Splashdown confirmed! The Dragon spacecraft has returned to Earth with nearly 3,300 pounds of space station cargo, ending its fourth operational flight to the complex.

SpaceX says the splashdown occurred at approximately 3:38 p.m. EDT (1938 GMT).

Mission control in Houston just told the space station crew that Dragon is descending under parachutes.

After deploying two drogue parachutes for stability, Dragon should now be descending through 10,000 feet under three 116-foot main parachutes, which are designed to slow the craft's speed to a gentle 11 mph at the time of splashdown.

There are no updates from SpaceX yet confirming a good parachute deployment.

Temperatures outside the Dragon spacecraft are expected to reach up to 3,000 degrees Fahrenheit during re-entry.

The spacecraft is approaching the splashdown zone on a southwest-to-northeast trajectory.

Dragon should now be encountering the upper reaches of the atmosphere - a point known as entry interface - over the Pacific Ocean. Officials expect a communications blackout in the next few minutes, followed by deployment of the capsule's parachutes beginning at 3:30 p.m. EDT (1930 GMT).

As with its previous missions, SpaceX is not providing live coverage of the re-entry and splashdown of the Dragon supply ship. We'll post updates here as we get them.

At this time, the unpressurized trunk of the Dragon spacecraft should have separated from the ship's entry capsule. The trunk will burn up in the atmosphere.

The deorbit burn should now be complete. Jettison of the 12-foot-diameter trunk section with its solar arrays should be coming up in a few minutes, but we don't have confirmation of those events from SpaceX.

Flying high above the Indian Ocean, the Dragon spacecraft should now be firing firing its Draco thrusters for the deorbit burn, committing the capsule for return to Earth. The burn is expected to last approximately 10 minutes.

Dragon is carrying more than 1.6 tons of cargo from the space station in its pressurized cabin. The capsule is the only robotic cargo freighter able to retrieve equipment from the space station and return it to Earth for analysis or repairs.

A recovery team on a 150-foot boat is in position near the Dragon splashdown zone. The vessel carries a crane to pluck the floating capsule from the Pacific Ocean, along with two inflatable boats to support the capsule's retrieval and safing.

About a dozen SpaceX engineers and technicians are at the splashdown site, which lies about 265 miles west of Baja California southwest of San Diego.

The SpaceX crew includes a four-person dive team to help retrieve the capsule after splashdown.

Coming up in a few hours, the Dragon spacecraft will close the door to its guidance, navigation and control bay at around 1:29 p.m. EDT (1729 GMT).

Ignition of the capsule's thrusters is set for 2:43:07 p.m. EDT (1843:07 GMT) for an appoximately 10-minute deorbit burn. Splashdown 265 miles west of Baja California is scheduled for 3:39:38 p.m. EDT (1939:38 GMT).

NASA Television coverage of the Dragon resupply flight has ended. No live video is expected of the Dragon's splashdown, but you can check back here for updates on the status of the mission as we receive information.

You can also follow us on Twitter to get periodic updates.

Coming up in a few hours, the Dragon spacecraft will close the door to its guidance, navigation and control bay at around 1:29 p.m. EDT (1729 GMT).

Ignition of the capsule's thrusters is set for 2:43:07 p.m. EDT (1843:07 GMT) for an appoximately 10-minute deorbit burn. Splashdown 265 miles west of Baja California is scheduled for 3:39:38 p.m. EDT (1939:38 GMT).

NASA Television coverage of the Dragon resupply flight has ended. No live video is expected of the Dragon's splashdown, but you can check back here for updates on the status of the mission as we receive information.

You can also follow us on Twitter to get periodic updates.

Dragon's third and final departure burn is complete, moving the craft beyond the 200-meter keep-out sphere, an imaginary bubble around the space station.

The Dragon spacecraft has finished its second departure burn. A yaw maneuver is coming up at 10:05 a.m. EDT (1405 GMT), then a final departure maneuver is planned about a minute later.

The first departure burn is complete.

Astronaut Reid Wiseman has backed the robotic arm away to a distance of about 4 feet. The first of three rocket burns to guide Dragon away from the space station is coming up soon.

