BY JUSTIN RAY

Follow the countdown and launch of the Orbital Sciences Pegasus rocket with NASA's AIM spacecraft. Reload this page for updates.

WEDNESDAY, APRIL 25, 2007

NASA has launched a clue-seeking satellite to track eerily mysterious clouds at the threshold of space that some scientists believe are the harbingers of global climate change. Read our launch story.

VIDEO: AIM LAUNCHED ABOARD PEGASUS ROCKET PLAY
VIDEO: LONGER LENGTH MOVIE OF ENTIRE FLIGHT TO ORBIT PLAY
VIDEO: POST-FLIGHT INTERVIEW WITH NASA LAUNCH MANAGER PLAY

VIDEO: NARRATED MOVIE OF AIM'S PRE-FLIGHT PREPARATIONS PLAY
VIDEO: NARRATED MOVIE OF PEGASUS' LAUNCH CAMPAIGN PLAY
VIDEO: PRE-LAUNCH NEWS CONFERENCE PLAY
VIDEO: AIM MISSION SCIENCE PREVIEW PLAY
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2245 GMT (6:45 p.m. EDT; 3:45 p.m. local)

"The count went well. We had a small intrusion into the drop box by a freighter, and that was early on before (the L-1011) took off," NASA launch manager Omar Baez says. "That was cleared in time. We worked virtually no technical issues both on the spacecraft side or on the launch vehicle during the countdown."

The Pegasus rocket was dropped from the L-1011 over the Pacific Ocean at 2026:03 GMT (4:26:03 p.m. EDT; 1:26:03 p.m. local), NASA reports. Ignition of the first stage occurred five seconds later.

The AIM spacecraft separated from the Pegasus third stage at 2036:23 GMT (4:36:23 p.m. EDT; 1:36:23 p.m. local).

2205 GMT (6:05 p.m. EDT; 3:05 p.m. local)

The AIM spacecraft is in good health following today's ascent into orbit, flight controllers report. Contact with the satellite via a ground station in Norway at 2144 GMT verified that AIM was working normally.

"Everything was exactly as it should be," NASA spokesman George Diller says.

"This has been a very happy launch without a doubt. Everyone is walking around with grins."

2051 GMT (4:51 p.m. EDT; 1:51 p.m. local)

"The flight appears good. We are hitting all of the parameters we needed to hit as far as our orbital requirements," NASA launch manager Omar Baez says. "The spacecraft is power positive, the solar arrays have started deploying and (the satellite is) in the right place. So you can't call it any better than that."

2042 GMT (4:42 p.m. EDT; 1:42 p.m. local)

Communications from the AIM spacecraft are being received through NASA's Tracking and Data Relay Satellite System. The satellite has begun its post-launch sequence, which includes deployment of the power-generating solar array. Ground station passes over Norway and Alaska occur during the first orbit of the Earth, and officials plan to give an initial state of health report on the craft about 90 minutes into the flight.

2037 GMT (4:37 p.m. EDT; 1:37 p.m. local)

T+plus 11 minutes. The preliminary data indicates the Pegasus has placed the satellite into a good orbit.

2036 GMT (4:36 p.m. EDT; 1:36 p.m. local)

T+plus 10 minutes, 20 seconds. SPACECRAFT SEPARATION! The AIM spacecraft has been deployed from the Orbital Sciences Pegasus XL rocket, completing today's launch!

2035 GMT (4:35 p.m. EDT; 1:35 p.m. local)

T+plus 9 minutes. The rocket is 373 miles in altitude and traveling at 17,000 mph. Standing by for release of the satellite a little more than a minute from now.

2034 GMT (4:34 p.m. EDT; 1:34 p.m. local)

T+plus 8 minutes, 30 seconds. Burnout of the third stage motor has been confirmed. AIM is in orbit.

2033 GMT (4:33 p.m. EDT; 1:33 p.m. local)

T+plus 7 minutes, 40 seconds. Pegasus altitude is 368 miles and velocity is 13,000 mph.

2033 GMT (4:33 p.m. EDT; 1:33 p.m. local)

T+plus 7 minutes, 15 seconds. The spent second stage has separated. And the solid-fueled third stage motor has ignited, accelerating the AIM spacecraft to orbit.

2032 GMT (4:32 p.m. EDT; 1:32 p.m. local)

T+plus 6 minutes, 20 seconds. The vehicle is now reorienting in preparation for stage separation and third stage burn.

2031 GMT (4:31 p.m. EDT; 1:31 p.m. local)

T+plus 5 minutes, 40 seconds. Pegasus is now 300 miles up and traveling at 11,100 mph.

