0258 GMT on Tues. (10:58 p.m. EDT on Mon.)
ESA confirms acquisition of signal from Sentinel 2A, and solar array deployment has started.
0248 GMT on Tues. (10:48 p.m. EDT on Mon.)
Spacecraft separation! The 2,513-pound Sentinel 2A satellite has been released from its adapter on the Vega rocket, beginning a more than seven-year mission to track vegetation, urban sprawl, pollution and other changes to Earth's land masses.
0246 GMT on Tues. (10:46 p.m. EDT on Mon.)
The AVUM's liquid-fueled engine has shut down on time. Deployment of the Sentinel 2A satellite is coming up in less than a minute.
0246 GMT on Tues. (10:46 p.m. EDT on Mon.)
The AVUM's liquid-fueled engine has shut down on time. Deployment of the Sentinel 2A satellite is coming up in less than a minute.
0244 GMT on Tues. (10:44 p.m. EDT on Mon.)
T+plus 54 minutes. Ignition of the AVUM stage's RD-869 engine confirmed to circularize the rocket's altitude at 488 miles, or 786 kilometers. This burn will last about 126 seconds. The rocket is currently flying in range of a tracking site in Perth, Australia.
0208 GMT on Tues. (10:08 p.m. EDT on Mon.)
The Vega rocket's AVUM fourth stage and Sentinel 2A have reached an initial elliptical transfer orbit after tonight's launch. Next up is a 35-minute coast before restarting the rocket to circularize at an altitude of 786 kilometers (488 miles).
0200 GMT on Tues. (10:00 p.m. EDT on Mon.)
The AVUM fourth stage's Ukrainian engine is now firing to inject the Vega and its payload into an initial transfer orbit.
0158 GMT on Tues. (9:58 p.m. EDT on Mon.)
T+plus 6 minutes, 40 seconds. Burnout and separation of the Zefiro 9 third stage motor. The Ukrainian-made fourth stage engine will ignite at T+plus 7 minutes, 42 seconds.
0157 GMT on Tues. (9:57 p.m. EDT on Mon.)
T+plus 5 minutes, 15 seconds. The third stage Zefiro 9 motor will burn out in about a minute.
0156 GMT on Tues. (9:56 p.m. EDT on Mon.)
T+plus 4 minutes, 10 seconds. The clamshell-like 8.5-foot-diameter Swiss-built payload fairing has been jettisoned.
0155 GMT on Tues. (9:55 p.m. EDT on Mon.)
T+plus 3 minutes, 55 seconds. The Zefiro 23 seconds stage has burned out and separated, giving way to the third stage Zefiro 9A motor, which is now firing at a downrange distance of 470 kilometers. Velocity is now 3.83 kilometers per second.
0153 GMT on Tues. (9:52 p.m. EDT on Mon.)
T+plus 2 minutes. First stage shutdown and separation confirmed after consuming 194,000 pounds of solid propellant, and Vega's Zefiro 23 second stage has ignited.
0152 GMT on Tues. (9:52 p.m. EDT on Mon.)
T+plus 1 minute. Now approaching 50,000 feet high, Vega has surpassed the region of maximum aerodynamic pressure. The first stage P80FW motor, the largest single-segment solid rocket ever built, continues firing as expected.
0152 GMT on Tues. (9:52 p.m. EDT on Mon.)
T+plus 40 seconds. The 98-foot-tall Vega rocket is racing into the night sky over the Guiana Space Center, already surpassing the speed of sound.
TUESDAY, JUNE 23, 2015
0151:58 GMT (9:51:58 p.m. EDT on Mon.)
LIFTOFF! The Vega rocket has launched on its fifth mission with the Sentinel 2A land imaging satellite for the European Space Agency and the European Commission.
TUESDAY, JUNE 23, 2015
0150:58 GMT (9:50:58 p.m. EDT on Mon.)
T-minus 60 seconds and counting.
TUESDAY, JUNE 23, 2015
0150 GMT (9:50 p.m. EDT on Mon.)
T-minus 90 seconds and counting. The four-stage launcher is being transitioned to internal battery power and disconnected from its ground power source.
TUESDAY, JUNE 23, 2015
0150 GMT (9:50 p.m. EDT on Mon.)
T-minus 2 minutes and counting. The target launch time of 0135:15 GMT is being loaded into the Vega's on-board computer.
TUESDAY, JUNE 23, 2015
0148 GMT (9:48 p.m. EDT on Mon.)
T-minus 4 minutes and counting. The synchronized launch sequence has begun for the Vega's final countdown. This computer-controlled sequence monitors thousands of parameters in the countdown's last moments, ensuring all systems are ready for flight.
TUESDAY, JUNE 23, 2015
0145 GMT (9:45 p.m. EDT on Mon.)
T-minus 7 minutes and counting. The countdown's synchronized sequence begins at T-minus 4 minutes.
TUESDAY, JUNE 23, 2015
0142 GMT (9:42 p.m. EDT on Mon.)
The final weather check shows all conditions are green for launch tonight.
TUESDAY, JUNE 23, 2015
0136 GMT (9:36 p.m. EDT on Mon.)
The Vega rocket has just one second to launch tonight or else liftoff will be delayed to another day. The time is fixed for 0151:58 GMT (9:51:58 p.m. EDT; 10:51:58 French Guiana time).
TUESDAY, JUNE 23, 2015
0132 GMT (9:32 p.m. EDT on Mon.)
T-minus 20 minutes and counting. Live streaming video from the Guiana Space Center is due to begin in about 5 minutes.