Dragon is now flying on its own, having been released from the grasp of the space station robotic arm at 9:57 a.m. EDT (1357 GMT) as the craft flew off the northwest coast of Australia.

Five minutes until release of Dragon. Spacecraft communicator has radioed the space station astronauts they are "go" for release of the Dragon capsule at 1357 GMT (9:57 a.m. EDT).

NASA and SpaceX report they are in good shape for the departure of Dragon with 3,563 pounds of cargo for the return trip to Earth.

The spacecraft are flying over the southern Gulf of Thailand right now.

Space station mission control in Houston and SpaceX mission control in Hawthorne are "go" for release of Dragon.

The Dragon spacecraft has been placed into free drift, a mode in which its Draco maneuvering thrusters are inhibited. This is a planned step required before release of the cargo craft.

The Dragon's laser rendezvous sensor is reported to be operating as planned.

Grasped by the robotic arm, the Dragon spacecraft is near its planned release point below the space station.

Astronaut Reid Wiseman will command the arm to release the capsule at 9:57 a.m. EDT (1357 GMT), while Russian cosmonaut Barry "Butch" Wilmore will assist. The duo will man a communications panel to issue commands to Dragon if necessary.

The crew will monitor the spacecraft until it exits the so-called keep-out sphere 200 meters around the space station.

Grasped by the robotic arm, the Dragon spacecraft is near its planned release point below the space station.

Astronaut Reid Wiseman will command the arm to release the capsule at 9:57 a.m. EDT (1357 GMT), while Russian cosmonaut Barry "Butch" Wilmore will assist. The duo will man a communications panel to issue commands to Dragon if necessary.

The crew will monitor the spacecraft until it exits the so-called keep-out sphere 200 meters around the space station.

Closing out a five-week mission, a SpaceX Dragon cargo craft will depart the International Space Station on Saturday and dive back into Earth's atmosphere, deploy parachutes and splash down in the Pacific Ocean.

The spaceship is packed with nearly 3,300 pounds of gear, including research specimens housed inside refrigerators, 10 mice launched to study muscle atrophy in microgravity, spacewalk hardware, computer components, cameras and other equipment.

Astronauts living on the space station loaded the return cargo into the Dragon spacecraft's pressurized cabin over the last few weeks.

The Dragon cargo craft launched Sept. 21 aboard a Falcon 9 rocket from Cape Canaveral. It reached the space station Sept. 23, delivering nearly 5,000 pounds of supplies and experiments, including a 3D printer, spacesuit batteries, a small satellite deployer, and a $26 million NASA instrument to help meteorologists study the intensification of hurricanes.

The gumdrop-shaped re-entry capsule, measuring 12 feet diameter and 14 feet tall, will streak through the atmosphere flying southwest-to-northeast over the Pacific Ocean, heading for a splashdown zone a few hundred miles west of Baja California.

SpaceX's resupply freighter is the only spacecraft capable of returning significant amounts of cargo to Earth. Russia's Soyuz crew capsule can land with limited cargo, and the space station's other supply ships from Orbital Sciences Corp., Russia, Europe and Japan are designed to burn up during re-entry to dispose of trash.

Operating on commands from mission control, the space station's robotic arm grappled the Dragon cargo capsule and removed it from the Harmony module's Earth-facing docking port early Saturday.

Release from the robot arm is set for 9:56 a.m. EDT (1356 GMT).

The Dragon's Draco maneuvering thrusters will conduct three burns to depart the vicinity of the space station, then the craft will close and latch the door to its navigation bay before setting up for a de-orbit burn at 2:43 p.m. EDT (1843 GMT).

The spaceship will jettison its unpressurized trunk section and solar panels a few minutes later to burn up in the atmosphere, while the main module re-enters cocooned inside a specialized ablative heat shield developed by NASA and SpaceX to withstand temperatures reaching up to 3,000 degrees Fahrenheit on its hypersonic approach to a landing zone off the coast of Baja California.

Dual drogue parachutes will deploy when the capsule passes an altitude of about 45,000 feet, then three 116-foot-diameter main chutes will open to slow down the craft's descent to a gentle 10 mph for splashdown at 3:39 p.m. EDT (1939 GMT).

