Two injuries have been reported in the efforts to battle the expanding fire at Vandenberg Air Force Base that has consumed at least 4,528 acres.

The two injured workers were transported to a local hospital in Lompoc for treatment, according to the Santa Barbara County Fire Dept.

The fire remains completely uncontained as it moves towards the southern base boundary and the Sudden Ranch area. Difficult terrain is making direct fights against the flames a challenge.

Officials say no structures have been harmed by the fire so far, and resources are deployed to protect facilities from the fire's advancements.

It has been classed a "high priority" fight by Vandenberg, U.S. Forestry Service, CalFire and Santa Barbara County firefighters due to the assets on South Base.

The fire has severed power to several facilities on South Base, requiring generator power to kick in.

South Base is home to several active launch pads -- Space Launch Complex 3-East where a United Launch Alliance Atlas 5 rocket is awaiting flight to deploy the commercial WorldView 4 Earth-imaging satellite for DigitalGlobe, Space Launch Complex 4 where a SpaceX Falcon 9 rocket and 10 Iridium mobile communications satellites are stored inside the pad hangar and Space Launch Complex 6 where United Launch Alliance Delta 4 rockets are flown. There's also SLC-8 at the foot of SLC-6 that has been used for Orbital ATK Minotaur boosters.

Hundreds of personnel are fighting the fire on the ground with air support from tanker aircraft and helicopters.

Extremely dry vegetation and warm temperatures are fueling the fire.

The Air Force says teams early this morning used a helicopter to map fire lines and better understand the precise boundaries of the wildfire to more effectively distribute fire personnel and resources.

Vandenberg fire and security forces continue to investigate possible causes of the blaze.

The Vandenberg fire south of the Atlas 5 launch pad has increased to 1,200 acres and continues to grow. South Base has been closed to all but mission-essential personnel effective immediately.

The Air Force says "aggressive" air tanker drops, new fire breaks and attacking spot fires directly by engine crews are being employed.

As of early this afternoon, the fire was zero percent contained and there was no estimate on when the blaze will be brought under control. Extremely dry brush, warm temperatures and breezy conditions are fueling the fire, which has jumped roads and man-made fire breaks.

It is not known what sparked the fire, which began around 5:20 p.m. Saturday.

Nearly 800 firefighters from Vandenberg Air Force Base, U.S. Forestry Service, CalFire and Santa Barbara County are battling the blaze today. It has grown from 50 acres last night to 500 acres of wildland today.

“We’re using Santa Barbara County helicopters and aircraft based out of Santa Maria and Paso Robles airports,” said Vandenberg Fire Chief Clem Marrero.

Some power lines have been damaged by the fire, the Air Force says.

“The team work exhibited between the Santa Barbara County, CalFire, U.S. Forestry Service and Air Force firefighters is why we have been as successful as we have been fighting this blaze,” said Lt. Col. Edward Simpson, Emergency Operations Center director. “We are grateful to have their support.”

The launch target has been moved to no earlier than Monday, Sept. 26 due to availability on the Western Range schedule. The Range provides the required tracking, communications and safety services for activities at Vandenberg.

Launch is rescheduled for no sooner than Tuesday. The Atlas 5 rocket and WorldView 4 spacecraft remain safe and secure inside the mobile service gantry at Vandenberg Air Force Base's Space Launch Complex 3-East.

Today's launch was scrubbed due to a wildfire that began last night in a remote canyon south of the pad.

Approximately 250 firefighters including hand-crews, bulldozers, and air assets are on-site, the Air Force said.

No facilities have been damaged by the fire and no critical assets are in immediate danger, according to the Air Force.

"We've delayed the launch in order to concentrate our resources on the situation at hand," said Col. Paul Nosek, Vandenberg's Emergency Operations Center commander.

SCRUB. The countdown is being stopped and the team will stand down for today due to the wildfire burning on Vandenberg Air Force Base south of the pad. This will allow the firefighters to remain in place to continue battling the blaze. A new target launch date has not been announced.

With a leaky hydrogen fill-and-drain valve replaced, a new countdown has begun at Vandenberg Air Force Base in California for today's launch of the Atlas 5 rocket to deploy the WorldView 4 commercial satellite into space.

Liftoff was scrubbed at 10:58 a.m. Friday after the small leak caused ice to form around an umbilical. Officials opted to take the safe route and resolve the leak before launching.

As the countdown gets started, the launch team will power up the rocket to conduct standard pre-flight tests and ready the vehicle.

