A kerosene-fueled Falcon 9 launch vehicle owned and operated by SpaceX climbed away from Florida's Space Coast on Tuesday, steering into orbit more than 50,000 miles above Earth with a television broadcasting satellite in a successful flight signaling the changing landscape of the commercial launch industry.

Read our full story.

SPACECRAFT SEPARATION! The 6,918-pound SES 8 television broadcasting satellite has been deployed in the correct orbit following tonight's launch.

The satellite was supposed to be placed in an orbit with a high point above 80,000 kilometers, or 49,709 miles, a low point of 295 kilometers, or 183 miles, and an inclination of 20.75 degrees.

The second burn was supposed to boost SES 8 into a higher orbit and reduce its inclination, moving it closer to its ultimate operating position over the equator and reducing the fuel the satellite needs to complete its mission.

Based on information from SpaceX and sources, it appears the burn did what it was designed to do.

SES 8 is designed to adjust its orbit and settle into position 22,300 miles over the equator within about two weeks of launch. Five burns of the satellite's on-board liquid-fueled engine are required to lower its apogee, raise its perigee, and change its inclination to move over the equator.

The first orbital maneuver by SES 8 is expected about 39 hours after launch.

We expect more details to be released by SpaceX and SES in the next few hours.

SpaceX and SES are awaiting acquisition of signal from the SES 8 satellite before calling this launch a success. All appears OK, a source says.

SpaceX says the engine restart was a success. Spacecraft separation is due in a couple of minutes.

Elon Musk has posted on Twitter: "Reached parking orbit. Now coasting towards equator, where the upper stage will, if all goes well, restart to raise apogee."

Re-ignition of the upper stage should occur at about 6:08 p.m. EST (2308 GMT) for a burn of about 71 seconds.

Separation of the SES 8 satellite will come a few minutes later.

We expect an update from SpaceX soon after those milestones are achieved.

After a loss of the live video transmission from the Falcon 9 second stage, SpaceX confirms the rocket has arrived in its preliminary parking orbit.

The Falcon 9 second stage is now in a coast phase scheduled to last about 18 minutes. The Merlin 1D engine will fire again at about T+plus 27 minutes for approximately 71 seconds.

Spacecraft separation is scheduled for T+plus 31 minutes, 15 seconds, but SpaceX plans to end the webcast in a few minutes. News of the outcome of the critical second burn and deployment of SES 8 will come later.

T+plus 8 minutes. About 30 seconds until the second stage Merlin engine is supposed to shut down as the vehicle reaches orbit. The rocket is aiming for an initial parking orbit with SES 8, and it will re-ignite later to boost the satellite into a supersynchronous transfer orbit.

T+plus 7 minutes, 30 seconds. The vehicle remains in a nominal trajectory. Velocity is 4.5 kilometers per second, and the Falcon 9 is flying east of Cape Canaveral.

T+plus 6 minutes. The kerosene-fueled Merlin 1D upper stage engine generates about 161,000 pounds of thrust in vacuum.

T+plus 5 minutes, 25 seconds. Everything reported to be going well with this second stage engine firing. The Merlin vacuum engine uses an ultra-thin niobium nozzle extension for greater efficiency in the upper atmosphere.

T+plus 3 minutes, 45 seconds. The SpaceX-built 5.2-meter diameter payload fairing has separated.

T+plus 3 minutes. The Falcon 9 first stage engines have cut off, the stages have separated, and the rocket's second stage Merlin vacuum engine has ignited for its approximately six-minute firing to reach orbital velocity.

T+plus 2 minutes. Now soaring at an altitude of more than 20 miles, the Falcon 9 rocket's first stage will shut down and jettison in about one minute. Two engines will be turned off first, followed a few moments later by the remaining seven engines.

And chilldown of the second stage's vacuum-rated Merlin 1D engine has started in preparation for its ignition.

T+plus 1 minute. The Falcon 9 rocket is approaching the speed of sound and the phase of maximum aerodynamic pressure.

T+plus 30 seconds. The Falcon 9 rocket's pitch program has initiated to put the 224-foot-tall rocket on an easterly trajectory from Cape Canaveral.

LIFTOFF of the Falcon 9 rocket with SES 8, inaugurating a new Falcon 9 launch capability while serving television markets in the Asia-Pacific.

T-minus 60 seconds. In the final minute of the countdown, the flight computer will command checks of the first stage Merlin engine steering system and the Falcon 9 propellant tanks will be pressurized for flight. Thousands of gallons of water from the ground facility's Niagara system will also be dumped onto the launch pad deck to suppress the sound and acoustics of liftoff.

The command to start the ignition sequence for the first stage will be issued at T-minus 3 seconds, triggering the Merlin engines' ignitor moments before the powerplants actually ramp up to full power.

T-minus 90 seconds and counting. The SpaceX launch director and the Air Force Eastern Range have given their final approvals for liftoff of the Falcon 9 rocket at 5:41 p.m. EST (2241 GMT).

T-minus 2 minutes and counting. The rocket's Merlin 1D engines have been chilled down for ignition.

T-minus 2 minutes, 30 seconds. The strongback has been locked in to launch position.

T-minus 3 minutes and counting. The rocket's destruct system is on internal power and being armed, and liquid oxygen topping is being terminated.

The strongback has retracted into the launch position more than 20 degrees from the rocket.

The second stage thrust vector steering system has checked out and is ready for flight.

T-minus 5 minutes and counting. The cradles connecting the strongback to the Falcon 9 rocket have opened.

T-minus 6 minutes and counting. The Falcon 9 rocket is now operating on internal power.

The strongback umbilical tower will soon be lowered a few degrees to clear the rocket for launch. The procedure begins with opening of cradles gripping the rocket at attach points, then hydraulics lower the tower into launch position.

T-minus 6 minutes, 30 seconds. The Falcon 9's heaters are being deactivated, and the rocket will be transitioned to internal power in a few seconds.

T-minus 7 minutes and counting. Within the next minute, the Falcon 9's flight computer will be commanded to its alignment state. The Merlin engine pumps are continuing to chill down.

The launch danger area around Cape Canaveral is clear for launch.

T-minus 8 minutes and counting. Good chilldown continues on the first stage engines, and closeouts of the upper stage's gaseous nitrogen attitude control system are underway.

T-minus 9 minutes and counting. Prevalves leading to the Falcon 9's Merlin 1D first stage engines are opening, permitting super-cold liquid oxygen to flow into the engines to condition the turbopumps for ignition.

T-minus 10 minutes and counting. The terminal countdown autosequence has started. Any hold after this point will result in an automatic abort and recycle to T-minus 13 minutes.

T-minus 12 minutes. The launch team has verified all consoles are go for liftoff at 5:41 p.m. EST (2241 GMT).

