Seeking a missing ingredient to understanding Earth's environmental changes, a new satellite conceived through unique international collaborations was launched today to map the planet's salty seas from space.

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And see a dazzling three-page launch photo gallery.

"Data from this mission will advance our understanding of the ocean and prediction of the global water cycle," said Michael Freilich, director of NASA's Earth Science Division in the Science Mission Directorate at agency headquarters in Washington. "This mission demonstrates the power of international collaboration and accurate spaceborne measurements for science and societal benefit. This would not be possible without the sustained cooperation of NASA, CONAE and our other partners."

"Aquarius is a critical component of our Earth sciences work, and part of the next generation of space-based instruments that will take our knowledge of our home planet to new heights," NASA Deputy Administrator Lori Garver says in a statement. "The innovative scientists and engineers who contributed to this mission are part of the talented team that will help America win the future and make a positive impact across the globe."

"The Delta 2 vehicle continues to offer excellence, best value and continuous improvement to our customers," Jim Sponnick, ULA's vice president for mission operations, also said in a post-launch statement. "The reliability of this vehicle is a testament to the dedicated employees that ensure mission success is the top priority for each and every launch."

"ULA is extremely proud to be a part of the Aquarius/SAC-D mission, which will offer scientists NASA's first global observations of ocean surface salinity from space to better understand ocean circulation and the resulting effects on our climate," said Jim Sponnick, ULA's vice president for mission operations. "Today's successful launch is the culmination of years of hard work by NASA and the ULA launch team, along with our many other mission partners."

The pair of power-generating solar arrays on the SAC-D spacecraft have unfurled following today's successful ascent into orbit, NASA launch director Omar Baez says.

"Team Vandenberg performed brilliantly once again in ensuring safe and successful launch operations," Col. Richard Boltz, 30th Space Wing commander at Vandenberg Air Force Base, said in a post-launch statement. "We wish our mission partners at NASA well as they begin their important work with Aquarius."

This is the 94th consecutive successful Delta 2 rocket launch dating back to May 1997. The Delta 2's overall history since debuting in 1989 has achieved 147 successes in 149 flights.

Two more Delta 2 rockets are scheduled for this year, including NASA's GRAIL mission to the moon on September 8 from Cape Canaveral and the NPP polar-orbiting civilan weather satellite on October 18 from Vandenberg.

ULA also has five additional Delta 2 vehicles it hopes to use for additional launches in the future.

T+plus 56 minutes, 55 seconds. SPACECRAFT SEPARATION! Argentina's Satelite de Aplicaciones Cientificas-D spacecraft with NASA's Aquarius ocean salinity instrument has been released from the Delta 2 rocket's second stage, completing today's launch!

T+plus 56 minutes, 20 seconds. Clampband release has been confirmed.

T+plus 55 minutes, 50 seconds. Roll, pitch and yaw rates have nulled out.

T+plus 54 minutes, 30 seconds. The deployment of SAC-D from the Delta second stage is a two-step process. The payload attach fitting's clampband will be released at T+plus 55 minutes, 50 seconds. A set of secondary latches then disengage at T+plus 56 minutes, 20 seconds, allowing the satellite to physically separate from the rocket.

The second stage then performs a retro maneuver to back away from SAC-D. That will be followed by a firing of the stage's engine to move the rocket further away from the spacecraft and then another firing to deplete the remaining fuel supply as a safety measure.

T+plus 54 minutes. The rocket is repositioning itself to the proper orientation for release of SAC-D.

T+plus 52 minutes, 36 seconds. SECO 2. The orbit adjustment burn occurred as planned just south of Madagascar.

T+plus 52 minutes, 23 seconds. The second stage engine has ignited for the 12-second firing to propel its 3,000-pound spacecraft payload into the proper polar orbit.

T+plus 50 minutes, 30 seconds. The second stage is completing its maneuver into the proper orientation for the upcoming engine firing.

T+plus 42 minutes. The next firing by the Delta rocket's second stage is coming up in 10 minutes while flying on the other side of the world from Vandenberg. The orbiting Tracking and Data Relay Satellite System will continue receiving the rocket's telemetry for transmission back to the launch site, providing the confirmation of the second stage burn and release of the SAC-D satellite.

