WEDNESDAY, JANUARY 12, 2005

Look out Comet Tempel 1, here comes Deep Impact! A washing machine-sized projectile tucked inside its mothership spacecraft launched from Earth today on a 268-million-mile collision course that promises to create spectacular July Fourth fireworks when the 820-pound copper-tipped bullet smashes into the comet's frigid heart. Read our full story.

2301 GMT (6:01 p.m. EST)

The Deep Impact project manager says engineers believe they know what glitch triggered the spacecraft's safe-mode protection system shortly after launch today and the situation should be easy to fix.

As the probe was performing its pre-programmed series of events after being released from the Delta rocket, the temperature limit for the catalyst bed heaters in the propulsion system was violated by a few degrees. The spacecraft did what it was supposed to when such a problem is detected by configuring itself into a safe configuration so controllers can resolve the issue.

"The first thing I'd like to say is our spacecraft is healthy," Rick Grammier told reporters in an afternoon teleconference. "It's currently in safe mode. All systems and indications are nominal, i.e., everything is as expected."

The temperature limit is probably set too low and the temperatures experienced aboard the craft today didn't harm any hardware, he said.

"This is not a concern from a hardware view point, this is simply what we sometimes find is a natural part of setting the temperature limits and ranges that we expect to see once we get on orbit," Grammier said. "It is not uncommon for us to find we may have to tune some of those parameters."

Engineers want to downlink data logs stored aboard the craft to verify their current understanding of the situation. Grammier said Deep Impact should be restored to normal operating conditions within 24 hours.

"We don't see this as a long-term threat by any means."

This concludes our live play-by-play coverage of today's mission. Check back later for a wrap-up story with pictures and movie clips.

2129 GMT (4:29 p.m. EST)

Deep Impact appears to be a healthy spacecraft, a NASA spokeswoman from the agency's headquarters says. The solar arrays were deployed minutes after separation from the Delta rocket as planned and the craft oriented itself for sun-pointing.

The initial sequence of events after launch vehicle separation progressed, but then Deep Impact entered a safe-mode configuration. Controllers do not have enough data to fully understand what triggered the fault-protection system on the spacecraft to kick in.

A mission scientist told reporters it is believed to be a non-critical glitch with a temperature sensor. The low-data-rate communications in the safe-mode is somewhat hampering efforts to diagnose the problem, officials said.

Nonetheless, an engineering meeting is being held this afternoon to analyze the data and what information is known. NASA intends to issue a status report later today.

Watch this page for further updates as they become available.

2050 GMT (3:50 p.m. EST)

Solar array deployment has been confirmed! However, the spacecraft has entered a safe-mode, which is a protective configuration when a problem is detected on board. We're awaiting details from NASA on what the exact nature of the glitch.

A NASA spokesman says the data came through Goldstone, which was able to support a communications linkup afterall.

2040 GMT (3:40 p.m. EST)

This is a low-data-rate communications session, NASA says. Controllers are still working to determine Deep Impact's status.

2030 GMT (3:30 p.m. EST)

An agency spokesman says data is being received from Deep Impact via the Madrid site.

We have posted several movie clips from today's countdown for Spaceflight Now Plus subscribers. Click here to watch the launch as seen live. An extended clip following the mission through second stage ignition is available here.

2015 GMT (3:15 p.m. EST)

NASA says the Goldstone station is not configured to support Deep Impact at this time. So controllers must wait until the Madrid site can acquire the spacecraft later today.

To recap, Deep Impact was launched aboard a Boeing Delta 2 rocket at 1:47 p.m. EST (1847 GMT) today from Cape Canaveral Air Force Station, Florida. Following a 34-minute flight by the three-stage launcher, the comet probe was released to fly on its own.

Mission control acquired the craft's signal through the Deep Space Network tracking station in Canberra, Australia a few minutes later. However, confirmation that the two power-generating solar arrays had swung into position and locked could not be verified. The wait continues for data to prove Deep Impact is healthy following its launch.

1959 GMT (2:59 p.m. EST)

T+plus 72 minutes. The NASA spokesman says the inability to confirm solar array deployment could be a data flow problem through the Canberra tracking station in Australia. Controllers will await data from the next Deep Space Network tracking station in Goldstone, California.