2031 GMT (4:31 p.m. EDT; 1:31 p.m. local)

T+plus 5 minutes. The rocket remains in a good orientation and the power system is strong.

2030 GMT (4:30 p.m. EDT; 1:30 p.m. local)

T+plus 4 minutes. The rocket has passed 200 miles in altitude as it continues in the ballistic climb.

2029 GMT (4:29 p.m. EDT; 1:29 p.m. local)

T+plus 3 minutes. No problems have been reported in today's flight thus far. Altitude is currently 133 miles, traveling at 12,000 miles per hour.

2028 GMT (4:28 p.m. EDT; 1:28 p.m. local)

T+plus 2 minutes, 50 seconds. The solid-fueled second stage has burned out. The Pegasus rocket is now in a coast period for the next couple of minutes. During this time the rocket will compute the performance of the flight thus far and adjust the third stage ignition time if necessary.

2028 GMT (4:28 p.m. EDT; 1:28 p.m. local)

T+plus 2 minute, 10 seconds. The two halves of the payload fairing enclosing the AIM spacecraft on the end of the Pegasus rocket has been jettisoned. Second stage continues to burn.

2027 GMT (4:27 p.m. EDT; 1:27 p.m. local)

T+plus 1 minute, 50 seconds. The vehicle is over 55 miles in altitude.

2027 GMT (4:27 p.m. EDT; 1:27 p.m. local)

T+plus 1 minute, 35 seconds. The first stage is jettisoned. The Pegasus' second stage has ignited.

2027 GMT (4:27 p.m. EDT; 1:27 p.m. local)

T+plus 1 minute, 20 seconds. The solid-propellant first stage has burned out. The vehicle is now in a ballistic coast for a few seconds before the spent stage is jettisoned and the second stage ignites.

2026 GMT (4:26 p.m. EDT; 1:26 p.m. local)

T+plus 45 seconds. Passing through the region of maximum aerodynamic pressure.

2026 GMT (4:26 p.m. EDT; 1:26 p.m. local)

T+plus 30 seconds. The Pegasus rocket is pitched up 35 degrees as it climbs into the sky on the power of its solid-fuel first stage motor at over 1,500 mph.

2026 GMT (4:26 p.m. EDT; 1:26 p.m. local)

IGNITION of the Pegasus rocket launching NASA's AIM satellite to observe clouds at the edge of space.

2026 GMT (4:26 p.m. EDT; 1:26 p.m. local)

DROP. The Orbital Sciences Pegasus XL rocket has been released from the L-1011 aircraft off the California coastline.

2025 GMT (4:25 p.m. EDT; 1:25 p.m. local)

T-minus 45 seconds. The batteries for the first stage flight control fins are being activated, allowing the fins to undergo a sweep test prior to launch. The fins are used to steer the rocket during its initial climb to space.

With the batteries activated there is just 90 seconds to launch today or else an abort will be called. That is due to the limited life of the batteries.

In the final moments prior to release of Pegasus, the L-1011 carrier aircraft crew will oversee the last seconds of the countdown and flip the switch that will drop the vehicle, with the AIM spacecraft aboard, from the belly of the jet.

2024 GMT (4:24 p.m. EDT; 1:24 p.m. local)

T-minus 1 minute, 45 seconds. The L-1011 is adjusting its course to acquire the proper heading. Pegasus will be launching along a 192-deg flight azimuth.

2023 GMT (4:23 p.m. EDT; 1:23 p.m. local)

T-minus 3 minutes. The rocket's SIGI guidance computer is being configured for flight.

2022 GMT (4:22 p.m. EDT; 1:22 p.m. local)

T-minus 3 minutes, 30 seconds. The L-1011 has entered the drop zone. The box is 40 miles long and 10 miles wide.

2022 GMT (4:22 p.m. EDT; 1:22 p.m. local)

T-minus 4 minutes. The launch team is going through its final checklist now.

2021 GMT (4:21 p.m. EDT; 1:21 p.m. local)

T-minus 4 minutes, 20 seconds. The launch team has been given a "go" to enter the final phase of today's countdown.

2021 GMT (4:21 p.m. EDT; 1:21 p.m. local)

T-minus 5 minutes.

2020 GMT (4:20 p.m. EDT; 1:20 p.m. local)

T-minus 6 minutes. The Air Force-controlled Western Range is confirmed clear for launch.

2018 GMT (4:18 p.m. EDT; 1:18 p.m. local)

T-minus 7 minutes, 30 seconds. NASA Launch Manager Omar Baez has polled his team for entering terminal count. All elements remain "go."