A maritime recovery team will be on standby to recover the capsule from the Pacific Ocean and ferry it back to port in Long Beach, Calif., where SpaceX will hand over time-sensitive samples to NASA for delivery to science teams around the world.

The Dragon's splashdown will end SpaceX's fourth commercial resupply flight to the space station, which began with a middle-of-the-night launch Sept. 21 aboard a Falcon 9 rocket from Cape Canaveral.

SpaceX's next cargo mission to the orbiting research lab is set for launch around Dec. 9.

Orbital Sciences, NASA's other cargo transportation provider, is preparing its third operational mission to the space station for liftoff Oct. 27.

Rough seas in the Pacific Ocean will keep SpaceX's Dragon cargo capsule in space a few days longer than planned, with the unpiloted supply ship's return to Earth now set for Saturday hauling a load of research specimens from the International Space Station back to the ground.

Read our full story.

A $26 million science instrument carried to the International Space Station last month by SpaceX's Dragon cargo capsule has been switched on and is measuring winds over the world's oceans to help forecasters track the intensity of tropical cyclones, NASA officials said.

Read our full story.

Check out photos showing the launch and rendezvous of SpaceX's Dragon cargo craft earlier this week.

A Dragon cargo craft closed in on the International Space Station on Tuesday after a two-day pursuit following Sunday's launch from Cape Canaveral, delivering more than 2.5 tons of supplies for scientists and the lab's residents.

Read our full story.

All 16 bolts in the common berthing mechanism have driven to create a firm connection between Dragon and the Harmony module. The commercial spacecraft is now part of the International Space Station.

Today's arrival marks the fifth time a Dragon spacecraft has reached the space station, the 72nd unmanned cargo ship to arrive at the complex, and the 152nd overall mission to reach the outpost.

The next step this morning will be to move Dragon to an Earth-facing berthing port on the space station's Harmony module in the next few hours.

"This was, indeed, a great flight of Dragon toward the station, and we're happy to have a new vehicle on board," Gerst just radioed mission control.

Capture confirmed. European Space Agency astronaut Alexander Gerst grappled Dragon at 6:52 a.m. EDT (1052 GMT) as the space station flew 260 miles above the Pacific Ocean.

Gerst is now moving the robot arm toward Dragon.

Mission control just radioed the crew they are "go" to capture Dragon.

While Gerst is at the controls of the Canadian-built robotic arm, astronaut Reid Wiseman is overseeing the Dragon spacecraft's position and status from the space station's windowed cupola module. Wiseman has a command panel to order Dragon to retreat or abort if a problem develops.

Dragon has arrived at the capture point 10 meters, or 32 feet, beneath the space station and within the reach of the 58-foot robotic arm, which will be operated by European Space Agency astronaut Alexander Gerst.

Less than 50 feet separate the Dragon spacecraft and the International Space Station as the two vehicles fly into an orbital sunset off the southern coast of Australia.

Dragon is now 20 meters, or 65 feet, from the space station.

With the space station crew, Houston and Hawthorne all ready for final approach, Dragon has resumed its glacial flight toward the complex to the so-called capture box, which is about 10 meters, or 32 feet, beneath the outpost.

Dragon has arrived at a hold point 30 meters, or 98 feet, from the space station. There will be polls of teams in Houston and Hawthorne in the next few minutes before departing this hold point.

Astronaut Reid Wiseman says the Dragon appears to be in the correct position for this point in the rendezvous. The crew has a control panel linked with Dragon via UHF radio to issue simple commands in case of any problem. For example, the astronauts could tell the spacecraft to hold, abort or retreat.

Wiseman and ESA astronaut Alexander Gerst, who will operate the station's robot arm to grapple Dragon, are inside the space station's cupola module for this morning's arrival.

Range is now about 72 meters, or 230 feet.

The Dragon spacecraft is approaching the space station from below, now about 100 meters, or 328 feet, from the complex.

A Dragon cargo craft is closing in on the International Space Station after a two-day pursuit following Sunday's launch from Cape Canaveral, poised to deliver more than 2.5 tons of supplies to the complex after an automated laser-guided final approach.

The rendezvous will culminate with grapple by the outpost's robotic arm around 7:04 a.m. EDT (1104 GMT).

