BY JUSTIN RAY

Follow the countdown and launch of the Boeing Delta 2 rocket with NASA's Mars Exploration Rover-A. Reload this page for the very latest on the mission.

TUESDAY, JUNE 10, 2003
1859 GMT (2:59 p.m. EDT)

The crew of the International Space Station were not able to see today's launch from their orbital perch, according to NASA launch commentator George Diller. The space station was passing over Georgia at the time of lift off and it was thought they might catch a glimpse of the rocket's climb to orbit. They were however said to be "delighted" at the news of the successful launch.

Video coverage for subscribers only:
   VIDEO: MARS ROVER SPIRIT LAUNCHED QT
   VIDEO: SPACEFLIGHT NOW LAUNCH VIEW FROM PRESS AREA QT
   VIDEO: TRACKING CAMERA VIEW FROM PATRICK AFB QT
   VIDEO: POWERFUL TRACKER FOLLOWS THE ROCKET QT
   VIDEO: CAPE CANAVERAL PRESS SITE 1 REPLAY QT
   VIDEO: VIEW FROM THE SKID STRIP RUNWAY QT
   VIDEO: POST-LAUNCH NEWS CONFERENCE QT
   VIDEO: NAMING CEREMONY FOR MARS ROVERS QT
   VIDEO: WEATHER SCRUBS SUNDAY LAUNCH ATTEMPT QT
   VIDEO: PRE-LAUNCH NEWS CONFERENCE QT
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1858 GMT (2:58 p.m. EDT)

Flight controllers at NASA's Jet Propulsion Laboratory in California appear happy with the health of the Spirit Mars Rover and its cruise spacecraft.

1850 GMT (2:50 p.m. EDT)

Today's official lift off time was 1:58:46.773 p.m. EDT (1758:46.773 GMT).

1848 GMT (2:48 p.m. EDT)

SPACECRAFT ACQUISITION! A ground station in Canberra, Australia, has picked up the signal from NASA's Mars Exploration Rover "Spirit".

1835 GMT (2:35 p.m. EDT)

T+plus 36 minutes, 40 seconds. SPACECRAFT SEPARATION! NASA's Mars Exploration Rover "Spirit" is headed for the Red Planet! The spacecraft has been released from the Delta rocket's third stage following launch today from Cape Canaveral. Liftoff occurred at 1:58:47 p.m. EDT.

Later this hour, flight controllers expect to establish contact with the rover to assess its health. A post-launch news conference is scheduled for around 4 p.m. EDT to give mission managers a chance to review the Delta 2 rocket's flight and status of the rover.

1830 GMT (2:30 p.m. EDT)

T+plus 32 minutes. Burnout of the solid-fueled third stage should have occurred, completing the powered phase of launch for Mars rover "Spirit" aboard the Delta 2 rocket. Separation of the payload is about four minutes away.

1829 GMT (2:29 p.m. EDT)

T+plus 30 minutes, 30 seconds. The third stage has ignited!

1828 GMT (2:28 p.m. EDT)

T+plus 30 minutes. The solid-fueled Star 48B third stage with the attached Mars rover has separated from the Delta 2's second stage.

1827 GMT (2:27 p.m. EDT)

T+plus 29 minutes. SECO 2. The liquid-fueled Aerojet AJ10-118K engine has fired, raising the orbital altitude. Over the next minute, tiny thrusters on the side of the rocket will be fired to spin up the vehicle in preparation for stage separation.

1825 GMT (2:25 p.m. EDT)

T+plus 26 minutes, 40 seconds. Second stage engine has re-ignited to raise the current orbit of the vehicle and Mars rover as the launch sequence continues this afternoon.

1810 GMT (2:10 p.m. EDT)

T+plus 12 minutes. The rocket is coasting until the second stage restarts at T+plus 26 minutes, 29 seconds. That will be followed by separation between the second and third stages. The upper stage will burn to propel the Mars Rover into its escape trajectory for the trek to Mars. Deployment of the payload to complete the launch is expected at T+plus 36 minutes, 20 seconds.

