BY JUSTIN RAY

Follow the countdown and launch of the Boeing Delta 2 rocket with the U.S. Air Force's GPS 2R-12 navigation spacecraft. Reload this page for the very latest on the mission.

Additional coverage for subscribers:
VIDEO: DELTA 2 ROCKET BLASTS OFF WITH GPS 2R-12 QT
VIDEO: LIFTOFF AS SEEN FROM PRESS SITE QT
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WEDNESDAY, JUNE 23, 2004

Finally winning the battle over Florida's summertime weather after three earlier losses, a Boeing Delta 2 rocket roared to space Wednesday and deployed a Global Positioning System military navigation satellite in a mission dedicated to the memory of President Ronald Reagan. Read our full story.

2325 GMT (7:25 p.m. EDT)

Preliminary data indicates the GPS spacecraft was launched into a good orbit this evening with an apogee of 11,016 miles, perigee of 101.4 miles and inclination of 38.99 degrees to the equator.

The spacecraft will use its onboard kick motor to circularize the orbit at 11,000 miles and raise the inclination to 55 degrees to join the GPS constellation.

This marks the 111th successful Delta 2 rocket launch out of 113 flights since 1989 and extends the string of consecutive successes to 58 dating back to 1997. It was the third Delta launch in 2004.

The next Delta 2 launch will occur from Vandenberg Air Force Base in California no sooner than July 10 when NASA's Aura atmospheric research satellite is carried into polar orbit. Upcoming at Cape Canaveral is the planned July 30 launch of NASA's MESSENGER probe to orbit the planet Merucry.

2319 GMT (7:19 p.m. EDT)

T+plus 25 minutes, 35 seconds. SPACECRAFT SEPARATION! The U.S. Air Force's NAVSTAR Global Positioning System Block 2R-12 spacecraft has been released from the Boeing Delta 2 rocket's third stage to complete today's launch from Cape Canaveral.

The GPS satellite will boost itself into the GPS constellation in the coming days to begin checkout period by ground controllers. The $45 million craft will fill the Plane F, Slot 4 position in the GPS network. After on-orbit testing, GPS 2R-12, also known as SVN-60, is expected to enter service next month.

The new satellite replaces the ailing GPS 2A-16 craft launched in November 1992.

This concludes our live play-by-play coverage of today's mission. Check back later for a wrap-up story, pictures and a movie clip of the launch.

2318 GMT (7:18 p.m. EDT)

T+plus 24 minutes, 20 seconds. About one minute remains until spacecraft deploy.

2317 GMT (7:17 p.m. EDT)

T+plus 23 minutes, 29 seconds. The third stage has burned out of its solid fuel, ending the Delta 2 rocket's powered flight for this evening's launch of the GPS 2R-12 spaeccraft. Separation of the payload is about two minutes away.

About two seconds after release of the satellite, a small "yo" will be strung out from the third stage put the motor into a tumble and keep it from running into the GPS spacecraft.

2316 GMT (7:16 p.m. EDT)

T+plus 22 minutes, 54 seconds. The SECO 2 orbit was on target.

2316 GMT (7:16 p.m. EDT)

T+plus 22 minutes, 45 seconds. The chamber pressure on the third stage is reported normal as the motor continues to fire.

2316 GMT (7:16 p.m. EDT)

T+plus 22 minutes, 4 seconds. Third stage ignition! The Thiokol Star 48B motor is firing to propel the GPS 2R-12 satellite into its targeted orbit for this launch.

2315 GMT (7:15 p.m. EDT)

T+plus 21 minutes, 30 seconds. The solid-fueled third stage has separated from the Delta 2's second stage.

As the launch sequence continues with the third stage burn and subsequent deployment of the GPS 2R-12 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.

2315 GMT (7:15 p.m. EDT)

T+plus 21 minutes, 25 seconds. Spin up has begun.

2314 GMT (7:14 p.m. EDT)

T+plus 20 minutes, 35 seconds. SECO 2. 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.

2314 GMT (7:14 p.m. EDT)

T+plus 20 minutes, 15 seconds. Engine chamber pressures look good as the engine continues to fire.

