2016 GMT (4:16 p.m. EDT; 1:16 p.m. PDT)

Launch team polling is underway. No technical problems were reported. Standing by for further information on the winds.

2010 GMT (4:10 p.m. EDT; 1:10 p.m. PDT)

T-minus 4 minutes and holding. The countdown has entered the final planned built-in hold. This is a scheduled 10-minute pause leading to today's liftoff time of 1:24 p.m. local (4:24 p.m. EDT; 2024 GMT) for the Delta 2 rocket with STSS-ATRR.

However, winds are a constraint. Conditions will have to improve before the launch can proceed.

A weather balloon can be seen rising into the sky right now to measure the current speeds and directions.

2006 GMT (4:06 p.m. EDT; 1:06 p.m. PDT)

The launch team continues to monitor the wind conditions. Weather balloon data shows winds are out of limits for the launch. But there's still another balloon run planned to relay data today. The countdown is marching onwards in hopes the winds will cooperate.

1959 GMT (3:59 p.m. EDT; 12:59 p.m. PDT)

T-minus 15 minutes and counting. Countdown clocks are running again following the planned 20-minute hold. The count will continue to the T-minus 4 minute mark where another planned hold is scheduled. Launch remains set to occur at 1:24 p.m. local time (4:24 p.m. EDT; 2024 GMT).

1955 GMT (3:55 p.m. EDT; 12:55 p.m. PDT)

A readiness poll of the launch team has resulted in a "go" to restart the countdown as scheduled.

1946 GMT (3:46 p.m. EDT; 12:46 p.m. PDT)

The Delta rocket will be flying in its configuration known as the 7920-10 vehicle. The two-stage launcher is fitted with nine strap-on solid-propellant motors and a 10-foot diameter composite nose cone.

Flying away from its coastal pad, the rocket will head southward over the Pacific Ocean. Six of the solid boosters are ignited on the ground, the other three light a minute into flight to give the Delta's first stage added thrust through the initial ascent. Once the solids burn out and separate, the kerosene-powered main engine will continue pushing the rocket to an altitude of 65 nautical miles.

The spent first stage will jettison to let the hydrazine-fueled second stage ignite and achieve a preliminary parking orbit 10 minutes into flight.

The rocket then settles into a quiet coast along a trajectory the cruises above the South Pacific before crossing Antarctica and proceeding northbound toward Africa. The second stage reignites its engine for 21 seconds over Madagascar to reach a near-circular polar orbit above the planet.

The payload is expected to be released from the rocket 58 minutes after blastoff.

1939 GMT (3:39 p.m. EDT; 12:39 p.m. PDT)

T-minus 15 minutes and holding. Clocks have entered the next planned hold period during the Terminal Countdown. This pause will last 20 minutes in duration.

These holds are designed to give the launch team a chance to deal with any problems and catch up on work that could be running behind schedule.

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1935 GMT (3:35 p.m. EDT; 12:35 p.m. PDT)

The first stage engine steering checks just finished.

1931 GMT (3:31 p.m. EDT; 12:31 p.m. PDT)

The second stage engine slews are complete. First stage tests have begun.

1929 GMT (3:29 p.m. EDT; 12:29 p.m. PDT)

The launch team is beginning the "slew" or steering checks of the first and second stage engines. These are gimbal tests of the nozzles on the first stage main engine and twin vernier engines and second stage engine to ensure the rocket will be able to steer itself during launch.

1924 GMT (3:24 p.m. EDT; 12:24 p.m. PDT)

Launch is one hour away. Weather appears to be the only worry right now in the countdown. Low-level winds are gusty, which is something launch managers will have to closely watch as liftoff time nears.

1908 GMT (3:08 p.m. EDT; 12:08 p.m. PDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been accomplished. The process took 27 minutes and 10 seconds today, concluding at 12:07:57 p.m. local time. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

The rocket is now fully fueled for launch. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel a little while ago. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels last Friday. And the nine strap-on booster rockets are solid-propellant.

1906 GMT (3:06 p.m. EDT; 12:06 p.m. PDT)

The liquid oxygen tank has reached the 95 percent mark.