The sun has just set here at Cape Canaveral, and the Falcon 9 rocket is bathed in light as the terminal countdown autosequence is about to begin at the T-minus 10 minute mark.

T-minus 15 minutes and counting. Here are some statistics on today's launch:

• 7th launch of a Falcon 9 rocket since 2010
• 12th launch of Falcon rocket family since 2006
• 6th Falcon 9 launch from Cape Canaveral
• 2nd launch of a Falcon 9 v1.1 rocket
• 1st Falcon 9 v1.1 launch from Cape Canaveral
• 1st Falcon 9 launch to geostationary transfer orbit
• 3rd Falcon 9 night launch
• 3rd Falcon 9 launch of 2013
• 10th launch from Cape Canaveral in 2013
• 55th launch of an SES satellite
• 3rd launch of an SES satellite in 2013

T-minus 17 minutes and counting. The Falcon 9 rocket stands 224 feet tall and measures 12 feet in diameter. At liftoff, its nine Merlin 1D first stage engines will generate about 1.3 million pounds of thrust.

T-minus 20 minutes and counting. The final poll of the 20-person launch team will begin at T-minus 13 minutes before the countdown enters the final phase.

Liquid oxygen topping continues on the Falcon 9 rocket's first and second stages.

See our Facebook page for quick images of today's countdown and launch!

T-minus 30 minutes. Today's launch is heading for a "supersynchronous" transfer orbit with an apogee, or high point, of 86,500 kilometers (53,748 miles) and a perigee, or low point, of 295 kilometers (183 miles).

The 6,918-pound SES 8 satellite is destined for a slot 22,300 miles above the equator in geostationary orbit at 95 degrees east longitude, where its Ku-band and Ka-band payload will beam direct-to-home television broadcasts and other services to India, Southeast Asia and surrounding regions for 15 years.

Today's mission marks the first SpaceX Falcon 9 launch with a satellite heading for a geostationary transfer orbit. Such an orbit requires two burns of the Falcon 9's upper stage Merlin 1D engine, first to place the satellite into a low-altitude parking orbit, then to raise its apogee to geostationary altitude or higher.

SpaceX CEO Elon Musk just tweeted: "About an hour away from launch. I'd like to thank @SES_Satellites for taking a chance on @SpaceX. We've given it our all."

T-minus 60 minutes. Clear skies above the Falcon 9 launch pad tell the weather story this afternoon. Officials say surface conditions are nearly perfect for an on-time launch, and weather balloons are being launched to monitor winds aloft.

The Falcon 9 rocket is fully fueled with super-cold liquid oxygen and kerosene propellants. Both stages are being replenished with cryogenic oxidizer until the final minutes of the countdown to replace propellant that gradually boils off due to the warm ambient temperatures in Florida.

SpaceX says the webcast of today's launch will begin at 5:25 p.m. EST (2225 GMT), about 16 minutes prior to liftoff, and continue through cutoff of the second stage engine.

We will have the live webcast on this page.

If you are heading out to the beach or Port Canaveral to watch the launch, sign up for our Twitter feed to get occasional countdown updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

SpaceX has begun the hour-long fueling process to load kerosene and liquid oxygen into the two-stage Falcon 9 rocket.

RP-1 fuel, a type of highly refined kerosene, is being pumped into both stages of the Falcon 9 rocket. Liquid oxygen, which is stored at cryogenic temperatures, will follow shortly.

SpaceX teams are arriving on console to support a Falcon 9 launch attempt this evening at 5:41 p.m. EST (2241 GMT).

The critical commercial launch is SpaceX's first mission requiring a re-ignition of the Falcon 9's second stage, a tricky feat that was unsuccessful on a test flight in September.

SpaceX traced the cause of the Sept. 29 restart anomaly to frozen fluid lines for the upper stage engine's igniter system. Engineers added insulation to keep super-cold liquid oxygen from impinging on the igniter fluid lines on this mission.

The payload today is the SES 8 communications satellite, a 6,918-pound spacecraft built by Orbital Sciences Corp. for SES of Luxembourg, the world's second-largest operator of commercial telecom satellites.

The destination: A "supersynchronous" transfer orbit stretching up to 86,500 kilometers, or more than 53,700 miles, above Earth with an inclination of 20.75 degrees.

The Falcon 9 will deploy the satellite about a half-hour after launch. Follow tonight's launch with this timeline of major events.

The SpaceX webcast is scheduled to begin around 5:25 p.m. EST (2225 GMT).

Tonight's launch window extends to 7:07 p.m. EST (0007 GMT).

The weather forecast for Cape Canaveral is unchanged from yesterday's outlook, with a 90 percent of good conditions for launch, partly cloudy skies, moderate winds out of the southeast, and a launch time temperature of 68 degrees Fahrenheit.

DELAY. Launch has been pushed back to Tuesday to allow more time to finish work on the Falcon 9 rocket.

"All known rocket anomalies resolved," SpaceX CEO Elon Musk posted on Twitter. "Will spend another day rechecking to be sure."

The launch window Tuesday is unchanged. It opens at 5:41 p.m. EST (2241 GMT) and extends 86 minutes.

The weather outlook Tuesday calls for good weather with just a 10 percent chance conditions will forbid launch.

The forecast for Tuesday predicts scattered clouds at 10,000 feet, southeast winds at 10 knots and a launch time temperature of 68 degrees Fahrenheit.

After cleaning and replacing first stage engine components following a last-second launch abort Thursday, SpaceX is finishing up work on the Falcon 9 rocket ahead of another potential launch attempt this evening.

Tonight's launch window opens at 5:41 p.m. EST (2241 GMT) and closes at 7:07 p.m. EST (0007 GMT).

Technicians are wrapping up hands-on work on the launcher this morning, and SpaceX officials will make the final decision to proceed with the countdown around 1:30 p.m. EST (1830 GMT), just before fueling of the rocket is expected to begin.

It would be the third attempt to launch the SES 8 television broadcasting satellite, which is waiting to start a mission beaming communications services over India, Thailand, Vietnam and neighboring regions.

The 6,918-pound spacecraft is SpaceX's first payload heading for a geostationary transfer orbit, the high-altitude orbit favored by commercial communications satellites.

Commercial geostationary payloads are an untapped mark for U.S. launchers, which are too expensive to be considered by most private satellite operators.

Two launch attempts last week were called off in the final minutes of the countdown.

On Nov. 25, a myriad of technical problems halted the countdown.

And the countdown on Thanksgiving Day was aborted moments before liftoff when the Falcon 9 rocket's nine Merlin 1D first stage engines were already running. The computer-controlled countdown sequencer called the hold when it detected the engines were not ramping up to full thrust as fast as expected.