1954 GMT (2:54 p.m. EST)

T+plus 67 minutes. "Technically, we should have it by now but we can't confirm it," NASA spokesman says of the continuing wait for solar array deploy confirmation.

1952 GMT (2:52 p.m. EST)

T+plus 65 minutes. The space agency has not yet confirmed a successful deployment of the power-generating solar arrays on Deep Impact.

1942 GMT (2:42 p.m. EST)

T+plus 55 minutes. NASA says a good signal is being received from Deep Impact. Controllers are analyzing the data to verify the craft's status.

1937 GMT (2:37 p.m. EST)

T+plus 50 minutes. We're still awaiting an initial health report on Deep Impact and confirmation of solar array deployment.

1932 GMT (2:32 p.m. EST)

T+plus 45 minutes. NASA reports that Canberra has received the first communications from Deep Impact, much earlier than expected.

1929 GMT (2:29 p.m. EST)

T+plus 42 minutes. NASA's Deep Space Network tracking station in Canberra, Australia will be the first site to acquire Deep Impact's signal following launch. That should occur in about seven minutes.

After separating from the third stage motor, Deep Impact was programmed to commence a sequence of critical events including deployment of its solar panels.

1926 GMT (2:26 p.m. EST)

"We had a perfect launch," NASA launch manager Omar Baez reports.

This marks the 116th successful Delta 2 rocket launch out of 118 flights since 1989 and extends the string of consecutive successes to 63 dating back to 1997. It was the first Delta launch in 2005 -- in fact the first space launch of the new year from any site on Earth.

The next Delta 2 flight will occur from Vandenberg Air Force Base in California on March 19 when the polar-orbiting NOAA-N civilian weather satellite is lofted. It will be May before another Delta 2 rocket is slated to fly from the Cape -- that one carrying another Global Positioning System satellite.

1921 GMT (2:21 p.m. EST)

T+plus 34 minutes, 36 seconds. SPACECRAFT SEPARATION! NASA's Deep Impact spacecraft has been released from the Boeing Delta 2 rocket's third stage to complete today's launch from Cape Canaveral. The probe has embarked on a six-month, 268-million-mile voyage to Comet Tempel 1!

Over the next few minutes, the craft's power-generating solar arrays will be deployed. Communications should be established shortly via a station in Australia.

1918 GMT (2:18 p.m. EST)

T+plus 31 minutes. Although the completion of the second stage's second burn was not called in real-time due to a telemetry drop-out, it appears that firing was normal. The third stage has since fired as planned.

1917 GMT (2:17 p.m. EST)

T+plus 30 minutes. A mobile tracking site deployed in southwest Africa is now receiving data from the rocket.

1916 GMT (2:16 p.m. EST)

T+plus 29 minutes, 30 seconds. The third stage has burned out of its solid fuel, ending the Delta 2 rocket's powered flight for the launch of Deep Impact. Separation of the payload is about five minutes away.

1915 GMT (2:15 p.m. EST)

T+plus 28 minutes, 15 seconds. An Air Force tracking and telemetry relay ship, called OTTR, is providing the data link now.

1915 GMT (2:15 p.m. EST)

T+plus 28 minutes. Third stage ignition! The Thiokol Star 48B motor is firing to propel Deep Impact out of Earth orbit.

1914 GMT (2:14 p.m. EST)

T+plus 27 minutes, 50 seconds. The solid-fueled third stage has separated from the Delta 2's second stage.

1914 GMT (2:14 p.m. EST)

T+plus 27 minutes, 15 seconds. Data has been restored. Spin up has begun.

1913 GMT (2:13 p.m. EST)

T+plus 26 minutes, 45 seconds. Once the second stage 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 third stage in preparation for jettison of the second stage.

1913 GMT (2:13 p.m. EST)

T+plus 26 minutes, 25 seconds. The engine shutdown should happened by now. However, the live data link with Ascension has been lost.

1912 GMT (2:12 p.m. EST)

T+plus 25 minutes, 20 seconds. Good chamber pressure reported on the second stage engine as it continues to fire.