2313 GMT (7:13 p.m. EDT)

T+plus 19 minutes, 59 seconds. Engine ignition! The Delta 2 rocket's second stage engine has restarted to nudge the vehicle into a higher orbit.

2313 GMT (7:13 p.m. EDT)

T+plus 19 minutes, 45 seconds. Ascension has picked up the rocket's signal.

2313 GMT (7:13 p.m. EDT)

T+plus 19 minutes. Second stage restart is about one-minute away. Standing by to acquire telemetry from the rocket via the Ascension island tracking station in the central Atlantic Ocean.

2311 GMT (7:11 p.m. EDT)

T+plus 17 minutes. As this coast phase of the launch continues, you can see a map of the rocket's planned track here.

2309 GMT (7:09 p.m. EDT)

T+plus 15 minutes. The official liftoff time was 6:54:00.693 p.m. EDT.

2307 GMT (7:07 p.m. EDT)

T+plus 13 minutes, 10 seconds. The rocket has passed out of range from the Antigua tracking site. This begins an expected 7-minute telemetry blackout while the vehicle coasts in the parking orbit. The Ascension island station will provide live coverage during the upcoming restart of the second stage, the third stage firing and subsequent separation of the GPS satellite.

2307 GMT (7:07 p.m. EDT)

T+plus 13 minutes. The rocket has successfully achieved a parking orbit with an apogee of 211.57 miles, perigee of 94.4 miles and inclination of 36.90 degrees. Boeing says the orbit parameters are a "mirror image" of the predicted values.

2305 GMT (7:05 p.m. EDT)

T+plus 11 minutes, 30 seconds. Restart of second stage engine is expected at about T+plus 19 minutes, 56 seconds. The stage will fire for approximately 35 seconds to raise the orbit's high point, or apogee, by nearly 500 miles. 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 25 minutes.

2304 GMT (7:04 p.m. EDT)

T+plus 10 minutes, 56 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-12 has arrived in a preliminary orbit around Earth following launch this evening from Cape Canaveral. The vehicle will coast for the next nine minutes before the second stage is re-ignited.

2304 GMT (7:04 p.m. EDT)

T+plus 10 minutes, 50 seconds. Velocity has reached 16,700 mph.

2303 GMT (7:03 p.m. EDT)

T+plus 9 minutes. The rocket is now 97 miles in altitude, 1,200 miles downrange from the launch site, traveling at 15,300 mph.

2302 GMT (7:02 p.m. EDT)

T+plus 8 minutes, 45 seconds. The second stage has just over two minutes remaining in this burn.

2301 GMT (7:01 p.m. EDT)

T+plus 7 minutes, 50 seconds. The downrange tracking station on Antiqua island has acquired the rocket's signal.

2301 GMT (7:01 p.m. EDT)

T+plus 7 minutes, 40 seconds. 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.

2300 GMT (7:00 p.m. EDT)

T+plus 6 minutes, 20 seconds. The second stage engine continues to burn as expected.

2259 GMT (6:59 p.m. EDT)

T+plus 5 minutes, 50 seconds. Chamber pressures look good on the second stage engine.

2259 GMT (6:59 p.m. EDT)

T+plus 5 minutes, 35 seconds. The rocket remains on the proper trajectory. Altitude 75 miles, downrange distance 484 miles, traveling over 13,000 mph.

2259 GMT (6:59 p.m. EDT)

T+plus 5 minutes, 1 second. The 9.5-foot diameter protective payload fairing enclosing the GPS spacecraft atop the rocket has jettisoned in two halves.

2258 GMT (6:58 p.m. EDT)

T+plus 4 minutes, 45 seconds. The Aerojet AJ10-118K engine of the Delta 2 rocket's second stage engine has ignited! This is the first of two critical firings that the second stage must perform to deliver the GPS 2R-12 satellite space.

2258 GMT (6:58 p.m. EDT)

T+plus 4 minutes, 38 seconds. MECO! Main engine cutoff. The Rocketdyne RS-27A first stage main engine has shut down to complete its firing during today's launch. The twin vernier steering thrusters fired a few additional seconds before they cut off. Then the spent stage was jettisoned to fall into the Atlantic.

2257 GMT (6:57 p.m. EDT)

T+plus 3 minutes, 20 seconds. The first stage continues to fire normally. The Delta 2 rocket is 41 miles in altitude, 152 miles east of the launch pad, traveling at 7,600 mph.