"Abort was caused by oxygen in ground side TEA-TEB," SpaceX chief executive Elon Musk posted on his Twitter account Saturday.

TEA-TEB stands for triethylaluminum-triethylborane, a hypergolic fluid used to ignite the rocket's Merlin engines.

Musk posted an update yesterday, saying workers replaced a gas generator on the Falcon 9 first stage's center engine as a "precautionary measure."

"The gas generator is a small rocket engine that powers the turbopump, which produces 7000 horsepower & weighs 160 lbs," Musk wrote on his Twitter page.

SpaceX chief executive Elon Musk says engineers are cleaning engine components on the first stage of the Falcon 9 rocket ahead of a planned launch attempt Monday evening.

The launch window opens at 5:41 p.m. EST (2241 GMT) and closes at 0007 GMT (7:07 p.m. EST).

"Rocket engines are healthy, but cleaning turbopump gas generators will take another day," Musk tweeted earlier today.

The Falcon 9's first stage features nine Merlin 1D engines. Each has a gas generator to drive the engine's turbopump.

Musk posted on Twitter that the last-second abort of Thursday's Falcon 9 launch attempt, which occurred after the engines ignited, was caused by oxygen on the ground system's "TEA-TEB" igniter system.

SpaceX's Merlin engines use pyrophoric igniters with a hypergolic fluid called triethylaluminum-triethylborane, or TEA-TEB. The system allows an engine to restart multiple times on the ground or in flight without refurbishment.

Musk tweeted the upper stage's Merlin engine is on a "separate internal circuit, so [it] doesn't face [the] same risk."

The official weather forecast issued today for Monday's launch opportunity calls for 60 percent chance of acceptable weather conditions.

An upper level weather system is scheduled to cross northern Florida on Sunday, brining a chance of rain and thunderstorms to the area.

"By the launch window Monday, clouds and unstable weather should be moving out of the spaceport area, allowing drier air to filter in with northwest winds," Air Force meteorologists wrote in today's forecast.

The primary weather concerns Monday are with the cumulus cloud and thick cloud rules.

Conditions at launch time should be mostly cloudy with a scattered cloud layer at 3,000 feet and a broken deck at 8,000 feet. There is a chance of isolated showers and winds will be out of the northwest at 10 knots with gusts to 15 knots. The temperature at launch time should be 70 degrees Fahrenheit.

The weather over Florida's Space Coast improves Tuesday, with just a 10 percent chance of weather violating one of the Falcon 9's launch rules.

SpaceX has announced the next Falcon 9 launch attempt will be no earlier than Monday. The Federal Aviation Administration has not granted approval for a Sunday launch due to heavy air traffic following the Thanksgiving holiday.

If SpaceX goes ahead with a launch attempt Saturday, the launch window opens at 5:40 p.m. EST (2240 GMT).

Officials say SpaceX is gearing up for another launch attempt for its Falcon 9 rocket as soon as Saturday, but there has not been an official announcement whether the company will proceed with the countdown after technical problems thwarted a Thanksgiving launch try.

The Falcon 9 rocket has stayed upright on the launch pad today as engineers investigate the issues that forced an abort of the Thanksgiving launch attempt after the rocket's nine engines ignited a few seconds before liftoff.

SpaceX chief executive Elon Musk posted an update on his Twitter account Thursday night saying the Falcon 9 countdown was held automatically due to a slower than expected ramp-up of thrust on the first stage.

The Hawthorne, Calif.-based company has not released any update on the launch since last night, but an official with SES, the owner of the launcher's communications satellite payload, said Friday the team was preparing for launch Saturday, at least for the moment.

SpaceX has a backup day to launch Monday.

Topped with a television broadcasting satellite, SpaceX's Falcon 9 rocket fired its engines and was moments away from liftoff from Cape Canaveral on Thursday, but the commercial booster aborted the launch after computers detected the engines were too slow building up thrust.

Read our full story.

SpaceX founder and CEO Elon Musk sent a tweet a few minutes ago saying launch would likely be delayed a few days while engineers lower it horizontal and move it into the hangar for inspections.

The scrub was called inside T-minus 1 minute because engineers had not completed a data review of the first abort earlier this evening.

Musk says engineers plan to bring down the rocket to a horizontal position and move it back into the hangar to borescope the Falcon's nine Merlin 1D first stage engines and see what triggered the abort this evening.

SCRUB. The launch director has officially declared a scrub.

The strongback support structuring is being raised back into position next to the Falcon 9 rocket.

This is likely a scrub for this evening, but we're waiting on official notification form SpaceX.

ABORT. Clocks have stopped at T-minus 48 seconds.

T-minus 60 seconds. In the final minute of the countdown, the flight computer will command checks of the first stage Merlin engine steering system and the Falcon 9 propellant tanks will be pressurized for flight. Thousands of gallons of water from the ground facility's Niagara system will also be dumped onto the launch pad deck to suppress the sound and acoustics of liftoff.

The command to start the ignition sequence for the first stage will be issued at T-minus 3 seconds, triggering the Merlin engines' ignitor moments before the powerplants actually ramp up to full power.

T-minus 90 seconds and counting. The SpaceX launch director and the Air Force Eastern Range have given their final approvals for liftoff of the Falcon 9 rocket at 5:37 p.m. EST (2237 GMT).

T-minus 2 minutes and counting. The rocket's Merlin 1D engines have been chilled down for ignition.

T-minus 2 minutes, 30 seconds. The strongback has been locked in to launch position.

T-minus 3 minutes and counting. The rocket's destruct system is on internal power and being armed, and liquid oxygen topping is being terminated.

The strongback has retracted into the launch position more than 20 degrees from the rocket.

The second stage thrust vector steering system has checked out and is ready for flight.

T-minus 5 minutes and counting. The cradles connecting the strongback to the Falcon 9 rocket have opened.

T-minus 6 minutes and counting. The Falcon 9 rocket is now operating on internal power.

The strongback umbilical tower will soon be lowered a few degrees to clear the rocket for launch. The procedure begins with opening of cradles gripping the rocket at attach points, then hydraulics lower the tower into launch position.

T-minus 6 minutes, 30 seconds. The Falcon 9's heaters are being deactivated, and the rocket will be transitioned to internal power in a few seconds.

T-minus 7 minutes and counting. Within the next minute, the Falcon 9's flight computer will be commanded to its alignment state. The Merlin engine pumps are continuing to chill down.

The launch danger area around Cape Canaveral is clear for launch.

T-minus 8 minutes and counting. Good chilldown continues on the first stage engines, and closeouts of the upper stage's gaseous nitrogen attitude control system are underway.