T+plus 35 minutes. The rocket is crossing Antarctica now as it flies in a polar orbit around Earth. A map of the rocket's planned flight path is available here.

T+plus 31 minutes. Delta is 207 miles in altitude and over 5,900 miles downrange from the launch pad.

T+plus 30 minutes. The rocket is coasting until the second stage restarts its engine at T+plus 52 minutes, 20 seconds for a brief 12-second firing to put the vehicle into a near-circular orbit 408 miles above Earth. Deployment of SAC-D from the launch vehicle is expected 56 minutes after liftoff.

T+plus 25 minutes. As the rocket coasts in this parking orbit, it performs a "BBQ roll" maneuver to keep the thermal conditions on the vehicle equal.

T+plus 20 minutes. Live telemetry continues to be received via NASA's Tracking and Data Relay Satellite System. Today's launch is the third Delta 2 flight to use TDRS during the long mission instead of ordering support from mobile telemetry assets and faraway ground sites after the rocket passes out of view from Vandenberg.

T+plus 14 minutes, 30 seconds. Delta is 102.7 miles in altitude, 2,078 miles downrange from the launch pad and traveling at 16,967 mph.

T+plus 11 minutes, 45 seconds. The Delta 2 rocket is 100 miles in altitude, 1,435 miles south from the launch pad with a velocity of 16,979.9 mph.

T+plus 11 minutes, 15 seconds. SECO 1 has been confirmed. The second stage's Aerojet-made engine completed its initial burn for the launch. Delta and SAC-D/Aquarius have reached orbit.

T+plus 10 minutes, 50 seconds. Speed now 16,200 mph.

T+plus 10 minutes, 10 seconds. The rocket is about 102.2 miles up, 1,096 miles downrange, traveling at at 15,264 mph.

T+plus 9 minutes, 30 seconds. About two minutes remain in this burn of the second stage engine to achieve the intended parking orbit.

T+plus 9 minutes. The second stage continues to fire normally.

T+plus 8 minutes, 40 seconds. Delta is 104 miles in altitude, 795 miles downrange from the launch pad and traveling at 13,200 mph.

T+plus 8 minutes. Delta is 103 miles in altitude, 682 miles downrange from the launch pad and traveling at 12,482 mph.

T+plus 7 minutes, 10 seconds. Delta is 98 miles up, 535 miles downrange traveling at 11,641 mph.

T+plus 6 minutes, 50 seconds. Mission events occurring at the planned times.

T+plus 6 minutes, 10 seconds. Delta is 87.4 miles in altitude, 384 miles downrange from the launch pad and traveling at 10,860 mph.

T+plus 5 minutes, 45 seconds. Second stage looking good as this initial burn up gets underway.

T+plus 5 minutes, 3 seconds. The rocket's nose cone enclosing the satellite payload has been jettisoned.

T+plus 4 minutes, 40 seconds. The Delta's second stage has ignited! The engine is up and running.

T+plus 4 minutes, 35 seconds. MECO. The first stage main engine cutoff is confirmed, and the spent stage has been jettisoned.

T+plus 3 minutes, 55 seconds. The vehicle is 40.2 miles in altitude, 78.3 miles downrange from the launch pad and traveling at 6,383 mph. The first stage main engine continues to burn normally.

T+plus 3 minutes, 45 seconds. Still looking good on the first stage.

T+plus 3 minutes, 25 seconds. The vehicle is 32.8 miles in altitude, 42.3 miles downrange from the launch pad and traveling at 4,339 mph. The first stage main engine continues to burn normally.

T+plus 2 minutes, 50 seconds. Now 26.7 miles in altitude, 17.9 miles downrange, 2,993 mph.

T+plus 2 minutes, 30 seconds. The first stage main engine still firing well. The Pratt & Whitney Rocketdyne powerplant consumes kerosene fuel and liquid oxygen to produce about 200,000 pounds of thrust.

T+plus 2 minutes. The Delta 2 rocket is 17.6 miles in altitude, 6.2 miles downrange from the pad, and traveling over 1,395 mph.

T+plus 1 minute, 40 seconds. The ground-lit boosters have jettisoned from the first stage. They remained attached until the rocket cleared off-shore oil rigs.