1900 GMT (3:00 p.m. EDT; 12:00 p.m. PDT)

Liquid oxygen loading is continuing. Once the first stage tank is 95 percent full, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the rocket.

1854 GMT (2:54 p.m. EDT; 11:54 a.m. PDT)

Now just 90 minutes away from the planned launch of the Delta 2 rocket. It's a foggy and windy day at the pad. But the countdown remains on schedule.

1850 GMT (2:50 p.m. EDT; 11:50 a.m. PDT)

This approximate 25-minute process to fill the first stage liquid oxygen tank has been underway for 10 minutes. As the super-cold liquid oxygen continues to flow into the first stage, a bright white plume of vapors begins streaming from a vent on the rocket and the bottom of the vehicle ices over.

1840 GMT (2:40 p.m. EDT; 11:40 a.m. PDT)

LOX loading begins. Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from a 28,000-gallon storage tank at Space Launch Complex 2, through plumbing and into the bottom of the Delta 2 rocket. The LOX will be consumed by the first stage main engine during the first four-and-a-half minutes of flight along with the 10,000 gallons of RP-1 kerosene already loaded aboard the vehicle.

1835 GMT (2:35 p.m. EDT; 11:35 a.m. PDT)

The launch team has received the official "go" to begin preparations for loading the rocket's first stage liquid oxygen tank as planned.

1824 GMT (2:24 p.m. EDT; 11:24 a.m. PDT)

The countdown is ticking along smoothly at Vandenberg Air Force Base for launch just two hours from now at 1:24 p.m. local time (4:24 p.m. EDT; 2024 GMT).

NASA's Launch Services Program is overseeing today's flight of the Delta 2 rocket. But instead of sending a space probe to another planet or a science observatory into orbit to study Earth, the rocket is carrying the Space Tracking and Surveillance System Advanced Technology Risk Reduction satellite for the U.S. Missile Defense Agency.

NASA's expendable launch vehicle experts are lending their expertise to get the spacecraft into orbit for its missile tracking research and development mission.

"It may not appear typical but in every way it's been typical to us. Other than different folks we're working with and not necessarily the Science or Exploration Directorate from Headquarters, we're performing the same job we always do in every sense of the word," said NASA launch manager Chuck Dovale.

"It really hasn't been any different. We don't want to come across as if it doesn't matter what's on top (of the rocket), but it truly hasn't been any different than a science mission."

How did the arrangement between NASA and the Missile Defense Agency come about?

"I think it had to do with the timing of things. We had a mechanism to buy Delta 2's at the time and the Air Force, their contract was expiring and they were moving on to EELV. So MDA had a need for two and we were buying several Delta 2's at the time, so it was just added on," Dovale said.

A second STSS launch is scheduled from Cape Canaveral later this summer using the other Delta 2 that was purchased.

The MDA is paying NASA for the launch services.

1822 GMT (2:22 p.m. EDT; 11:22 a.m. PDT)

Work to turn on and configure the Delta's onboard guidance computer has been completed.

1807 GMT (2:07 p.m. EDT; 11:07 a.m. PDT)

The first stage fuel tank of the Delta 2 rocket has been fully loaded for today's planned launch. The tank was filled with a highly refined kerosene, called RP-1, during a 18-minute, 25-second process that officially concluded at 11:07:25 a.m. local time.

The next major task in the count will be loading supercold cryogenic liquid oxygen into the first stage starting in about 30 minutes.

The kerosene and liquid oxygen will be consumed by the stage's Pratt & Whitney Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

1806 GMT (2:06 p.m. EDT; 11:06 a.m. PDT)

Rapid-loading of the RP-1 tank has concluded with 9,800 gallons already aboard the rocket. Fine load is continuing to finish filling the tank.

1802 GMT (2:02 p.m. EDT; 11:02 a.m. PDT)

The launch team has computed that today's full load for the first stage fuel tank is 9,983 gallons.

Once the tank is filled to 98 percent or 9,800 gallons, the "rapid load" valve will be closed and the slower "fine load" phase will continue to top off the tank.