T-minus 9 minutes and counting. Prevalves leading to the Falcon 9's Merlin 1D first stage engines are opening, permitting super-cold liquid oxygen to flow into the engines to condition the turbopumps for ignition.

T-minus 10 minutes and counting. The terminal countdown autosequence has started. Any hold after this point will result in an automatic abort and recycle to T-minus 13 minutes.

All stations on the launch team report they are GO for launch at 6:44 p.m. EST (2344 GMT).

A poll of the SpaceX launch team is scheduled for the T-minus 13 minute point in a few minutes.

Spacecraft engineers say they are willing to extend the launch window by 20 minutes to give more time to resolve whatever issue is being worked in the countdown. The window was scheduled to close at 6:44 p.m. EST (2344 GMT).

Still no word if the problem that caused the abort has been formally resolved.

NEW LAUNCH TIME. The countdown clock has resumed for another launch attempt 6:44 p.m. EST (2344 GMT).

The SpaceX launch team is still looking at the data from the abort caused by a slow ramp-up of thrust.

"They have yet fully committed to go forward tonight," says John Insprucker, SpaceX's Falcon 9 product manager. "They're still scrubbing the data."

SpaceX engineers have aborted countdowns after engine ignition before. Officials have previously said such aborts are often caused by conservative software limits that can be relaxed.

SpaceX CEO Elon Musk says the abort was triggered by a slower than normal ramp-up of thrust on the first stage's nine Merlin 1D engines. The condition looks OK upon closer inspection, he says.

The countdown is being recycled to set up for another launch try tonight.

The launch team is loading helium and nitrogen pressurant and maneuvering propellant into the rocket. This is part of the effort to set up for another potential launch attempt tonight.

John Insprucker, SpaceX's Falcon 9 product manager, says the launch team is planning to load more liquid oxygen propellant into the Falcon 9's two stages to configure the launcher for another attempt tonight.

The launch window extends to 6:44 p.m. EST (2344 GMT), so there is some time resolve the problem.

We're waiting on word on the cause of the abort. If the problem is minor, there could be another launch attempt this evening.

ABORT.

T-minus 30 seconds. All tanks are at flight pressure.

T-minus 45 seconds. The countdown's automatic sequence is now being run off of the Falcon 9's on-board computer, and propellant tank pressures are rising in preparation for launch.

T-minus 60 seconds. In the final minute of the countdown, the flight computer will command checks of the first stage Merlin engine steering system and the Falcon 9 propellant tanks will be pressurized for flight. Thousands of gallons of water from the ground facility's Niagara system will also be dumped onto the launch pad deck to suppress the sound and acoustics of liftoff.

The command to start the ignition sequence for the first stage will be issued at T-minus 3 seconds, triggering the Merlin engines' ignitor moments before the powerplants actually ramp up to full power.

T-minus 90 seconds and counting. The SpaceX launch director and the Air Force Eastern Range have given their final approvals for liftoff of the Falcon 9 rocket at 5:37 p.m. EST (2237 GMT).

T-minus 2 minutes and counting. The rocket's Merlin 1D engines have been chilled down for ignition.

T-minus 2 minutes, 30 seconds. The strongback has been locked in to launch position.

T-minus 3 minutes and counting. The rocket's destruct system is on internal power and being armed, and liquid oxygen topping is being terminated.

The strongback has retracted into the launch position more than 20 degrees from the rocket.

The second stage thrust vector steering system has checked out and is ready for flight.

T-minus 5 minutes and counting. The cradles connecting the strongback to the Falcon 9 rocket have opened.

T-minus 6 minutes and counting. The Falcon 9 rocket is now operating on internal power.

The strongback umbilical tower will soon be lowered a few degrees to clear the rocket for launch. The procedure begins with opening of cradles gripping the rocket at attach points, then hydraulics lower the tower into launch position.

T-minus 6 minutes, 30 seconds. The Falcon 9's heaters are being deactivated, and the rocket will be transitioned to internal power in a few seconds.

T-minus 7 minutes and counting. Within the next minute, the Falcon 9's flight computer will be commanded to its alignment state. The Merlin engine pumps are continuing to chill down.

The launch danger area around Cape Canaveral is clear for launch.

T-minus 8 minutes and counting. Good chilldown continues on the first stage engines, and closeouts of the upper stage's gaseous nitrogen attitude control system are underway.

T-minus 9 minutes and counting. Prevalves leading to the Falcon 9's Merlin 1D first stage engines are opening, permitting super-cold liquid oxygen to flow into the engines to condition the turbopumps for ignition.

T-minus 10 minutes and counting. The terminal countdown autosequence has started. Any hold after this point will result in an automatic abort and recycle to T-minus 13 minutes.

T-minus 12 minutes. The launch team has verified all consoles are go for liftoff at 5:39 p.m. EST (2239 GMT).

The sun has just set here at Cape Canaveral, and the Falcon 9 rocket is bathed in light as the terminal countdown autosequence is about to begin at the T-minus 10 minute mark.

The 6,918-pound SES 8 communications spacecraft is reported to be on internal power.

T-minus 15 minutes and counting. Here are some statistics on today's launch:

• 7th launch of a Falcon 9 rocket since 2010
• 12th launch of Falcon rocket family since 2006
• 6th Falcon 9 launch from Cape Canaveral
• 2nd launch of a Falcon 9 v1.1 rocket
• 1st Falcon 9 v1.1 launch from Cape Canaveral
• 1st Falcon 9 launch to geostationary transfer orbit
• 3rd Falcon 9 night launch
• 3rd Falcon 9 launch of 2013
• 10th launch from Cape Canaveral in 2013
• 55th launch of an SES satellite
• 3rd launch of an SES satellite in 2013
• 1st Thanksgiving launch from Cape Canaveral since 1959

T-minus 17 minutes and counting. The Falcon 9 rocket stands 224 feet tall and measures 12 feet in diameter. At liftoff, its nine Merlin 1D first stage engines will generate about 1.3 million pounds of thrust.

All downrange tracking stations report they are ready to support today's launch, and winds aloft remain acceptable for liftoff.

T-minus 20 minutes and counting. The final poll of the 20-person launch team will begin at T-minus 13 minutes before the countdown enters the final phase.

T-minus 24 minutes. The SpaceX webcast is beginning now.

Follow tonight's launch with this timeline of major events.

The SES 8 spacecraft is scheduled to transfer to internal power at this point in the countdown.

T-minus 30 minutes. No problems reported in the countdown. Ground systems, the launch vehicle, the SES 8 payload and the weather are all cooperating for an on-time launch this evening.

See our Facebook page for quick images of today's countdown to launch!

T-minus 45 minutes and counting. Everything is still on schedule for launch. The SpaceX webcast begins at 5:15 p.m. EST (2215 GMT).