The synchronized launch sequence takes over the countdown about four minutes prior to liftoff. The computer-controlled final sequence checks thousands of parameters in the final steps of the countdown.

After liftoff, Vega will clear the pad's four lightning towers and pitch north from the Guiana Space Center, heading over the Atlantic Ocean and surpassing the speed of sound in about 30 seconds.

The Vega's solid-fueled P80FW first stage, producing a maximum of 683,000 pounds of thrust, burns out 112 seconds after liftoff, giving way to the launcher's Zefiro 23 second stage at an altitude of about 33 miles.

After a 102-second burn, the second stage consumes its propellant 3 minutes, 37 seconds after launch and separates. The Vega's third stage, the Zefiro 9A motor, ignites 3 minutes, 51 seconds into the mission.

The fourth stage, known as AVUM, ignites its liquid-fueled Ukrainian engine 7 minutes, 42 seconds into the mission, burning more than eight minutes to reach a transfer orbit above Earth.

After coasting for about 35 minutes, the AVUM fourth stage will fire again to reach a circular 488-mile-high (786-kilometer) orbit with an inclination of 98.5 degrees.

Separation of the 2,513-pound (1,140-kilogram) Sentinel 2A payload is expected 54 minutes, 43 seconds into the flight.

TUESDAY, JUNE 23, 2015
0124 GMT (9:24 p.m. EDT on Mon.)
T-minus 28 minutes and counting. The downrange tracking stations report they are ready for launch, and the rocket is now being configured to enter the synchronized countdown sequence.
TUESDAY, JUNE 23, 2015
0052 GMT (8:52 p.m. EDT on Mon.)
T-minus 60 minutes and counting. There continue to be no problems reported in the countdown for launch of Vega this evening. Liftoff is set for 0151:58 GMT (9:51:58 p.m. EDT; 10:51:58 p.m. local time) from French Guiana.
TUESDAY, JUNE 23, 2015
0052 GMT (8:52 p.m. EDT on Mon.)
T-minus 60 minutes and counting. There continue to be no problems reported in the countdown for launch of Vega this evening. Liftoff is set for 0151:58 GMT (9:51:58 p.m. EDT; 10:51:58 p.m. local time) from French Guiana.
TUESDAY, JUNE 23, 2015
0107 GMT (9:07 p.m. EDT on Mon.)
T-minus 45 minutes. Some statistics on today's flight:
TUESDAY, JUNE 23, 2015
0124 GMT (9:24 p.m. EDT on Mon.)
T-minus 28 minutes and counting. The downrange tracking stations report they are ready for launch, and the rocket is now being configured to enter the synchronized countdown sequence.
TUESDAY, JUNE 23, 2015
0132 GMT (9:32 p.m. EDT on Mon.)
T-minus 20 minutes and counting. Live streaming video from the Guiana Space Center is due to begin in about 5 minutes.
2245 GMT (6:45 p.m. EDT)
All systems are reported to be "go" for launch tonight in an instantaneous launch opportunity at 0151:58 GMT (9:51:58 p.m. EDT).

