BY JUSTIN RAY

Follow the countdown and launch of the Delta 2 rocket with NASA's Phoenix spacecraft bound for Mars. Reload this page for the very latest on the mission.

Additional coverage for subscribers:
VIDEO: PHOENIX LAUNCHES! PLAY
VIDEO: POST-FLIGHT COMMENTS FROM LAUNCH MANAGER PLAY
VIDEO: WIDE-SCREEN FROM PATRICK AFB CAMERA PLAY
VIDEO: TRACKER FOLLOWS ROCKET TO MECO PLAY
VIDEO: LAUNCH AS SEEN FROM THE PRESS SITE PLAY
VIDEO: PAD'S MOBILE GANTRY ROLLED BACK FOR LAUNCH PLAY
VIDEO: NARRATED HIGHLIGHTS OF PHOENIX CAMPAIGN PLAY
VIDEO: NARRATED HIGHLIGHTS OF ROCKET CAMPAIGN PLAY
VIDEO: THE PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: OVERVIEW OF PHOENIX MISSION TO MARS PLAY
VIDEO: ANIMATION OF PHOENIX WITH NARRATION PLAY
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SUNDAY, AUGUST 5, 2007

When NASA's Phoenix lander arrives at Mars next May, it will join a flotilla of spacecraft already at the red planet working as a team of robotic scientists to probe the existence of water.

Read our full story.

SATURDAY, AUGUST 4, 2007

NASA's $420 million Phoenix Mars lander blasted off early today and began a 10-month voyage to the red planet, bound for the northern polar plains where scientists believe vast deposits of ice are hidden just beneath the frozen surface.

Read our launch story.

1800 GMT (2:00 p.m. EDT)

These collections of images show the Phoenix spacecraft leaving Earth for its interplanetary cruise to Mars. The mobile service gantry at pad 17A was rolled back Friday evening to reveal the Delta 2 rocket in the final hours of the countdown. The successful liftoff followed early Saturday.

See tower rollback and the launch.


From Cape Canaveral Air Force Station, these panoramas show the Complex 17 launch pads used by Delta 2 rockets. Spaceflight Now photographer Chris Miller captured the panoramas before and after the Phoenix launch from pad 17A. The rocket to loft the Dawn asteroid probe stands on pad 17B.

   PANORAMA 1 | PANORAMA 2 | PANORAMA 3 | PANORAMA 4
PANORAMA 5 | PANORAMA 6

1720 GMT (1:20 p.m. EDT)

Watch our latest podcast on the launch of Phoenix or subscribe free on iTunes

1210 GMT (8:10 a.m. EDT)

"The launch team did a spectacular job getting us on the way," said Barry Goldstein, Phoenix project manager. "Our trajectory is still being evaluated in detail; however we are well within expected limits for a successful journey to the red planet. We are all thrilled!"

1108 GMT (7:08 a.m. EDT)

Confirmation of a successful launch has been announced by Chuck Dovale, the NASA launch manager.

NASA's Phoenix spacecraft has embarked on its 10-month, 420-million-mile cruise from Earth to Mars, departing aboard a United Launch Alliance Delta 2 rocket this morning bound for the Red Planet to examine the frozen water in the northern plains that could be a habitable zone for life.

1102 GMT (7:02 a.m. EDT)

Data from Phoenix indicates the spacecraft reorienting itself to point its solar arrays toward the sun, a NASA spokesman says. Health checks of Phoenix systems are underway.

1056 GMT (6:56 a.m. EDT)

T+plus 90 minutes, 20 seconds. The Deep Space Network tracking site in Goldstone, California, has acquired a signal from the Phoenix spacecraft.

1051 GMT (6:51 a.m. EDT)

T+plus 84 minutes, 30 seconds. Phoenix should have separated from the third stage by now. However, live data is not available at the Cape at the moment to confirm.

1048 GMT (6:48 a.m. EDT)

T+plus 81 minutes, 30 seconds. Separation of the payload is about two minutes away.

1046 GMT (6:46 a.m. EDT)

T+plus 79 minutes, 35 seconds. The Thiokol Star 48B third stage has burned out of its solid fuel, ending the Delta 2 rocket's powered flight for the launch of Phoenix.

1045 GMT (6:45 a.m. EDT)

T+plus 79 minutes. The upper stage appears to be burning well.