1911 GMT (2:11 p.m. EST)

T+plus 24 minutes, 27 seconds. Engine ignition! The Delta 2 rocket's second stage engine has re-ignited to boost the vehicle into a higher orbit.

1910 GMT (2:10 p.m. EST)

T+plus 23 minutes, 51 seconds. Propellant tank settling thrusters are firing as planned.

1910 GMT (2:10 p.m. EST)

T+plus 23 minutes, 30 seconds. Second stage engine restart is about one minute away.

1908 GMT (2:08 p.m. EST)

T+plus 21 minutes, 10 seconds. Ascension has picked up the rocket's signal.

1906 GMT (2:06 p.m. EST)

T+plus 19 minutes, 30 seconds. About five minutes remaining in this coast. The 1-minute 40-second engine firing by the second stage will raise the orbit's apogee. Once that burn is completed, the third stage and attached Deep Impact payload will be released to continue the launch sequence.

1902 GMT (2:02 p.m. EST)

T+plus 15 minutes, 30 seconds. The Ascension Island tracking site will be next to acquire the rocket's telemetry stream. That is expected in about five minutes. Re-start of the second stage for a planned one-minute, 40-second firing is about nine minutes away.

1859 GMT (1:59 p.m. EST)

T+plus 12 minutes, 25 seconds. The rocket has passed out of range from the Antigua tracking site. This begins an expected telemetry blackout while the vehicle coasts in the parking orbit.

1859 GMT (1:59 p.m. EST)

T+plus 12 minutes. The rocket has successfully achieved a parking orbit with an apogee of 90.28 nautical miles, perigee of 89.95 miles and inclination of 29.735 degrees.

1858 GMT (1:58 p.m. EST)

T+plus 11 minutes. The vehicle is coasting for the next 15 minutes or so before the second stage is re-ignited.

1857 GMT (1:57 p.m. EST)

T+plus 10 minutes, 35 seconds. The second stage fired a few seconds longer than planned to compensate for a very slight underperformance from the first stage.

1856 GMT (1:56 p.m. EST)

T+plus 9 minutes, 46 seconds. SECO 1. The second stage engine cutoff has occurred, completing the motor's first firing of the day. The Delta 2 rocket with Deep Impact has arrived in a preliminary orbit around Earth following launch today from Cape Canaveral.

1856 GMT (1:56 p.m. EST)

T+plus 9 minutes, 10 seconds. The Delta 2 rocket is 93 miles in altitude, 1,267 miles downrange and traveling at 16,300 mph.

1855 GMT (1:55 p.m. EST)

T+plus 8 minutes, 30 seconds. The second stage systems reported normal. Just over a minute remaining in this burn.

1854 GMT (1:54 p.m. EST)

T+plus 7 minutes, 45 seconds. The Delta 2 rocket is 90 miles in altitude, 930 miles downrange and speeding along at nearly 15,000 mph.

1854 GMT (1:54 p.m. EST)

T+plus 7 minutes, 20 seconds. Antigua ground tracking station is acquiring the rocket's signal as the vehicle flies downrange. The second stage engine continues to fire.

1853 GMT (1:53 p.m. EST)

T+plus 6 minutes, 30 seconds. Second stage engine continues to burning well, consuming a hydrazine propellant mixture and nitrogen tetroxide oxidizer.

1852 GMT (1:52 p.m. EST)

T+plus 5 minutes, 30 seconds. The Delta 2 rocket is 75 miles in altitude, 520 miles east of the launch pad, traveling at 13,000 mph.

1852 GMT (1:52 p.m. EST)

T+plus 5 minutes. The 9.5-foot diameter protective payload fairing enclosing Deep Impact atop the rocket has jettisoned in two halves.

1851 GMT (1:51 p.m. EST)

T+plus 4 minutes, 43 seconds. The Aerojet AJ10-118K engine of the Delta 2 rocket's second stage engine has ignited! This is the first of two critical firings that the second stage must perform to loft Deep Impact into the proper orbit.

