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The Mission

Rocket: Pegasus XL
Payload: IBEX
Date: Oct. 19, 2008
Window: 1:44-1:51 p.m. EDT (1744-1751 GMT)
Site: Kwajalein Atoll

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MAVEN to Mars

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


Sunday's launch of a small eight-sided satellite marked the start of a two-year mission of long-distance exploration to study the little-known boundary between the solar system and the galaxy beyond.

Read our preview story here.

1945 GMT (3:45 p.m. EDT)

"It looks like we got a good Pegasus launch, actually a little bit hotter than we expected, so a little bit more energy. That's good. That means we'll have a little more hydrazine in our tanks," said David McComas, IBEX principal investigator.

"We're getting some limited engineering data (from the satellite). We're going through that. By and large that looks great. There's a couple points that weren't quite what we expected, but those don't seem to be a big issue at this point."

1835 GMT (2:35 p.m. EDT)

"The count went really smooth, launched on time and everything appears to be going well," said Omar Baez, the assistant NASA launch manager. "The spacecraft telemetry has been received by the TDRSS network. It is locked on, and they are assessing the health of the spacecraft as we speak.

"As far as the Pegasus, shortly after the third stage ignition we lost contact, which is expected as we fly over the horizon. Since we are in the South Pacific, there's not too many antenna stations to be able to bring that signal down. So we were completely expecting that.

"The way we recreate the flight, or the forensics of it, we store that data onboard and when we pass over a ground station that can receive it we downlink it. We're able to replay that data and see how the flight actually went from a telemetry point of view.

"Unfortunately, as we flew over Hawaii ground tracking station, we were not able to pull down the store-and-forward data...(next station will be Ascension Island).

"But from what we are getting from the TDRSS on the spacecraft, it looks like we did separate successfully, and that the satellite is on or near where it's supposed to be."

1827 GMT (2:27 p.m. EDT)

The Tracking and Data Relay Satellite System has gotten a lock on the IBEX satellite communications stream. The TDRSS information indicates the spacecraft is approximately where it's supposed to be, said Omar Baez, the assistant NASA launch manager.

1822 GMT (2:22 p.m. EDT)

Meanwhile, the L-1011 has landed back at Kwajalein.

1821 GMT (2:21 p.m. EDT)

The IBEX Mission Operations Center in Dulles, Virginia confirms that IBEX did separate.

1818 GMT (2:18 p.m. EDT)

The data received from the Pegasus prior to the rocket flying beyond the coverage area of the Kwajalein launch range indicated a good flight was proceeding. However, the subsequent communications link between the orbiting Tracking and Data Relay Satellite System and the IBEX spacecraft was not established as anticipated for reasons not yet known.

1812 GMT (2:12 p.m. EDT)

The official drop time today was 1:47:22.64 p.m. EDT.

1810 GMT (2:10 p.m. EDT)

The Orbital Sciences Pegasus XL rocket would have completed its job with release of the IBEX spacecraft and its attached kick motor, having hauled the 1,009-pound combined payload into an initial orbit around the Earth.

The added solid-fuel motor, known as a Star 27, is considered part of the satellite project, not the Pegasus.

Once that separation event occurred, the plan called for the adapter cone that served as the interface between the payload and Pegasus to be jettisoned. Then the Star 27 motor will light to propel IBEX into its highly elliptical transfer orbit stretching about 130,000 miles at its highest point.

1803 GMT (2:03 p.m. EDT)

After the Hawaii communications period, the next data pass from the Pegasus third stage would come via the Ascension Island tracking station in the Atlantic starting around 2:32 p.m. EDT. There's been no word from NASA yet on the expected TDRSS communications with IBEX.

1801 GMT (2:01 p.m. EDT)

That initial data report via Hawaii showed the third stage had performed its spinup maneuver prior to deploying IBEX with its attached kick motor. Still awaiting confirmation that the separation event occurred and that the IBEX motor has fired as planned.

1759 GMT (1:59 p.m. EDT)

T+plus 12 minutes, 30 seconds. A tracking station in Hawaii has acquired the first signals from the Pegasus' discard third stage to receive the store-and-forward data recorded aboard the rocket.

1753 GMT (1:53 p.m. EDT)

T+plus 6 minutes. As expected, the telemetry stream of the Pegasus has going silent now as the rocket flies over the horizon of Kwajalein's tracking coverage zone. The rocket will be recording its flight data onboard for later playback to ground stations in Hawaii and Ascension Island.

The IBEX spacecraft will power up and begin communicating with NASA's orbiting Tracking and Data Relay Satellite System at the point of separation from the Pegasus third stage. It is hoped that confirmation of that separation event, firing of the Star 27 kick stage attached to the satellite and subsequent jettison of the motor will be available via TDRSS.