T-minus 60 minutes and counting. This launch was delayed from Monday after several technical problems held up the countdown, forcing a scrub.

The last glitch was in the first stage's liquid oxygen pressurization system. A SpaceX spokesperson says engineers modified the countdown sequence to eliminate the fluctuations seen during the last attempt.

The fix included improved controls for ground operators to pressurize the tank and for topping it with liquid oxygen, the spokesperson said.

T-minus 2 hours and counting. The Falcon 9 rocket is fully fueled with super-cold liquid oxygen and kerosene propellants. Both stages are being replenished with cryogenic oxidizer until the final minutes of the countdown to replace propellant that gradually boils off due to the warm ambient temperatures in Florida.

All weather rules are currently observed "green" for launch, and there continues to be a 90 percent of acceptable conditions during this evening's 65-minute window opening at 5:39 p.m. EST (2239 GMT).

Kerosene and liquid oxygen are being pumped aboard the two-stage Falcon 9 rocket. Both stages burn the mix of liquid propellants to fuel 10 Merlin 1D engines.

SpaceX says the webcast of today's launch will begin at 5:15 p.m. EST (2215 GMT), about 39 prior to liftoff, and continue through the first cutoff of the second stage engine about 10 minutes into the mission.

We will have the live webcast on this page.

If you are heading out to the beach or Port Canaveral to watch the launch, sign up for our Twitter feed to get occasional countdown updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

There has not been a Thanksgiving Day launch from Cape Canaveral since 1959, when an Atlas-Able launch vehicle lifted off with the Pioneer P-3 lunar probe. The mission ended in a launch failure.

The last Thanksgiving launch from U.S. soil occurred in 1991 from Vandenberg Air Force Base in California, when an Atlas E rocket successfully lofted an Air Force weather satellite into orbit.

Nothing stands in the way of today's Falcon 9 launch at this time, and the official weather forecast has improved with a 90 percent chance conditions will cooperate for liftoff at 5:39 p.m. EST (2239 GMT).

"A low temperature of 42 degrees F at the launch pad this morning will quickly increase to the mid-60s by noon," Air Force forecasters said. "Winds will be from the north-northeast gusting to 25 knots during the daylight hours, diminishing to 10 knots after sunset."

The only concern is that winds will exceed launch constraints, but there's just a 10 percent chance that will happen.

Weather will be blustery at launch time with a temperature of 63 degrees Fahrenheit and winds out of the north-northeast at 15 knots gusting to 22 knots.

The Thanksgiving launch of SpaceX's Falcon 9 rocket is on schedule, with liftoff targeted for 5:39 p.m. EST (2239 GMT) at the opening of a 65-minute launch window.

It will mark the first Thanksgiving Day launch from Cape Canaveral since 1959, when an Atlas-Able launch vehicle lifted off with the Pioneer P-3 lunar probe. The mission ended in a launch failure.

The last Thanksgiving launch from U.S. soil occurred in 1991 from Vandenberg Air Force Base in California, when an Atlas E rocket successfully lofted an Air Force weather satellite into orbit.

The weather forecast for tomorrow calls for favorable conditions, with an 80 percent chance weather will permit launch.

"Clearing conditions and much colder temperatures will be ushered in this afternoon behind a cold front," Air Force meteorologists wrote in a forecast Wednesday morning. "On Thursday, winds will be northerly gusting to 25 knots, gradually diminishing and begin to turn onshore by the end of the launch window creating a slight risk of an onshore flow shower."

Forecasters predict mostly sunny skies with scattered clouds at 3,000 feet, a slight chance of rain showers and winds out of the northeast at 15 knots gusting to 22 knots.

The temperature will be approximately 65 degrees Fahrenheit and good visibility is expected.

The main concerns in the forecast are liftoff winds and the cumulus cloud rule, according to the Air Force's 45th Weather Squadron.

Concerned a rocket launch might add more congestion to the skies during Thanksgiving week, federal regulators blocked SpaceX's bid to launch a commercial broadcasting satellite Tuesday and Wednesday, two of the busiest travel days of the year.

Read our full story.

SpaceX called off launch of a Falcon 9 rocket with a commercial telecommunications satellite Monday after several technical problems held up the countdown, delaying the flight until Thanksgiving Day.

Read our full story.

SCRUB. Launch will not happen today, and the next try is likely Thursday, Thanksgiving Day in the United States.

Falcon 9 product manager John Insprucker says an "off-nominal condition" with the first stage liquid oxygen pressurization system caused the abort.

The launch is reset for 5:38 p.m. EST (2238 GMT) on Thursday.

The countdown stopped at T-minus 3 minutes, 41 seconds. SpaceX is running out of time with the launch window due to close in 15 minutes.

HOLD.

T-minus 5 minutes and counting. The cradles connecting the strongback to the Falcon 9 rocket have opened.

T-minus 6 minutes and counting. The Falcon 9 rocket is now operating on internal power.

The strongback umbilical tower will soon be lowered a few degrees to clear the rocket for launch. The procedure begins with opening of cradles gripping the rocket at attach points, then hydraulics lower the tower into launch position.

T-minus 6 minutes, 30 seconds. The Falcon 9's heaters are being deactivated, and the rocket will be transitioned to internal power in a few seconds.

T-minus 7 minutes and counting. Within the next minute, the Falcon 9's flight computer will be commanded to its alignment state. The Merlin engine pumps are continuing to chill down.

The launch danger area around Cape Canaveral is clear for launch.

T-minus 8 minutes and counting. Good chilldown continues on the first stage engines, and closeouts of the upper stage's gaseous nitrogen attitude control system are underway.

T-minus 9 minutes and counting. Prevalves leading to the Falcon 9's Merlin 1D first stage engines are opening, permitting super-cold liquid oxygen to flow into the engines to condition the turbopumps for ignition.

T-minus 10 minutes and counting. The terminal countdown autosequence has started. Any hold after this point will result in an automatic abort and recycle to T-minus 13 minutes.

"Initiate terminal count." That was the order from the launch director after the SpaceX team gave a unanimous GO for launch at 6:30 p.m. EST (2330 GMT).

T-minus 16 minutes. This will be the last chance to launch in tonight's window.

NEW LAUNCH TIME. The clock has picked up again as SpaceX has identified a solution to the issue that caused the terminal countdown abort. The new launch time is 6:30 p.m. EST (2330 GMT).

SpaceX Falcon 9 product manager John Insprucker reports it looks like the SpaceX team will have an opportunity to try another countdown this evening. A new launch time is currently being established.

The fix appears to be as simple as resetting a telemetry limit on a power supply.

The countdown is resetting for T-minus 13 minutes and holding as engineers study the problem that triggered the automatic abort.