Rollback of the mobile service tower from around the rocket is expected in about three hours. Once the gantry is removed, crews at the pad will make preparations to systems and equipment before the site is cleared of all personnel for fueling.

Supercold liquid oxygen begins flowing into the Centaur upper stage, followed by the Atlas first stage. Liquid hydrogen fuel loading for Centaur will be completed a short time later.

A final 30-minute built-in hold is scheduled when clocks hit the T-minus 4 minute mark. That will give the team a chance to finish any late work and assess the status of the rocket, payload, Range and weather before proceeding into the last moments of the countdown.

Liftoff is targeted for 11:30:33 a.m. local time (2:30:33 p.m. EDT; 1830:33 GMT).

Meanwhile, crews are fighting to contain a wildfire south of the Atlas pad in a remote canyon at Vandenberg. Air Force officials said no launch complexes or critical Range equipment are in immediate danger. No facilities or infrastructure have been damaged. What impact, if any, this will have on today's scheduled launch is not known. Smoke is blowing south.

The launch of the WorldView 4 spacecraft aboard the Atlas 5 rocket from Vandenberg Air Force Base in California has been confirmed for Sunday at 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT).

United Launch Alliance technicians were able to isolate Friday's scrub-causing hydrogen leak to the ground system fill-and-drain valve, the company said in a statement. The team has replaced the valve and conducted a successful retest of the system.

"The launch team has begun reconfiguring the vehicle for launch," officials said Saturday afternoon.

The 8-hour countdown begins early Sunday.

Weather forecasters predict a 90 percent chance of favorable conditions during the launch window.

WorldView 4 will join sister-satellite WorldView 3 in the DigitGlobe fleet to provide best-in-class high-resolution imagery to the commercial marketplace. The craft can see objects just 31 centimeters across from their orbits in space.

DigitalGlobe sells the imagery to the U.S. government, international allies and commercial clients such as land developers, the oil and gas industry, scientific researchers and agriculture companies.

The new target date for launching WorldView 4 aboard the Atlas 5 is Sunday. The launch window will open at 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT) from Vandenberg Air Force Base in California.

The 48-hour turnaround following this morning's scrub will give technicians enough time to remove and replace the hydrogen fill-and-drain valve that became suspect during fueling operations.

A small leak was detected around the ground-side umbilical today, causing a patch of ice to form and prompting officials to call off the launch attempt.

The Atlas 5 and payload were safed after the scrub, the cryogenics drained from the two-stage vehicle and the mobile service gantry rolled back around the rocket. Technicians will re-extend access platforms to reach the worksite tonight and perform the task tomorrow.

Sunday's countdown will begin at 3:30 a.m. local time.

This was the first day-of-launch Atlas 5 scrub for technical reasons in four years and over 30 flights.

"Always better to be on the ground, wishing you were in the air than the other way around," says United Launch Alliance President and CEO Tory Bruno.

Liftoff is tentatively rescheduled for Saturday at 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT). Weather forecasters predict a 90 percent chance of favorable conditions.

ULA CEO Tory Bruno says: "Very small ground side LH2 leak. Forming an ice ball on the umbilical. Outside our history. Standing down attempt today to resolve."

To recap, today's launch attempt is being called off. The launch team is beginning to drain the cryogenics off the vehicle. A new launch date has not yet been confirmed.

SCRUB! The launch team is halting today's countdown due to a technical problem.

T-minus 4 minutes and holding. The countdown has entered the planned hold to give the launch team a chance to review all systems before pressing ahead with liftoff.

T-minus 5 minutes and counting. Standing by to go into the final built-in hold that will last for 30 minutes.

WorldView 4 will join sister-craft WorldView 3 in providing best-in-class 30cm imagery. Atlas 5 launched WorldView 3 in 2014.

The workhorse Centaur upper stage has flown in various configurations for decades. For this launch, the stage will use one Aerojet Rocketdyne-built RL10C-1 liquid oxygen/liquid hydrogen engine that develops a thrust of about 22,890 pounds.

The stage is 41.5 feet in length and 10 feet it diameter. It also houses the navigation unit that serves as the rocket's guidance brain.

The Atlas 5 rocket now stands fully fueled for launch and activities are proceeding toward a liftoff at 11:30:33 a.m. Pacific Time.

The liquid hydrogen tank in the Centaur upper stage just reached the 96 percent level. Topping is now beginning.