1800 GMT (2:00 p.m. EDT; 11:00 a.m. PDT)

The first stage tank has 7,000 gallons of kerosene aboard now.

1754 GMT (1:54 p.m. EDT; 10:54 a.m. PDT)

Kerosene fueling continues in progress. The rockets tank has been filled with 3,000 gallons so far.

Also, the launch team confirms the first stage helium and nitrogen systems are pressurized and in good shape.

1749 GMT (1:49 p.m. EDT; 10:49 a.m. PDT)

Fueling begins. About 10,000 gallons of the kerosene propellant are pumping into the base of the rocket from storage tanks at the pad as fueling of the Delta 2's first stage begins for today's launch.

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1744 GMT (1:44 p.m. EDT; 10:44 a.m. PDT)

First stage fueling preparations are starting. After verifying valves, sensors, flow meters and equipment are ready, a highly-refined kerosene fuel will begin flowing into the vehicle a few minutes from now.

1730 GMT (1:30 p.m. EDT; 10:30 a.m. PDT)

The rocket's control system and guidance computer are being turned on.

And the launch is starting the steps to pressurize the first and second stage helium and nitrogen systems and the second stage fuel and oxidizer tanks.

1724 GMT (1:24 p.m. EDT; 10:24 a.m. PDT)

The three-hour Terminal Countdown sequence begins now for today's launch of the Delta 2 rocket from Vandenberg Air Force Base in California. The booster will carry into orbit STSS-ATRR, the Space Tracking and Surveillance System Advanced Technology Risk Reduction satellite.

Liftoff from the Space Launch Complex 2 pad is scheduled for 1:24 p.m. local time (4:24 p.m. EDT; 2024 GMT). This afternoon's available launch window stretches 28 minutes to 1:52 p.m.

Between now and the launch time, the rocket's guidance system will be activated, onboard tanks pressurized, the kerosene and liquid oxygen supplies loaded into the first stage, checks performed on the safety system, steering tests conducted on the engines, then the final switches to internal power and arming of the ignitors.

This is a normal countdown for the Delta 2, a typical timeline to ready the vehicle for flight. But this relatively rare daytime liftoff from Vandenberg means the launch team gets to perform the count during regular hours.

"The thing that's not standard is the mid-day type of T-0. We're used to coming in here in the middle of the night," quipped Chuck Dovale, the NASA launch director.

1715 GMT (1:15 p.m. EDT; 10:15 a.m. PDT)

The launch conductor has just polled his team to ensure all stations are manned and systems are set for the Terminal Countdown. No problems were reported.

1710 GMT (1:10 p.m. EDT; 10:10 a.m. PDT)

"Man stations for Terminal Count." The launch team members are about to be polled confirm their readiness to enter into the final three hours of today's countdown.

1624 GMT (12:24 p.m. EDT; 9:24 a.m. PDT)

The Delta 2 rocket that will blast off four hours from now began taking shape at the Space Launch Complex 2 pad in early March when the first stage was erected. That was followed by the attachment of nine strap-on solid rocket motors and adding the second stage.

The Space Tracking and Surveillance System Advanced Technology Risk Reduction satellite was delivered to the launch pad on April 18 for hoisting into the tower and mounting atop the Delta.

The two-piece, 10-foot-diameter composite nose cone was installed around the payload last week.

NASA launch manager Chuck Dovale said the pad work and the major testing activities have proceeded smoothly. "It's been a cleaner than average processing."

1524 GMT (11:24 a.m. EDT; 8:24 a.m. PDT)

Launch day has dawned at Vandenberg Air Force Base for this afternoon's liftoff of the Delta 2 rocket carrying a research satellite for the Missile Defense Agency.

The mobile service gantry at the launch pad was rolled back earlier this morning, and ground crews are finishing up work to configure equipment and systems at Space Launch Complex 2 prior to the start of the Terminal Countdown at 10:24 a.m. local time.

A picture of the Delta 2 rocket taken overnight by United Launch Alliance photographer Carleton Bailie can be seen here.