1752 GMT (1:52 p.m. EDT)

T+plus 5 minutes, 10 seconds. The spent second stage has separated. And the solid-fueled third stage motor has ignited, accelerating the IBEX spacecraft to orbit.

1752 GMT (1:52 p.m. EDT)

T+plus 4 minutes, 45 seconds. The rocket is in a good orientation and the power system is strong.

1751 GMT (1:51 p.m. EDT)

T+plus 4 minutes, 30 seconds. The vehicle is now reorienting in preparation for stage separation and third stage burn.

1751 GMT (1:51 p.m. EDT)

T+plus 4 minutes, 15 seconds. Altitude is 115 miles as Pegasus continues in the ballistic climb.

1751 GMT (1:51 p.m. EDT)

T+plus 3 minutes, 50 seconds. Pegasus is traveling at 12,000 miles per hour.

1750 GMT (1:50 p.m. EDT)

T+plus 3 minutes. No problems have been reported in today's flight.

1750 GMT (1:50 p.m. EDT)

T+plus 2 minutes, 48 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.

1749 GMT (1:49 p.m. EDT)

T+plus 2 minute, 20 seconds. The two halves of the payload fairing enclosing the IBEX spacecraft on the end of the Pegasus rocket has been jettisoned. Second stage continues to burn.

1749 GMT (1:49 p.m. EDT)

T+plus 1 minute, 45 seconds. Now 50 miles up.

1749 GMT (1:49 p.m. EDT)

T+plus 1 minute, 40 seconds. The first stage is jettisoned. The Pegasus' second stage has ignited.

1748 GMT (1:48 p.m. EDT)

T+plus 1 minute, 18 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.

1748 GMT (1:48 p.m. EDT)

T+plus 1 minute. The rocket is more than 80,000 feet in altitude with a velocity now exceeding 2,500 mph.

1748 GMT (1:48 p.m. EDT)

T+plus 40 seconds. Passing through the region of maximum aerodynamic pressure.

1747 GMT (1:47 p.m. EDT)

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.

1747 GMT (1:47 p.m. EDT)

T+plus 20 seconds. Pegasus is supersonic.

1747 GMT (1:47 p.m. EDT)

IGNITION of the Pegasus rocket launching NASA's Interstellar Boundary Explorer to observe how our solar system interacts with the galaxy.

1747:23 GMT (1:47:23 p.m. EDT)

DROP. The Orbital Sciences Pegasus XL rocket has been released from the L-1011 aircraft over the Pacific Ocean north of Kwajalein Atoll.

1747 GMT (1:47 p.m. EDT)

The L-1011 has entered the drop zone. The box is 40 miles long and 4 miles wide.

1746 GMT (1:46 p.m. EDT)

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 IBEX spacecraft aboard, from the belly of the jet.

1746:22 GMT (1:46:22 p.m. EDT)

T-minus 1 minute. The L-1011 is adjusting its course to acquire the proper heading. Pegasus will be launching along a 81.5-deg flight azimuth.

1744 GMT (1:44 p.m. EDT)

The L-1011 is passing the final waypoint prior to the launch box.

1744:22 GMT (1:44:22 p.m. EDT)

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

1743:22 GMT (1:43:22 p.m. EDT)

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

1742 GMT (1:42 p.m. EDT)

The launch team has been given a "go" to enter the final phase of today's countdown.

1740 GMT (1:40 p.m. EDT)

The Range is confirmed clear for launch.

1740 GMT (1:40 p.m. EDT)

The Pegasus rocket's avionics have switched from power provided by the L-1011 to internal battery power.

1739 GMT (1:39 p.m. EDT)

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

1737 GMT (1:37 p.m. EDT)

Checks of the flight termination system have been completed without any problems reported.

1736 GMT (1:36 p.m. EDT)

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.

1735 GMT (1:35 p.m. EDT)

The spacecraft Mission Operations Center in Dulles, Virginia confirms IBEX is in good shape following the transition to internal power.

1734 GMT (1:34 p.m. EDT)

The IBEX spacecraft has switched to internal power for launch.

1734 GMT (1:34 p.m. EDT)

The aircraft has begun the 180-degree left-overhead turn on the course headed back toward the launch point.

1732 GMT (1:32 p.m. EDT)

T-minus 16 minutes and counting. The release mechanism that will drop the Pegasus rocket from the L-1011 carrier jet was just armed. This hydraulic system involves four main hooks holding the Pegasus to the aircraft as well as a nose hook.

