BY JUSTIN RAY

May 11, 2000 -- Follow the countdown and launch of a Boeing Delta 2 rocket with the U.S. Air Force's GPS 2R-4 navigation satellite. Reload this page for the very latest on the mission.

THURSDAY, MAY 11, 2000

A fresh spacecraft was launched into orbit for the U.S. Air Force's Global Positioning System on Wednesday night to fill a void created by the recent loss of the constellation's inaugural satellite. Boeing's Delta 2 rocket pierced the nighttime Florida sky at Cape Canaveral and successfully carried the GPS 2R-4 satellite aloft during a 25-minute flight. Read our complete launch story.

0233 GMT (10:33 p.m. EDT)

U.S. Air Force satellite controllers at the 1st Space Operations Squadron of Schriever Air Force Base in Colorado say they established communications with the Global Positioning System 2R-4 satellite at 10:26 p.m. EDT tonight as planned. The satellite was delivered into the correct elliptical orbit and the launch of the Boeing Delta 2 rocket has been declared a success.

0213 GMT (10:13 p.m. EDT)

T+plus 25 minutes, 40 seconds. SPACECRAFT SEPARATION! The NAVSTAR Global Positioning System 2R-4 military navigation satellite has been released from the Delta rocket's third stage following a successful launch tonight.

Over the coming month, activities to prepare the satellite for service will include deploying its solar arrays in order to generate power and recharge onboard batteries, manuevers to circularize the orbital altitude and testing and of the spacecraft bus and communications payload.

Check back later tonight for a full report on the launch, movie clips and images.

0211 GMT (10:11 p.m. EDT)

T+plus 23 minutes, 35 seconds. Confirmation of burnout for the solid-fueled third stage. Coming up on deployment of the GPS satellite in less than two minutes.

0211 GMT (10:11 p.m. EDT)

T+plus 23 minutes. The third stage continues to fire. Limited data being returned to the Cape via the Ascension Island tracking station.

0210 GMT (10:10 p.m. EDT)

T+plus 22 minutes. The second stage has separated and the third stage ignition confirmed. This burn of the third stage will continue until T+plus 23 minutes, 25 seconds.

0208 GMT (10:08 p.m. EDT)

T+plus 20 minutes, 42 seconds. The Delta rocket's second stage has completed its second burn tonight to deliver the third stage and attached GPS spacecraft into the proper orbit. Coming up on second and third stage separation in less than one minute.

0208 GMT (10:08 p.m. EDT)

T+plus 20 minutes. The second stage has restarted.

0206 GMT (10:06 p.m. EDT)

T+plus 18 minutes. Just under two minutes until the second stage engine is restarted for a 35-second firing as the GPS 2R-4 satellite continues its journey to space.

0203 GMT (10:03 p.m. EDT)

T+plus 15 minutes. Nothing much to report at this point in the flight with the quiet coast period continuing.

0200 GMT (10:00 p.m. EDT)

T+plus 12 minutes. The rocket has entered a coast period that will continue for another eight minutes before the second stage performs another firing.

0159 GMT (9:59 p.m. EDT)

T+plus 11 minutes. SECO 1. The second stage engine has cut off as planned and the Delta 2 rocket with GPS 2R-4 spacecraft have arrive in a preliminary orbit around Earth.

0158 GMT (9:58 p.m. EDT)

T+plus 10 minutes. Boeing reports the launch is going very cleanly with no problems to report. Also, the Antigua tracking station downrange has picked up the rocket's signal.

0155 GMT (9:55 p.m. EDT)

T+plus 7 minutes. The second stage continues to fire with just under four minutes to go during this first burn.

0154 GMT (9:54 p.m. EDT)

T+plus 6 minutes. Vehicle continues flying on the proper track.

0153 GMT (9:53 p.m. EDT)

T+plus 5 minutes. The protective payload fairing enclosing the GPS satellite atop the rocket has separated with no recontact detected.

0152 GMT (9:52 p.m. EDT)

T+plus 4 minutes, 40 seconds. MECO. The first stage main engine cutoff confirmed, the stage has been jettisoned and second stage engine ignition has occurred.

0152 GMT (9:52 p.m. EDT)

T+plus 4 minutes. About 20 seconds from shutdown of the first stage main engine.