2018 GMT (4:18 p.m. EDT; 1:18 p.m. local)

T-minus 8 minutes. The Pegasus rocket's avionics have switched from power provided by the L-1011 to internal battery power.

2017 GMT (4:17 p.m. EDT; 1:17 p.m. local)

T-minus 8 minutes, 30 seconds. The weather officer confirms conditions are "go" for launch.

2015 GMT (4:15 p.m. EDT; 1:15 p.m. local)

T-minus 11 minutes. Checks of the flight termination system have been completed without any problems reported.

2013 GMT (4:13 p.m. EDT; 1:13 p.m. local)

T-minus 13 minutes. The launch team members report they are ready to switch the rocket's flight termination system to internal power. The safety system would be used to destroy the Pegasus rocket in the event a problem during launch.

2012 GMT (4:12 p.m. EDT; 1:12 p.m. local)

T-minus 14 minutes. The AIM spacecraft has switched to internal power for launch.

2011 GMT (4:11 p.m. EDT; 1:11 p.m. local)

T-minus 15 minutes and counting. The release mechanism that will drop the Pegasus rocket from the L-1011 carrier jet is now being armed. This hydraulic system involves four main hooks holding the Pegasus to the aircraft as well as a nose hook.

2008 GMT (4:08 p.m. EDT; 1:08 p.m. local)

T-minus 18 minutes and counting. Stargazer is flying at an altitude just shy of 40,000 feet.

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

T-minus 20 minutes and counting. Soon the pace of countdown activities will quicken as final configuring of the Pegasus rocket is performed.

2001 GMT (4:01 p.m. EDT; 1:01 p.m. local)

T-minus 30 minutes and counting. The carrier jet is passing through the launch box west of Monterey. The aircraft is heading northward right now but will soon make a wide, sweeping U-turn for return to the rocket drop zone on a southerly heading.

1956 GMT (3:56 p.m. EDT; 12:56 p.m. local)

T-minus 30 minutes and counting. To honor the victims of last week's Virginia Tech tragedy, memorial decals have been placed on the Pegasus rocket. The AIM mission has a direct link to the school. The deputy principal investigator on the science team, Scott Bailey, is a professor at Virginia Tech.

"We will be flying the Virginia Tech logo on the side of the AIM rocket in honor and in memory of those who lost their lives," said Jim Russell, the AIM principal investigator.

1951 GMT (3:51 p.m. EDT; 12:51 p.m. local)

Now 35 minutes from the planned launch time. Today marks the 38th flight of the air-launched Pegasus rocket and the 28th using the XL version.

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

T-minus 40 minutes and counting. The chase plane is performing the standard visual inspection of the Pegasus rocket. The carrier aircraft continues to climb to launch altitude, passing the waypoints along the route as planned.

1941 GMT (3:41 p.m. EDT; 12:41 p.m. local)

T-minus 45 minutes and counting. The man flying the L-1011 aircraft today is Capt. Bill Weaver. Although the countdown is managed by the ground-based team, the aircraft crew actually pushes the button to launch Pegasus on its journey into space.

The circuitry for the release system is armed approximately 15 minutes before the drop by the launch panel operator aboard the aircraft. Later a switch will be flipped in the cockpit by the co-pilot. This switch, located on the right-hand portion of the center console between the captain and pilot, "enables" the release to be become active.

In the final seconds of the countdown the Orbital Sciences launch conductor on the ground will call out "drop on my mark...3, 2, 1, drop." At that point, co-pilot Don Moor will push a button next to the enable switch, releasing the Pegasus rocket and AIM to fall away from the L-1011 aircraft. See a photo of the drop button taken during a tour of the L-1011.

"It takes a couple seconds and then it releases," Weaver explained during a previous interview. "There is no doubt about it that the rocket has released. There is a tremendous reaction throughout the airplane. It weighs 52,000 pounds, so we experience an instantaneous weight loss of 52,000 pounds and the center of gravity shifts aft 10 percent, so the nose comes up in a pretty pronounced fashion, which is good because we like that for separation.

"We drop it at 39,000 feet and after the drop we end up eventually around 41,000, we gain a couple thousand feet altitude or separation and also we do about a 10 degree heading change to get out of the rocket exhaust.

"Five seconds after we drop it, (Pegasus) is about 500 feet below drop altitude and the first stage lights off and it pulls up. In the meantime, we have turned 10 degrees off the heading. By the time we roll out we can see it. We can hear it. When that rocket motor lights off it sounds like a freight train roaring underneath the plane. It is a pretty impressive event.