1808 GMT (2:08 p.m. EDT)

T+plus 10 minutes. SECO 1. Confirmation that the second stage engine has shut down as planned. The Delta 2 rocket with Mars rover has arrived in a preliminary orbit around Earth following launch this afternoon.

1807 GMT (2:07 p.m. EDT)

T+plus 9 minutes. Just under a minute remaining in this first firing of the second stage engine.

1805 GMT (2:05 p.m. EDT)

T+plus 6 minutes, 30 seconds. Good chamber pressure reported on the second stage engine.

1804 GMT (2:04 p.m. EDT)

T+plus 5 minutes, 25 seconds. Second stage engine is burning normally.

1803 GMT (2:03 p.m. EDT)

T+plus 5 minutes. The protective payload fairing enclosing the Mars rover spacecraft atop the rocket has separated.

1803 GMT (2:03 p.m. EDT)

T+plus 4 minutes, 45 seconds. The Aerojet AJ118-K liquid-fueled second stage engine has ignited to continue the push to orbit

1803 GMT (2:03 p.m. EDT)

T+plus 4 minutes, 36 seconds. MECO. The Delta 2 rocket's Rocketdyne RS-27A first stage main engine has shut down and the spent stage has been jettisoned.

1802 GMT (2:02 p.m. EDT)

T+plus 3 minutes, 30 seconds. First stage engine continues to fire.

1801 GMT (2:01 p.m. EDT)

T+plus 2 minutes, 15 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.

1800 GMT (2:00 p.m. EDT)

T+plus 1 minute, 25 seconds. The air-start solid motors are building up to maximum thrust.

1759 GMT (1:59 p.m. EDT)

T+plus 1 minute, 10 seconds. All six ground-start solid rocket boosters have burned out and separated. The three remaining motors strapped to first stage have ignited to continue assisting the rocket's RS-27A main engine on the climb to space.

1759 GMT (1:59 p.m. EDT)

T+plus 53 seconds. Vehicle has passed maximum dynamic pressure.

1759 GMT (1:59 p.m. EDT)

T+plus 30 seconds. The six ground-lit solid rocket motors have passed the period of maximum thrust.

1759 GMT (1:59 p.m. EDT)

T+plus 20 seconds. The 126-foot tall Delta rocket has maneuvered to the proper course -- heading eastward away from the launch pad at Cape Canaveral on a flight azimuth of 93 degrees.

1758:47 GMT (1:58:47 p.m. EDT)

LIFTOFF! Liftoff of NASA's Spirit rover -- taking the next leap in exploring the mysterious past of the Red Planet. And the Boeing Delta 2 rocket has cleared the tower!

1758 GMT (1:58 p.m. EDT)

T-minus 30 seconds. Hydraulics and electronics status checks are 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-lit solid rocket motors then light at T-0 for liftoff.

1757 GMT (1:57 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.

1756 GMT (1:56 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.

1756 GMT (1:56 p.m. EDT)

T-minus 2 minutes, 25 seconds. The Mars rover spacecraft has been declared "go" for launch.

1755 GMT (1:55 p.m. EDT)

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

1755 GMT (1:55 p.m. EDT)

T-minus 3 minutes, 40 seconds and counting. The Delta 2 rocket's systems are now transferring to internal power for launch.

1754:47 GMT (1:54:47 p.m. EDT)

T-minus 4 minutes and counting. The final phase of the countdown has commenced! Launch of the Mars Exploration Rover-A remains set to occur at 1:58:47 p.m. EDT from pad 17A at Cape Canaveral Air Force Station in Florida. No problems are standing in the way of the 298th Delta rocket launch.

1754 GMT (1:54 p.m. EDT)

Now less than five minutes from launch! Standing by for release of the hold in just under a minute.

1753 GMT (1:53 p.m. EDT)

The Mars rover spacecraft cargo atop the Delta 2 rocket is now switching to internal power for launch.

1751 GMT (1:51 p.m. EDT)

The launch team has been polled by the Boeing Launch Conductor for a "go" to proceed with the countdown. No problems were reported. The team is now receiving final instructions on countdown procedures.