0151 GMT (9:51 p.m. EDT)

T+plus 3 minutes, 30 seconds. A very smooth flight reported so far.

0150 GMT (9:50 p.m. EDT)

T+plus 2 minutes, 30 seconds. The three air-start solid rocket boosters have burned out and separated. The rocket continues its trek to orbit on the power of the first stage liquid-fueled main engine.

0150 GMT (9:50 p.m. EDT)

T+plus 2 minutes. Good chamber pressures for the solid rocket boosters. Vehicle appears as a white comet streaking right down the proper course about 14 miles in altitude.

0149 GMT (9:49 p.m. EDT)

T+plus 70 seconds. Separation of all six ground-start solid rocket boosters confirmed. The three air-lit solids have ignited.

0148 GMT (9:48 p.m. EDT)

T+plus 30 seconds. Vehicle performance reported normal as the rocket approaches Mach 1.

0148 GMT (9:48 p.m. EDT)

LIFTOFF! Liftoff of the Boeing Delta 2 rocket launching a new satellite to fill a vacancy in the Air Force's Global Positioning System constellation. The vehicle has cleared the tower.

0147 GMT (9:47 p.m. EDT)

T-minus 30 seconds. Hydraulics and electronics reported go.

The launch ignition sequence will begin at T-minus 2 seconds when a Boeing engineer triggers the engine start switch. The process begins with ignition of the two vernier engines and first stage main engine start. The six ground-start solid rocket motors then light at T-0 for liftoff.

0147 GMT (9:47 p.m. EDT)

T-minus 1 minute. The Range has given its final clear-to-launch. The Delta 2 rocket's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable. At the telemetry receiving areas where data from the rocket will be transmitted, the data recording charts have gone to high speed as the liftoff nears. Also, the pad 17A water suppression system has started.

0146 GMT (9:46 p.m. EDT)

T-minus 2 minutes. The first stage liquid oxygen vents are now being closed so the LOX tank can be pressurized for launch. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

The U.S. Air Force has declared the NAVSTAR Global Positioning System 2R-4 spacecraft is officially "go" for launch this evening. The spacecraft will join 27 other operational GPS satellites in space to provide precision navigation and timing information to military forces and civilians on land, in the air and at sea around the globe. Officials are launching the craft to replace an older GPS satellite that has malfunctioned after reaching the end of its extended life.

0145 GMT (9:45 p.m. EDT)

T-minus 3 minutes. The safety destruct safe and arm devices are being armed.

0144 GMT (9:44 p.m. EDT)

T-minus 4 minutes and counting. Now in the final phase of the countdown as Delta launch vehicle systems begin transferring to internal power. All systems remain ready for an on-time launch this evening at 48 minutes past the hour from pad 17A at Cape Canaveral Air Force Station in Florida.

0143 GMT (9:43 p.m. EDT)

Launch team standing by to pick up the countdown in one minute. The Delta rocket is now five minutes away from liftoff. There are no problems being discussed tonight.

0142 GMT (9:42 p.m. EDT)

The management readiness poll just concluded and no problems were announced. Countdown clocks are scheduled to resume in two minutes for launch at 9:48 p.m. EDT.

0139 GMT (9:29 p.m. EDT)

A readiness poll of the launch team has been conducted and all parties reported "go" status for liftoff in nine minutes from Cape Canaveral Air Force Station, Florida.

0138 GMT (9:38 p.m. EDT)

Satellite officials report the GPS 2R-4 satellite is on internal power for launch in 10 minutes.

0136 GMT (9:36 p.m. EDT)

The GPS 2R-4 spacecraft sitting atop the Delta 2 rocket is now switching to internal power for launch.

0134 GMT (9:34 p.m. EDT)

T-minus 4 minutes and holding. The countdown has entered the final planned hold point for tonight's launch attempt. During this planned 10-minute hold, the launch team can catch up on any work that could be running behind schedule. In addition, officials will poll the various team members to ensure all systems are ready for launch. Lt. Col. Blaise Kordell, commander of the 1st Space Launch Squadron at Cape Canaveral Air Force Station, will give the approval to launch the Delta rocket and the Air Force's NAVSTAR Global Positioning System 2R-4 satellite. At present, there are no problems being discussed. Upper level winds, ground weather, the Range, launch vehicle and payload are go for liftoff at 9:48 p.m. EDT.