1044 GMT (6:44 a.m. EDT)

T+plus 78 minutes, 8 seconds. Third stage ignition! The second stage was separated and the upper stage motor has been lit.

1043 GMT (6:43 a.m. EDT)

T+plus 76 minutes, 30 seconds. The second stage has completed its second burn of this launch. In the next minute, tiny thrusters on the side of the rocket will be fired to spin up the vehicle in preparation for jettison of the second stage.

1042 GMT (6:42 a.m. EDT)

T+plus 76 minutes. Good chamber pressure reported from the second stage engine.

1041 GMT (6:41 a.m. EDT)

T+plus 75 minutes. The second stage is indeed firing as planned to continue pushing Phoenix on its way.

1040 GMT (6:40 a.m. EDT)

T+plus 74 minutes. The burn should be underway. However, engineers at the Cape have not yet received live telemetry from the tracking plane over the Pacific.

1036 GMT (6:36 a.m. EDT)

T+plus 70 minutes. About four minutes remain until second stage engine restart.

1031 GMT (6:31 a.m. EDT)

T+plus 65 minutes. The "Big Crow" tracking plane is expected to acquire the rocket's signal about eight minutes from now. The mobile telemetry aircraft will follow the vehicle during the second stage burn. A ground tracking station in Hawaii then acquires the telemetry stream for the final events of the launch.

And check out our podcast from this morning.

1025 GMT (6:25 a.m. EDT)

Spaceflight Now Plus subscribers can watch a movie of this morning's launch here.

To learn more about this service, click here.

1021 GMT (6:21 a.m. EDT)

T+plus 55 minutes. The rocket's launch trajectory following liftoff from the eastern coast of Florida has taken the vehicle across the Atlantic and southern Africa. The path continues over the Indian Ocean and northwestern Australia. The upcoming second and third stage burns will happen over the central Pacific, then deployment of the Phoenix spacecraft occurs as third stage nears North America.

1011 GMT (6:11 a.m. EDT)

T+plus 45 minutes. The Delta rocket is in the midst of its longest-ever coast period between burns of the second stage. The engine will ignite again at T+plus 74 minutes for a planned two-minute burn that will boost the vehicle into a higher elliptical orbit. That will be followed by separation between the second and third stages. The solid-fuel upper stage then burns to eject Phoenix from Earth orbit.

1006 GMT (6:06 a.m. EDT)

T+plus 40 minutes. The vehicle is placed in a slow rolling motion during the parking orbit coast period. This is designed to keep the thermal conditions even across the rocket.

1001 GMT (6:01 a.m. EDT)

T+plus 35 minutes. The official liftoff time this morning was 5:26:34.596 a.m., which was right in the middle of the one-second launch window.

0959 GMT (5:59 a.m. EDT)

T+plus 33 minutes. A review of data from the first and second stage burns of the Delta 2 rocket shows the vehicle has performed well.

"Everything seems to be indicating we've got a pretty good launch going," NASA spokesman George Diller says.

0940 GMT (5:40 a.m. EDT)

T+plus 14 minutes. The rocket has flown out of range from the Antigua tracking station. An airborne tracking plane over the Pacific Ocean will provide live data relay during the second stage engine re-start at T+plus 74 minutes. No telemetry from the rocket is expected until then.

0938 GMT (5:38 a.m. EDT)

T+plus 12 minutes. The rocket has successfully achieved a parking orbit with an apogee of 90.09 miles, perigee of 89.98 miles and inclination of 28.5 degrees. That is right on the pre-planned orbit parameters.

0936 GMT (5:36 a.m. EDT)

T+plus 9 minutes, 28 seconds. SECO 1. The second stage engine cutoff has occurred, completing the motor's first firing of the day. The Delta 2 rocket and Phoenix have arrived in a preliminary orbit around Earth following launch this morning from Cape Canaveral. The vehicle will coast for more than an hour before the second stage is re-ignited.

0935 GMT (5:35 a.m. EDT)

T+plus 8 minutes, 30 seconds. The second stage engine is consuming a hydrazine propellant mixture and nitrogen tetroxide oxidizer. This burn is needed to achieve a parking orbit around Earth.

0934 GMT (5:34 a.m. EDT)

T+plus 8 minutes. The Air Force's downrange tracking station on Antigua Island has acquired the rocket's signal.