2256 GMT (6:56 p.m. EDT)

T+plus 2 minutes, 14 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.

2255 GMT (6:55 p.m. EDT)

T+plus 1 minute, 50 seconds. The Delta 2 rocket is 17 miles in altitude, 37 miles east of the launch pad, traveling at 3,600 mph.

2255 GMT (6:55 p.m. EDT)

T+plus 1 minute, 10 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.

2254 GMT (6:54 p.m. EDT)

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

2254 GMT (6:54 p.m. EDT)

T+plus 48 seconds. The Delta 2 rocket is 1.5 miles in altitude, 10.5 miles east of the launch pad.

2254 GMT (6:54 p.m. EDT)

T+plus 40 seconds. With its kerosene and liquid oxygen-fed main engine and six solid-propellant motors continuing to fire normally, the vehicle is now traveling faster than the speed of sound and still accelerating rapidly.

2254 GMT (6:54 p.m. EDT)

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.

2254 GMT (6:54 p.m. EDT)

T+plus 20 seconds. The Delta 2 rocket has cleared the tower at Cape Canaveral's Complex 17B and begun maneuvering to the correct eastward trajectory from Florida's coastline for the flight over the open waters of the Atlantic Ocean.

2254 GMT (6:54 p.m. EDT)

LIFTOFF! Liftoff of the 305th Delta rocket and the next replacement satellite to reinforce the U.S. military's Global Positioning System constellation.

2253 GMT (6:53 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.

2253 GMT (6:53 p.m. EDT)

T-minus 1 minute. The Delta 2 rocket's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable.

2252 GMT (6:52 p.m. EDT)

T-minus 75 seconds. The Range has given its final clear-to-launch.

2252 GMT (6:52 p.m. EDT)

T-minus 2 minutes. The first stage liquid oxygen vents are 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.

2251 GMT (6:51 p.m. EDT)

T-minus 2 minutes, 30 seconds. The GPS 2R-12 spacecraft has been declared "go" for launch.

2251 GMT (6:51 p.m. EDT)

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

2250 GMT (6:50 p.m. EDT)

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

2250 GMT (6:50 p.m. EDT)

T-minus 4 minutes and counting. The final phase of the countdown is underway for launch of the Delta 2 rocket and the GPS 2R-12 military navigation satellite at 6:54 p.m. EDT from pad 17B at Cape Canaveral Air Force Station in Florida.

2249 GMT (6:49 p.m. EDT)

Now five minutes from launch! Standing by to resume the countdown in one minute.

2247 GMT (6:47 p.m. EDT)

The final Air Force poll of management has been performed. Weather conditions are still "go" for launch. Liftoff remains targeted for 6:54 p.m. EDT!

2245 GMT (6:45 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.

2244 GMT (6:44 p.m. EDT)

The countdown is half-way through this built-in hold. Launch of the 305th Delta rocket, the 113th in the Delta 2 series since 1989 and the GPS 2R-12 spacecraft is now just 10 minutes away.

There are no problems currently being reported by Boeing or the Air Force. Weather remains "go" for launch.

2240 GMT (6:40 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 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 6:54 p.m. EDT (2254 GMT).

2238 GMT (6:38 p.m. EDT)

The Air Force launch weather officer has declared that conditions are "go" for liftoff today.

2238 GMT (6:38 p.m. EDT)

The facility water tanks are being pressurized.

2235 GMT (6:35 p.m. EDT)

Now 19 minutes until launch. The spacecraft safe and arm devices have been armed.

2233 GMT (6:33 p.m. EDT)

GPS 2R-12 is now confirmed to be on internal battery power for flight.

2230 GMT (6:30 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.

2229 GMT (6:29 p.m. EDT)

The GPS 2R-12 spacecraft cargo atop the Delta 2 rocket is now switching to internal power for launch.

2224 GMT (6:24 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.

2220 GMT (6:20 p.m. EDT)

Boeing and Air Force officials have conducted readiness polls in preparation for continuing the countdown. No technical problems were reported. Clocks will resume counting at 6:24 p.m. EDT as scheduled.