T+plus 1 minute, 5 seconds. All three ground-start solid rocket boosters have burned out. The Delta 2's first stage RS-27A main engine is providing the sole thrust for the next few minutes.

T+plus 50 seconds. The rocket has flown through the area of maximum aerodynamic pressure in the lower atmosphere.

T+plus 40 seconds. Delta has broken the sound barrier, rapidly accelerating on the power of its first stage main engine and the three ground-lit strap-on solid-fuel boosters.

T+plus 15 seconds. The Delta 2 rocket is maneuvering on the course for southward journey carrying the SAC-D spacecraft.

LIFTOFF! Liftoff of the Delta 2 rocket launching an environmental satellite to study Earth's salty seas from space!

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

The launch ignition sequence will begin at T-minus 2 seconds when a launch team member triggers the engine start switch. The process begins with ignition of the two vernier thrusters and first stage main engine start. The three ground-lit solid rocket motors then light at T-0 for liftoff.

T-minus 1 minute. All remains "go" for launch.

T-minus 80 seconds. First stage liquid oxygen topping to 100 percent is underway.

T-minus 1 minute, 45 seconds. The launch pad water suppression system is being activated.

T-minus 2 minutes. The first stage liquid oxygen vents are now being closed so the LOX tank can be pressurized for launch. Puffs of vapor from a relief valve on the rocket will be seen in the remainder of the countdown as the tank pressure stabilizes.

T-minus 2 minutes, 30 seconds. The SAC-D payload has been declared "go" for launch.

T-minus 2 minutes, 45 seconds. Vehicle ordnance is being armed.

T-minus 3 minutes and counting down to the Delta rocket launch dedicated to deploying the SAC-D spacecraft with NASA's Aquarius instrument to measure the saltiness of the world's oceans.

T-minus 3 minutes, 45 seconds and counting. The Delta 2 rocket's systems are now transferring to internal power for launch. And the launch pad water system is being enabled.

T-minus 4 minutes and counting! Clocks are ticking down the final moments for liftoff of Delta 354 with the SAC-D spacecraft. Launch is set for 7:20:13 a.m. local time from California's Central Coast.

Now five minutes from launch! The "go" has been given for release of the hold in one minute.

The SAC-D spacecraft has undergone final configuring for launch.

All systems are "go" to fly today.

The launch team is being polled for the final time before liftoff to confirm systems are ready for the Delta 2 rocket and SAC-D/Aquarius spacecraft.

Now 10 minutes to go. The rocket's launch opportunity today is five minutes long beginning at exactly 7:20:13 a.m. PDT (10:20:13 a.m. EDT). The window is dictated by the SAC-D satellite mounted atop the 12-story booster. Launching at the time ensures optimum insertion of the payload into the desired orbit from the Vandenberg Air Force Base pad.

A previous weather balloon did find "red" high-altitude wind conditions. However, the most recent balloon is "green" and "go" for launch.

NASA launch director Omar Baez has polled his advisory team and the space agency is "go" to continue with the countdown.

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 7:20:13 a.m. local (10:20:13 a.m. EDT; 1420:13 GMT) for the Delta 2 rocket.

The launch weather officer confirms all conditions are "go" for liftoff.

The upper level wind conditions are being loaded into the Delta 2 rocket's flight computer for launch.

The first stage kerosene fuel tank is being pressurized for flight.

Twenty minutes from launch. The SAC-D satellite will become the 224th primary payload put into space by the venerable Delta 2 rocket over the past 20 years. Here's a look at some other stats about today's mission. This will be:

• The 354th Delta rocket launch since 1960
• The third Delta of 2011
• The 149th Delta 2 rocket mission since 1989
• The 10th Delta 2 rocket to fly in the 7320 configuration
• The 40th Delta 2 rocket launch from Vandenberg AFB
• The 48th Delta 2 mission overseen by NASA

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 hold is scheduled. Launch remains set to occur at precisely 7:20:13 a.m. local (10:20:13 a.m. EDT; 1420:13 GMT).

A poll of the launch team confirms everyone is ready to press ahead with the countdown after this pre-planned 20-minute hold.