Over the past few minutes, the rocket's first stage RP-1 fuel tank was pressurized and the third stage telemetry system was turned on.

0129 GMT (9:29 p.m. EDT)

The rocket's C-band beacon used by Range Safety to track the vehicle during launch has been verified to be working properly.

0128 GMT (9:28 p.m. EDT)

T-minus 10 minutes and counting. The countdown is heading to T-minus 4 minutes for a 10-minute long hold. Liftoff the Boeing Delta 2 rocket from Cape Canaveral Air Force Station is still slated to occur at 9:48 p.m. EDT to place the NAVSTAR Global Positioning System 2R-4 satellite into space.

For these NAVSTAR GPS launches, Boeing uses a model 7925-9.5 Delta 2 rocket. The expendable launch vehicle consists of three stages, nine strap-on solid rocket boosters and a 9.5-foot diameter payload fairing. The rocket stands 126 feet tall.

The rocket's first stage is powered by the liquid-fueled RS-27A main engine built by Rocketdyne, a division of Boeing. The engine will fire for the first 4 minutes, 20 seconds of flight, consuming the RP-1 kerosene and liquid oxygen loaded aboard the rocket early this evening. The first stage also features nine Alliant Techsystems solid-propellant thrust augmentation motors. Six will be ignited at liftoff and burn for 63 seconds. The remain three motors will be lit in flight 65 seconds after launch. At T+plus 66 and 67 seconds, the spent ground-start casings will separate in two groups of three to fall into the Atlantic Ocean. The air-start motors will be jettisoned 2 minutes, 11 seconds into flight.

Some 4 minutes, 30 seconds after liftoff, the first stage will be jettisoned and the second stage will take over. The Aerojet AJ10-118K engine will ignite for the first time at T+plus 4 minutes, 34 seconds, beginning 6-minute, 9-second firing. The engine burns Aerozine-50 fuel and nitrogen tetroxide oxidizer. The oxidizer and propellant were loaded aboard the rocket on April 19. The payload fairing will be jettisoned 4 minutes, 50 seconds into flight. Following the cutoff of the second stage engine, the second stage with the third stage and attached GPS spacecraft will coast for about nine minutes before another firing will occur. That 35-second burn will set up a fast-paced sequence of events to deliver GPS 2R-4 into its planned orbit. Following the second stage's second burn, at T+plus 21 minutes, 19 seconds, the stage will separate from the third stage. The Thiokol-built Star 48B solid-fuel third stage will then ignite 40 seconds later. The stage will fire for one minute and 26 seconds. Spacecraft separation will complete this 278th Delta mission at T+plus 25 minutes and 19 seconds.

0124 GMT (9:24 p.m. EDT)

Checks are now under way of the Range Safety command destruct receivers that would be used to destroy the Delta rocket should a problem arise during the launch. A little earlier, the Range completed RF link checks with the rocket.

0118 GMT (9:18 p.m. EDT)

T-minus 20 minutes and counting. The countdown has resumed as scheduled from this 20-minute-long built-in hold and clocks are now ticking toward the T-minus 4 minute mark where another pause is planned. Launch remains scheduled for 9:48 p.m. EDT and no problems are being reported with the rocket, GPS satellite, ground systems or weather tonight.

0106 GMT (9:06 p.m. EDT)

A readiness check with the GPS 2R-4 spacecraft team reports a "go" to continue with the countdown to launch tonight at 9:48 p.m. EDT. Countdown clocks continune holding at T-minus 20 minutes where another 12 minutes remain in this planned pause.

0058 GMT (8:58 p.m. EDT)

T-minus 20 minutes and holding. The countdown has gone into the first of two planned hold periods during the last 20 minutes of the Terminal Count for tonight's 9:48 p.m. EDT (0148 GMT) launch. Over the past few minutes, the "slew" or steering checks of the first and second stage engines were completed and RF link tests between the Range and rocket started. There are no technical problems to report with the rocket, GPS satellite cargo or Range systems. Weather is also reported to be acceptable.