1728 GMT (1:28 p.m. EDT)

T-minus 20 minutes and counting. 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, the co-pilot will push a button next to the enable switch, releasing the Pegasus rocket and IBEX 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," Capt. Bill 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."

1722 GMT (1:22 p.m. EDT)

The aircraft crew reports just light turbulence and no clouds in the drop box.

1721 GMT (1:21 p.m. EDT)

The carrier jet is passing through the launch box north of Kwajalein. The aircraft is heading westward right now but will soon make a wide, sweeping U-turn for return to the rocket drop zone on an easterly heading.

1718 GMT (1:18 p.m. EDT)

Now 30 minutes from the planned launch time. Today marks the 40th flight of the air-launched Pegasus rocket and the 30th using the XL version.

1708 GMT (1:08 p.m. EDT)

T-minus 40 minutes and counting. This launch will be the second time NASA has launched a Pegasus from the Marshall Islands. But unlike the previous mission conducted in 2000 that used a remote launch control center back at the agency's facilities in Cape Canaveral, Florida, the nerve center for today's mission is located at Kwajalein.

"We kind of build our own control room, bring in our laptops and put it all together," said Orbital Sciences' Eric Denbrook.

Also in contrast to the earlier launch that featured only a small group of workers being deployed to the launch site, about 85 people from NASA, Orbital Sciences and other partners have traveled to the Central Pacific in support the IBEX launch.

"One of the lessons learned, it was frustrating for some of the engineering and management team to be away from the hardware when there was an issue," Denbrook said.

Working on such an isolated island, about 4,700 miles from California, presents quite a logistical challenge for launch officials.

"Kwajalein says 'if you need it, bring it' because it's not there," said Chuck Dovale, the NASA launch manager.

And freighting in what you plan to use is not enough.

"We have to bring extra equipment and supplies in case something goes wrong we're not waiting for shipments," Denbrook added.

Conducting this launch from Florida was once considered. But the payload weight nixed that option, prompting mission designers to select the equatorial site at Kwajalein where the Earth's rotation gives an added advantage to the rocket.

1658 GMT (12:58 p.m. EDT)

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.

1651 GMT (12:51 p.m. EDT)

WHEELS UP. The "Stargazer" carrier aircraft with the Orbital Sciences Pegasus XL rocket has departed the Kwajalein Atoll in the Marshall Islands for today's launch for NASA's IBEX spacecraft. The booster will be released from the jet over the Pacific Ocean around 1:48 p.m. EDT to propel the satellite into orbit.

1650 GMT (12:50 p.m. EDT)

Stargazer has begun its takeoff roll down Kwajalein's runway.

1648 GMT (12:48 p.m. EDT)

The Orbital Sciences launch conductor just completed a poll of his ground launch team. And all systems are reported ready for the L-1011's takeoff.

1644 GMT (12:44 p.m. EDT)

NASA Launch Manager Chuck Dovale has polled the space agency team to verify all is in readiness for departure of the L-1011 aircraft. "Team is ready for takeoff," Dovale said.

1622 GMT (12:22 p.m. EDT)

The L-1011 is taxiing to the runway from the staging area, called the Hot Pad, where the carrier aircraft has been parked for the past week.

1615 GMT (12:15 p.m. EDT)

A NASA spokesman says the countdown continues to run on schedule for launch of the IBEX spacecraft aboard the Orbital Sciences Pegasus XL rocket. There's some rain along the carrier jet's planned flight path, but officials are looking at options to fly around the weather.

1603 GMT (12:03 p.m. EDT)

T-minus 1 hour, 45 minutes. The L-1011 aircraft's engines have been started and the launch team is proceeding through final testing prior to takeoff.

1430 GMT (10:30 a.m. EDT)

Launch morning activities are underway at the Kwajalein Atoll for today's flight of the Pegasus XL rocket carrying NASA's Interstellar Boundary Explorer spacecraft. The launch team and mission managers are on duty, running through the official countdown checklist.

Takeoff of the L-1011 carrier aircraft headed to the launch box remains scheduled for about 12:50 p.m. EDT (1650 GMT), with the release of Pegasus targeted for 1:48 p.m. EDT (1748 GMT).

The weather forecast predicts an 80 percent chance of acceptable conditions.


A compact satellite will be shot into a looping orbit Sunday to observe how our solar system interacts with the galaxy.

The Interstellar Boundary Explorer, a $169 million NASA mission, will map the hot solar wind mixing with the cold vastness of the galaxy's interstellar medium.

"This will be our first panoramic view of this gateway into our galaxy. We are in for some incredible discoveries," said Herb Funsten, principal investigator on the High Energy Neutral Atom Imager instrument.