Now just 35 minutes away from blastoff. The Delta rocket will be flying in its configuration known as the 7320-10 vehicle. The two-stage launcher is fitted with three strap-on solid-propellant motors and a 10-foot diameter composite nose cone.

After quickly climbing away from its coastal pad, the rocket will soar southward over the Pacific Ocean. The solid boosters burn out and separate in 99 seconds, leaving the kerosene-powered main engine to continue pushing the rocket through four-and-a-half minutes into the flight. The spent stage then jettisons to let the hydrazine-fueled second stage ignite.

Within 11 minutes, the vehicle settles into an initial 98 x 416 mile parking orbit along a trajectory the cruises above the South Pacific before crossing Antarctica and then proceeding northbound towards Africa. The second stage reignites its engine for 12 seconds to reach a near-circular polar orbit of 408 miles above the planet.

The 3,000-pound payload is expected to be released from the rocket about 56 minutes after blastoff.

T-minus 15 minutes and holding. Clocks have entered the first of two planned hold periods during the final portion of 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.

Now moving into data link checks to verify good telemetry connections.

The first stage engine steering checks are complete.

The second stage engine slews just finished. First stage tests are starting.

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.

Sixty minutes to launch of Satelite de Aplicaciones Cientificas-D. Built by Argentina, the SAC-D spacecraft is equipped with multiple scientific instruments from several countries including NASA's Aquarius sensor package designed to make exceptionally precise global measurements of salt content at the ocean surface.

"Measuring ocean surface salinity from space is NASA's latest technology achievement and it's really going to be a great leap forward for the science of oceanography," said Eric Lindstrom, Aquarius program scientist at NASA Headquarters.

"For many of you, salinity is a rather obscure quantity, but I must tell you it's of critical importance in the ocean circulation, in the climate system and in diagnosing the flow of fresh water through our Earth system."

The second stage's fuel and oxidizer tanks, which were filled with storable propellants last Friday and Monday in a two-step fashion, have been pressurized for launch.

Checks of the rocket's safety system have been accomplished in the past few minutes of the countdown.

The spacecraft team reports that SAC-D/Aquarius is ready to fly today. The international ground communications and control network is up and running to support this morning as well.

Loading of the Delta 2 rocket's first stage liquid oxygen tank has been accomplished. The process took 26 minutes and 10 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

And now the Delta 2 rocket stands fully fueled its launch of the Satelite de Aplicaciones Cientificas-D spacecraft at 7:20 a.m. local (10:20 a.m. EDT; 1420 GMT). The vehicle's first stage was successfully loaded with RP-1 kerosene fuel earlier today. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels a few days ago. And the three strap-on booster rockets are solid-propellant.

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.

Liftoff is just 90 minutes away. Everything is looking good for today's launch of the Delta 2 rocket with SAC-D/Aquarius, a satellite born from international partnerships in the pursuit of environmental science data.

Ten minutes into the flow. LOX loading is an approximate 25-minute process to fill the first stage liquid oxygen tank.

The rocket's guidance and control system has been brought online.

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.

The launch team is performing the preparatory steps for filling the liquid oxygen tank.

The official "go" has been given to start first stage liquid oxygen loading right on time.

Now two hours from launch.

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The weather outlook continues to be acceptable for launch time, albeit not great for viewing. The forecast calls for overcast skies at 300 feet with the marine layer of stratus clouds extending to 1,600 feet, visibility of 2 to 3 miles in fog, a temperature between 47 and 51 degrees F, surface winds from the northwest at 10 to 15 knots.

Typically at this point in a Delta 2 rocket countdown, the launch team loads 10,000 gallons of highly refined kerosene fuel into the first stage. However, this operation was completed last night prior to retraction of the mobile service tower.

The early fuel loading was performed to give the rocket added weight and stability while the Delta is exposed to the weather.

The kerosene, called RP-1, will be consumed along with liquid oxygen by the first stage RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

Filling of the stage with cryogenic liquid oxygen will begin about an hour from now.

The first stage helium and nitrogen systems have been pressurized.

Hazardous operations to pressurize the first and second stage helium and nitrogen systems and the second stage fuel and oxidizer tanks are getting underway at Space Launch Complex 2.

