commander of the Air Force's Global Positioning Systems Wing.

The craft will replace the aging GPS 2A-26 satellite launched in July 1996 and now well past its design life.

The new GPS 2R-21 spacecraft will take over the Plane E, Slot 3 location of the navigation network, considered one of the primary positions in the constellation that is divided into six orbital groupings with multiple satellites flying in each.

After the Air Force flies this last GPS Block 2R satellite, the military will transition to the next series of enhanced GPS 2F satellites built by Boeing that's slated to begin launching in 2010 on the larger Atlas 5 and Delta 4 rockets.

The Air Force also says goodbye to the Delta 2 after Monday's launch. The service oversaw more than 50 flights of the rocket since 1989, including the launches of GPS, National Reconnaissance Office and other research satellites.

"This launch will mark the end of an era, but we are focused first and foremost on making this last GPS 2R launch a complete success," said Lt. Col. Erik Bowman, the Air Force launch director and the commander of the 1st Space Launch Squadron at the Cape.

Watch this page for live coverage throughout the countdown and launch!