1749 GMT (1:49 p.m. EDT)

The crew of the International Space Station will be passing over Georgia at the time of today's first launch opportunity. The may catch a glimpse of the Delta 2 rocket's climb to orbit about 90 seconds into flight according to NASA launch commentator George Diller.

1744 GMT (1:44 p.m. EDT)

T-minus 4 minutes and holding. The countdown has entered the final planned hold point for today's launch attempt. During this planned 10-minute, 47-second hold, officials will poll the various team members in the soft blockhouse, Range Operations Control Center and Mission Directors Center. If all systems are go, the countdown will resume for liftoff at 1:58:47 p.m. EDT.

1741 GMT (1:41 p.m. EDT)

The first stage fuel tank vent is being closed and the tank is being pressurized for launch. And the spacecraft safe and arm devices have been armed.

1739 GMT (1:39 p.m. EDT)

The U.S. Air Force range is "green" for launch.

1738 GMT (1:38 p.m. EDT)

T-minus 10 minutes and counting.

1736 GMT (1:36 p.m. EDT)

Inhibited checks are now beginning for the Range Safety command destruct receivers that would be used in destroying the Delta rocket should the vehicle veer off course and malfunction during the launch.

1728 GMT (1:28 p.m. EDT)

T-minus 20 minutes and counting. The planned hold in the countdown has been released. Clocks will now tick down to T-minus 4 minutes where the final hold is planned.

1726 GMT (1:26 p.m. EDT)

The Boeing and NASA readiness polls of the launch team have been completed. No technical problems were reported. So the "go" was given to resume the countdown at 1:28:47 p.m. EDT as planned.

1718 GMT (1:18 p.m. EDT)

Now half-way through this built-in hold at T-minus 20 minutes.

1715 GMT (1:15 p.m. EDT)

Launch Weather Officer Joel Tumbiolo has just completed a weather briefing for the launch team. He reports that conditions are currently "green" and are expected to remain so throughout the remainder of the count.

1708 GMT (1:08 p.m. EDT)

T-minus 20 minutes and holding. The countdown has entered the 20-minute built-in hold. This pause is designed to give the launch team a chance to work any problems or catch up on activities that might be running behind schedule. Engineers will also have time to examine all the date from the just-completed steering tests. Launch is slated for 1:58:47 p.m. EDT from pad 17A at Cape Canaveral Air Force Station, Florida.

In the past couple of minutes, gimbal checks of the nozzles on the Delta 2 first and second stage engines have been completed.

1759 GMT (1:59 p.m. EDT)

Liftoff is now just 60 minutes away. The launch team will soon begin 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.

And in the next few minutes, RF link tests between the Range and rocket are scheduled.

The launch team is dealing with two range issues involving problems with a communications link between the launch site an Jupiter Inlet, Florida, and a radar in the Cape Canaveral area. Both issues are expected to be resolved in time for today's launch.

1640 GMT (12:40 p.m. EDT)

The launch team reports that the Delta 2 rocket's first stage liquid oxygen tank has been loaded. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket is now fully fueled for launch. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel along with the liquid oxygen over the past hour. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels a few days ago; the third stage and nine strap-on booster rockets are solid-propellant.

1619 GMT (12:19 p.m. EDT)

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

Once the liquid oxygen tank reaches the 95 percent full level, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the tank.

1614 GMT (12:14 p.m. EDT)

Super-cold liquid oxygen, chilled to Minus-298 degrees F, is being pumped into the first stage of the Boeing Delta 2 rocket as the countdown continues for today's 1:58:47 p.m. EDT launch attempt. The liquid oxygen is flowing from a storage tank at pad 17A, through plumbing and into the bottom of the rocket. The LOX and the RP-1 kerosene fuel loaded aboard the vehicle in the last half-hour will be consumed by the first stage main engine.

1613 GMT (12:13 p.m. EDT)

The "go" has been given to the launch team to begin preparations for loading the rocket's first stage liquid oxygen tank.

1543 GMT (11:43 a.m. EDT)

The first stage fuel tank of the Boeing Delta 2 rocket has been fully loaded for today's planned 1:58:47 p.m. EDT liftoff from Cape Canaveral Air Force Station in Florida.