The weather outlook is favorable with acceptable high-altitude winds currently observed and forecast for tonight's launch time. There is a slight chance of lightning in the area, so officials will continue tracking weather throughout the countdown.

Arianespace has also confirmed no impact, so far, from the ongoing geomagnetic storm on tonight's flight.

So far in the countdown, Vega's systems have been powered on and launch controllers have checked communications, tracking and command links between the rocket and ground facilities at the Guiana Space Center.

Officials confirm the launch pad's 16-story mobile gantry is moving to its launch position about 260 feet from the rocket.

The 270-square-mile space center, run by the French space agency, CNES, and the European Space Agency, is located on the jungle coastline of French Guiana, situated on the northeast corner of South America.

The Vega launch pad, known by its French acronym SLV, is about 1 kilometer southwest of the Ariane 5 launch complex. It was built on the former site of ELA-1, the home of Ariane 1, Ariane 2 and Ariane 3 launchers from 1979 until 1989.

Construction of the Vega launch pad began in 2004, including the building of a new 16-story mobile gantry weighing some 1000 metric tons. A fixed umbilical mast standing 105 feet tall provides air conditioning to the Vega's payload.

Workers also added four lightning towers at the pad to protect the Vega rocket from thunderstorms.

Unlike the Ariane 5 rocket, the Vega's stages are stacked on the pad inside the mobile gantry, which provides protection of the launcher from weather at the spaceport.

Vega's countdown is managed from Guiana Space Center's prime control center less than a mile from the launch pad, the same building where Ariane 5's countdown is controlled.

2110 GMT (5:10 p.m. EDT)
The countdown for tonight's launch is underway, beginning with testing of the Vega launcher's systems and the ground segment at the Guiana Space Center, ensuring their readiness for liftoff at 0151:58 GMT (9:51:58 p.m. EDT).

The initial weather briefing shows conditions on the ground and at high altitude are acceptable for launch tonight. Officials will make more checks on the weather throughout the countdown.

Officials are also watching a geomagnetic storm to ensure it does not pose a problem for tonight's launch.

So far, no issues are reported with the Vega launcher, the Sentinel 2A spacecraft, or ground systems.

SUNDAY, JUNE 21, 2015
The first in a planned multi-decade series of European land imaging satellites is fastened on top of a solid-fueled Vega launcher at a French Guiana space base for liftoff Monday, kicking off a mission to track everything from global crop growth to urban sprawl.

The Sentinel 2A satellite is slated to blast off at 0151:58 GMT Tuesday (9:51:58 p.m. EDT; 10:51:58 p.m. French Guiana time Monday) aboard the 10-story Vega rocket.

The spacecraft, built by Airbus Defense and Space, is folded up inside the launcher’s nose shroud. Technicians spent the last few weeks finishing tests on the satellite, filling it with hydrazine fuel for in-space maneuvers, and completing the delicate job of attaching the craft to the top of the Vega rocket on its launch pad at the French-run Guiana Space Center in South America.

After flying north from French Guiana and over the North Pole, the four-stage rocket will deploy the 2,513-pound (1,140-kilogram) satellite in space less than 55 minutes after liftoff when it is flying above Australia. The Vega is programmed to release Sentinel 2A into orbit 488 miles (786 kilometers) above Earth.

Read our preview story.