The Falcon 9's autosequencer called the abort just as the rocket was supposed to transition to internal power, but there's no word on the exact cause of the hold.

The launch team is safing the Falcon 9 rocket and preparing to recycle the countdown. It's not clear what caused the abort, but the launch window extends until 6:43 p.m. EST (2343 GMT), so there's time to resolve any minor issue.

ABORT. The countdown was aborted at T-minus 6 minutes, 11 seconds.

T-minus 6 minutes, 30 seconds. The Falcon 9's heaters are being deactivated, and the rocket will be transitioned to internal power in a few seconds.

T-minus 7 minutes and counting. Within the next minute, the Falcon 9's flight computer will be commanded to its alignment state. The Merlin engine pumps are continuing to chill down.

The launch danger area around Cape Canaveral is clear for launch.

T-minus 8 minutes and counting. Good chilldown continues on the first stage engines, and closeouts of the upper stage's gaseous nitrogen attitude control system are underway.

T-minus 9 minutes and counting. Prevalves leading to the Falcon 9's Merlin 1D first stage engines are opening, permitting super-cold liquid oxygen to flow into the engines to condition the turbopumps for ignition.

T-minus 10 minutes and counting. The terminal countdown autosequence has started. Any hold after this point will result in an automatic abort and recycle to T-minus 13 minutes.

T-minus 12 minutes. The launch team has verified all consoles are go for liftoff at 5:54 p.m. EST (2254 GMT).

The sun has just set here at Cape Canaveral, and the Falcon 9 rocket is bathed in light as the terminal countdown autosequence is about to begin at the T-minus 10 minute mark.

T-minus 15 minutes and counting. Here are some statistics on today's launch:

• 7th launch of a Falcon 9 rocket since 2010
• 12th launch of Falcon rocket family since 2006
• 6th Falcon 9 launch from Cape Canaveral
• 2nd launch of a Falcon 9 v1.1 rocket
• 1st Falcon 9 v1.1 launch from Cape Canaveral
• 1st Falcon 9 launch to geostationary transfer orbit
• 3rd Falcon 9 night launch
• 3rd Falcon 9 launch of 2013
• 10th launch from Cape Canaveral in 2013
• 55th launch of an SES satellite
• 3rd launch of an SES satellite in 2013

NEW LAUNCH TIME. SpaceX is now aiming for a launch at 5:54 p.m. EST (2254 GMT). The clock has reset to T-minus 17 minutes and counting.

LAUNCH DELAY. The countdown is holding at T-minus 13 minutes as the SpaceX launch team studies a first stage valve issue. Launch will not occur at 5:37 p.m. EST (2237 GMT).

The launch window extends until 6:43 p.m. EST (2343 GMT).

T-minus 17 minutes and counting. The Falcon 9 rocket stands 224 feet tall and measures 12 feet in diameter. At liftoff, its nine Merlin 1D first stage engines will generate about 1.3 million pounds of thrust.

T-minus 20 minutes and counting. The final poll of the 20-person launch team will begin at T-minus 13 minutes before the countdown enters the final phase.

At this point in the countdown, the SES 8 communications satellite should be transferring to internal power.

Liquid oxygen topping continues on the Falcon 9 rocket's first and second stages.

See our Facebook page for quick images of today's countdown to launch!

T-minus 40 minutes. No problems reported in the countdown. Ground systems, the launch vehicle, the SES 8 payload and the weather are all cooperating for an on-time launch this evening.

The latest weather brief showed conditions are "green" for an on-time liftoff.

T-minus 50 minutes. Today's launch is heading for a "supersynchronous" transfer orbit with an apogee, or high point, of 86,500 kilometers (53,748 miles) and a perigee, or low point, of 295 kilometers (183 miles).

The 6,918-pound SES 8 satellite is destined for a slot 22,300 miles above the equator in geostationary orbit at 95 degrees east longitude, where its Ku-band and Ka-band payload will beam direct-to-home television broadcasts and other services to India, Southeast Asia and surrounding regions for 15 years.

Today's mission marks the first SpaceX Falcon 9 launch with a satellite heading for a geostationary transfer orbit. Such an orbit requires two burns of the Falcon 9's upper stage Merlin 1D engine, first to place the satellite into a low-altitude parking orbit, then to raise its apogee to geostationary altitude or higher.

We're reporting live from Cape Canaveral Air Force Station. Weather is still favorable for launch this evening, and there are no issues being worked at this point in the countdown.

The mission's primary payload is the 6,918-pound SES 8 communications satellite for SES of Luxembourg.

Clouds blanketed Cape Canaveral throughout the day are thinning out, but conditions are blustery with stiff winds out of the east.

T-minus 90 minutes. The countdown continues tracking toward an on-time liftoff at 5:37 p.m. EST (2237 GMT).

Today's launch is the second flight of SpaceX's upgraded Falcon 9 rocket, which features more powerful engines, a protective payload fairing for satellite passengers, stretched fuel tanks, and a more robust avionics system.

The upgraded rocket, known as the Falcon 9 v1.1, first launched Sept. 29 on a demonstration flight from Vandenberg Air Force Base, Calif.

All of the Falcon 9's previous launches originated from Space Launch Complex 40 at Cape Canaveral Air Force Station, Fla.

Today's flight is from Space Launch Complex 40, which was formerly used by the Air Force's Titan 4 rocket until its last flight from Florida in April 2005. SpaceX took over the pad and launched the first Falcon 9 rocket from there on June 4, 2010.

The second Falcon 9 launch on Dec. 8, 2010, sent SpaceX's first Dragon capsule into space on a two-orbit test flight for SpaceX's commercial cargo services to the space station. The December 2010 flight did not go to the space station, but it demonstrated Dragon's avionics and heat shield, culminating with splashdown in the Pacific Ocean.

SpaceX's next launch on May 22, 2012, launched the Dragon spacecraft on a NASA-sponsored test flight to the International Space Station. The 9-day Dragon mission delivered cargo to the space station and returned hardware from orbit with a splashdown in the Pacific Ocean on May 31.

On Oct. 7, 2012, SpaceX launched its fourth Falcon 9 rocket on the first operational Dragon resupply flight to the space station. The three-week mission delivered 882 pounds of cargo to the complex and returned to Earth on Oct. 28 with 1,673 pounds of equipment.

A Falcon 9 launch on March 1, 2013, put up another automated Dragon cargo craft en route to the space station with 1,869 pounds of supplies. It arrived at the outpost March 3 and stayed for 23 days before coming back to Earth with 2,668 pounds of return cargo.

The most recent Falcon 9 launch on Sept. 29 from California deployed Canada's Cassiope space weather research and communications demonstration satellite into polar orbit.