The RP-1 propellant will be guzzled along with liquid oxygen -- to be pumped into the rocket a little later -- by the first stage Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

1532 GMT (11:32 a.m. EDT)

This approximate 20-minute process to load the rocket's first stage with about 10,000 gallons of refined kerosene fuel continues without any problems reported. Just over 5,000 gallons have been loaded to this point.

1524 GMT (11:24 a.m. EDT)

The Boeing launch team has completed the steps to prepare for loading the Delta 2 rocket's first stage fuel tank. After verifying valves, sensors, flow meters and equipment are ready, the highly refined kerosene fuel started flowing into the vehicle.

About 10,000 gallons of a highly refined kerosene propellant, called RP-1, are being pumped into the base of the rocket from a storage tank at pad 17A.

The stage's liquid oxygen tank will be filled a little later in the countdown.

1458 GMT (10:58 a.m. EDT)

T-minus 150 minutes and counting. The terminal countdown has begun for the launch of the Boeing Delta 2 rocket carrying NASA's Mars Exploration Rover-A, which has been named Spirit. Over the next three hours, the launch team will ready the three-stage rocket, payload and ground support systems for the planned 1:58:47 p.m. EDT (1758:47 GMT) blastoff from pad 17A at Cape Canaveral Air Force Station in Florida.

With the countdown underway, the Complex 17 area will be verified cleared of workers as a safety precaution. A warning horn will be sounded at the seaside complex to alert personnel to depart and head back to road blocks.

Upcoming in the next few minutes, launch team members in the Delta Operations Building, or "soft blockhouse", located about eight miles west of the pad will oversee the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages; and the second stage fuel and oxidizer tanks will be pressurized for launch. In addition, the Delta's onboard guidance computer -- called the Redundant Inertial Flight Control Assembly or RIFCA -- will be turned on and configured for the mission.

The loading of 10,000 gallons of RP-1 fuel into the first stage is scheduled to start about 20 minutes from now.

The weather outlook appears much better today than the past couple of days. There is a 70 percent chance of favorable conditions at launch time. 1449 GMT (10:49 a.m. EDT)

The launch team has been polled to ensure all the console operators are in position and ready to continue with the countdown this morning. No issues were reported. The Terminal Countdown is scheduled to commence in about 9 minutes.

1358 GMT (9:58 a.m. EDT)

T-minus 150 minutes and holding. The countdown has entered the planned 60-minute built-in hold for today's 1:58:47 p.m. EDT liftoff of Delta 2 from Cape Canaveral.

1258 GMT (8:58 a.m. EDT)

Launch Weather Officer Joel Tumbiolo's latest forecast, issued this morning, has been posted here.

1145 GMT (7:45 a.m. EDT)

At launch complex 17A the mobile service tower is being retracted from around the Delta 2 rocket in preparation for today's planned launch of NASA's first Mars Exploration Rover "Spirit." Lift off remains scheduled for 1:58:47 p.m. EDT (1758:47 GMT).

0230 GMT (10:30 p.m. EDT Mon.)

If NASA can catch a break with the weather, the space agency's Mars Exploration Rover "Spirit" will depart Earth at 1:58:47 p.m. EDT (1758:47 GMT) today for the seven-month cruise to the Red Planet. The liftoff was scrubbed for the past two days because of stormy weather conditions at Cape Canaveral launch site.

We have posted the launch events timeline for Tuesday's flight of the Boeing Delta 2 rocket carrying the Mars Exploration Rover-A. The times of key events during the ascent change slightly from day to day.

See the timeline for launch at 1:58:47 p.m. EDT.

See the timeline for launch at 2:36:49 p.m. EDT.

MONDAY, JUNE 9, 2003
1745 GMT (1:45 p.m. EDT)

The weather forecast for Tuesday's launch opportunity calls for just a 30 percent chance of not meeting the launch rules. See the full forecast here.

1428 GMT (10:28 a.m. EDT)

It will be another day before the Mars Exploration Rover "Spirit" begins its journey to the Red Planet. Liftoff has been scrubbed for today due to weather.