NASA says the pre-flight preps are proceeding well and liftoff remains targeted to occur at 1:24 p.m. local time (4:24 p.m. EDT; 2024 GMT).

"There are no technical issues or concerns at this time," an agency spokesperson says.

Watch this page for live updates throughout the countdown and launch of the Delta 2 rocket.

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MONDAY, MAY 4, 2009
2330 GMT (6:30 p.m. EDT; 3:30 p.m. PDT)

A Delta 2 rocket will rumble out of California's Vandenberg Air Force Base on Tuesday afternoon carrying a quasi-classified surveillance satellite for the U.S. Missile Defense Agency.

Approval to proceed with the planned countdown preparations was given this morning after final meetings were held to review the readiness for launch.

Liftoff from the Space Launch Complex 2 pad is scheduled for 1:24 p.m. local time (4:24 p.m. EDT; 2024 GMT), which is the opening of a 28-minute window of opportunity for the rocket to fly.

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The launch will deploy the Space Tracking and Surveillance System Advanced Technology Risk Reduction satellite, a research and development craft that will test new sensors and their ability to track ballistic missiles.

The $400 million mission, known as STSS-ATRR for short, is designed to be a stepping stone that will ease the riskiness of new technologies for the MDA's Ballistic Missile Defense System.

According to information provided by the MDA, STSS-ATRR is a small experimental satellite that serves as a pathfinder aimed at proving prototype sensor technology, rocket and satellite integration, launch site processing and security planning.

The STSS-ATRR satellite was built by General Dynamics and has a planned mission life of one year, the MDA told Spaceflight Now.

Specific information about the sensors and other details related to the spacecraft haven't been released. "STSS-ATRR has classified aspects," the MDA says.

Tuesday's STSS-ATRR launch will be followed by another Delta rocket flight this summer from Florida's Cape Canaveral that will deploy a pair of STSS demonstration satellites. The two STSS test missions are supposed to show how the technologies perform in space and determine the quality of data produced.

"They are both satellite launches, both being launched using the Delta 2's, but they are different missions MDA is funding towards a space-based sensor component of the Ballistic Missile Defense System," the MDA said in written responses to questions.

"MDA is pursuing the Space Tracking and Surveillance System program as a space-based component of a layered Ballistic Missile System to detect, track, and provide engagement data to intercept ballistic missiles. From this perspective both missions will provide data, when compiled and analyzed may compliment each other's experiments," the MDA said.

1915 GMT (3:15 p.m. EDT; 12:15 p.m. PDT)

Air Force meteorologists continue to forecast a 60 percent chance of good weather for tomorrow's launch. Surface winds at the 1:24 p.m. PDT liftoff time remain the only concern for violating the launch rules.

The outlook includes low stratus clouds at just 500 feet and high cirrus clouds at 35,000 feet, northwesterly winds of 12 to 15 knots with gusts to 22 knots from 310 to 340 degrees in direction and a temperature between 56 and 60 degrees F.

"Weak high pressure continues to build in behind a low pressure system which pushed through the region this weekend," weather forecasters reported this morning. "The offshore positioning of the high will keep winds out of the northwest between 12 and 15 knots with occasional higher gusts between 20 and 22 knots. Exposure winds are expected to remain below 15 knots and will not be a concern for MST removal. Visibility will remain poor until late morning. Scattered low clouds and thin high level cirrus are expected, but will not impact the launch. Visibility at T-0 will be between 3 and 5 miles due to marine layer fog along the shoreline. Max upper-level winds are forecast to be westerly at 50 knots at 32,000 feet with weak directional wind shear throughout the vertical column."

If the launch is delayed to Wednesday for some reason, the chance of winds being out of limits increases.

"Slight changes are expected for the following 24-hour period," Air Force forecasters say. "Winds will strengthen out of the northwest between 15 and 18 knots with isolated higher gusts near 25 knots. Marine layer fog is expected to push slightly offshore and associated cloud tops will lower to 1,000 feet. Visibility is expected to improve slightly between 5 and 7 miles as the fog will move further offshore. Max upper-level winds will shift slightly to the southwest and remain at 50 knots at 32,000 feet."