2214 GMT (6:14 p.m. EDT)

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

Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned.

The Delta 2 rocket can launch between 6:54 and 7:21 p.m. EDT today. The weather is still being watched closely, but there is growing optimism that conditions will be acceptable for an on-time liftoff.

2204 GMT (6:04 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 data from the just-completed steering tests. Launch is slated for 6:54 p.m. EDT from pad 17B at Cape Canaveral Air Force Station, Florida.

2200 GMT (6:00 p.m. EDT)

The first and second stage steering checks are complete.

2157 GMT (5:57 p.m. EDT)

Weather is now 60 percent "go" for launch! That is a big improvement from earlier when there was only a 30 percent chance of acceptable conditions.

The launch weather officer says the storms to the south are beginning to dissipate somewhat. It remains to be seen if they will stay outside the restricted area around the launch site.

The expectation is the beginning of the launch window will offer the best chance of favorable weather. The clouds and storms could begin moving into the area by the middle-to-end of the window, the weather officer reported.

Today's window extends from 6:54 to 7:21 p.m. EDT.

2155 GMT (5:55 p.m. EDT)

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.

2154 GMT (5:54 p.m. EDT)

Launch time is now 60 minutes away. Eyes are focused on the southerly sky at Cape Canaveral where storms are developing. If the weather remains far enough away, the Delta 2 rocket could finally make it off the launch pad today.

2139 GMT (5:39 p.m. EDT)

The launch team reports the loading of the Delta 2 rocket's first stage liquid oxygen tank was completed at 5:38 p.m. EDT. The operation took 27 minutes and 51 seconds today. 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 last week. The nine strap-on booster rockets are solid-propellant.

2128 GMT (5:28 p.m. EDT)

Cryogenic tanking of the Delta rocket's first stage continues without any reports of problems. 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.

2124 GMT (5:24 p.m. EDT)

The countdown is entering the final 90 minutes to launch. Weather conditions at the launch site remain the primary concern this evening. Meteorologists say there could be a shot at launching the Delta 2 rocket around 6:54 p.m. EDT (2254 GMT) before the storms approaching from the south arrive over Cape Canaveral.

2120 GMT (5:20 p.m. EDT)

Liquid oxygen loading has passed the 10-minute mark. The bottom of the Boeing Delta 2 rocket is icing over as the super-cold liquid oxygen continues to flow into the first stage.

2115 GMT (5:15 p.m. EDT)

A plume of white vapor is streaming from the vent port of the first stage as the cryogenic tanking passes the five-minute mark of this approximate 25-minute process.

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

Super-cold liquid oxygen is beginning to flow into the first stage of the Boeing Delta 2 rocket as the countdown continues for today's 6:54 p.m. EDT launch.

The liquid oxygen, chilled to Minus-298 degrees F, is being pumped from a storage tank at pad 17B, through plumbing and into the bottom of the rocket. The LOX and the RP-1 kerosene fuel -- loaded aboard the vehicle in the past hour -- will be consumed by the first stage main engine.

2103 GMT (5:03 p.m. EDT)

The weather officer says there is a chance of acceptable weather at the very opening of today's launch window at 6:54 p.m. EDT. Conditions would then degrade as the weather moves in from the south.

With that outlook, officials have given approval to begin loading the liquid oxygen tank.

2057 GMT (4:57 p.m. EDT)

The launch weather officer just provided a detailed briefing to the management team in advance of loading liquid oxygen into the Delta 2 rocket's first stage. There is now a 70 percent chance of violating the weather rules for today's launch opportunity -- a slight improvement from the outlook issued this morning.

A large area of storms has developed to the south-southwest of the Cape. Meteorologists say that system is growing larger. Additional storms will be forming along the coast as the afternoon continues, too.

So the prediction is that conditions will gradually degrade. Cumulus clouds within five miles of the launch pad and then a high electrical charge in the air will be the issues that the weather team keep a close eye on.

At the present time, no weather rules are being broken at the Cape.

The forecast for tomorrow is also 70 percent "no go" for launch.

2055 GMT (4:55 p.m. EDT)

The launch team has completed work to turn on and configure the Delta's onboard guidance computer -- called the Redundant Inertial Flight Control Assembly, or RIFCA.