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

Countdown begins! The three-hour Terminal Countdown sequence has been initiated for today's launch of the Delta 2 rocket from Vandenberg Air Force Base in California. The booster will carry into orbit the Satelite de Aplicaciones Cientificas-D spacecraft for Argentina and NASA.

Liftoff from the Space Launch Complex 2 pad is scheduled for 7:20:13 a.m. local (10:20:13 a.m. EDT; 1420:13 GMT). Today's available launch window is open for exactly five minutes.

Between now and the launch time, the rocket's guidance system will be activated, onboard helium and nitrogen tanks brought up to pressure, the liquid oxygen supply loaded into the first stage, checks performed on the safety system and steering tests conducted on the engines.

This is a standard countdown for the Delta 2, a typical timeline to ready the vehicle for flight. Pre-planned holds are built into the countdown at the T-minus 15 and T-minus 4 minute points. The first will last 20 minutes; the second will be 10 minutes in length. Those pauses are designed to give the launch team the opportunity to work problems or catch up on items perhaps running behind schedule.

Polls of the various launch team members and managers occur during that T-minus 4 minute 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.

"Man stations for Terminal Count." That's the call to the launch team in preparation for a readiness check to ensure all consoles are "go" for starting the countdown 15 minutes from now.

T-minus 150 minutes and holding. At this time, the countdown is entering a planned 60-minute built-in hold. The Terminal Countdown begins once the hold concludes.

Launch remains targeted for 7:20 a.m. local (10:20 a.m. EDT; 1420 GMT) from Vandenberg Air Force Base in California.

Check out this photo collection of the Delta 2 rocket taken during gantry rollback.

The Delta 2 rocket has been unveiled from the mobile servicing gantry at Vandenberg's Space Launch Complex 2. The cocoon-like tower was wheeled away to get activities underway for this launch shot.

The 177-foot tall service tower was used to stack the two-stage vehicle, the three strap-on solid rocket motors and the SAC-D/Aquarius payload atop the pad's launch mount. The tower also provided the primary weather protection and worker access to the rocket during its stay at the oceanside complex on North Vandenberg.

Ground teams will spend the next few of hours getting the pad configured and secured in advance of the Terminal Countdown. Launch remains targeted for 7:20 a.m. local (10:20 a.m. EDT; 1420 GMT).

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Rollback of the launch pad gantry has begun. The structure is being retracted to uncover the Delta 2 rocket for its mission carrying Argentina's SAC-D spacecraft with NASA's Aquarius ocean mapper.

The full flight profile has been successfully loaded aboard the Delta 2 rocket and checked out, a NASA spokesman says, clearing the earlier software concern for Friday's scheduled blastoff from California.

Engineers determined that a data formatting problem was to blame for truncating the program's initial transfer to the vehicle. But even if the problem hadn't been discovered, the spokesman says, there wouldn't have been much consequence to the ascent.

Nonetheless, the launch was postponed by 24 hours so the team could sort through the situation before pressing ahead with the satellite deployment mission.

The latest weather outlook for Friday's 7:20 a.m. local time launch still calls for a zero percent chance of conditions violating the liftoff rules. But there will be overcast skies at 400 feet with the marine layer of stratus clouds extending to 1,000 feet, visibility of 2 to 4 miles in fog, a temperature between 48 and 53 degrees F, surface winds from the northwest at 10 to 15 knots and maximum upper level winds of 50 knots from the west-southwesterly at 35,000 feet.

If the launch should slip to Saturday for some reason, the weather odds drop to 70 percent favorable due to the chance for high winds at the pad.

Officials delayed the Delta 2 rocket launch carrying Argentina's SAC-D satellite with NASA's Aquarius oceanography instrument to allow engineers more time to sort through a software issue.

A review of the flight program for steering the rocket through high-altitude winds found that the last few seconds of the profile got truncated and the team isn't sure why, a NASA spokesman explained.

The time needed to examine the situation and determine how best to reload the software data meant a launch attempt wasn't feasible early Thursday.

Friday's five-minute launch window opens at 7:20 a.m. local time (10:20 a.m. EDT; 1420 GMT).

Weather forecasters predict another 100 percent chance of acceptable conditions at liftoff time. But the marine layer is expected to remain entrenched at Vandenberg, producing very low ceilings and restricted visibility with fog.