"Similar weather condition as experienced in yesterday's launch attempt are beginning and it is anticipated that thunderstorm conditions could be present in the launch pad vicinity by the launch time at 2 p.m.," NASA spokesman George Diller said in explaining the reason for today's postponement.

The launch is now targeted to occur at 1:58:47 p.m. EDT (1758:47 GMT) on Tuesday.

1414 GMT (10:14 a.m. EDT)

The launch times available for tomorrow are 1:58:47 p.m. EDT and 2:36:49 p.m. EDT. The weather forecast improves to a 70 percent chance of favorable conditions.

1411 GMT (10:11 a.m. EDT)

SCRUB! Today's launch attempt has been scrubbed because of a forecast for severe weather. The mobile service tower will be moved around the vehicle to protect the vehicle. It is the second day running that bad weather has delayed the launch of the first Mars Exploration Rover.

1402 GMT (10:02 a.m. EDT)

T-minus 150 minutes and holding. Clocks enter a planned 60-minute built-in hold at this point in the countdown for today's 2:02:23 p.m. EDT liftoff of Delta 2 from Cape Canaveral.

Holds are added to the countdown to give workers a chance to catch up on any activities that may be running behind.

Over the next hour, the entire launch team and management will be seated at their consoles. A series of polls will be conducted to verify all is in readiness for entering Terminal Count at end of the built-in hold.

1255 GMT (8:55 a.m. EDT)

The launch team is gearing up for the second attempt to deploy NASA's Mars Exploration Rover "Spirit" to the Red Planet using Boeing's Delta 2 rocket from Cape Canaveral. Liftoff is scheduled to occur at precisely 2:02:23 p.m. EDT (1802:23 GMT) today.

At pad 17A, the mobile service tower is back in the launch position.

There are no technical problems being worked this morning, a NASA spokesman said. The only concern is the weather forecast, which is similar to the forecast on Sunday.

During that first launch attempt on Sunday, officials were worried about severe thunderstorms hitting the Cape while the Delta 2 rocket was sitting fully fueled on the pad without the protection from its mobile service tower. So the countdown was scrubbed before loading liquid oxygen aboard the vehicle and safing operations were started in advance of the storms' arrival.

1245 GMT (8:45 a.m. EDT)

Launch Weather Officer Joel Tumbiolo has issued his latest forecast this morning, which is still calling for a 60 percent chance of unacceptable conditions for today's launch attempt. See the full forecast here.

SUNDAY, JUNE 8, 2003
2230 GMT (6:30 p.m. EDT)

We have posted the launch events timeline for Monday's flight of the Boeing Delta 2 rocket carrying the Mars Exploration Rover-A. The times of key events during the ascent change slightly from day to day.

See the timeline for launch at 2:02:23 p.m. EDT.

See the timeline for launch at 2:40:30 p.m. EDT.

1827 GMT (2:27 p.m. EDT)

The rain is falling around the Cape area now. The mobile tower is near the rocket but not completely enclosing the vehicle.

1801 GMT (2:01 p.m. EDT)

The mobile service tower is currently being rolled back into position around the Delta 2 rocket.

1735 GMT (1:35 p.m. EDT)

The launch weather forecast for Monday's launch attempt and the backup opportunities on Tuesday and Wednesday is available here.

1640 GMT (12:40 p.m. EDT)

The RP-1 fuel is now being offloaded from the Delta 2 as launch controllers work to safe the rocket before severe weather hits the Cape Canaveral area. An approaching line of heavy thunderstorms is currently about 40 miles from the launch site.

1630 GMT (12:30 p.m. EDT)

The launch of NASA's Mars Exploration Rover "Spirit" has been postponed 24 hours due to severe weather headed for Cape Canaveral from the west. Workers are preparing to begin draining the RP-1 fuel from the first stage of the Delta 2 rocket. The mobile service tower will be rolled back around the rocket as soon as possible this afternoon to protect the vehicle and payload from the high winds and weather expected.

Liftoff is rescheduled for 2:02:23 p.m. EDT (1802:23 GMT) Monday.