0048 GMT (8:48 p.m. EDT)

Now one hour from tonight's scheduled launch of the Boeing Delta 2 rocket carrying the GPS 2R-4 satellite for the U.S. Air Force Station.

The Navigation Signal Timing and Ranging Global Positioning System (NAVSTAR GPS) was established in the 1970s to provide the military with navigation data for ground, sea and air forces. The first 11 satellites, known as Block 1, were launched from 1978 through 1985 and served to test the fundamentals behind the GPS concept. Beginning in 1989, the Block 2 and 2A series satellites began flying to form the current constellation that provides precise navigation data not only to the military but civilians as well.

In 1997 a newer, more advanced series of GPS satellites, the Block 2R, debuted. However, the first was lost in a launch failure. The second was successfully launched in July of that year. This evening, the fourth of 21 is scheduled to leave the Earth aboard the Delta 2 rocket. The craft are considered to be operational replenishment satellites and are developed by Lockheed Martin. They will carry GPS into the next century. Block 2R satellites are designed to provide at least 14 days of operation without contact from controllers and up to 180 days of operation when operating in the autonomous navigation (AUTONAV) mode. The spacecraft maintain their accuracy by communicating with other Block 2R satellites in orbit. This so-called cross-link ranging will be used to estimate and update the parameters in the navigation message of each Block 2R satellite without contact from ground control. Other enhancements include reprogrammable micro-processors for upgrading in-flight, additional radiation protection, greater fuel capacity, the ability to determine their own position and two atomic clocks working at all times, providing a "hot backup."

The GPS constellation is comprised of 24 primary satellites divided into six orbital planes with four spacecraft in each. They circle in formation about 10,900 nautical miles above Earth every 12 hours in orbits inclined 55 degrees to the equator.

The continuous navigation signals sent from the satellites allow users to find their position in latitude, longitude and altitude and measure time. A GPS user receiver measures the time delay for the signal to reach the receiver, which is the direct measure of the apparent range to the satellite. Measurements collected simultaneously from four satellites are processed to solve for the three dimensions of position, velocity and time. Military users can determine their location to within feet, speed within a fraction of a mile per hour and time to within a millionth of a second. Positioning accuracy for military users is nominally 16 meters, while accuracy for civilian users is nominally 100 meters.

Countless uses have been found for the revolutionary GPS system. Everyday, GPS guides U.S. military troops, aircraft, submarines and ships around the globe. Troops also relied on the system extensively in the featureless desert battlefield of the Gulf War. Weapons can use GPS data for guidance. GPS also found its way into the civilian commercial market - assisting planes, automobiles, boats, hikers and map makers.

0040 GMT (8:40 p.m. EDT)

The countdown is continuing smoothly at Cape Canaveral for launch of the Delta 2 rocket is just over an hour at 9:48 p.m. EDT. Just completed was pressurization of the second stage tanks and spheres. The next significant event in the count, now that the rocket is fully fueled, will be steering checks of the rocket's first and second stage engine nozzles. A 20-minute planned hold in the countdown will follow at the T-minus 20 minute mark starting at 8:58 p.m. EDT.

0030 GMT (8:30 p.m. EDT)

The Delta 2 rocket's first stage liquid oxygen tank has now been filled with its flight load, completing the fueling process for launch tonight at 8:30:09 p.m. EDT. However, given the nature of the super-cold cryogenic, the liquid oxygen will boil away and must be replenished thorughout the remainder of the countdown. The liquid oxygen is consumed along with the RP-1 fuel by the first stage main engine.

The second stage was loaded with its storable nitrogen tetroxide and Aerozine 50 fuels on April 19; and the third stage and strap-on booster rockets are solid-propellant.

0028 GMT (8:28 p.m. EDT)

Rapid-filling of the first stage liquid oxygen tank has been completed to the 95-percent level. A slower loading process will now start to bring the tank to flight level.

0018 GMT (8:18 p.m. EDT)

Now 90 minutes away from the planned launch of Delta 278 from Cape Canaveral.

0014 GMT (8:14 p.m. EDT)

The rocket's guidance computer -- the Redundant Inertial Flight Control Assembly -- has been turned on for launch. First stage liquid oxygen loading has been underway for 10 minutes.