1851 GMT (1:51 p.m. EST)

T+plus 4 minutes, 34 seconds. MECO! Main engine cutoff. The Rocketdyne RS-27A first stage main engine has shut down to complete its firing during today's launch. The twin vernier steering thrusters fired a few additional seconds before they cut off. Then the spent stage was jettisoned to fall into the Atlantic.

1850 GMT (1:50 p.m. EST)

T+plus 3 minutes, 30 seconds. A smooth flight is being reported for the Delta 2 rocket as it heads to space with Deep Impact.

1849 GMT (1:49 p.m. EST)

T+plus 2 minutes, 50 seconds. The Delta 2 rocket is 35 miles in altitude, 110 miles east of the launch pad, traveling at 6,300 mph.

1849 GMT (1:49 p.m. EST)

T+plus 2 minutes, 20 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.

1849 GMT (1:49 p.m. EST)

T+plus 2 minute, 5 seconds. Chamber pressures tailing off on the air-lit solids.

1848 GMT (1:48 p.m. EST)

T+plus 1 minute, 50 seconds. The Delta 2 rocket is 19 miles in altitude, 45 miles east of the launch pad, traveling at 4,000 mph.

1848 GMT (1:48 p.m. EST)

T+plus 1 minute, 20 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.

1848 GMT (1:48 p.m. EST)

T+plus 60 seconds. The Delta 2 rocket has passed through the region of maximum aerodynamic pressure during its atmospheric ascent. The vehicle is already three miles up and 13 miles downrange.

1847 GMT (1:47 p.m. EST)

T+plus 40 seconds. The vehicle has broken the sound barrier as it accelerates rapidly on the combined power from the kerosene- and liquid oxygen-fed main engine and six solid-propellant motors.

1847 GMT (1:47 p.m. EST)

T+plus 30 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.

1847 GMT (1:47 p.m. EST)

T+plus 20 seconds. The Boeing Delta 2 rocket is maneuvering to the eastward heading for the flight over the open waters of the Atlantic Ocean.

1847 GMT (1:47 p.m. EST)

T-minus 11 seconds, the solid rocket booster ignitors are armed, T-8, 7, 6, 5, 4, 3, 2, main engine ignition, T-0 and LIFTOFF! Liftoff of the Boeing Delta 2 rocket launching NASA's Deep Impact space probe to give humanity its first glimpse into the frozen heart of a comet!

1846 GMT (1:46 p.m. EST)

T-minus 30 seconds. Hydraulics and electronics are "go."

1846 GMT (1:46 p.m. EST)

T-minus 45 seconds. The launch ignition sequence will begin at T-minus 2 seconds when a Boeing engineer triggers 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.

1846 GMT (1:46 p.m. EST)

T-minus 1 minute. The Delta 2 rocket's second stage hydraulic pump has gone to internal power after its pressures were verified acceptable.

1845 GMT (1:45 p.m. EST)

T-minus 75 seconds. The Air Force-controlled Eastern Range, which provides the tracking, communications and safety services for all launches from Cape Canaveral, has just given its final approval to proceed with liftoff.

1845 GMT (1:45 p.m. EST)

T-minus 1 minute, 45 seconds. The liquid oxygen tank topping off at 100 percent.

1845 GMT (1:45 p.m. EST)

T-minus 2 minutes. The first stage liquid oxygen vents are 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.

1844 GMT (1:44 p.m. EST)

T-minus 2 minutes, 30 seconds. The Deep Impact spacecraft manager just announced the final "go" for launch. This confirms the probe is functioning normally on its internal power system.

1844 GMT (1:44 p.m. EST)

T-minus 3 minutes and counting. The rocket's third stage safe and arm devices are being armed. This solid-propellant kick motor will propel Deep Impact out of Earth orbit for its six-month trek to Comet Tempel 1.

1843 GMT (1:43 p.m. EST)

T-minus 3 minutes, 45 seconds. The Boeing launch team is transferring the Delta 2 rocket's systems to internal battery power for flight.

1843:08 GMT (1:43:08 p.m. EST)

T-minus 4 minutes and counting! Countdown clocks are ticking toward a liftoff at 47 minutes and 8 seconds past the hour. The Delta rocket and Deep Impact remain in readiness for launch from pad 17B at Cape Canaveral Air Force Station along Florida's east-central coast.