0933 GMT (5:33 a.m. EDT)

T+plus 7 minutes, 24 seconds. Delta is 88 miles in altitude, 900 miles downrange from the launch pad and traveling at nearly 15,100 mph.

0933 GMT (5:33 a.m. EDT)

T+plus 6 minutes, 50 seconds. Good chamber pressure reported on the second stage engine.

0933 GMT (5:33 a.m. EDT)

T+plus 6 minutes, 30 seconds. The rocket has passed 81 miles in altitude.

0932 GMT (5:32 a.m. EDT)

T+plus 6 minutes. The vehicle continues to accelerate on the power provided by the second stage engine.

0931 GMT (5:31 a.m. EDT)

T+plus 5 minutes, 25 seconds. The rocket's 9.5-foot diameter nose cone enclosing the spacecraft has been jettisoned.

0931 GMT (5:31 a.m. EDT)

T+plus 4 minutes, 47 seconds. The Delta's second stage engine has ignited following jettison of the spent first stage.

0931 GMT (5:31 a.m. EDT)

T+plus 4 minutes, 27 seconds. MECO. Main engine cutoff is confirmed. The first stage has completed its firing.

0929 GMT (5:29 a.m. EDT)

T+plus 3 minutes, 30 seconds. First stage systems continue to look good. The chamber pressures in the main engine and the twin vernier steering thrusters are normal.

0929 GMT (5:29 a.m. EDT)

T+plus 2 minutes, 50 seconds. Delta is 34 miles in altitude.

0928 GMT (5:28 a.m. EDT)

T+plus 2 minutes, 14 seconds. The three air-ignited solid rocket boosters have burned out and separated. The rocket is now flying solely on the power generated by the liquid-fueled first stage main engine.

0928 GMT (5:28 a.m. EDT)

T+plus 1 minute, 45 seconds. The air-lit boosters continue to burn along with the main engine. The vehicle is 17 miles in altitude.

0927 GMT (5:27 a.m. EDT)

T+plus 1 minute, 12 seconds. All six ground-start solid rocket boosters have burned out of propellant and separated from the Delta 2's first stage. A moment before the jettison occurred, the three remaining motors strapped to rocket ignited to continue assisting the rocket's RS-27A main engine on the push to space.

0927 GMT (5:27 a.m. EDT)

T+plus 56 seconds. The Delta 2 rocket has passed through the region of maximum aerodynamic pressure during its atmospheric ascent.

0927 GMT (5:27 a.m. EDT)

T+plus 45 seconds. The six solid rocket motors ignited on the launch pad have surpassed their period of maximum thrust. Each of the Alliant Techsystems-made boosters generate roughly 100,000 pounds of thrust.

0927 GMT (5:27 a.m. EDT)

T+plus 35 seconds. The Delta 2 rocket has broken the sound barrier as it powers into the predawn skies.

0926:54 GMT (5:26:54 a.m. EDT)

T+plus 20 seconds. The United Launch Alliance Delta 2 rocket has darted off Cape Canaveral's pad 17A with the main engine and all six ground-lit solid boosters burning to generate more than 700,000 pounds of thrust.

0926:34 GMT (5:26:34 a.m. EDT)

LIFTOFF! Liftoff of Phoenix spacecraft bound for the arctic plains of the Red Planet to taste the water of Mars.

0926:04 GMT (5:26:04 a.m. EDT)

T-minus 30 seconds. SRB ignitors will be armed at T-minus 11 seconds.

The launch ignition sequence will begin in the final two seconds of the countdown when a ULA engineer pushes the engine start switch. The process begins with ignition of the two vernier engines and first stage main engine start. The six ground-lit solid rocket motors then light at T-0 for liftoff.

0925 GMT (5:25 a.m. EDT)

T-minus 1 minute. Sixty seconds from launch. The vehicle's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable.

0925 GMT (5:25 a.m. EDT)

T-minus 75 seconds. The Air Force's Eastern Range has given the all-clear to launch.

0924 GMT (5:24 a.m. EDT)

T-minus 90 seconds. Topping of the liquid oxygen tank to the 100 percent level is underway.

0924:34 GMT (5:24:34 a.m. EDT)

T-minus 2 minutes. Pressurization of the first stage liquid oxygen is now beginning. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

0924:04 GMT (5:24:04 a.m. EDT)

T-minus 2 minutes, 30 seconds. The Phoenix spacecraft has been declared "go" for launch.