0005 GMT (8:05 p.m. EDT)

The loading of liquid oxygen aboard the Delta 2 rocket's first stage started at 8:04:25 p.m. EDT. This process will take about 20 minutes to complete.

0003 GMT (8:03 p.m. EDT)

T-minus 75 minutes and counting. Super-cold liquid oxygen will now start flowing from a storage tank at pad 17A into the Boeing Delta 2 rocket for tonight's launch from Cape Canaveral Air Force Station, Florida. Liftoff remains set to occur at 9:48 p.m. EDT.

WEDNESDAY, MAY 10, 2000
2357 GMT (7:57 p.m. EDT)

The Boeing launch team located in the operations control center a few miles away from pad 17A are now preparing to load super-cold liquid oyxgen into the Delta rocket's first stage. The stage was fueled with RP-1 kerosene earlier.

2348 GMT (7:48 p.m. EDT)

Now one hour into the terminal countdown for Delta 278 and the GPS 2R-4 military navigation and two hours away from liftoff at Cape Canaveral Air Force Station, Florida. Activities are continuing on schedule toward the planned 9:48 p.m. EDT (0148 GMT) launch. Weather conditions are still looking good, too, as the sun sets here in East Central Florida.

2248 GMT (6:48 p.m. EDT)

Terminal Count is scheduled to start at this time for tonight's launch of the Boeing Delta 2 rocket and the U.S. Air Force NAVSTAR Global Positioning System 2R-4 navigation satellite. Liftoff is scheduled for 9:48 p.m. EDT (0148 GMT).

Once the countdown gets underway, the launch team will begin pressurizing the first and second stage helium and nitrogen systems and second stage fuel tanks. In addition, the rocket's guidance computer will be turned on. Loading of 10,000 gallons RP-1 fuel, a highly refined kerosene, into the first stage is slated to start in about 20 minutes, and liquid oxygen tanking will follow at about 8 p.m. EDT.

2100 GMT (5:00 p.m. EDT)

A Boeing-built Delta 2 rocket is less than five hours away from its appointed liftoff time today at Cape Canaveral Air Force Station, Florida. Tonight's launch window opens at 9:48 p.m. EDT and extends 29 minutes to 10:17 p.m. EDT (0148-0217 GMT). Air Force weather forecasters are still predicting a 70 percent chance of good conditions. The only concern will be electrically-charged clouds moving too close to the rocket's projected flight path.

At pad 17A, the 12-story mobile service tower has been retracted to the launch position and final work is underway to prepare the complex for liftoff. Tower rollback occurred at about 4:15 p.m. EDT, nearly four hours later than planned due to the threat of local thunderstorms.

The terminal countdown will be started at 6:48 p.m. EDT at the T-minus 150 minute mark. Two holds are scheduled into the countdown -- 20 minutes at T-minus 20 minutes and 10 minutes at T-minus 4 minutes.

The rocket will deploy the NAVSTAR Global Positioning System 2R-4 military navigation satellite into orbit for the Air Force some 25 minutes after launch.

1600 GMT (12 noon EDT)

The U.S. Air Force and Boeing report all systems are go for tonight's launch of a Delta 2 rocket carrying a NAVSTAR Global Positioning System satellite. Preparations are underway at Cape Canaveral's pad 17A to roll back the mobile service tower from around the rocket.

TUESDAY, MAY 9, 2000

A Boeing Delta 2 rocket is once again poised for liftoff at Cape Canaveral to place a crucial military navigation satellite into space after two false starts last month. The launch is scheduled for Wednesday night during a window of 9:48 to 10:17 p.m. EDT (0148-0217 GMT Thursday).

Launch attempts for the Delta 2 and its U.S. Air Force Global Positioning System Block 2R-4 satellite cargo on April 21 and 22 were scrubbed by a problem with ground support equipment and then by a last-minute concern with the payload.

The equipment glitch was fixed after the first night's delay. But Air Force officials called off the second try a few hours before the launch window opened to allow engineers time to conduct a precautionary assessment of the solar array deployment mechanism used by the Lockheed Martin-built GPS satellite.

"A potential issue was identified while inspecting another spacecraft being prepared for launch which led the Air Force to stand down from the launch and conduct an analysis," the Air Force said in a statement to Spaceflight Now.