1842 GMT (1:42 p.m. EST)

Standing by to resume the countdown in one minute.

1842 GMT (1:42 p.m. EST)

The one remaining issue involved the red-line limits. It has been cleared. All is "go" for liftoff.

1841 GMT (1:41 p.m. EST)

Now six minutes from launch. The Deep Impact spacecraft atop the Delta 2 rocket is switching to internal power for launch.

1839 GMT (1:39 p.m. EST)

The launch team has been polled by the Boeing launch conductor for a "go" to proceed with the countdown. The team is now receiving final instructions on countdown procedures. There has been no further indication from NASA on the problem being worked.

1837 GMT (1:37 p.m. EST)

NASA launch manager Omar Baez just performed a final readiness poll of the space agency team. There was one problem reported. We're awaiting word on the nature of that issue.

1833 GMT (1:33 p.m. EST)

T-minus 4 minutes and holding. The countdown has entered the final planned hold point for today's launch attempt. During this planned 10-minute hold, officials will poll the various team members in the soft blockhouse, Range Operations Control Center and Mission Directors Center. If all systems are "go," the countdown will resume for liftoff at 1:47:08 p.m. EST (1847:08 GMT).

1829 GMT (1:29 p.m. EST)

Vents on the first stage propellant tank are being closed to permit pressurization for launch. The tank is loaded with 10,000 gallons of a highly refined kerosene fuel called RP-1. The stage's Rocketdyne RS-27A main engine will consume the propellant during the first four-and-a-half minutes of launch. The first stage's liquid oxygen tank will be pressurized at the T-minus 2 minute mark.

1827 GMT (1:27 p.m. EST)

T-minus 10 minutes and counting. Clocks are heading to T-minus 4 minutes where a 10-minute hold is planned. Launch is still targeted for 1:47 p.m. EST. The high-altitude winds are "go", ground weather is fine and no technical glitches are being reported by the launch team.

1824 GMT (1:24 p.m. EST)

The Range radar that had been sidelined by a problem is back in operation. The radar is a required asset needed to support the launch. So at this point there are problems being worked.

1823 GMT (1:23 p.m. EST)

NASA launch manager Omar Baez reports that upper level winds are improving. Officials have optimism that the winds will be acceptable for launch today.

1817 GMT (1:17 p.m. EST)

T-minus 20 minutes and counting. The planned hold in the countdown has been released. Clocks will now tick down to T-minus 4 minutes where the final hold is scheduled.

1813 GMT (1:13 p.m. EST)

The launch team has been polled for "ready" status to resume the countdown. The clocks will resume counting at the end of the hold as scheduled.

1810 GMT (1:10 p.m. EST)

NASA launch manager Omar Baez has just polled his management team to verify there are no constraints to continuing the countdown. Upper level wind conditions are "no go" for launch at this time. But the countdown will continue in hopes the winds become more favorable before the 1:47 p.m. EST launch time.

No technical issues are being tracked on the Delta 2 rocket or Deep Impact spacecraft. There is a Range radar problem but that should be fixed shortly.

1804 GMT (1:04 p.m. EST)

RF link checks have been completed successfully.

Now inhibited checks are beginning for the Range Safety command destruct receivers that would be used in destroying the Delta rocket should the vehicle veer off course and malfunction during the launch.

1757 GMT (12:57 p.m. EST)

T-minus 20 minutes and holding. The countdown has entered the 20-minute built-in hold. This 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.

1754 GMT (12:54 p.m. EST)

The first stage steering checks are finished. Coming up on the T-minus 20 minute hold point in the countdown.

1751 GMT (12:51 p.m. EST)

The second stage engine slews have been completed.

1748 GMT (12:48 p.m. EST)

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.

1747 GMT (12:47 p.m. EST)

The countdown is entering the final 60 minutes to launch. Everything remains on schedule for blastoff of Deep Impact aboard the Delta 2 rocket from pad 17B at Cape Canaveral Air Force Station, Florida. While there are no technical glitches being addressed in the countdown, high-altitude winds are a major worry right now.