1626 GMT (12:26 p.m. EDT)

Tomorrow's launch times are 2:02:23 p.m. EDT and 2:40:30 p.m. EDT.

The weather forecast for those liftoff opportunities calls for a 60 percent chance of unacceptable conditions.

The forecast on Tuesday improves to a 40 percent chance of bad weather.

1621 GMT (12:21 p.m. EDT)

SCRUB! Today's launch attempt has been called off due to thunderstorms headed for Cape Canaveral this afternoon. Boeing Mission Director Rich Murphy and NASA Launch Manager Omar Baez concluded that it was not safe to continue with the countdown and load liquid oxygen with the possibility of severe weather in the area. So the mobile service tower will be rolled back around the vehicle later today to protect the Delta 2 rocket and Mars Exploration Rover from the conditions.

1618 GMT (12:18 p.m. EDT)

The launch team reports that the Delta rocket's RIFCA guidance computer has been turned on for flight.

So the countdown clock does continue to tick while mission managers discuss the weather forecast.

1616 GMT (12:16 p.m. EDT)

The weather forecast has taken a turn for the worse. Thunderstorms with unacceptable clouds and strong winds later today has prompted the weather team to change the odds of scrubbing the launch to 80 percent. Managers are discussing whether the protective mobile service tower should be rolled back around the vehicle to shield the rocket from those strong winds.

1615 GMT (12:15 p.m. EDT)

The first stage fuel tank of the Boeing Delta 2 rocket has been fully loaded for today's planned 2:05:55 p.m. EDT liftoff from Cape Canaveral Air Force Station in Florida. The tank was filled with a highly refined kerosene, called RP-1, during a 20-minute, 5-second process that concluded at 12:15 p.m. EDT.

1609 GMT (12:09 p.m. EDT)

The launch team has computed that the full load for the first stage fuel tank is 9,971 gallons. Over 8,000 gallons are already aboard.

Once the tank is filled with 9,770 gallons, or 98 percent, the "rapid load" valve will be closed and the slower "fine load" phase will continue top off the tank.

The propellant will be guzzled along with liquid oxygen -- to be pumped into the rocket a little later -- by the first stage Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

1606 GMT (12:06 p.m. EDT)

Now two hours from launch.

1604 GMT (12:04 p.m. EDT)

This approximate 20-minute process to load the rocket's first stage with about 10,000 gallons of refined kerosene fuel continues without any problems reported. Just over 5,000 gallons have been loaded to this point.

1554 GMT (11:54 a.m. EDT)

The Boeing launch team has completed the steps to prepare for loading the Delta 2 rocket's first stage fuel tank. After verifying valves, sensors, flow meters and equipment are ready, the highly refined kerosene fuel started flowing into the vehicle. The work started a little later than expected.

About 10,000 gallons of a highly refined kerosene propellant, called RP-1, are being pumped into the base of the rocket from a storage tank at pad 17A.

The stage's liquid oxygen tank will be filled a little later in the countdown.

1520 GMT (11:20 a.m. EDT)

The countdown continues to run smoothly for today's planned launch of the first Mars Exploration Rover atop a Delta 2 rocket. Our detailed countdown coverage will begin shortly from the Cape Canaveral press site.

1506 GMT (11:06 a.m. EDT)

T-minus 150 minutes and counting. The terminal countdown has begun for the launch of the Boeing Delta 2 rocket carrying NASA's Mars Exploration Rover-A, which has been named Spirit. Over the next three hours, the launch team will ready the three-stage rocket, payload and ground support systems for the planned 2:05:55 p.m. EDT (1805:55 GMT) blastoff from pad 17A at Cape Canaveral Air Force Station in Florida.

With the countdown underway, the Complex 17 area will be verified cleared of workers as a safety precaution. A warning horn will be sounded at the seaside complex to alert personnel to depart and head back to road blocks.

Upcoming in the next few minutes, launch team members in the Delta Operations Building, or "soft blockhouse", located about eight miles west of the pad will oversee the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages; and the second stage fuel and oxidizer tanks will be pressurized for launch. In addition, the Delta's onboard guidance computer -- called the Redundant Inertial Flight Control Assembly or RIFCA -- will be turned on and configured for the mission.