"Additional data was collected from all the satellites in storage. That data was reviewed along with design requirements. The resulting assessment is that the satellite currently awaiting launch is ready to go into orbit."

The $42 million satellite will be put to work soon after reaching space to replace a sister-craft that failed on March 26 when its onboard reaction wheels, which are need for orienting in orbit, shut down. The now-decommissioned satellite was 11 years old and had well exceeded its design life. It was the first operational GPS spacecraft launched to construct a network of 24 orbiting satellites that provide precision location and timing information for U.S. military forces around the globe. Civilians can also use the GPS system.

The flurry of recent launches and related tests at Cape Canaveral have extended the wait before another launch opportunity was possible for the Delta 2 rocket. And with even more launches scheduled over the next two weeks, officials have only Wednesday and Thursday night to get the rocket airborne or else delay until around May 20.

Launch pad technicians on Tuesday were making final preparations for Wednesday's countdown and mission. Steering checks of the rocket's bell-shaped engine nozzles were performed, along with loading ordnance aboard the vehicle and sealing the protective nose cone enclosing the GPS satellite atop the Delta 2, a Boeing spokesman reported.

Senior officials held a brief Flight Readiness Review Update to discuss the status of the rocket, satellite, Range, weather and other factors associated with the launch. With no significant problems addressed, managers cleared the mission preparations to continue.

Meteorologists are calling for generally favorable conditions for liftoff with a 70 percent chance of meeting the launch weather rules. The main threats will be thunderstorm anvil and debris clouds approaching the rocket's flight path. Launch Weather Officer Joel Tumbiolo gave this overview on Tuesday:

"Currently, surface high pressure will continue to drift southward over the next 24-48 hours. This will result in a more southerly low level flow and an increase in moisture content. This increase in moisture, along with surface heating and both west coast and east coast sea breezes moving inland will result in a slight chance for afternoon and evening thunderstorms over interior sections of Florida on Tuesday and Wednesday. Mid and upper level steering flow may cause these thunderstorms, and any associated anvil and debris clouds to drift towards the Cape during the countdown and launch window on Wednesday."

The launch time forecast calls for a few clouds at 3,000 feet and scattered clouds at 12,000 and 25,000 feet, visibility of 10 miles or better, southerly winds at 10 gusting to 15 knots, a temperature between 74 and 76 degrees F, relative humidity of 50 percent and isolated thunderstorms in the vicinity.

Should the launch be delayed to Thursday evening for some reason, there is an 80 percent chance of good conditions with the same weather concerns. The 29-minute launch window that night will open at 9:44 p.m. EDT.

On Wednesday, the 12-story mobile service tower at pad 17A will be rolled away from the rocket just after 12 noon EDT. The terminal countdown is slated to get underway at 6:48 p.m. EDT.

We will provide live extensive coverage of the launch throughout the day tomorrow with play-by-play reports during the final three hours of the countdown and 25-minute-long launch. In addition, Spaceflight Now will offer a live QuickTime streaming video broadcast of the launch beginning at about 9 p.m. EDT.

WEDNESDAY, APRIL 26, 2000

After halting the launch of its newest NAVSTAR Global Positioning System satellite on Saturday evening for checks of the craft's solar arrays, officials have now cleared the last-minute concern.

The spacecraft is now due for launch on May 10 at 9:48 p.m. EDT (0148 GMT on 11th) aboard a Boeing Delta 2 rocket. Liftoff will occur from pad 17A at Cape Canaveral Air Force Station in Florida.

The Air Force decided to delay the launch to make sure an issue recently uncovered with the deployment mechanisms on similar Lockheed Martin Space Systems-built satellites still at the factory would not affect the $42 million spacecraft once in Earth orbit.

Officials said this week the concern was put to rest and the GPS 2R-4 satellite was ready for flight. It will replace the very first GPS satellite launched into the Air Force's space-based navigation system 11 years ago.

The new launch date could have been sooner but the Air Force-controlled Range is booked with other launches and tests that will preclude the Delta from trying before May 10.