If liftoff does not occur at exactly 1:47:08 p.m. EST (1847:08 GMT) today, the Deep Impact must wait 24 hours before the next opportunity to launch on the trajectory to Comet Tempel 1.

Coming up next in the countdown will be steering tests for the Delta 2 launch vehicle.

1743 GMT (12:43 p.m. EST)

The latest weather balloon dispatched to gather data on the speed and direction of high-altitude winds has revealed continued concerns that conditions are unfavorable for liftoff today. Further balloons will be reporting data through the remainder of the countdown, providing at least the chance that the winds could ease.

1738 GMT (12:38 p.m. EST)

Work to turn on and configure the Delta's onboard guidance computer -- called the Redundant Inertial Flight Control Assembly, or RIFCA -- just finished. Also, pressurization of the second stage propellant tanks has been accomplished.

1730 GMT (12:30 p.m. EST)

The launch team reports the loading of the Delta 2 rocket's first stage liquid oxygen tank has been completed successfully. The operation took nearly 27 minutes. 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 along with the liquid oxygen over the past hour. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels on Monday. The nine strap-on boosters and third stage are solid-propellant.

1723 GMT (12:23 p.m. EST)

Cryogenic tanking of the Delta rocket's first stage has reached the 20-minute mark of this approximate 25-minute process. Once the liquid oxygen tank reaches the 95 percent full level, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the tank.

1714 GMT (12:14 p.m. EST)

The bottom of the Boeing Delta 2 rocket is icing over as the super-cold liquid oxygen continues to flow into the first stage.

1708 GMT (12:08 p.m. EST)

The normal plume of bright white vapor is streaming from a vent on the rocket's side as liquid oxygen loading progresses.

1703 GMT (12:03 p.m. EST)

Super-cold liquid oxygen is beginning to flow into the first stage of the Boeing Delta 2 rocket as the countdown continues.

The liquid oxygen, chilled to Minus-298 degrees F, is being pumped from a storage tank at pad 17B, through plumbing and into the bottom of the rocket. The LOX and the RP-1 kerosene fuel -- loaded aboard the vehicle in the past hour -- will be consumed by the first stage main engine.

1657 GMT (11:57 a.m. EST)

The launch team has been given approval to begin preps for loading the liquid oxygen tank.

1647 GMT (11:47 a.m. EST)

The countdown is entering the final two hours to launch. Liftoff remains set for 1:47 p.m. EST today.

Launch weather officer Johnny Weems has just given a briefing to management. There are no worries about clouds, surface winds or rain around Cape Canaveral today.

However, weather balloons being sent up to measure high-altitude winds are revealing stiff conditions. The winds aloft are monitored to ensure the rocket can safely ascend.

1632 GMT (11:32 a.m. EST)

The first stage fuel tank of the Boeing Delta 2 rocket has been fully loaded for today's launch.

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

There are no significant technical issues being worked by the launch team and the ground weather is favorable. Upper level winds are being watched closely, however.

1630 GMT (11:30 a.m. EST)

Rapid-loading of the RP-1 tank has concluded. Fine load is continuing.

1627 GMT (11:27 a.m. EST)

The launch team has computed that today's full load for the first stage fuel tank is 10,026 gallons.

Once the tank is filled to 98 percent or 9,840 gallons, the "rapid load" valve will be closed and the slower "fine load" phase will continue to top off the tank.

1622 GMT (11:22 a.m. EST)

Now 10 minutes, or half-way, through this 20-minute process to load the rocket's first stage with kerosene fuel.

The propellant will be used along with liquid oxygen -- to be pumped into the rocket a little later -- by the first stage Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.

1619 GMT (11:19 a.m. EST)

About 4,000 gallons of fuel have been loaded into the rocket so far.

1612 GMT (11:12 a.m. EST)

Fueling of the Delta 2 rocket's first stage has begun. About 10,000 gallons of a highly refined kerosene propellant, called RP-1, are being pumped into the base of the rocket from a storage tank at pad 17B.

1607 GMT (11:07 a.m. EST)

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

1557 GMT (10:57 a.m. EST)

The pressurization work has started. Fueling of the rocket's first stage is coming up in about 10 minutes.