Launch of the Delta 2 rocket originally planned for Thursday morning from Vandenberg Air Force Base in California has been postponed 24 hours. Further details to follow.

The launch team is resting at this hour before the late-night countdown operations kick off. Liftoff remains on schedule for tomorrow morning at 7:20 a.m. local time (10:20 a.m. EDT).

The latest weather outlook issued today still predicts no chance of violating any of the launch rules.

"A frontal system will push into the Central Coast today keeping an onshore flow to Vandenberg AFB and the marine layer in throughout the count," forecasters say.

The launch time conditions are expected to include stratus clouds at 200 feet, visibility of 2 to 4 miles with fog, surface winds from the north-northwest of 10 to 15 knots and maximum upper level winds from the west-southwest of 55 knots at 35,000 feet.

Watch this page for live coverage overnight, plus live streaming video!

A satellite born from international partnerships in the pursuit of environmental science data will be launched into space from California early Thursday to measure the saltiness of world's oceans.

"In just a two short days, the Aquarius/SAC-D satellite will be launched into orbit and those of us on the mission team could not be more excited," said Eric Lindstrom, Aquarius program scientist. "This important Earth science mission is NASA's first attempt to measure ocean surface salinity from space. Obtaining global measurements of salinity is the key to our better understanding of ocean circulation, climate and Earth's water cycle."

The Satelite de Aplicaciones Cientificas-D spacecraft will ride a United Launch Alliance Delta 2 rocket into a 408-mile-high sun-synchronous orbit.

A five-minute launch window opens at 7:20:13 a.m. local (10:20:13 a.m. EDT; 1420:13 GMT) for the liftoff to occur from Vandenberg Air Force Base.

Weather forecasters predict a 100 percent chance of acceptable conditions for launch. However, fog and a ground-hugging marine layer is expected to hamper viewing conditions at the base.

The outlook calls for overcast conditions from 200 to 1,200 feet, restricted visibility between 1 and 2 miles, north-northwesterly winds of 10 to 15 knots and a temperature between 46 and 51 degrees F.

Loading of storable hypergolics in the rocket's second stage began last Friday with the oxidizer and finished Monday with the fuel fill. The final launch readiness reviews held Tuesday granted approval to continue with preparations.

Technicians plan to load highly refined kerosene fuel into the first stage Wednesday night, followed by procedures to retract the mobile service gantry from around the 12-story rocket. The tower rollback is anticipated at approximately 10 p.m. local time (1 a.m. EDT Thursday).

The Terminal Countdown will start at 4:20 a.m. local time (7:20 a.m. EDT), beginning the formal three-hour process to bring the rocket to life, load the liquid oxygen for the main engine, conduct extensive final testing and then send it into orbit.

Built by Argentina, the SAC-D satellite is equipped with multiple scientific instruments from several countries including NASA's Aquarius sensor package designed to make exceptionally precise global measurements of salt content at the ocean surface.

"This mission is about measuring how salty the ocean is from space. It's one of the key missing parameters that we haven't studied about this world," said Amit Sen, Aquarius project manager from NASA's Jet Propulsion Laboratory.

Never before has the U.S. entrusted such a key instrument to fly aboard an Argentinian satellite. But the cooperation between the nations' space agencies -- NASA and CONAE -- led to the SAC-D spacecraft and its instruments being integrated together in Argentina, then shipped to Brazil for pre-flight testing before finally traveling to Vandenberg Air Force Base for launch.

"Our team has worked hard with NASA and CONAE over the last few years to get to this point and we're ready to launch this unique mission," said Vernon Thorp, United Launch Alliance program manager for NASA missions.

"We anticipate our Delta 2 vehicle will perform well and we hope to accurately place the spacecraft into its planned orbit to allow Aquarius to offer scientists the first space-based global observations of ocean surface salinity."

Watch this page for live updates during the countdown and SAC-D's trek to orbit aboard the Delta rocket.

And if you will be away from your computer but would like to receive occasional countdown updates, sign up for our Twitter feed to get text message updates on your cellphone. U.S. readers can also sign up from their phone by texting "follow spaceflightnow" to 40404. (Standard text messaging charges apply.)