SATURDAY, APRIL 22, 2000
2220 GMT (6:20 p.m. EDT)

SCRUB! The U.S. Air Force has scrubbed the launch of a Delta 2 rocket carrying a $42 million NAVSTAR Global Positioning System satellite for the second straight night. Officials made the decision a short time ago at Cape Canaveral Air Force Station so engineers can double check the solar array deployment mechanisms on the Lockheed Martin-built satellite. A possible problem with the mechanisms on a different GPS spacecraft being built for a future launch prompted this last-minute concern.

"The decision to delay the launch was made to ensure the spacecraft is absolutely prepared for launch," said Lt. Col. Blaise Kordell, Air Force Launch Director.

A ground power supply problem that originally cancelled Friday night's attempt has been resolved.

When the next launch try will be made is not yet known. The Air Force-run Eastern Range that governs all Cape Canaveral and Kennedy Space Center launches in Florida previously needed 48 hours between flights of different space vehicles to reconfigure its tracking, communications and safety systems.

However, recent upgrades that went into effect April 1, now allow the range to switch its networks within 24 hours for different rockets, Air Force spokeswoman Lt. Alana Austin said.

The space shuttle Atlantis has reserved the Range for Monday's planned launch, with backup attempts on Tuesday and Wednesday. In addition, the Air Force plans to conduct a mission rehearsal involving a Titan 4 rocket on Friday.

We will provide additional information on this launch when it becomes available.

2110 GMT (5:10 p.m. EDT)

The Boeing is pressing ahead with plans to launch a Delta 2 rocket tonight from Cape Canaveral. Officials report a ground equipment problem experienced last night has been fixed but a formal announcement from the Air Force clearing the launch to occur has not been made.

The next major event leading up tonight's flight will be starting the Terminal Countdown at 8:01 p.m. EDT. Officials scrubbed the launch last night before starting the count.

The launch time remains set for 11:01 p.m. EDT, the opening of a 29-minute window. Weather forecasters say there is less than a 10 percent chance conditions would halt the launch.

1910 GMT (3:10 p.m. EDT)

The mobile service tower has been rolled away from a Boeing Delta 2 rocket at Cape Canaveral Air Force Station's pad 17A in preparation for another launch attempt tonight. Meetings, however, are still underway to verify the ground equipment problem last night has been fixed and the mission can go off as planned, a spokeswoman said.

If the launch is cleared, liftoff will occur during a window of 11:01 to 11:30 p.m. EDT (0301-0330 GMT). Air Force weather forecasters are predicting near-perfect conditions tonight.

0137 GMT (9:37 p.m. EDT)

A problem with ground support equipment has caused the U.S. Air Force to call off tonight's attempt to launch a Boeing Delta 2 rocket. The troublesome equipment is used to supply electrical power to the NAVSTAR Global Positioning System satellite while its waits for launch atop the Delta 2 rocket. The $42 million satellite itself is not believed to be the cause of the glitch.

Engineers are working to correct the problem and officials hope to make another try at launching the rocket in 24 hours. Saturday's launch window extends from 11:01 to 11:30 p.m. EDT (0301-0330 GMT Sunday).

"The Air Force launch director is very confident" the problem will be resolved in time for an attempt on Saturday night, Air Force spokeswoman Lt. Alana Austin said.

Air Force weather forecasters say there is a 90 percent chance of good weather Saturday night. The only slight concern is gusty ground winds.

If the Delta does not fly tomorrow, the Air Force will have to delay the mission until at least the middle of next week because of the upcoming space shuttle launch on Monday. Exact availability of the Air Force-run Eastern Range that governs all Cape launches was not immediately known, Austin said. However, it might be possible for the Delta to squeeze in another try on Wednesday provided the shuttle launches on schedule. A mission rehearsal is planned involving a Titan 4 rocket on April 28 and an Atlas rocket is slated for launch on May 3. The Range needs 48 hours between events to reconfigure its systems.

Be sure to watch our time-lapsed movie of today's mobile service tower retraction from around the Delta 2 rocket at launch pad 17A.

We will update this page as events dictate on Saturday. When the launch does occur, you can follow the final hours of the countdown and the 25-minute flight through our play-by-play reports.

0006 GMT (8:06 p.m. EDT)

Tonight's launch has been scrubbed. We will post more details as soon as we have them.