0923:34 GMT (5:23:34 a.m. EDT)

T-minus 3 minutes and counting. The rocket's third stage safe and arm devices are being armed. The third stage will boost Phoenix out of Earth orbit for the trek to the Red Planet.

0922 GMT (5:22 a.m. EDT)

T-minus 3 minutes, 45 seconds. The Delta 2 rocket's systems are now transferring to internal power for launch.

0922:34 GMT (5:22:34 a.m. EDT)

T-minus 4 minutes and counting! Clocks are running again for the final minutes to liftoff of the United Launch Alliance Delta 2 rocket that will propel NASA's Phoenix spacecraft on a 10-month, 420-million-mile cruise from Earth to Mars. Launch will occur at 5:26:34 a.m. from pad 17A at Cape Canaveral Air Force Station in Florida.

0921 GMT (5:21 a.m. EDT)

One minute away from picking up the countdown.

0920 GMT (5:20 a.m. EDT)

The Phoenix spacecraft atop the Delta 2 rocket is switching to internal power for launch.

0919:34 GMT (5:19:34 a.m. EDT)

Three minutes remain in the built-in hold.

0918 GMT (5:18 a.m. EDT)

The launch team readiness poll has been conducted. All members voiced "ready" to pick up the count, including the ULA launch director, for liftoff at 5:26 a.m. EDT.

0916 GMT (5:16 a.m. EDT)

Following a NASA management poll, the agency's launch manager Chuck Dovale has given a "go" to proceed with the count.

0912:34 GMT (5:12:34 a.m. EDT)

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 at 5:26:34 a.m. for the Delta 2 rocket and Phoenix spacecraft.

During the hold, officials will poll the various team members in the "soft blockhouse," Range Operations Control Center and Mission Directors Center.

0910 GMT (5:10 a.m. EDT)

Weather conditions remain "go."

0907 GMT (5:07 a.m. EDT)

The first stage kerosene fuel tank is being pressurized. Now 19 minutes from liftoff.

0901 GMT (5:01 a.m. EDT)

T-minus 15 minutes and counting. The countdown has resumed following the planned hold. Clocks will tick down to T-minus 4 minutes where the final hold is scheduled. Liftoff of the Delta rocket from Cape Canaveral is slated to occur at 5:26 a.m. EDT.

0857 GMT (4:57 a.m. EDT)

A launch team poll for a "ready" status to resume the countdown reported no constraints to continuing onward this mornign.

0856 GMT (4:56 a.m. EDT)

Now 30 minutes to launch.

0854 GMT (4:54 a.m. EDT)

Launch team and management polls will be coming up shortly. Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned.

At this time, everything remains "go" for launch at 5:26 a.m. EDT.

0846 GMT (4:46 a.m. EDT)

Phoenix is targeting a landing zone in the northern plains of Mars where the Odyssey orbiter found evidence of water ice near the surface. The robotic arm on Phoenix will scoop up samples of the ice and soil for examination by science instruments on the lander.

"Our entire mission is trying to understand the history of this ice, in particular does it melt over time and provide a habitat for some sort of Martian biology," said Peter Smith, the Phoenix principal investigator.

"We want to spend the short amount of time that we have in the northern polar summer inside the arctic circle on Mars digging down under the surface rather than exploring horizontally. This is a vertical mission."

Unlike the Mars rovers Spirit and Opportunity that have driven away from their initial landing sites, Phoenix is a stationary lander.

"We don't have wheels or ice skates. We like to call it vertical mobility - we dig down," said Barry Goldstein, the Phoenix project manager.

0841 GMT (4:41 a.m. EDT)

T-minus 15 minutes and holding. The countdown has entered a planned 20-minute built-in hold. The pause is designed to give the launch team a chance to work any problems or catch up on activities that might be running behind schedule. Engineers will also have time to examine all the data from the just-completed steering tests.

0839 GMT (4:39 a.m. EDT)

"In summary, we are looking real good," launch weather officer Joel Tumbiolo says. All conditions are acceptable at the present time and there's now less than a 10 percent chance of violating the weather rules at launch.

0837 GMT (4:37 a.m. EDT)

The first stage steering checks just finished, completing these slew tests for today's countdown.

0833 GMT (4:33 a.m. EDT)

Slews of the second stage engine are complete.

