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Planes track Discovery
To gain a new perspective on space shuttle Discovery's ascent and gather additional imagery for the return to flight mission, NASA dispatched a pair of high-flying WB-57 aircraft equipped with sharp video cameras in their noses.

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Rocket booster cams
When space shuttle Discovery launched its two solid-fuel booster rockets were equipped with video cameras, providing dazzling footage of separation from the external fuel tank, their free fall and splashdown in the sea.

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Discovery ferried home
Mounted atop a modified Boeing 747, space shuttle Discovery was ferried across the country from Edwards Air Force Base, California, to Kennedy Space Center, Florida.

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Shuttle tank returned
Shuttle fuel tank ET-119 is loaded onto a barge at Kennedy Space Center for the trip back to Lockheed Martin's Michoud Assembly Facility in New Orleans. The tank will be used in the investigation to determine why foam peeled away from Discovery's tank on STS-114 in July.

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Delta 4 launch delayed
Launch of the GOES-N weather observatory aboard a Boeing Delta 4 rocket is postponed at Cape Canaveral, Florida.

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Mars probe leaves Earth
The Mars Reconnaissance Orbiter lifts off aboard a Lockheed Martin Atlas 5 rocket from Cape Canaveral's Complex 41.

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Shuttle delayed to 2006
NASA Administrator Mike Griffin and Associate Administrator for Space Operations Bill Gerstenmaier hold a news conference from Agency Headquarters in Washington on August 18 to announce a delay in the next shuttle flight from September to next March. (38min 02sec)

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Launch pad demolition
Explosives topple the abandoned Complex 13 mobile service tower at Cape Canaveral Air Force Station. This video was shot from the blockhouse roof at neighboring Complex 14 where John Glenn was launched in 1962.

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How to build a big star
Posted: August 31, 2005

The most massive stars in our galaxy weigh as much as 100 small stars like the Sun. How do such monsters form? Do they grow rapidly by swallowing smaller protostars within crowded star-forming regions? Some astronomers thought so, but a new discovery suggests instead that massive stars develop through the gravitational collapse of a dense core in an interstellar gas cloud via processes similar to the formation of low mass stars.

"In the past, theorists have had trouble modeling the formation of high-mass stars and there has been an ongoing debate between the merger versus the accretion scenarios." said astronomer Nimesh Patel of the Harvard-Smithsonian Center for Astrophysics (CfA). "We've found a clear example of an accretion disk around a high-mass protostar, which supports the latter while providing important observational constraints to the theoretical models."

Patel and his colleagues studied a young protostar 15 times more massive than the Sun, located more than 2,000 light-years away in the constellation Cepheus. They discovered a flattened disk of material orbiting the protostar. The disk contains 1 to 8 times as much gas as the Sun and extends outward for more than 30 billion miles - eight times farther than Pluto's orbit.

The existence of this disk provides clear evidence of gravitational collapse, the same gradual process that built the Sun. A disk forms when a spinning gas cloud contracts, growing denser and more compact. The angular momentum of the spinning material forces it into a disk shape. The planets in our solar system formed from such a disk 4.5 billion years ago.

Evidence in favor of high-mass accretion has been elusive since massive stars are rare and evolve quickly, making them tough to find. Patel and his colleagues solved this problem using the Submillimeter Array (SMA) telescope in Hawaii, which offers much sharper and highly sensitive imaging capabilities compared to single-dish submillimeter telescopes. SMA is currently a unique instrument that makes such studies possible by allowing astronomers to directly image the dust emission at submillimeter wavelengths and also to detect emission from highly excited molecular gas.

The team detected both molecular gas and dust in a flattened structure surrounding the massive protostar HW2 within the Cepheus A star formation region. SMA data also showed a velocity shift due to rotation, supporting the interpretation that the structure is a gravitationally bound disk. Combined with radio observations showing a bipolar jet of ionized gas, a type of outflow often observed in association with low-mass protostars, these results support theoretical models of high-mass star formation via disk accretion rather than by the merging of several low-mass protostars.

"Merging low-mass protostars wouldn't form a circumstellar disk and a bipolar jet," said co-author Salvador Curiel of the National Autonomous University of Mexico (UNAM), who is on sabbatical leave at CfA. "Even if they had circumstellar disks and outflows before the merger, those features would be destroyed during the merger."

The team plans more detailed observations using the SMA and the National Radio Astronomy Observatory's Very Large Array, which initially detected the bipolar jet.

The researchers, in addition to Patel, Ho, and Curiel, are: P. T. Ho, T. K. Sridharan, Q. Zhang, T. R. Hunter and J. M. Moran, of CfA; Jose M. Torrelles, Institute for Space Studies of Catalonia (IEEC)-Spanish Research Council (CSIC), Spain; and J. F. Gomez and G. Anglada, Institute of Astrophysics of Calunia (CSIC), Spain.

This research is being reported in the September 1, 2005, issue of Nature.

The SMA is a joint project between the Smithson Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan and is funded by the Smithsonian Institution and the Academia Sinica.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.