The million mile-per-hour wind streaming from the sun blows a protective bubble in which we live, shielding our neighborhood from galactic cosmic rays.

"The continuous wind from the sun keeps the bubble inflated and the edges of our solar system are defined by the interaction between this wind and the surrounding interstellar medium," said Stephen Fuselier, lead investigator for IBEX-Lo instrument. "By measuring the number of arriving neutral atoms at a variety of energies, we can determine many of the properties of the boundaries of our solar system."

That bubble, known as the heliosphere, keeps the deadly radiation from sources deep in the galaxy out of our inner solar system. But are there places where the shield isn't as strong or thick? IBEX will measure the protective walls from the inside out.

The two-year IBEX mission should yield four global maps. "Every six months as the spacecraft spins and we precess around the sun, we get an all-sky survey, or map, at very high resolution," said Mark Phillips, the IBEX deputy project manager.

IBEX rides into space aboard the air-launched Pegasus XL rocket made by Orbital Sciences. Final assembly was completed at Vandenberg Air Force Base in California before being ferried last weekend to the U.S. Army's launch range in the Marshall Islands of the Central Pacific.

Testing, rehearsals and reviews were completed earlier this week, clearing the way for Sunday's countdown.

A modified L-1011 carrier aircraft, called the Stargazer, should be airborne by 12:50 p.m. EDT (1650 GMT) for the 58-minute trip to the Pegasus drop point over the Pacific Ocean north of Kwajalein Atoll. The launch box is 4 miles wide and 40 miles long, the targeted drop point located at 10.5 degrees latitude and 167.6 degrees longitude.

Sunday's available launch window extends from 1:44:20 to 1:51:50 p.m. EDT (1744:20-1751:50 GMT).

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+plus 5 seconds to begin the powered journey to orbit on an 81.5 degree easterly heading.

At T+plus 1 minute, 18 seconds, the Orion 50S XL first stage motor consumes all of its solid-fuel propellant and burns out. 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+plus 1 minute, 33 seconds to continue the trek to orbit. During the firing, at T+plus 2 minutes, 18 seconds, the payload fairing that protected the satellite during atmospheric ascent is jettisoned.

Having consumed its supply of solid-fuel propellant, the second stage motor burns out at T+plus 2 minutes, 47 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 5 minutes, 14 seconds to deliver IBEX spacecraft into a temporary 125-mile circular orbit parking around Earth. That orbit is achieved with cutoff of the third stage at T+plus 6 minutes, 22 seconds.

A rapid spinup to 60 rpm initiates at T+plus 7 minutes, 47 seconds, followed by separation between the spent third stage and payload at T+plus 8 minutes, 22 seconds. At that point, the Pegasus rocket will have completed its portion of the IBEX mission, marking the 40th launch of the winged booster since 1990.

The "payload" for this mission consists of IBEX and its attached kick motor. The adapter cone that served as the interface between the Pegasus and payload jettisons from the Star 27 solid-fuel motor. And seconds later, the kick stage ignites for a burn that hurls the satellite into an egg-shaped orbit with the high point of roughly 130,000 miles.

After waiting three-and-a-half minutes to allow the Star 27 to finish emitting any residual thrust, the motor is jettisoned from IBEX.

In the subsequent weeks, hydrazine thrusters on IBEX will be fired to raise the high and low points of the orbit, eventually achieving the desired altitude where the science instruments can perform their observations.

The looping orbit will range from 4,400 miles at its closest pass to 200,000 miles at its furthest point from Earth, about 50 times the planet's radius, and taking 8 days to complete just one revolution.

Watch this page for live reports during the countdown and launch!


A Combined Systems Test was conducted Wednesday to ensure all elements of the Pegasus rocket, IBEX satellite, L-1011 carrier aircraft and ground network are working properly for Sunday's launch.

Later today, a full countdown dress rehearsal will be held for the teams located in Kwajalein and sites back in the U.S.

All remains on schedule for the mission.


The Pegasus rocket traveled to Kwajalein over the weekend as planned, leaving Vandenberg on Saturday, making an overnight stop in Hawaii and arriving at the launch site on Sunday. An IBEX state of health check was performed the day after landing.


An Orbital Sciences Pegasus rocket with a NASA satellite nestled in its nose cone will fly away from California's Vandenberg Air Force Base on Saturday, but the winged booster won't be soaring into space.

Slung beneath an L-1011 carrier aircraft, the fully assembled rocket will leave its home port destined for the Kwajalein Atoll in the central Pacific Ocean, part of the U.S. Army's vast missile range, where the launch will occur next weekend.

Read our preview story here.

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