0832 GMT (4:32 a.m. EDT)

Technicians are starting 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.

0826 GMT (4:26 a.m. EDT)

Sixty minutes for the start of the Phoenix mission to the Red Planet.

"It's a wonderful morning to go to Mars," says Barry Goldstein, the Phoenix project manager.

0822 GMT (4:22 a.m. EDT)

Range Safety is performing inhibited checks of the command destruct receivers. The CRDs would be used in destroying the Delta rocket should the vehicle veer off course or malfunction during the launch.

0810 GMT (4:10 a.m. EDT)

Loading of the Delta 2 rocket's first stage liquid oxygen tank has concluded. The operation took 27 minutes and 24 seconds today. The tank will be replenished through the countdown to replace the supercold liquid oxygen that naturally boils away.

The rocket now stands fully fueled for liftoff at 5:26 a.m. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel along with the liquid oxygen over the past hour-and-a-half. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels earlier this week. The nine strap-on booster rockets and third stage use solid propellants.

0807 GMT (4:07 a.m. EDT)

The first stage liquid oxygen tank just reached the 95 percent full level. The "rapid load" valve was closed, with the slower "fine load" phase continuing to fill the tank.

0756 GMT (3:56 a.m. EDT)

Now 90 minutes to launch. Weather looks good, there are no technical problems and the countdown is progressing on schedule for liftoff at exactly 5:26:34 a.m. EDT.

0753 GMT (3:53 a.m. EDT)

The 25-minute process to load the liquid oxygen tank has been underway for 10 minutes. No problems have been reported. The outer skin of the rocket is beginning to ice over as the supercold oxidizer pumps into the vehicle.

0743 GMT (3:43 a.m. EDT)

Cryogenic liquid oxygen, chilled to Minus-298 degrees F, has started flowing from the storage reservoir at Complex 17, through plumbing and into the bottom of the ULA 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.

0741 GMT (3:41 a.m. EDT)

The official "go" has been given to start filling the rocket's first stage with liquid oxygen.

0738 GMT (3:38 a.m. EDT)

Preps for liquid oxygen loading are starting.

0735 GMT (3:35 a.m. EDT)

Here's some stats on this launch:

• The 325th Delta rocket launch since 1960
• The 129th Delta 2 rocket mission since 1989
• The 3rd of 2007
• The 63rd Delta 2 to fly in the 7925 configuration

0732 GMT (3:32 a.m. EDT)

The launch team has completed work to turn on and configure the Delta's onboard guidance computer.

0730 GMT (3:30 a.m. EDT)

NASA launch manager Chuck Dovale just polled the agency's management team to verify there are no constraints with proceeding into liquid oxygen loading. No technical issues with rocket systems, the spacecraft or Range are being worked.

0722 GMT (3:22 a.m. EDT)

Weather is looking ideal for a launch this morning, the launch weather officer just told management in a planned briefing in advance of the decision to begin liquid oxygen loading into the first stage.

0711 GMT (3:11 a.m. EDT)

The first stage fuel tank of the Delta 2 rocket has been fully loaded for today's planned 5:26 a.m. launch. The tank was filled with a highly refined kerosene, called RP-1, during a 19-minute, 34-second process that concluded at 3:11 a.m. EDT.

The next major task in the count will be loading super-cold cryogenic liquid oxygen into the first stage starting later this hour.

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.

0709 GMT (3:09 a.m. EDT)

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.

0707 GMT (3:07 a.m. EDT)

The launch team has computed that today's full load for the first stage fuel tank is 10,003 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.

0700 GMT (3:00 a.m. EDT)

First stage RP-1 fuel loading is passing the 5,000-gallon mark.

0656 GMT (2:56 a.m. EDT)

Launch of the Delta rocket with the Phoenix spacecraft is two-and-a-half hours away.

0652 GMT (2:52 a.m. EDT)

About 10,000 gallons of the kerosene propellant are pumping into the base of the rocket from storage tanks at pad 17A as fueling of the Delta 2's first stage begins for today's launch.

0649 GMT (2:49 a.m. EDT)

Preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank are starting. After verifying valves, sensors, flow meters and equipment are ready, the highly-refined kerosene fuel will start flowing into the vehicle a few minutes from now.

0626 GMT (2:26 a.m. EDT)

T-minus 150 minutes and counting. The Terminal Countdown has commenced for today's launch of NASA's Phoenix mission aboard the Delta 2 rocket.

