Launch time conditions are predicted to be partly cloudy skies with scattered clouds at 5,000 feet, 16,000 feet and 23,000 feet. Winds will be from the northwest at 10 to 15 mph, and temperature will be about 50 degrees Fahrenheit.
The only minor concern is a 10 percent chance of a violation of the thick cloud rule.
Among the supplies packed inside are spacewalk tools and equipment to help prepare the space station to receive commercial crew vehicles, an IMAX camera for filming during four space station increments, and science payloads that will enable model organism research using fruit flies and will study flatworms to better understand wound healing in space.
The Dragon's total internal payload includes 1,272 pounds of science and research gear, 1,080 pounds of crew provisions, 1,495 pounds of vehicle hardware, 35 pounds of computer tools, 51 pounds of spacesuit equipment, and 86 pounds of Russian hardware.
NASA's Cloud-Aerosol Transport System is bolted inside Dragon's unpressurized trunk. The space station's robotics system will unpack the CATS instrument and mount it outside the station to monitor cloud and aerosol coverage which directly impacts global climate.
Today's launch marks SpaceX's fifth operational resupply run to the space station under a 12-mission, $1.6 billion contract with NASA covering cargo services through 2016.
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 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 14th launch of a Falcon 9 rocket since debuting in June 2010. It's the 9th 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 in 2013:
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.
Read our full story.
The main concerns are with violating the thick cloud and flight through precipitation rules.
"Late Friday and into Saturday, winds back northerly in response to a high pressure surge in the Southeast U.S., but a slight risk of precipitation remains," the forecast team wrote in a summary. "Also on Saturday, an upper level feature transits the northern portions of the Florida Peninsula, bringing upper level cloudiness and a slight risk of thick clouds."
The outlook calls for scattered clouds at 3,000 feet and 16,000 feet, plus a broken cloud deck at 23,000 feet.
Winds will be from the north at 17 to 22 mph, and the temperature at launch time is forecast to be about 57 degrees Fahrenheit.
If the Falcon 9 rocket does not take off Saturday, the next opportunity will be no earlier than Tuesday at 3:36 a.m. EST (0836 GMT).
The weather forecast for Tuesday worsens with a chance of rain and clouds. The outlook for Tuesday calls for a 60 percent probability of weather prohibiting launch.
Saturday's instantaneous launch window is set for 4:47 a.m. EST (0947 GMT), a day later than officials previously hoped to send up the rocket.
The weather forecast calls for an 80 percent of favorable conditions for Saturday’s launch attempt. The prime concerns are violations of the thick cloud and flight through precipitation rules. Read our full story.
The next possible launch opportunity is Friday.
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.
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.
The terminal countdown autosequence is about to begin at the T-minus 10 minute mark.
Fully fueled for launch, the Falcon 9 contains about 1.05 million pounds of kerosene and liquid oxygen propellants.
Linkup with the complex is scheduled at 6 a.m. EST (1100 GMT) Thursday, when astronaut Butch Wilmore will grapple the Dragon spacecraft with the space station's robotic arm.
The roughly 15-story rocket stage will attempt to refire its Merlin engines three times, deploy four landing legs and small winglets for aerodynamic stability, and descend to a soft landing on the ocean-going platform.
The final descent will occur on the power of one of the first stage's nine Merlin engines.
SpaceX's Hans Koenigsmann said not to expect real-time updates on the stage's descent. The live coverage of the mission will focus on the rocket's deployment of the Dragon capsule.
Koenigsmann described the procedure to reporters Monday: "It will turn around, and it will perform what's called the boost-back burn. That boost-back burn brings the stage closer back in, it will then continue to just coast and as it gets closer to the atmosphere, it will perform an entry burn. The entry burn will slow the stage down, and that reduces the loads on the stage."
"It's supposed to bring the stage through the atmosphere, and that will be followed by a landing burn, and the landing burn is targeted to the autonomous spaceport drone ship."
"The drone ship sits there right now and it's basically waiting for the mission to happen ... This is an experiment. There is a certain likelihood that this will not work outright -- that something will go wrong. It's the first time we've tried this. Nobody has ever tried to that our knowledge."
The objective is to advance SpaceX's goal of mastering rocket reusability in hopes of reducing the cost of space launches.
Among the supplies packed inside are spacewalk tools and equipment to help prepare the space station to receive commercial crew vehicles, an IMAX camera for filming during four space station increments, and science payloads that will enable model organism research using fruit flies and will study flatworms to better understand wound healing in space.
The Dragon's total internal payload includes 1,272 pounds of science and research gear, 1,080 pounds of crew provisions, 1,495 pounds of vehicle hardware, 35 pounds of computer tools, 51 pounds of spacesuit equipment, and 86 pounds of Russian hardware.
NASA's Cloud-Aerosol Transport System is bolted inside Dragon's unpressurized trunk. The space station's robotics system will unpack the CATS instrument and mount it outside the station to monitor cloud and aerosol coverage which directly impacts global climate.
Today's launch marks SpaceX's fifth operational resupply run to the space station under a 12-mission, $1.6 billion contract with NASA covering cargo services through 2016.
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 will be a few clouds at 3,000 feet and 12,000 feet, and a broken cloud deck around 25,000 feet, according to the U.S. Air Force weather office.
The temperature at launch time will be 69 degrees Fahrenheit, and winds will be out of the northeast at about 8 mph.
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 14th launch of a Falcon 9 rocket since debuting in June 2010. It's the 9th 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 in 2013:
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.
Read our full story.
The 208-foot-tall rocket is set for liftoff Tuesday at 6:20 a.m. EST (1120 GMT).
Check out photos of the Falcon 9 rocket on the launch pad Monday night.
Read our full story.
Read our full story.
"A frontal boundary has settled in over Central Florida," the U.S. Air Force's 45th Weather Squadron wrote in a forecast issued early Monday. "This front and its associated cloudiness will be very slow to move south of the Space Coast. With the clouds only slowly eroding overhead, the primary weather concern remains thick clouds."
Forecasters predict scattered clouds at 2,000 feet and 12,000 feet, and a broken cloud deck at 24,000 feet for Tuesday's predawn launch opportunity for SpaceX's Falcon 9 rocket.
Officials are watching a sunspot on the Earth-facing side of the sun, but they do not expect any space weather launch criteria to be violated Tuesday.
The forecast calls for north-northeast winds of 5 to 10 mph, a temperature of around 64 degrees Fahrenheit, and good visibility.
The next launch attempt after Tuesday would likely come Friday, when there is an 80 percent chance of good weather.
"A strong push of cold air associated with a large high pressure area to the north will move the frontal boundary fully south of the spaceport on Wednesday," Air Force forecasters said. "Winds will be northerly and brisk, ushering in cold air Thursday. On Friday winds veer and weaken, adding a slight risk of coastal showers. The primary weather concern for Friday is flight through precipitation."
The primary concern is with thick clouds over Florida's Space Coast at the Falcon 9 rocket's launch time of 6:20 a.m. EST (1120 GMT).
A cold front will pass over Central Florida on Monday, bringing moisture to the area.
"This front will bring another bout of upper level clouds and increased rain chances. And, like the last boundary, this front is expected to stall and linger over the area for a day or so. With the boundary overhead, the primary weather concern remains thick clouds," the U.S. Air Force's 45th Weather Squadron wrote in a forecast summary.
If launch does not occur Tuesday, the next launch opportunity is scheduled for Friday morning.
Watch this page for live updates and video of Tuesday's launch.
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