The Centaur liquid hydrogen tank is 50 percent loaded so far. The cryogenic propellant will be consumed with liquid oxygen by the stage's Aerojet Rocketdyne-made RL10 engine.

The Atlas 5 rocket's rigid body first stage is known as the Common Core Booster. The CCB replaced the "balloon" pressure-stabilized stage used by previous Atlas vehicles.

It is equipped with the RD-180 liquid-fueled main engine. This liquid oxygen/kerosene powerplant is a two-thrust chamber, two-nozzle engine.

As the CCB's name suggests, the stage is common and is used in all the various configurations of the Atlas 5 family. The booster stage is 106.6 feet long and 12.5 feet diameter.

Now 60 minutes from launch.

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The final step in fueling has started with the loading of liquid hydrogen into Centaur.

Liquid oxygen loading has been completed to Atlas and Centaur stages. Awaiting start of hydrogen load.

The team is assessing an issue that is holding up the start of liquid hydrogen loading.

Fast-filling of the first stage liquid oxygen has been completed. Topping mode is now underway.

Now beyond the three-quarters level of liquid oxygen on the first stage.

Now 90 minutes from liftoff. Fueling operations remain in work for the launch time of exactly 11:30:33 a.m. local.

Today's available launch window extends to 11:45:21 a.m. local (1845:21 GMT) from Vandenberg Air Force Base in California.

First stage liquid oxygen tank is passing the 40 percent mark. Chilled to Minus-298 degrees F, the liquid oxygen will be used with RP-1 kerosene by the RD-180 main engine on the first stage during the initial minutes of flight today. The 25,000 gallons of RP-1 were loaded into the rocket earlier.

Centaur liquid oxygen is topping to flight level.

The Centaur liquid oxygen tank is 75 percent full now.

And the chilldown conditioning of liquid hydrogen propellant lines is starting to prepare the plumbing for transferring the Minus-423 degree F fuel into the rocket. The Centaur holds about 12,300 gallons of the cryogenic propellant.

The first stage liquid oxygen loading is transitioning from slow-fill to fast-fill mode.

Half of the Centaur liquid oxygen tank has been filled so far.

The Centaur liquid oxygen tank is nearing 20 percent full already.

The conditioning of the systems for the first stage liquid oxygen tank have been completed. And a "go" has been given to begin flowing supercold liquid oxygen into the Atlas 5's first stage.

The Common Core Booster stage's liquid oxygen tank is the largest tank to be filled today. It holds about 48,800 gallons of cryogenic oxidizer for the RD-180 main engine.

Filling of the Centaur upper stage with about 4,150 gallons of liquid oxygen is beginning at Vandenberg's Space Launch Complex 3 following the thermal conditioning of the transfer pipes.

The liquid oxygen -- chilled to Minus-298 degrees F -- will be consumed during the launch by the Centaur's single RL10 engine along with liquid hydrogen to be loaded into the stage a little later in the countdown.

The Centaur liquid oxygen system's pad storage area has been prepped. The next step is conditioning the transfer lines, which is now beginning to prepare the plumbing for flowing the cryogenic oxidizer.

T-minus 2 hours and counting! The launch countdown has resumed for today's flight of the Atlas 5 rocket following the planned half-hour built-in hold.

Clocks have one more hold scheduled at T-minus 4 minutes. That pause will last 30 minutes during which time the final "go" for launch will be given.

All remains targeted for liftoff at exactly 11:30:33 a.m. local time (1830:33 GMT) from Vandenberg Air Force Base in California.

Today's available launch window extends to 11:45:21 a.m. local (1845:21 GMT).

The launch team and all systems are "ready" to proceed with the countdown and begin fueling the Atlas 5 rocket as planned.

Loading of cryogenic liquid oxygen and liquid hydrogen into the Atlas 5 rocket will be getting underway a short time from now.

The Atlas launch conductor is briefing his team on procedures before entering into the final two hours of the countdown. A readiness check of the team members is next.

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T-minus 2 hours and holding. The countdown just entered the first of the planned holds over the course of the day that will lead to the 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT) launch of the Atlas-Centaur rocket.

This initial pause lasts 30 minutes, giving the team some margin in the countdown timeline to deal with technical issues or any work that is running behind. The final hold is scheduled to occur at T-minus 4 minutes.

Workers are leaving the pad area in advance of today's propellant loading and launch of the Atlas 5 rocket.

In the pre-fueling weather update, it is very foggy at the pad right now. The marine layer is draped over Vandenberg with an overcast ceiling at 100 feet. But forecasters expect the stratus and fog to burn off and lift over the next couple of hours to improve visibility by launch time.