The next three hours will be spent fueling the rocket, activating systems and performing final testing before liftoff at 5:26 a.m. EDT from pad 17A at Cape Canaveral Air Force Station in Florida.

Workers have cleared the Complex 17 area in advance of the hazardous portion in today's launch operation. But a warning horn is now being sounded three times at the seaside complex as a precaution to alert any remaining personnel in the vicinity that they should leave immediately.

The pad clear status will allow the start of activities such as pressurizing the helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

The countdown clocks currently stand at T-minus 150 minutes. Two holds -- totaling 30 minutes in duration -- are planned at T-minus 15 minutes and T-minus 4 minutes that will lead toward a T-0 and liftoff.

0300 GMT (11:00 p.m. EDT Fri.)

Rollback of the gantry is now complete.

0220 GMT (10:20 p.m. EDT Fri.)

The fully assembled United Launch Alliance Delta 2 rocket to will hurl NASA's Phoenix spacecraft on an interplanetary journey to Mars is being revealed at Cape Canaveral's pad 17A right now.

The mobile service tower that was used to stack the multi-stage vehicle atop the pad's launch mount, attach the nine strap-on solid motors and hoist the payload aboard the rocket is slowly rolling away from the Delta as countdown activities continue for Saturday morning's liftoff.

Once the tower is secured in the launch position a suitable distance from the rocket, crews will spend the next few hours putting the final touches on the Delta and configuring pad equipment.

Liftoff remains on schedule for 5:26 a.m. EDT.

0035 GMT (8:35 p.m. EDT)

Preparations are underway to move the mobile service tower at launch complex 17A in readiness for the launch of NASA's Phoenix probe. The tower doors that enclose the top of the Delta 2 rocket have just opened.

FRIDAY, AUGUST 3, 2007

NASA's Phoenix spacecraft is poised for launch early Saturday to begin a 10-month, 420-million-mile cruise from Earth to Mars. Liftoff of the Delta 2 rocket from Florida's Cape Canaveral remains targeted to occur at 5:26 a.m. EDT.

"The launch team is ready," NASA launch manager Chuck Dovale said Thursday. "Mars is a great opportunity. We always have exciting missions but missions to Mars just seem to capture the imagination."

Phoenix is headed for the arctic northern plains of the Red Planet where it will touch down using small rocket engines similar to the Viking spacecraft 30 years ago. Equipped with an 8-foot robotic arm, Phoenix will dig up samples of the surrounding soil and water ice for examination within instruments on the lander's science deck.

"I see this mission as a stepping stone towards the search for life on other planets. We're hoping to find a place that we consider really a habitable zone on Mars. To me, if we can find that out, that would be a tremendous success in this mission," said Peter Smith, the Phoenix principal investigator from the University of Arizona-Tucson.

"We're also really interested in following up on the discovery of water ice by the Odyssey spacecraft in 2002 and trying to understand how the ice got there and what it's source was and what its history has been."

Recent NASA missions sent to Mars, including the long-lived rovers Spirit and Opportunity, were launched under the theme of "follow the water." On Earth, where there is water, even in the harshest of environments, there is life. Scientists are applying that to the Mars exploration efforts to determine if Mars once had enough liquid water to support life in the past or even today.

"The way I like to describe it is the Mars Exploration Rovers, which was an equatorial mission, went to study the past history of water and the discoveries they have made have been very successful in finding out where the water was. What Phoenix is doing is using a stationary lander and going to where the water is," said Barry Goldstein, Phoenix project manager from the Jet Propulsion Laboratory.

"If we are successful, we'll be able to taste the water on another planet and tell humans what is inside that water."

The $414 million Phoenix mission rose from the ashes of NASA's cancelled 2001 lander project. Following the failure of the Mars Polar Lander in late 1999, the agency opted to kill the '01 mission and mothball the hardware. But in 2003, the Phoenix team's proposal to use the existing hardware was selected by NASA for the 2007 launch opportunity to Mars.

"We basically decided we were going to spend a large, fundamental activity on this project to try and understand the details what went wrong on Polar Lander, test the heck out of this '01 spacecraft and make sure it had a higher degree of confidence at the time we launch," Goldstein said.

The team was faced with recommendations from the Polar Lander investigation, plus a board that gave to-do actions to ready the '01 lander for flight.