The SpaceX-owned spaceship is carrying more than 5,100 pounds of cargo to reinforce the space station's stocks of research experiments, crew provisions and spare parts.

The Dragon capsule has fired its Draco thrusters multiple times since it launched aboard a Falcon 9 rocket Sunday at 1:52 a.m. EDT (0552 GMT), raising its altitude to match the orbit of the space station and set up for today's final rendezvous sequence.

By about 2:25 a.m. EDT (0625 GMT), the Dragon spacecraft was about 28 kilometers, or 17 miles, below and behind the space station. At that distance, the Dragon was within range of a UHF communications panel the space station's crew can use to issue simple commands to the supply ship in the event of a problem.

Several height-adjustment and midcourse correction rocket burns fine-tuned Dragon's rendezvous, guiding the ship into position 350 meters, or about 1,150 feet, directly beneath the space station at 5:10 a.m. EDT (0910 GMT).

The Dragon initially relied on relative GPS navigation data to guide its approach to the space station. Once directly beneath the complex, its computers were to switch to laser and thermal sensors.

Dragon carries a laser guidance sensor package and and a pair of thermal cameras to aid its final rendezvous with the space station.

Before leaving the initial hold point 1,150 feet beneath the space station, the cargo craft conducted a 180-degree yaw maneuver to align its grapple fixture with the position of the space station's robot arm.

Soon after beginning its final approach sequence, the Dragon spacecraft halted again at a hold position 250 meters, or 820 feet, below the space station. This brief hold allowed ground controllers to assess the status of the rendezvous and issue a "go" for the Dragon to enter the so-called keep-out sphere, an imaginary circle around the space station in which traffic is tightly controlled for safety reasons.

The Dragon spacecraft departed the 250-meter hold point around 5:34 a.m. EDT (0934 GMT), heading for a 30-meter hold position before pressing on to a final point about 10 meters, or 33 feet, beneath the space station.

Arrival at the final hold point is scheduled around 6:46 a.m. EDT (1046 GMT).

Astronauts Alexander Gerst and Reid Wiseman will monitor the final phase of the Dragon's approach, including manning the space station's robotic arm to grapple the free-flying cargo craft. Gerst will grapple Dragon with the robot arm around 7:04 a.m. EDT (1104 GMT).

Once the Dragon is firmly snared by the robotic arm, the 58-foot Canadarm will move the capsule into position for berthing with the Earth-facing port on the space station's Harmony module around 9:30 a.m. EDT (1330 GMT).

SpaceX launched a Dragon supply ship packed with mice, an experimental 3D printer, a hurricane research instrument, and a bundle of crew provisions on a two-day pursuit of the International Space Station with a thunderous middle-of-the-night sendoff from Cape Canaveral on Sunday aboard a Falcon 9 rocket booster.

Read our full story.

The guidance, navigation, and control systems door has been opened. The instruments inside the navigation bay can now be activated and tested.

The Dragon spacecraft will reach the International Space Station on Tuesday, with grapple scheduled for approximately 7:04 a.m. EDT (1104 GMT).

Video beamed back from the Dragon spacecraft show both solar array wings have unfurled. They span 54 feet tip-to-tip.

Dragon is deploying its two solar array wings now.

The Dragon spacecraft has separated from the Falcon 9 rocket. Solar array deployment should begin within 2 minutes.

Second stage shutdown! Falcon 9 has achieved orbit.

T+plus 8 minutes, 40 seconds. About one minute until the second stage Merlin 1D engine is supposed to shut down as the vehicle reaches orbit. The launcher is aiming for an orbit with a low point of 310 kilometers (192 miles), a high point of 360 kilometers (223 miles), and an inclination of 51.6 degrees.

T+plus 7 minutes, 40 seconds. The vehicle remains in a nominal trajectory. The terminal guidance phase of the launch will start soon.

T+plus 7 minutes. The kerosene-fueled Merlin 1D upper stage engine generates about 161,000 pounds of thrust in vacuum.

T+plus 6 minutes, 20 seconds. The rocket is at an altitude of 202 kilometers, traveling at 3.7 kilometers per second and flying 420 kilometers downrange from Cape Canaveral. The vehicle is now in communications range of a ground station in New Hampshire.