FRIDAY, APRIL 21, 2000
2305 GMT (7:05 p.m. EDT)

The countdown for tonight's launch of the Boeing Delta 2 rocket and GPS 2R-4 military navigation satellite has entered the planned one-hour built-in hold at T-minus 150 minutes. This hold allows the launch time a chance to catch up in preparations for starting the Terminal Countdown at 8:05 p.m. EDT. Launch remains scheduled for 11:05 p.m. EDT tonight from pad 17A at Cape Canaveral Air Force Station in Florida. The weather here in Central Florida is absolutely beautiful tonight.

1925 GMT (3:25 p.m. EDT)

At launch pad 17A, the mobile service tower has been retracted from around the Boeing-built Delta 2 rocket in readiness for tonight's planned launch of a Global Positioning System satellite. The ten-minute operation began at 2:50 p.m. EDT (1850 GMT).

The weather forecast looks good for tonight's 11:05 p.m. EDT (0305 GMT Saturday) liftoff, with meteorologists reporting only a 10 percent chance of a weather-related delay.

Check back later today for photos of the tower rollback, continuous countdown updates, and live streaming video coverage of the liftoff.

THURSDAY, APRIL 20, 2000
2300 GMT (7:00 p.m. EDT)

A Boeing Delta 2 rocket today was cleared for launch on Friday evening to deliver a needed replacement satellite into space for the U.S. Air Force's Global Positioning System.

Boeing and Air Force officials this morning completed the traditional Launch Readiness Review to determine if the rocket, satellite and ground systems were prepared for the mission. No significant problems were uncovered and the launch was cleared to go forward as planned.

Liftoff is planned for 11:05 p.m. EDT Friday (0305 GMT Saturday) from pad 17A at Cape Canaveral Air Force Station in east-central Florida. There will be a 30-minute window extending to 11:35 p.m. in which to launch the rocket before having to wait 24 hours.

Weather forecasters are optimistic conditions will allow the launch to go off on schedule. There is only a 20 percent chance of weather problems. The main concern will be thunderstorm anvil clouds, which might develop near a weather front expected to approach the Cape late Friday. If the clouds move within 10 nautical miles of the rocket's flight path, the launch would have to be delayed. Such electrically-charged clouds are troublesome because they could cause the rocket to trigger lightning, potentially destroying itself.

At liftoff time, Air Force Launch Weather Officer Joel Tumbiolo predicts a few clouds at 3,000 feet and scattered clouds at 25,000 feet, visibility of 10 miles or better, west-southwesterly winds 15 gusting to 20 knots, a temperature of 74 to 76 degrees F and relative humidity of 50 percent.

If the launch is delayed until Saturday night for some reason, there is a 90 percent chance of acceptable conditions with the only concern being gusty ground winds.

The passenger for this 278th Delta rocket launch is formally known as the Navigation Signal Timing and Ranging Global Positioning System Block 2R-4 satellite. More simply put, it is NAVSTAR GPS 2R-4.

The $42 million craft is the fourth in a series of advanced GPS satellites built by Lockheed Martin Space Systems to replace older spacecraft in the Air Force's navigation constellation. The GPS network relies on 24 primary satellites orbiting 10,900 miles above Earth, providing highly accurate position, speed and timing information to military forces around the world.

GPS 2R-4 is slated to take over for the failed GPS 2-1 satellite, which reached the end of its life on March 26 after suffering a shutdown of its onboard reaction wheels need for orienting in space. The Air Force decommissioned the satellite -- the first GPS spacecraft launched to form the current constellation 11 years ago -- on April 14.

Read our launch preview story for further details on the satellite, rocket and the mission. This will be Boeing's third launch in 2000 and second to occur from Cape Canaveral.

On Friday, Boeing workers plan to retract the 12-story mobile service tower from around the rocket at about 3 p.m. EDT. The terminal countdown will be started at T-minus 150 minutes at 8:05 p.m. EDT. Two built-in hold are scheduled at T-minus 20 minutes and T-minus 4 for a total duration of 30 minutes. That will lead to the opening of the launch window at 11:05 p.m. EDT.

Check back on Friday for updates throughout the day and live continuous reports during the final three hours of the countdown and 25-minute long launch.