"We attacked each one of those findings," Goldstein said, but added: "That was not enough. That was not nearly enough."

Indeed, Phoenix engineers uncovered a dozen other potential mission-ending problems during testing that weren't on the previous lists.

"I'm confident we have worked as hard as any group of people can. Am I confident in the landing? I'll be nervous. If my fingernails survive that day, it will be a miracle. It's not the things that we know that will hurt us. It's the things we don't know."

The trip to Mars begins Saturday morning aboard a United Launch Alliance Delta 2 rocket. The three-stage booster will propel Phoenix on the interplanetary trajectory.

The launch countdown at Cape Canaveral's Complex 17 begins this evening. Rollback of the pad's mobile service gantry from around the Delta rocket is expected shortly after 8 p.m. EDT.

The Terminal Countdown commences in the final three hours to launch. Fueling of the rocket will be completed, including the pumping of kerosene propellant and supercold liquid oxygen into the first stage, as clocks tick down.

A pair of instantaneous launch times -- meaning one-second shots for the rocket to lift off -- will be available at precisely 5:26:34 a.m. and 6:02:59 a.m. EDT. If the Delta doesn't launch at either of those two times, the flight would have to be postponed until Sunday morning.

Weather forecasters predict an 80 percent chance of favorable conditions on Saturday, with some scattered clouds, good visibility and light winds on the ground and at high-altitudes.

Watch this page for live updates during the countdown and throughout the Delta's flight.

THURSDAY, AUGUST 2, 2007

The Phoenix spacecraft and the United Launch Alliance Delta 2 rocket are being buttoned up in preparation for the final countdown and Saturday morning's blastoff.

Mission managers held the Launch Readiness Review earlier today to discuss the progress of work in advance of proceeding into the count on Friday evening. Officials asked an engineering board to meet at 4 p.m. to review short interruptions of the air conditioning feeding into the rocket's nose cone because of power outages this week. Engineers will make sure the brief instances posed no harm to the Phoenix spacecraft hardware.

There are no other technical issues being discussed and the weather outlook is favorable for Saturday's 5:26 a.m. EDT liftoff time.

Check back later tonight for a full launch preview.

WEDNESDAY, AUGUST 1, 2007

The latest weather forecast for Saturday morning's launch of Phoenix is available here.

TUESDAY, JULY 31, 2007

Anticipated stormy weather in the Cape Canaveral area this afternoon has caused a ripple effect in preparations to launch the Phoenix lander bound for Mars, forcing NASA to postpone the liftoff aboard a Delta 2 rocket by 24 hours.

Originally set for early Friday, the launch has been rescheduled for Saturday morning. Liftoff will be possible during a pair of one-second launch windows at 5:26 and 6:02 a.m. EDT.

Today's expected bad weather is interrupting work to pump storable propellants into the rocket's second stage at pad 17A. Technicians filled the stage's oxidizer tank this morning. However, the forecast of afternoon thunderstorms will preclude the loading of hydrazine fuel into the stage later today as planned.

Air Force meteorologists monitor the conditions across the Cape and issue lightning advisories when the weather becomes unsafe for technicians to remain at the launch pads. Clearing the pads for weather alerts then causes work to fall behind schedule.

The hydrazine loading will occur tomorrow morning. But fitting that activity into the timeline wrecks the overall schedule for other pre-flight activities, prompting the one-day slip in the launch date.

"There is not enough contingency time," a NASA spokesperson said.

The second stage uses storable nitrogen tetroxide and a hydrazine blend called Aerozine 50 to power its Aerojet AJ118-K engine. The stage fires twice during the launch to boost Phoenix toward its Earth departure trajectory.

The weather outlook for Saturday morning's launch times predicts an 80 percent chance of favorable conditions, with clouds the only worry.

Phoenix will spend 10 months cruising from Earth to Mars. The craft is targeting the arctic plains of the Red Planet where it will land on May 25, 2008, then use a robotic arm to dig up samples of the surrounding icy-rich soil to examine with onboard instruments during a three-month mission.

MONDAY, JULY 30, 2007

The Mars lander Phoenix is scheduled for launch before dawn Friday aboard a Delta 2 rocket. The early weather forecast predicts an 80 percent chance of favorable conditions for the liftoff from Cape Canaveral. See the full forecast here.