T+plus 5 minutes, 20 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.

The rocket is now traveling more than 6,000 mph.

T+plus 4 minutes. The nose cone covering the Dragon spacecraft's berthing port should be be jettisoned now.

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. Engines no. 1 and 9 will shut down about 10 seconds before the remaining seven Merlin 1D first stage 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 20 seconds. The Falcon 9 rocket's pitch program has initiated to put the 208-foot-tall rocket on an northeasterly trajectory from Cape Canaveral.

LIFTOFF of the Falcon 9 rocket, resupplying the International Space Station through the private sector.

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 53 water nozzles on 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 1:52 a.m. EDT (0552 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.

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, 30 seconds. 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 1:52:03 a.m. EDT (0552:03 GMT).

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:

• 13th launch of a Falcon 9 rocket since 2010
• 18th launch of Falcon rocket family since 2006
• 12th Falcon 9 launch from Cape Canaveral
• 8th launch of a Falcon 9 v1.1 rocket
• 7th Falcon 9 v1.1 launch from Cape Canaveral
• 2nd launch of a Dragon on a Falcon 9 v1.1 rocket
• 5th SpaceX mission to the space station
• 6th Falcon 9 night launch
• 6th Falcon 9 launch of 2014
• 6th flight of a Dragon spacecraft
• 14th launch from Cape Canaveral in 2014

T-minus 17 minutes and counting. The Falcon 9 rocket stands 208 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.

Fully fueled for launch, the Falcon 9 contains about 1.05 million pounds of kerosene and liquid oxygen propellants.

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.

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

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

The cargo-carrying Dragon capsule is being transitioned to internal power at this time.

T-minus 30 minutes. At the time of launch, the International Space Station will be flying 262 miles up over a point southwest of New Zealand.

Linkup with the complex is scheduled at 7:04 a.m. EDT (1104 GMT) Tuesday, when astronauts Alexander Gerst will grapple the Dragon spacecraft with the space station's robotic arm.

The launch weather officer reports all weather rules are currently "green" and expected to remain so for the rest of the countdown.

T-minus 60 minutes and counting. All four propellant tanks on the Falcon 9 rocket are now in topping mode. The cryogenic liquid oxygen tanks on the first and second stages will continue to be slowly replenished until the final minutes before launch to replace propellant that gradually boils off due to the warm ambient temperatures in Florida.

We will also be tweeting countdown updates. 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.

The weather forecast has improved again, now with just a 10 percent chance conditions will violate one of the Falcon 9's launch weather rules at 1:52:03 a.m. EDT (0552:03 GMT).

NASA TV coverage of the Falcon 9 launch is beginning now.

Filling of the Falcon 9 rocket's first stage with RP-1 fuel has been completed.

The Dragon spacecraft is packed with more than 2.5 tons of scientific experiments, provisions and maintenance items.

Among the supplies packed inside are the first 3D printer to be launched into space, 20 mice riding in a specially-made habitat, an instrument to monitor ocean winds, and a commercial experiment that could improve the design of golf clubs.

The Dragon's total internal payload includes 1,644 pounds of science and research gear, 1,380 pounds of crew provisions, 403 pounds of vehicle hardware, 101 pounds of computer tools and 55 pounds of spacesuit equipment.

A $26 million NASA instrument is mounted inside the Dragon capsule's external trunk section. Named RapidScat, the instrument will be placed outside the space station to measure ocean winds and aid in hurricane forecasting.

Today's launch marks SpaceX's fourth operational resupply run to the space station under a 12-mission, $1.6 billion contract with NASA covering cargo services through 2016.

Fueling of the 208-foot-tall Falcon 9 rocket is about to get underway at Cape Canaveral's Complex 40 launch pad after the SpaceX launch team issued a "go" to begin propellant loading.

The two-stage rocket burns RP-1 fuel -- a high-refined kerosene -- and liquid oxygen during today's nine-minute launch sequence.

Today's flight marks the 13th launch of a Falcon 9 rocket since debuting in June 2010. It's the 8th mission of the improved Falcon 9 v1.1 version, which made its inaugural launch in September 2013 from Vandenberg Air Force Base.