The loading of 10,000 gallons of RP-1 fuel into the first stage is scheduled to start about 20 minutes from now.

1421 GMT (10:21 a.m. EDT)

NASA's twin Mars Exploration Rover have been named Spirit and Opportunity following a contest by schoolchildren. Sofi Collis, a 9-year old third grader from Scottsdale, Arizona, submitted the winning suggestion among nearly 10,000 contest entries. Born in Siberia, Sofi was adopted and moved the United States when she was two years old.

The naming contest was managed for NASA by the LEGO Company.

1406 GMT (10:06 a.m. EDT)

T-minus 150 minutes and holding. Clocks enter a planned 60-minute built-in hold at this point in the countdown for today's 2:05:55 p.m. EDT liftoff of Delta 2 from Cape Canaveral.

Holds are added to the countdown to give workers a chance to catch up on any activities that may be running behind.

Over the next hour, the entire launch team and management will be seated at their consoles. A series of polls will be conducted to verify all is in readiness for entering Terminal Count at end of the built-in hold.

The weather forecast continues to call for a 60 percent chance of conditions prohibiting liftoff today. Clouds and lightning from thunderstorms, expected to develop later today, are the main concerns.

1134 GMT (7:34 a.m. EDT)

The mobile service tower is now fully retracted from the Delta 2 rocket. Workers will now get the tower secured into its launch position and configure the pad for liftoff. The Terminal Countdown remains scheduled to begin at 11:06 a.m. EDT.

Meanwhile, NASA Administrator Sean O'Keefe will hold an event at 10 a.m. this morning at the Kennedy Space Center press site to reveal the names given to the two Mars Exploration Rovers. O'Keefe will be joined by LEGO Senior Vice President Brad Justus and the elementary school student who submitted the rover's names. The winning names were selected from more than 10,000 student entries in a contest managed for NASA by the LEGO Company.

1110 GMT (7:10 a.m. EDT)

The metal cocoon-like mobile service tower enclosing the Boeing Delta 2 rocket at Cape Canaveral's pad 17A is being retracted in preparation for today's 2:06 p.m. EDT (1806 GMT) launch of the Mars Exploration Rover-A spacecraft.

The tower structure is used to assemble the rocket on the seaside pad and provide weather protection. Rollback of the tower is a major milestone on the road to launch.

SUNDAY, JUNE 8, 2003
0100 GMT (9:00 p.m. EDT Sat.)

After a three-year, $800 million campaign to dispatch a pair of Mars Exploration Rovers to the Red Planet, the first craft is just hours away from launch.

Liftoff is scheduled for 2:05:55 p.m. EDT (1805:55 GMT) aboard a Boeing Delta 2 rocket from Cape Canaveral.

Launch day activities will begin around 1 a.m. as workers put the final touches on the MER-A rover spacecraft at launch pad 17A. The mobile service tower enclosing the rocket is expected to roll away from the vehicle for launch around 6 a.m. Engineers will start powering up the rocket and spacecraft at 7:30 a.m.

The Terminal Countdown should commence at 11:05:55 a.m. from the T-minus 150 minute mark.

The loading of RP-1 fuel into the first stage should start at 11:26 a.m. That will be followed by the pumping of super-cold liquid oxygen into the first stage at 12:21 p.m. EDT.

Two planned holds -- T-minus 20 minutes and T-minus 4 minutes -- will lead to the instantaneous liftoff time at the end of the three-hour countdown sequence.

If weather or a minor technical problem prevents an on-time liftoff, officials can re-target for a second launch opportunity at 2:44:07 p.m. EDT (1844:07 GMT).

We will post live updates throughout the day on this page starting with confirmation of tower rollback.

SATURDAY, JUNE 7, 2003
1800 GMT (2:00 p.m. EDT)

The Launch Readiness Review was successfully completed earlier today, clearing the way for tomorrow's countdown and flight of the Boeing Delta 2 rocket carrying the Mars Exploration Rover-A. There are no technical problems being reported, however, the weather remains a concern. Forecasters say there is a 60 percent chance clouds or lightning from thunderstorms will prevent liftoff on Sunday.