The Falcon 9 rocket is fully fueled with super-cold liquid oxygen and kerosene propellants. Both stages are being replenished with cryogenic oxidizer until the final minutes of the countdown to replace propellant that gradually boils off due to the warm ambient temperatures in Florida.

SpaceX says the webcast of today's launch will begin at 5 p.m. EST (2200 GMT), about 37 prior to liftoff, and continue through cutoff of the second stage engine.

We will have the live webcast on this page.

If you are heading out to the beach or Port Canaveral to watch the launch, sign up for our Twitter feed to get occasional countdown updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)

And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.

Everything is on schedule for today's Falcon 9 launch from Cape Canaveral Air Force Station, Fla.

Preliminary checks on the 224-foot-tall launcher are underway, and propellants are being loaded into the Falcon 9 rocket. Both stages of the Falcon 9 burn kerosene and liquid oxygen.

Check out a countdown timeline for more details on prelaunch activities.

Those of you watching this page will see two launches today.

Coming up at 3:30 p.m. EST (2030 GMT), we will stream live video from the Baikonur Cosmodrome in Kazakhstan as a Soyuz rocket blasts off with the Progress M-21M resupply craft heading for the International Space Station.

Packed with 2.9 tons of fuel and supplies, the Progress cargo freighter will launch at 3:53 p.m. EST (2053 GMT), and the Soyuz rocket will inject the automated spaceship into low Earth orbit about 9 minutes later.

The Progress is due to link up with the space station Friday.

Then at 5 p.m. EST (2200 GMT), we will stream SpaceX's live webcast of the Falcon 9 launch at Cape Canaveral, Fla. That launch is set for 5:37 p.m. EST (2237 GMT).

The weather outlook for this evening's launch window continues to show an 80 percent chance of favorable conditions, with partly cloudy skies, breezy winds and a chance of isolated showers in the area.

The 66-minute launch window opens at 5:37 p.m. EST (2237 GMT), just after sunset at Cape Canaveral.

The outlook calls for scattered clouds at 3,000, 8,000 and 20,000 feet, winds out of the east at 15 knots gusting to 22 knots, and a launch time temperature of 69 degrees Fahrenheit.

"Easterly winds and light coastal showers will continue today, but there is a very low threat of lightning. Elsewhere, a low pressure system has developed in the Gulf of Mexico and will move rapidly east towards the Florida Panhandle. There is a slight chance that thick clouds ahead of this system could encroach on the Spaceport towards the end of the window," Air Force meteorologists wrote in a forecast issued this morning.

"Primary launch day concerns are cumulus clouds with onshore flow showers and thick clouds," forecasters said.

If today's launch is scrubbed due to weather or a technical problem, SpaceX does not plan to make another launch attempt until Thursday - Thanksgiving Day in the United States.

The Federal Aviation Administration, which grants launch licenses to commercial rocket operators, has not approved launch on Tuesday or Wednesday because those are two of the busiest travel days of the year.

The forecast Thanksgiving Day also shows an 80 percent chance of favorable weather conditions, with the only concerns being liftoff winds and cumulus clouds.

SpaceX technicians rolled the Falcon 9 rocket out of its hangar and mounted the booster and its transporter-erector atop Cape Canaveral's Complex 40 launch pad overnight, plugging into electrical and propellant lines ahead of the start of the countdown today.

The 224-foot-tall rocket is one of the tallest in the world. The Falcon 9's first and second stages measure 12 feet in diameter, and the SpaceX-built payload fairing housing the SES 8 communications satellite is 17 feet in diameter (5.2 meters) and 43 feet tall.

Made of two clamshell-like halves that open and fall away about 4 minutes after liftoff, the fairing is adorned with the U.S. flag on one side and the SES corporate logo on the other side.

Today's launch marks the first flight of the upgraded Falcon 9 rocket, known as version 1.1, from Cape Canaveral after the configuration first launched from Vandenberg Air Force Base in California on Sept. 29.

In an interview in September, SpaceX CEO Elon Musk said engineers added simplicity, reliability and capacity to the previous version of the Falcon 9, which flew successfully five times.

Here is part of our story on the Falcon 9 v1.1 from September:

Musk said the redesigned Falcon 9 is the prototype for a reusable rocket SpaceX envisions could drastically reduce launch costs, decreasing the price of a Falcon 9 flight even lower than SpaceX's advertised rate, which undercuts competing rockets, such as the Russian Proton and Europe's Ariane 5 launcher.

It is this version of the Falcon 9 that SpaceX hopes will safely deliver astronauts to orbit on the way to the space station, beginning as soon as 2017.

Reliability is paramount in the launch business, and cost and schedule are right behind in a matrix of concerns for rocket buyers.

Musk said SpaceX answered these appeals, and added power and efficiency to the Falcon 9's Merlin engines to loft heftier payloads into higher orbits.

SpaceX engineers installed a triple-redundant flight computer in the Falcon 9 rocket, adding another level of confidence in the launcher's avionics. They also wrote new software for the computer, which is based on a flight-proven unit from SpaceX's Dragon cargo-carrying space station freighter.

"You could put a bullet hole in any one of the avionics boxes and it would just keep flying," Musk said.

Designers adjusted the connection points between the Falcon 9's first and second stages, replacing nine hardware interfaces and three spring-like pusher elements - pneumatic devices which ensure stage separation occurs - with three connectors with integrated pushers.

"We go from 12 things that can go wrong to three at the point of staging," Musk said.

The Falcon 9 v1.1 is powered by 10 Merlin 1D engines - nine on the first stage and one on the second stage - each generating 147,000 pounds of sea level thrust. The vacuum-rated upper stage engine, sporting a niobium nozzle to radiate engine heat, produces 161,000 pounds of thrust once out of the atmosphere.

The Merlin 1C engine, used on all five of the Falcon 9's previous missions, was capable of firing with 95,000 pounds of thrust at sea level.

Along with greater performance, the Merlin 1D is easier to manufacture thanks to high-efficiency processes, increased robotic construction and a reduced parts count, according to SpaceX's press kit.

SpaceX upgraded the propellant injection system inside the Merlin 1D, replacing two valves dedicated to fuel and oxidizer with a single unit to improve reliability and save weight.

Musk said the Merlin 1D engine weighs in at less than 1,000 pounds.

"If we don't have the world record for thrust-to-weight ratio, we're very close," Musk said.

Musk's rocket team modified the engine arrangement on the first stage, an effort he said allows engineers to remove aerodynamic manifolds around the perimeter of the rocket.

Earlier Falcon 9s featured a square "tic-tac-toe" layout of the nine first stage engines arrayed in a three-by-three pattern. The Falcon 9 v1.1 uses what SpaceX calls an "octaweb" design, with eight engines surrounding a center engine in a circular pattern.