1547 GMT (10:47 a.m. EST)

T-minus 150 minutes and counting. The Terminal Countdown is now underway for today's launch of the Boeing Delta 2 rocket carrying NASA's Deep Impact spacecraft for a six-month voyage to Comet Tempel 1. The next three hours will be spent fueling the rocket, activating systems and performing final testing before liftoff at 1:47:08 p.m. EST (1847:08 GMT) from pad 17B at Cape Canaveral Air Force Station in Florida.

The Complex 17B area has been cleared of workers. A warning horn will be 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 clearing will allow the start of hazardous operations such as the pressurization of helium and nitrogen storage tanks inside the rocket's first and second stages, along with the second stage fuel and oxidizer tanks.

The countdown currently stands at T-minus 150 minutes. However, there will be two holds accounting for 30 minutes built into the count at T-minus 20 and T-minus 4 minutes.

1538 GMT (10:38 a.m. EST)

The launch team members have been polled for a "ready" status to resume the countdown as planned at the end of this hold. No problems were reported. Clocks will start ticking at 10:47 a.m. EST as the Terminal Countdown begins.

1517 GMT (10:17 a.m. EST)

Terminal Count begins a half-hour from now. Coming up in about 20 minutes, the launch team will be polled to ensure all the consoles are staffed and everyone is ready to press ahead with today's countdown. A NASA spokesman says all is looking good for liftoff at 1:47 p.m. EST (1847 GMT).

1440 GMT (9:40 a.m. EST)

A second batch of photos from this morning show the Delta 2 rocket atop 17B at daybreak. You can see the pictures here.

1425 GMT (9:25 a.m. EST)

The mobile service tower was rolled away from the Delta rocket and into its launch position before dawn this morning. You can see some pictures of the event here.

1405 GMT (9:05 a.m. EST)

Engineers are not working any significant technical glitches today as countdown activities progress to the planned 1:47 p.m. EST (1847 GMT) liftoff of the Boeing Delta 2 rocket with NASA's Deep Impact. The mission management team will arrive at their stations in the coming hour.

1310 GMT (8:10 a.m. EST)

Air Force meteorologists continue to predict near-perfect weather conditions for today's launch. There is less than a 10 percent chance that weather will prohibit liftoff. But the outlook for tomorrow -- if liftoff is postponed for any reason -- has worsened to a 30 percent chance of weather problems. Read the latest forecast here.

1141 GMT (6:41 a.m. EST)

Rollback of the mobile service tower is nearing completion as dawn begins to break. The Boeing Delta 2 rocket is now exposed atop Cape Canaveral's pad 17B and stands bathed in floodlights. The tower was used to assemble the rocket on the pad and provided access for workers during the booster's stay on the seaside complex. Its retraction is a key milestone in today's countdown for the Deep Impact launch attempt.

Workers will get the tower locked in its launch position, move portable pieces of the exhaust ducting into place and put the final touches on rocket and ground equipment before evacuating the pad by about 10 a.m. EST (1500 GMT).

The Terminal Countdown commences at 10:47 a.m. EST (1547 GMT) for the final three hours to launch. The count will feature two built-in holds at T-minus 20 minutes and T-minus 4 minutes. The planned pauses will last a total duration of 30 minutes.

The launch team will start loading a highly refined kerosene propellant into the rocket's first stage just after 11 a.m. EST (1600 GMT). Filling of the first stage liquid oxygen tank will follow an hour later. The upper two stages are already fueled and ready.

The last hour of the countdown will be spent conducting engine steering tests, Range safety system checks and final arming. Deep Impact and the Delta rocket's systems transition from ground-fed power to internal batteries in the closing minutes.

Launch is possible today at exactly 1:47:08 p.m. EST (1847:08 GMT). If the rocket misses that precise launch opportunity, the mission will be delayed 24 hours until the next shot at sending Deep Impact on its proper trajectory to Comet Tempel 1.

Watch this page for live play-by-play reports once Terminal Count begins.

1115 GMT (6:15 a.m. EST)

The mobile service tower is in motion, slowly being wheeled away from the Delta 2 rocket.