All weather rules are observed "go" at this time.

The official forecast now calls for a 70 percent chance of favorable weather for the Falcon 9 rocket's instantaneous launch opportunity.

Launch time is set for 1:52:03 a.m. EDT (0552:03 GMT), roughly the moment Earth's rotation carries the Cape Canaveral launch base into the path of the International Space Station's orbit.

The main weather concerns are with the cumulus cloud rule and the flight through precipitation rule.

The outlook at launch time calls for isolated rain showers, scattered clouds at 3,000 feet, and broken clouds at 20,000 feet, with northwest winds at 10 to 15 mph and a temperature of 73 degrees Fahrenheit.

T-minus 4 hours. Two weather rules are currently observed "no go" at the Falcon 9 launch site, but there is plenty of time for conditions to improve overnight.

SpaceX is preparing to begin fueling operations, in which kerosene and liquid oxygen propellants, along with helium pressurant, will be pumped aboard the two-stage Falcon 9 rocket.

A second launch attempt for SpaceX's Falcon 9 rocket is on tap overnight, with liftoff on a space station resupply flight targeted for 1:52 a.m. EDT (0552 GMT).

The weather has improved over Florida's Space Coast on Saturday, but meteorologists will be closely watching scattered rain showers and thick clouds that have a 60 percent chance of prohibiting liftoff during Sunday's instantaneous early morning launch opportunity.

Persistent rain showers and clouds at SpaceX's Cape Canaveral launch base kept a Falcon 9 rocket grounded Saturday, delaying the start of a resupply mission to the International Space Station by at least one day.

Read our full story.

Sunday's launch opportunity is set for precisely 1:52:04 a.m. EDT (0552:04 GMT), and officials predict a 40 percent chance of favorable weather.

SCRUB. SpaceX has called off this morning's launch attempt due to bad weather.

The Dragon spacecraft is packed with more than 2.5 tons of scientific experiments, provisions and maintenance items.

Among the supplies packed inside are the first 3D printer to be launched into space, 20 mice riding in a specially-made habitat, an instrument to monitor ocean winds, and a commercial experiment that could improve the design of golf clubs.

The Dragon's total internal payload includes 1,644 pounds of science and research gear, 1,380 pounds of crew provisions, 403 pounds of vehicle hardware, 101 pounds of computer tools and 55 pounds of spacesuit equipment.

A $26 million NASA instrument is mounted inside the Dragon capsule's external trunk section. Named RapidScat, the instrument will be placed outside the space station to measure ocean winds and aid in hurricane forecasting.

Today's launch marks SpaceX's fourth operational resupply run to the space station under a 12-mission, $1.6 billion contract with NASA covering cargo services through 2016.

The updated weather forecast shows a 90 percent chance conditions will prevent liftoff during this morning's instantaneous Falcon 9 launch opportunity at 2:14:38 a.m. EDT (0614 GMT).

Two launch weather rules are currently observed "no go" for liftoff -- the thick cloud rule and the disturbed weather rule.

The Air Force weather officer sees little chance conditions will improve in time for launch.

The Falcon 9 and Dragon were powered up Friday evening for countdown activities, with computer and systems testing being completed before the start of fueling.

All four propellant tanks on the Falcon 9 rocket are now in topping mode. The cryogenic liquid oxygen tanks on the first and second stages will continue to be slowly replenished until the final minutes before launch to replace propellant that gradually boils off due to the warm ambient temperatures in Florida.

We will also be tweeting countdown updates. 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 is now just a 30 percent chance weather conditions will permit liftoff of a Falcon 9 rocket tonight.

The main concerns are with thick clouds and precipitation over Cape Canaveral as a weather system traverses Central Florida. Two weather rules -- the thick cloud and disturbed weather rules -- are currently "no go" at the launch site.

Liftoff time has been adjusted by one second to 2:14:38 a.m. EDT (0614:38 GMT) based on the latest orbit data for the International Space Station.

Fueling of the 208-foot-tall Falcon 9 rocket is about to get underway at Cape Canaveral's Complex 40 launch pad after the SpaceX launch team issued a "go" to begin propellant loading.

The two-stage rocket burns RP-1 fuel -- a high-refined kerosene -- and liquid oxygen during today's nine-minute launch sequence.