According to Musk, engineers installed ablative bumpers between the engines to prevent a mishap with one engine from damaging another.

The first stage upgrades also include a heat shield and stretched propellant tanks for the Merlin engines' supply of kerosene and liquid oxygen.

"We put a stronger heat shield at the base of the rocket to better enable the first stage to survive the high dynamic pressure on re-entry," Musk said.

The new Falcon 9 first stage is 60 percent longer but has the same diameter as the Falcon 9's previous version, permitting the rocket to be fabricated with the same tooling already inside SpaceX's rocket factory in Hawthorne, Calif.

The launch of a high-definition television broadcasting satellite by SpaceX's Falcon 9 rocket Monday will mark the first commercial communications craft to take off from the United States in four years, a gap representative of America's diminished place in the commercial launch market as more affordable Russian and European boosters gobbled up contracts.

Read our full story.

Ready to test the commercial mettle of the Falcon 9 rocket, SpaceX engineers are preparing to loft a television broadcasting satellite into orbit from Cape Canaveral on Monday in a mission that could usher in a new paradigm in the global launch services industry.

Read our full story.

SpaceX founder Elon Musk told reporters this afternoon that officials have signed off on the fix to resolve the problem that aborted an upper stage engine restart test on the Falcon 9's last launch in late September.

The Sept. 29 launch from Vandenberg Air Force Base in California was a success, delivering Canada's Cassiope space weather research and communications demonstration satellite into polar orbit as planned.

But SpaceX attempted to re-ignite the Falcon 9's upper stage Merlin 1D engine as a test, and the restart was aborted.

"What appeared to be the case on the last mission was that the igniter lines froze due to impingement from the liquid oxygen bleed. There's a liquid oxygen chill that occurs during coast, and the igniter fluid freezes at a relatively high temperature," Musk said. "Obviously, what we've done to correct that is to insulate those lines and ensure the liquid oxygen bleed does not impinge on the lines. We looked carefully to see if there were any other possible issues that were a near-miss that we could encounter on this flight. We could not find any. We reviewed it with the SES technical team and they seemed comfortable as well."

The launch of SES 8 requires the upper stage restart to boost the satellite into a high-altitude transfer orbit on the way to a final operating position in geostationary orbit 22,300 miles above the equator.

Martin Halliwell, chief technical officer of Luxembourg-based SES, said he was comfortable the issue is behind SpaceX.

"We believe we've retired all the risk," Halliwell said this afternoon in a meeting with media in Cocoa Beach, Fla. "We've looked at the first stage, the first stage lights up OK, works perfectly. We've looked at the second stage ... we've looked at that and we're comfortable with that.

"We've worked extremely closely with the SpaceX team and we'd like to thank them for the openness and the comaraderie they've shown us during this entire process," Halliwell said. "It's been quite extraordinary, quite honestly, very different from working with some of the other launch vehicle providers."

According to Halliwell, SES engineers analyzed data on the upper stage engine provided by SpaceX and inspected the repair work on the igniter system.

"We've had our crews crawling all around the engine space," Halliwell said. "They've been embedded with the SpaceX propulsion team ... it's given us a real feel-good factor."

In order to comply with U.S. arms trade regulations, SES had to restrict the engineering team working with SpaceX on the engine anomaly to U.S. citizens.

SpaceX said engineers from NASA and the U.S. Air Force also reviewed data from the engine. "It was not a complicated issue to fix," said Gwynne Shotwell, SpaceX's president. "We're glad we caught it on a mission where we were only demonstrating that [capability]."

The weather forecast hasn't changed much since yesterday.

There is still an 80 percent chance of favorable weather during Monday's launch window, which opens at 5:37 p.m. EST and closes at 6:43 p.m. (2237-2343 GMT).

The primary concerns at launch time are thick clouds and cumulus clouds, according to U.S. Air Force meteorologists.

"Blustery conditions behind a cold front peak this afternoon as winds slowly swing northeasterly increasing the coastal shower threat overnight. As the front makes its way into South Florida, winds continue to weaken and turn more easterly through the day on Monday decreasing below liftoff constraints," forecasters wrote Sunday.

"There is a low lightning threat, but coastal showers could be in the area. The boundary to our south is quick to return to our area in response to a low pressure system developing in the northern Gulf of Mexico which strengthens and moves east. There is a slight chance clouds ahead of this system could encroach on the spaceport towards the end of the window so thick clouds have been added and winds removed as concerns."

Launch time conditions should be partly cloudy with scattered cloud layers at 3,000 feet, 8,000 feet and 20,000 feet. Isolated showers are possible, and the temperature is forecast to be 69 degrees Fahrenheit. Winds will be out of the east at 15 knots with gusts to 22 knots.

Technicians are in the final stages of readying a SpaceX Falcon 9 rocket for launch Monday on the launcher's first mission to geostationary transfer orbit with a commercial communications satellite for television broadcasters in India and Southeast Asia.

The 224-foot-tall rocket will be rolled to the launch pad and erected vertical ahead of Monday's launch, which is set for a 66-minute launch window opening at 5:37 p.m. EST (2237 GMT) from Cape Canaveral's Complex 40.

SpaceX CEO Elon Musk says the launch will be the Falcon 9's "toughest mission to date," according to a post on his Twitter account.

"Requires coast + upper stage restart + going to 80,000 km altitude (~1/4 way to moon)," Musk wrote on Twitter.

The 6,918-pound mass of the SES 8 communications satellite gives the Falcon 9 ample performance to boost the spacecraft into a high-altitude "supersynchronous" transfer orbit. The high orbit will help SES 8 save propellant when it uses an on-board propulsion system to circularize its orbit at an altitude of 22,300 miles over the equator.

The weather forecast for Monday calls for an 80 percent chance of acceptable conditions for launch.

"Winds weaken and become more easterly through the day on Monday, decreasing below liftoff constraints by the launch window opening," Air Force meteorologists wrote in a forecast summary Saturday. "There is a low lightning threat, but coastal showers could be in the area. The primary concerns for launch day are cumulus clouds and liftoff winds."

The outlook predicts scattered cloud layers at 3,000 feet and 20,000 feet with isolated showers in the area. Winds will be out of east at 15 knots with gusts to 22 knots, and the temperature is forecasted to be 69 degrees Fahrenheit.

The forecast worsens Tuesday, with just a 30 percent chance of good weather for launch.

SpaceX says frozen fluid lines prevented the Falcon 9 rocket's second stage engine from re-igniting on a Sept. 29 test flight, but engineers are confident extra insulation will resolve the thermal problem on the Falcon 9's next mission set for liftoff Monday on the company's first launch to geostationary transfer orbit.

Read our full story.