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Discovery demate preps
Technicians ready space shuttle Discovery for demating from the external fuel tank inside the Vehicle Assembly Building. (1min 24sec file)
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Shuttle removed from tank
Space shuttle Discovery is demated from its original external fuel tank and solid rocket boosters. The ship is lowered to its transport trailer in the Vehicle Assembly Building. (2min 38sec file)
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Discovery in the VAB
Shuttle Discovery enters into the Vehicle Assembly Building after a 10-hour journey from launch pad 39B. (4min 29sec file)
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Memorial Day message
The International Space Station's Expedition 11 crew pays tribute to our fallen heroes for Memorial Day. (1min 00sec QuickTime file)
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Apollo-era transporter
In the predawn hours, the Apollo-era crawler-transporter is driven beneath shuttle Discovery's mobile launch platform at pad 39B in preparation for the rollback to the Vehicle Assembly Building. (2min 37sec QuickTime file)
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Unplugging the shuttle
Workers disconnect a vast number of umbilicals running between launch pad 39B and Discovery's mobile launch platform for the rollback. The cabling route electrical power, data and communications to the shuttle. (2min 32sec file)
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Shuttle rollback
The crawler-transporter begins rolling space shuttle Discovery off launch pad 39B at 6:44 a.m. EDT May 26 for the 4.2-mile trip back to the Vehicle Assembly Building. (7min 28sec file)
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Voyager adventures
This animation shows the Voyager spacecraft heading into the solar system's final frontier and the edge of interstellar space. (1min 24sec file)
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Mike Griffin at KSC
NASA Administrator Mike Griffin and Kennedy Space Center Director Jim Kennedy chat with reporters at the Cape on a wide range of topics. The press event was held during Griffin's tour of the spaceport. (27min 48sec file)
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Delta rocket blasts off
The NOAA-N weather satellite is launched aboard a Boeing Delta 2 rocket from Vandenberg Air Force Base, California.

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   Liftoff | Extended clip
   Umbilicals | IR tracker

NOAA pre-launch
Officials from NASA, NOAA, the Air Force and Boeing hold the pre-launch news conference at Vandenberg Air Force Base to preview the mission of a Delta 2 rocket and the NOAA-N weather satellite. (29min 54sec file)

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Countdown culmination
Watch shuttle Discovery's countdown dress rehearsal that ends with a simulated main engine shutdown and post-abort safing practice. (13min 19sec file)
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Going to the pad
The five-man, two-woman astronaut crew departs the Operations and Checkout Building to board the AstroVan for the ride to launch pad 39B during the Terminal Countdown Demonstration Test countdown dress rehearsal. (3min 07sec file)
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Suiting up
After breakfast, the astronauts don their launch and entry partial pressure suits before heading to the pad. (3min 14sec file)
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Cosmic mystery: Where is that missing neutron star?
Posted: June 6, 2005

In 1987, earthbound observers saw a star explode in the nearby dwarf galaxy called the Large Magellanic Cloud. Astronomers eagerly studied this supernova -- the closest seen in the past 300 years -- and have continued to examine its remains. Although its blast wave lit up surrounding clouds of gas and dust, the supernova appears to have left no core behind. Astronomers now report that even the sharp eyes of the Hubble Space Telescope failed to locate the black hole or ultracompact neutron star they believe was created by the star's death 18 years ago.

The remnant of supernova 1987A shows no sign of the neutron star scientists believe is lurking at its heart. The Hubble Space Telescope took this image in December 2004. Credit: P. Challis & R. Kirshner (Harvard-Smithsonian Center for Astrophysics)
"We think a neutron star was formed. The question is: Why don't we see it?" said astronomer Genevieve Graves of UC Santa Cruz, first author on the paper announcing these results.

"Therein lies the mystery -- where is that missing neutron star?" mused co-author Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics (CfA).

When a massive star explodes, it leaves behind some sort of compact object, either a city-sized ball of subatomic particles called a neutron star, or a black hole. The outcome depends on the mass of the progenitor star. Smaller stars form neutron stars while larger stars form black holes.

The progenitor of supernova (SN) 1987A weighed 20 times as much as the sun, placing it right on the dividing line and leaving astronomers uncertain about what type of compact object it produced. All observations to date have failed to detect a light source in the center of the supernova remnant, leaving the question of the outcome unanswered.

Detecting a black hole or neutron star is challenging. A black hole can be detected only when it swallows matter, because the matter heats up and emits light as it falls into the black hole. A neutron star at the distance of the Large Magellanic Cloud can be detected only when it emits beams of radiation as a pulsar, or when it accretes hot matter like a black hole.

"A neutron star could just be sitting there inside SN 1987A, not accreting matter and not emitting enough light for us to see," said astronomer Peter Challis (CfA), second author on the study.

Observations have ruled out the possibility of a pulsar within SN 1987A. Even if the pulsar's beams were not aimed at the earth, they would light the surrounding gas clouds. However, theories predict that it can take anywhere from 100 to 100,000 years for a pulsar to form following a supernova, because the neutron star must gain a sufficiently strong magnetic field to power the pulsar beam. SN 1987A may be too young to hold a pulsar.

As a result, the only way astronomers might detect the central object is to search for evidence of matter accreting onto either a neutron star or a black hole. That accretion could happen in one of two ways: spherical accretion in which matter falls in from all directions, or disk accretion in which matter spirals inward from a disk onto the compact object.

The Hubble data rule out spherical accretion because light from that process would be bright enough to detect. If disk accretion is taking place, the light it generates is very faint, meaning that the disk itself must be quite small in both mass and radial extent. Also, the lack of detectable radiation indicates that the disk accretion rate must be extremely low -- less than about one-fifth the mass of the Moon per year.

In the absence of a definitive detection, astronomers hope to learn more about the central object by studying the dust clouds surrounding it. That dust absorbs visible and ultraviolet light and re-radiates the energy at infrared wavelengths.

"By studying that reprocessed light, we hope to find out what's powering the supernova remnant and lighting the dust," said Graves. Future observations by NASA's Spitzer Space Telescope should provide new clues to the nature of the hidden object.

Additional observations by Hubble also could help solve the ystery. "Hubble is the only existing facility with the resolution and sensitivity needed to study this problem," said Kirshner.

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.