The 8-million-pound mobile service tower has been retracted from around the Atlas 5 rocket, revealing the 19-story-tall vehicle for liftoff at 11:30 a.m. local time today.

The ground crews are getting the gantry's doors closed, plus finishing the final buttoning up of pad equipment before all workers clear the pad for the remainder of the countdown.

Rollback of the launch pad's service gantry is underway. This is a major milestone in today's countdown, getting the mobile tower retracted to uncover the Atlas 5 rocket.

The structure's internal crane was instrumental in bringing the rocket stages and payload together. And now the fully assembled Atlas 5 is being unveiled for its 66th launch, the 12th to originate from Vandenberg.

A readiness poll of the team has verified all systems are GO for retraction of the gantry at Space Launch Complex 3-East this morning.

The mobile service tower has been jacked up and is ready to roll.

Officials just received an updated weather forecast, and conditions are looking good for launching the Atlas 5 rocket from California today.

There are no constraints to proceeding with mobile service tower rollback in about an hour. That will reveal the rocket to the elements, allowing the vehicle to be fueled and launched.

For launch time, the odds of acceptable weather have improved to 90 percent. There is a chance for a shallow deck of clouds around 1,600 feet, but visibility should be unrestricted. Winds will be light.

Atlas and Centaur have been powered up. Guidance system testing is next.

Clocks have begun ticking for today's flight by the Atlas 5 rocket from Vandenberg Air Force Base in California to deploy the WorldView 4 commercial satellite into space.

As the countdown gets started, the launch team will power up the rocket to conduct standard pre-flight tests and ready the vehicle.

Rollback of the mobile service tower from around the rocket is expected in about three hours. Once the gantry is removed, crews at the pad will make preparations to systems and equipment before the site is cleared of all personnel for fueling.

Supercold liquid oxygen begins flowing into the Centaur upper stage around 9:15 a.m., followed by the Atlas first stage. Liquid hydrogen fuel loading for Centaur will be completed a short time later.

A final 30-minute built-in hold is scheduled when clocks hit the T-minus 4 minute mark. That will give the team a chance to finish any late work and assess the status of the rocket, payload, Range and weather before proceeding into the last moments of the countdown.

Liftoff remains targeted for 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT).

Countdown clocks will begin ticking in the middle-of-the-night Friday morning to ready an Atlas 5 rocket at America's western spaceport to launch a commercial Earth-imagery observatory.

The Launch Readiness Review today formally gave approval to proceed into countdown operations at Vandenberg Air Force Base in California to deploy the WorldView 4 satellite for DigitalGlobe.

Friday's liftoff is targeted for 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT) at the opening of a 14-minute launch opportunity.

A live launch webcast can be viewed on this page.

Meteorologists give 80 percent odds that the weather will allow the launch to occur. Visibility is the only concern.

Air Force meteorologists said a high pressure system building into the region is bringing light winds and a shallow marine layer along the Vandenberg coast.

"Some lingering low level clouds on the South Base ridgeline will create a concern for visibility on day of launch," forecasters say.

Winds will be variable between 5-10 knots with temperatures between 58 and 63 degrees F at launch time.

"Team V is excited to launch the Atlas 5 WorldView 4 mission from Vandenberg's Western Range. The combined 30th Space Wing and United Launch Alliance team has spent months preparing to ensure this launch is both safe and successful. We have a very strong partnership with ULA and we're proud to have teamed with them on this fantastic mission," said Col. Chris Moss, 30th Space Wing commander at Vandenberg and the launch decision authority.

It will be the 12th Atlas 5 to fly from Vandenberg.

The launch countdown begins just after 3:30 a.m. local time for the start of an eight-hour sequence to prepare the launch pad and rocket for flight.

This is United Launch Alliance's 112th flight, the 9th just this year, and the company's 19th for a commercial client.

PREVIEW: Resuming space launches from the U.S. Western Range at Vandenberg Air Force Base in California after a half-year infrastructure outage, an Atlas 5 rocket will boost a commercial Earth-imaging bird into orbit on Friday. Liftoff is scheduled for 11:30 a.m. local time (2:30 p.m. EDT; 1830 GMT).

Read our full story.

SHIPMENT: More than three years after its launch was delayed by a corporate merger, a commercial Earth-imaging satellite has finally shipped to its California rocket base for liftoff aboard an Atlas 5 in September.

Read our full story.