Today's flight marks the 13th launch of a Falcon 9 rocket since debuting in June 2010. It's the 8th mission of the improved Falcon 9 v1.1 version, which made its inaugural launch in September 2013 from Vandenberg Air Force Base.

For details on the Falcon 9 v1.1, here is part of our story on the rocket stemming from an interview with SpaceX boss Elon Musk last year:

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.

Rainfall is starting to taper off here at Cape Canaveral, but two weather rules are still observed "no go" at this time. Those are the disturbed weather and thick cloud rules.

Persistent rain showers over Cape Canaveral may clear in time for liftoff at 2:14 a.m. EDT (0614 GMT), but weather conditions at the Falcon 9 launch site are currently observed "no go" for launch at this time.

Seven weather criteria -- the surface electric field mill rule, the lightning rule, the cumulus cloud rule, the attached anvil cloud rule, the disturbed weather rule, the thick cloud rule and the flight through precipitation rule -- are currently in a "red" status.

The International Space Station is ready to receive more than 5,000 pounds of supplies and experiments packed inside a SpaceX Dragon cargo capsule set for liftoff from Cape Canaveral early Saturday.

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The weather forecast for Saturday's launch calls for a 50-50 chance of favorable conditions for liftoff, which must occur during an instantaneous window for SpaceX's Dragon capsule to reach the International Space Station.

The main worries are with the thick cloud rule and the flight through precipitation rule in the rocket's launch commit criteria.

Liftoff is set for 2:14:37 a.m. EDT (0614:37 GMT) Saturday.

An approaching upper level trough will bring moisture to Florida's Space Coast on Friday, creating thick clouds, rain showers and developing a low pressure area north of the Bahamas, according to a forecast issued by the U.S. Air Force's 45th Weather Squadron.

The official outlook predicts rain showers and overcast clouds at 25,000 feet, with scattered and broken cloud levels at 3,000 feet and 13,000 feet.

Winds will be from the northeast at 12 to 17 mph, the launch time temperature will be 74 degrees Fahrenheit, and relative humidity will be 85 percent, according to the forecast.

Clouds and rain will diminish over Central Florida later Saturday, so forecasters say there is a 70 percent chance of good weather for Sunday morning's launch opportunity at about 1:53 a.m. EDT (0553 GMT).

The SpaceX launch team fueled up a two-stage Falcon 9 rocket, rehearsed countdown procedures and lit the booster's first stage engines for a final preflight checkout late Wednesday, setting the stage for liftoff early Saturday with cargo for the International Space Station.

Wednesday night's practice countdown was punctuated by ignition of the Falcon 9 rocket's nine Merlin 1D first stage engines for several seconds while the launcher was restrained on the ground.

Engineers planned an exhaustive data review before clearing the rocket for launch.

Saturday's liftoff, planned for 2:14 a.m. EDT (0614 GMT) from Cape Canaveral's Complex 41 launch pad, will kick off SpaceX's fourth resupply run to the space station under a $1.6 billion contract with NASA.

The Falcon 9 rocket's ascent into orbit will take less than 10 minutes, when the launcher's single-engine upper stage will release a SpaceX-owned Dragon cargo capsule to start a two-day pursuit of the space station.

After a laser-guided rendezvous, the Dragon spacecraft will hold its approach 30 feet beneath the complex for grapple by the space station's Canadian-built robotic arm.

It is carrying more than 5,000 pounds of experiments, provisions for the station's crew, spacesuit batteries, electronics and a research package for mounting on the outpost's exterior to track winds over the world's oceans.

The Dragon freighter will be mated to the space station's Harmony module, where astronauts can enter the craft's pressurized cabin to unload cargo and pack equipment tagged for return to Earth.

In mid-October, after nearly a month attached to the space station, the Dragon capsule will depart and descend back to Earth for a parachute-assisted splashdown in the Pacific Ocean, returning home with 3,800 pounds of cargo and research samples.

SpaceX's next resupply mission to the International Space Station is set for takeoff as soon as Saturday after a rapid rebound from the company's last flight from Cape Canaveral, but the company does not plan to use the launch as another chance to practice rocket recovery procedures.

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