2038 GMT (4:38 p.m. EDT)

The first stage fuel tank of the Boeing Delta 2 rocket has been fully loaded for today's planned 6:54 p.m. EDT launch. The tank was filled with a highly refined kerosene, called RP-1, during a 20-minute process that concluded moments ago.

The next major task in the count will be loading super-cold cryogenic liquid oxygen into the first stage.

2035 GMT (4:35 p.m. EDT)

The launch team has computed that the full load for the first stage fuel tank is 10,033 gallons.

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

2028 GMT (4:28 p.m. EDT)

Now 10 minutes, or half-way, through this 20-minute process to load the rocket's first stage with kerosene fuel. Some 6,000 gallons have been loaded to this point.

The propellant will be used 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.

2018 GMT (4:18 p.m. EDT)

Fueling of the Delta 2 rocket's first stage has begun for today's launch. 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 17B.

2014 GMT (4:14 p.m. EDT)

Boeing technicians are starting preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank. After verifying valves, sensors, flow meters and equipment are ready, the highly-refined kerosene fuel will start flowing into the vehicle.

1954 GMT (3:54 p.m. EDT)

T-minus 150 minutes and counting. The Terminal Countdown is now underway today's launch of the Delta 2 rocket and the Global Positioning System 2R-12 satellite. The next three hours will be spent fueling the rocket, activating systems and performing final testing before liftoff at 6:54 p.m. EDT (2254 GMT) from pad 17B at Cape Canaveral Air Force Station in Florida.

The Complex 17B area is verified cleared of workers. A warning horn will be 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 hazardous operations such as the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

The countdown currently stands at T-minus 150 minutes. However, there are a pair of holds -- totaling 30 minutes in duration -- planned at T-minus 20 minutes and T-minus 4 minutes.

1945 GMT (3:45 p.m. EDT)

The launch team members have been polled for a "ready" status to resume the countdown as planned at the end of this hold. Clocks will start ticking again at 3:54 p.m. EDT as the Terminal Countdown begins.

1924 GMT (3:24 p.m. EDT)

Now half-way through this scheduled built-in hold in the countdown.

1904 GMT (3:04 p.m. EDT)

Satellite imagery and weather radar are showing much, much better conditions today than experienced across Central Florida over the past several days.

1854 GMT (2:54 p.m. EDT)

T-minus 150 minutes and holding. Clocks are entering a planned 60-minute built-in hold in the countdown. Holds are scheduled into the count to give workers a chance to catch up on any activities that may be running behind.

The final launch pad preps have been completed and workers have departed the hazard area.

Over the next hour, all launch team members and management officials will be seated at their consoles. A series of polls will be conducted to verify everyone is ready tor enter Terminal Count at end of the built-in hold.

Liftoff of the Delta 2 rocket remains scheduled for the 6:54 p.m. EDT from Cape Canaveral, Florida.

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

We have posted a gallery of photos taken earlier today as the mobile service tower was rolled away from the Delta 2 rocket at launch pad 17B. See the pictures here.

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

The countdown is entering the final five hours to the launch of Delta 305 and the NAVSTAR Global Positioning System 2R-12 spacecraft. Workers at pad 17B are continuing to step through their procedures to reconfigure the complex for liftoff following this morning's rollback of the mobile service tower.

The skies over Central Florida look pretty good at this point. Development of widespread thunderstorms has not yet occurred today. Fingers remain crossed...

1545 GMT (11:45 a.m. EDT)

The mobile service tower is currently being wheeled away from the Delta 2 rocket at pad 17B as Boeing begins another countdown to launch this GPS deployment mission. Liftoff is scheduled for 6:54 p.m. EDT (2254 GMT) today from Cape Canaveral.

The latest weather forecast is still predicting an 80 percent chance of unacceptable conditions at launch time.

TUESDAY, JUNE 22, 2004
1640 GMT (12:40 p.m. EDT)

The Boeing Delta 2 rocket will try again Wednesday to launch a military navigation satellite after three consecutive countdowns were thwarted by Florida's summertime thunderstorms. Officials remain committed to launching the mission before NASA's Mercury orbiter, which has a two-week planetary window this summer. Read our full story.

Read our earlier status center coverage.