"We don't really see till we get out of the bank, then we have a really good view. We can see it all the way through first stage burn out, second stage ignition. We can't normally see the stage 3. One time we did at Vandenberg. Conditions were just right -- perfect sun, perfect atmosphere."

1936 GMT (3:36 p.m. EDT; 12:36 p.m. local)

T-minus 50 minutes and counting. Stargazer is following a predetermined course commonly called "the racetrack pattern" to reach the precise point where the Pegasus can be released for launch. This ferry flight lasts 58 minutes.

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

The chase plane is now airborne. The F-18 will fly alongside the carrier jet and provide live video of the launch.

1928 GMT (3:28 p.m. EDT; 12:28 p.m. local)

WHEELS UP. The "Stargazer" carrier aircraft with the Orbital Sciences Pegasus XL rocket has departed Vandenberg Air Force Base in California for today's launch for NASA's AIM spacecraft. The booster will be released from the jet over the Pacific Ocean at 2026 GMT to propel the cloud-observing satellite into polar orbit.

1927 GMT (3:27 p.m. EDT; 12:27 p.m. local)

Stargazer has begun its takeoff roll down Vandenberg's concrete runway.

1925 GMT (3:25 p.m. EDT; 12:25 p.m. local)

The Orbital Sciences launch conductor Adam Lewis just completed a poll of the ground launch team. All systems are poised for takeoff.

1920 GMT (3:20 p.m. EDT; 12:20 p.m. local)

NASA Launch Manager Omar Baez has polled the space agency team to verify all is in readiness for takeoff of the L-1011 aircraft. There are no issues with the Pegasus rocket, AIM spacecraft, weather or downrange tracking assets. "The team is ready for takeoff," Baez said.

1918 GMT (3:18 p.m. EDT; 12:18 p.m. local)

Coming up in about five minutes, the launch team will begin the pre-takeoff checklist. Takeoff is now 10 minutes away.

1910 GMT (3:10 p.m. EDT; 12:10 p.m. local)

No technical problems are being worked. Plans call for the L-1011 to depart Vandenberg at 1928 GMT for launch of the Pegasus rocket at 2026 GMT.

1903 GMT (3:03 p.m. EDT; 12:03 p.m. local)

The aircraft with its six-man crew has completed the taxi to the end of the runway for takeoff 25 minutes from now.

1901 GMT (3:01 p.m. EDT; 12:01 p.m. local)

NASA says the countdown remains on schedule for launch of the AIM spacecraft aboard the Orbital Sciences Pegasus XL rocket. The Stargazer carrier jet continues to taxi out to the 10,000-foot long runway at Vandenberg Air Force Base for takeoff at 1928 GMT.

1857 GMT (2:57 p.m. EDT; 11:57 a.m. local)

The L-1011 Stargazer carrier aircraft is taxiing from the staging area at Vandenberg Air Force Base to the runway for today's takeoff.

1827 GMT (2:27 p.m. EDT; 11:27 a.m. local)

The purge hose running to the rocket's nose cone from ground support equipment has been removed in advance of the aircraft's eventual move to the runway and takeoff for the launch location 39,000 feet above the Pacific Ocean.

1810 GMT (2:10 p.m. EDT; 11:10 a.m. local)

The six-man crew is aboard the L-1011 carrier jet. The doors on the L-1011 carrier jet have been closed and the mobile stairs pulled back.

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

NASA says all continues to go well in the countdown. The aircraft's engines will be started shortly.

1720 GMT (1:20 p.m. EDT; 10:20 a.m. local)

The launch team is proceeding through testing of the Pegasus rocket systems and monitoring the health of the AIM spacecraft.

1700 GMT (1:00 p.m. EDT; 10:00 a.m. local)

The AIM satellite should be en route to space less than three-and-a-half hours from now.

1640 GMT (12:40 p.m. EDT; 9:40 a.m. local)

The current and forecast weather conditions for today's launch of the Pegasus rocket remain acceptable, NASA says. The Air Force weather team at Vandenberg predicts a zero percent chance of violating the launch rules.

1615 GMT (12:15 p.m. EDT; 9:15 a.m. local)

The launch team and mission managers are on duty at their consoles in the control facilities. The official countdown checklist was opened a little while ago to guide the day's launch preparations.

1540 GMT (11:40 a.m. EDT; 8:40 a.m. local)

Launch morning activities are getting underway at Vandenberg Air Force Base for today's flight of the Pegasus XL rocket carrying NASA's AIM cloud-watching spacecraft.

There are no technical problems being worked, a NASA spokesman says, and takeoff of the L-1011 carrier aircraft headed for the launch box off the coast of California remains scheduled for about 1930 GMT (3:30 p.m. EDT; 12:30 p.m. local).

