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STS-121 program perspective
A comprehensive series of press briefings for space shuttle Discovery's upcoming STS-121 begins with a program overview conference by Wayne Hale, NASA's manager of the shuttle program, and Kirk Shireman, the deputy program manager of the International Space Station. The two men discuss the significance of Discovery's mission to their respective programs. The briefing was held June 8 at the Johnson Space Center.

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Exploration work
NASA officials unveil the plan to distribute work in the Constellation Program for robotic and human moon and Mars exploration. This address to agency employees on June 5 was given by Administrator Mike Griffin, Associate Administrator for the Exploration Systems Mission Directorate Scott Horowitz and Constellation Program Manager Jeff Hanley.

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Exploration news briefing
Following their announcement on the Exploration work assignments to the various NASA centers, Mike Griffin, Scott Horowitz and Jeff Hanley hold this news conference to answer reporter questions.

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Shuttle status check
Space shuttle program manager Wayne Hale and launch director Mike Leinbach hold this news conference May 31 from Kennedy Space Center to offer a status report on STS-121 mission preparations. The briefing was held at the conclusion of the debris verification review, which examined the external fuel tank and threats to the shuttle from impacts during launch.

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STS-29: Tracking station in the sky
NASA created its Tracking and Data Relay Satellite (TDRS) system to serve as a constellation of orbiting spacecraft that would replace the costly ground tracking stations scattered around the globe for communications with space shuttles and other satellites. Space shuttle Discovery's STS-29 mission in March 1989 launched the massive TDRS-D craft. This post-flight film narrated by the crew shows the deployment, the astronauts running a series of medical tests and the monitoring of a student-developed chicken embryo experiment.

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Delta 4 launches GOES
The Boeing Delta 4 rocket launches from pad 37B at Cape Canaveral Air Force Station with the GOES-N spacecraft, beginning a new era in weather observing for the Americas.

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Hubble observes star birth in the extreme
Posted: June 13, 2006

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Staring into the crowded, dusty core of two merging galaxies, NASA's Hubble Space Telescope has uncovered a region where star formation has gone wild.

The interacting galaxies appear as a single, odd-looking galaxy called Arp 220. The galaxy is a nearby example of the aftermath of two colliding galaxies. In fact, Arp 220 is the brightest of the three galactic mergers closest to Earth. This latest view of the galaxy is yielding new insights into the early universe, when galactic wrecks were more common.

The sharp eye of Hubble's Advanced Camera for Surveys has unveiled more than 200 mammoth star clusters. The newly found clusters far outnumber the six spied by Hubble in a 1992 observation of Arp 220 taken by the Wide Field Planetary Camera, which did not have the sharpness of the Advanced Camera. The heftiest Arp 220 cluster observed by Hubble contains enough material to equal about 10 million suns, which is twice as massive as any comparable star cluster in the Milky Way Galaxy.

The clusters are so compact, however, that even at their moderate distance they look to Hubble like brilliant single stars. Astronomers know the clusters are not stars because they are much brighter than a star would be at that distance, 250 million light-years away in the constellation Serpens.

The star birth frenzy is happening in a very small region, about 5,000 light-years across (about 5 percent of the Milky Way's diameter), where the gas and dust is very dense. There is as much gas in that tiny region as there is in the entire Milky Way Galaxy.

"This is star birth in the extreme," said astronomer Christine D. Wilson of McMaster University in Hamilton, Ontario, Canada, and the leader of the study. "Our result implies that very high star-formation rates are required to form supermassive star clusters. This is a nearby look at a phenomenon that was common in the early universe, when many galaxies were merging."

Wilson's team obtained measurements of the masses and ages for 14 of the clusters, which allowed them to more accurately estimate the masses and ages for all the clusters. The observations revealed two populations of star clusters. One population is less than 10 million years old; the second, 70 to 500 million years old. Clusters in the younger group are more massive than those in the older group.

Wilson doesn't know whether the flurry of star birth occurred at two different epochs or at a continuous frantic pace and perhaps they are not seeing the intermediate-age population. She does know that the starburst was fueled by a collision between two galaxies that began about 700 million years ago. The effects of the merger have stretched out over hundreds of millions of years.

The team's results appeared in the April 20 issue of the Astrophysical Journal. The finding is based on new observations with Hubble's Advanced Camera for Surveys and on a previous study by the Near Infrared Camera and Multi-Object Spectrometer. The Advanced Camera observations, taken in visible light in August 2002, revealed the large cluster population and produced ages for the older grouping of clusters. The near infrared camera study snapped images of the younger cluster population.

Although the new Hubble image showcases Arp 220 in visible light, the galaxy shines brightest in infrared light. In fact, Arp 220 is called an ultra-luminous infrared galaxy (ULIRG). ULIRGs are the products of mergers between galaxies, which can create firestorms of star birth. Starlight from the new stars heats the surrounding dust, causing the galaxies to glow brilliantly in infrared light.

Only a small amount of visible light escapes through the dust-enshrouded galaxy. If astronomers had an unobstructed view of Arp 220 in visible light, the galaxy would shine 50 times brighter than our Milky Way Galaxy because of the light from its massive clusters and associated star formation.

Arp 220 shares a kinship with other interacting galaxies, such as the well-known Antennae galaxies. Both are the products of galactic mergers. The merging process in Arp 220, however, is farther along than in the Antennae. In fact, said Wilson, one cannot even see the two galaxies that combined to make up Arp 220. Radio data show two objects 1,000 light-years apart that may represent the cores of the original galaxies.

The galaxy will continue to manufacture star clusters until it exhausts all of its gas, which at the current rate will happen in about 40 million years. This may seem like a long time, but it is practically a blink of an eye for a process occurring on a galactic scale. Then Arp 220 will look like the elliptical galaxies seen today, which have little gas. Some of the giant clusters -- those that are now 100 million years old -- will still be there.

The galaxy is the 220th object in Halton Arp's Atlas of Peculiar Galaxies.

The Hubble Space Telescope is an international cooperative project between NASA and the European Space Agency. The Space Telescope Science Institute is operated for NASA by the Association of Universities for Research in Astronomy, Inc., Washington.