The two instantaneous launch times on Sunday are 2:05:55 p.m. EDT (1805:55 GMT) and 2:44:07 p.m. EDT (1844:07 GMT).

1225 GMT (8:25 a.m. EDT)

The latest version of the launch weather forecast is available here.

Managers will hold the Launch Readiness Review today at Cape Canaveral to give approval to begin the countdown early Sunday. A pre-launch news conference is scheduled for 1 p.m. EDT today. Look here for a full countdown preview later tonight.

FRIDAY, JUNE 6, 2003
1350 GMT (9:50 a.m. EDT)

Today's updated launch weather forecast is available here.

THURSDAY, JUNE 5, 2003

The Boeing Delta 2 rocket's second stage was being loaded with its supply of storable hypergolic propellants today at launch pad 17A. The stage's Aerojet AJ10-118K engine consumes a fuel called Aerozine 50, which is a mixture of hydrazine and dimethyl hydrazine, and nitrogen tetroxide as an oxidizer.

Earlier this morning, the Mission Dress Rehearsal was successfully held.

"Everything is going just fine," NASA spokesman George Diller said.

The latest version of the launch weather forecast, which was issued today, is posted here.

Launch remains scheduled for 2:05:55 p.m. EDT (1805:55 GMT) on Sunday. A second instantaneous launch time is available at 2:44:07 p.m. EDT (1844:07 GMT), if needed.

Watch this page for continuing updates on the Mars Exploration Rover-A launch campaign. We will be providing live play-by-play reports during Sunday's countdown and flight of the Boeing Delta 2 rocket.

WEDNESDAY, JUNE 4, 2003
1610 GMT (12:10 p.m. EDT)

NASA's Mars Exploration Rover-A has been cleared for launch Sunday at 2:05:55 p.m. EDT (1805:55 GMT) following the Flight Readiness Review held this morning.

"Everything is resolved," NASA spokesman George Diller said.

Officials had delayed the launch three days to give more time to complete pre-flight reviews.

"Now the wildcard will be the weather," Diller added. Air Force meteorologists are calling for a 60 percent chance that cumulus clouds and lightning from afternoon thunderstorms could scrub the launch.

Workers will fuel the rocket's second stage with its load of storable propellants on Thursday.

1315 GMT (9:15 a.m. EDT)

The early weather forecast was issued by Launch Weather Officer Joel Tumbiolo this morning. Tumbiolo is calling for a 60 percent chance of bad weather during the launch opportunities on Sunday, Monday and Tuesday. See the full forecast here.

TUESDAY, JUNE 3, 2003

NASA has put off making the final decision, which had been expected today, of when to launch the Mars Exploration Rover-A. The Flight Readiness Review is scheduled for Wednesday morning. An announcement on the launch date could be made then. For now, workers continue to prepare for liftoff on Sunday.

MONDAY, JUNE 2, 2003

Senior NASA officials meeting on Tuesday will review plans to launch the agency's first of two rovers to Mars this month, deciding whether to press ahead with the targeted June 8 liftoff from Cape Canaveral.

Launch was delayed from June 5 to give managers more time to perform their deliberations before committing to flight.

An announcement on the firm launch date isn't expected until late Tuesday afternoon. We'll update this page as soon as the news is available.

TUESDAY, MAY 27, 2003

NASA has postponed the launch of its first Mars Exploration Rover at least three days to give managers more time to complete pre-flight engineering reviews. The liftoff is now targeted to occur June 8 aboard a Boeing Delta 2 rocket from Cape Canaveral Air Force Station in Florida.

The liftoff, which had been scheduled for June 5, is now targeted to occur at 2:05:55 p.m. EDT (1805:55 GMT) June 8 aboard a Boeing Delta 2 rocket from Cape Canaveral Air Force Station in Florida.

Read our full story.

NASA has until June 19 to launch the first Mars Exploration Rover. Two instantaneous launch times are available each day during the planetary alignment window. See the complete launch time chart here.