The available window in which to launch the rocket extends from 2023:34 to 2030:03 GMT. However, analysis of the trajectory coupled with objects already in space has prompted a small blackout period for today's window. That means there will be an unusable portion of the window to ensure Pegasus isn't launched at a time that would place it too close to something already in orbit.

The times are being refined and a final update on the window and blackout period will be given later in the countdown.

TUESDAY, APRIL 24, 2007

Mysterious night-shining clouds at the edge of space are the focus of a NASA satellite to be launched aboard a winged rocket off the coast of California on Wednesday afternoon.

The $140 million mission, called the Aeronomy of Ice in the Mesosphere, or AIM, is seeking new insights into silvery-blue polar mesospheric clouds. While the clouds have been observed since the 19th century, scientists say they have become more frequent, brighter and appearing further away from the poles in recent times.

"We don't know why these clouds are forming or why they are changing. We do know, though, that since the atmosphere is all connected the changes we are seeing in the mesosphere could be a result of changes occurring in other parts of the atmosphere. It is vitally important that we understand the processes causing these (clouds) so that we can know the implications of the changes that we are seeing," said Vicki Elsbernd, the AIM program executive from NASA Headquarters.

"AIM will gather the data to answer these unknowns and to help determine if there's a relationship to global climate change."

Some scientists speculate that these clouds could be related to increases in carbon dioxide and methane emissions.

"We have seen a definite increase in the brightness of these clouds in the past 25 years, which gives us cause for concern," said Dave Rusch of the University of Colorado at Boulder's Laboratory for Atmospheric and Space Physics and principal investigator for one of AIM's instruments. "This mission will give us an unprecedented look at how the mesosphere, which is a very sensitive region of Earth's atmosphere, is changing."

AIM will be blasted into space by the air-launched Pegasus XL rocket made by Orbital Sciences. A modified L-1011 carrier aircraft, called the Stargazer, hauls the three-stage booster off the California coast from Vandenberg Air Force Base where the rocket will drop at approximately 2026 GMT (4:26 p.m. EDT; 1:26 p.m. local).

"It's been almost a year since our last Pegasus mission," said Omar Baez, the NASA launch director. "I'm excited about going into the count tomorrow."

On Saturday, the 50,000-pound rocket was wheeled out of its hanger aboard a transport trailer and attached to the aircraft. Crews completed testing of the combined L-1011 and Pegasus on Monday. Management held the final launch readiness review on Tuesday, clearing the way for the mission to proceed.

Air Force launch weather officer Captain Damon Vorhees says there is no chance of conditions violating rules at the Vandenberg airfield for the L-1011 takeoff, the flight offshore or in the launch zone.

The aircraft should be airborne by 1928 GMT (3:28 p.m. EDT; 12:28 p.m. local) for the 58-minute trip to the Pegasus drop point over the Pacific Ocean west of Monterey. The launch box is 10 miles wide and 40 miles long, Baez said.

With the push of a button in the Stargazer's cockpit, the Pegasus rocket is cast free to fall for five seconds, dropping 300 feet below the aircraft. During the plunge, the onboard flight computer will sense the rocket's separation from the carrier jet and issue a command to release the safety inhibits in preparation for ignition.

The first stage solid-fueled motor of Pegasus is lit at T+5 seconds to begin the powered journey to orbit on a southerly heading.

At T+1 minute, 17 seconds, the Orion 50S XL first stage motor consumes all of its solid-fuel propellant and burns out at an altitude of 33 miles. A short ballistic coast period begins before the spent first stage, including the wing structure, is separated to fall into the Pacific.

The Pegasus rocket's Orion 50 XL second stage begins firing at T+1 minute, 32 seconds to continue the trek to orbit. During the firing, at T+2 minutes, 8 seconds, the payload fairing that protected the satellite during atmospheric ascent is jettisoned 71 miles above Earth.

Having consumed its supply of solid-fuel propellant, the second stage motor burns out at T+2 minutes, 45 seconds. The rocket will coast for a couple of minutes before releasing the spent stage.

The solid-fueled Orion 38 third stage ignites at T+plus 7 minutes, 4 seconds to deliver the AIM spacecraft into the planned 373-mile circular orbit around Earth inclined 97.77 degrees to the equator. The orbit is achieved with cutoff of the third stage at T+8 minutes, 12 seconds.

Release of the 440-pound craft from the launcher occurs at T+plus 10 minutes, 12 seconds to complete the Pegasus rocket's 38th launch since debuting in 1990.

Watch this page for live reports during the launch!