SUNDAY, MAY 3, 2009

Officials running this week's flight of the Delta 2 rocket that will put a research and development testbed craft into orbit for enemy missile tracking will gather up Monday for a final round of pre-launch readiness reviews.

A NASA-led meeting at 7:30 a.m. PDT and an Air Force review at 10 a.m. PDT will determine whether all systems are prepared to enter into the countdown.

If all remains as planned, the rocket will launch Tuesday at 1:24 p.m. PDT (4:24 p.m. EDT; 2024 GMT) from Vandenberg Air Force Base carrying its experimental payload for the new Space Tracking and Surveillance System.

The early weather forecast calls for a 60 percent chance of acceptable conditions at launch time. Gusty winds are the main concern. The outlook predicts northwesterly winds 12 to 15 knots with gusts up to 22 knots, a temperature of 58 degrees F and visibility of 3 to 5 miles in light fog.

Tuesday's launch countdown activities will begin before dawn with final closeouts of the rocket's compartments and buttoning up the vehicle for flight before the pad's gantry-like mobile service tower is retracted away.

Mission managers will be on-station by 7 a.m. launch morning to oversee the final hours of the pre-flight procedures. All workers should be out of the pad area by 9:30 a.m. local. And the Terminal Countdown commences at 10:24 a.m. local (1:24 p.m. EDT), leading to liftoff exactly three hours later.

Once the three-hour sequence is running, the rocket's guidance computer system will be powered up, the first stage will be loaded with kerosene propellant and supercold liquid oxygen. Steering tests of the engines on both stages of the Delta then follow.

Planned holds are built into the countdown at the T-minus 15 and T-minus 4 minute points lasting 20 minutes and 10 minutes long in duration, respectively. Those pauses are designed to give the launch team the opportunity to work problems or catch up on items perhaps running behind the timeline.

Polls of the various launch team members and managers occur during the T-minus 4 hold to ensure everything is ready to proceed into the busy final minutes that see the rocket put on internal power, pressurized and armed for liftoff from California's Central Coast.

FRIDAY, MAY 1, 2009

The Delta 2 rocket that will boost an experimental research satellite into orbit for the Missile Defense Agency received its load of hypergolic propellants Friday, as preparations proceed smoothly for next week's launch.

Liftoff is scheduled for Tuesday at 1:24 p.m. local time (4:24 p.m. EDT; 2024 GMT) from Space Launch Complex 2 at Vandenberg Air Force Base in California.

A 28-minute window for the launch to occur stretches to 1:52 p.m., if weather or a technical glitch should interfere and prompt a brief delay. Officials plan to target the window's opening, but say the entire period is usable.

The Flight Readiness Review took place Thursday and gave approval to fill the Delta 2 rocket's second stage with a storable hydrazine propellant mixture and nitrogen tetroxide oxidizer. The fuels will power the stage's main engine during the two firings needed to place the satellite into polar orbit.

While the fueling was underway at the pad, a countdown dress rehearsal was conducted in the control rooms to practice launch day scripts and procedures.

"That all went well," NASA launch manager Chuck Dovale said in an interview. The space agency is lending its expertise to the Missile Defense Agency and overseeing the Delta rocket's flight.

The United Launch Alliance-built rocket will deliver into a low-Earth orbit the Space Tracking and Surveillance System Advanced Technology Risk Reduction satellite, or STSS-ATRR. It is a research and development spacecraft designed to test prototype sensor technology as part of the missile defense program.

After getting Saturday off, workers Sunday will focus on Range Safety beacon checks.

A pair of Launch Readiness Reviews will be held Monday morning for senior management to discuss the progress of pre-flight work, any technical issues and the status of the rocket, payload and ground support systems. Assuming there are no outstanding problems, the meeting concludes with officials giving the formal approval to proceed with Tuesday's launch.

The early weather outlook predicts a system will move through the area over the weekend but clear out by Tuesday. The concern for launch day will be strong northwesterly winds of 20 to 25 knots. The limit at liftoff time is 26 knots.

Watch this page for a full launch preview and continuing updates on the mission.

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