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Discovery's debut
In our continuing look back at the classic days of the space shuttle program, today we show the STS-41D post-flight presentation by the mission's astronauts. The crew narrates this film of home movies and mission highlights from space shuttle Discovery's maiden voyage in August 1984. STS-41D deployed a remarkable three communications satellites -- a new record high -- from Discovery's payload bay, extended and tested a 100-foot solar array wing and even knocked free an icicle from the shuttle's side using the robot arm.

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"Ride of Your Life"
As the title aptly describes, this movie straps you aboard the flight deck for the thunderous liftoff, the re-entry and safe landing of a space shuttle mission. The movie features the rarely heard intercom communications between the crewmembers, including pilot Jim Halsell assisting commander Bob Cabana during the landing.

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Message from Apollo 8
On Christmas Eve in 1968, a live television broadcast from Apollo 8 offered this message of hope to the people of Earth. The famous transmission occurred as the astronauts orbited the Moon.

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ISS receives supply ship
The International Space Station receives its 20th Russian Progress cargo ship, bringing the outpost's two-man Expedition 12 crew a delivery of fresh food, clothes, equipment and special holiday gifts just in time for Christmas.

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Rendezvous with ISS
This movie features highlights of the December 23 rendezvous between the Russian Progress 20P vessel and the International Space Station. The footage comes from a camera mounted on the supply ship's nose.

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Stardust return preview
NASA's Stardust spacecraft encountered Comet Wild 2 two years ago, gathering samples of cometary dust for return to Earth. In this Dec. 21 news conference, mission officials and scientists detail the probe's homecoming and planned landing in Utah scheduled for January 15, 2006.

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Science of New Horizons
The first robotic space mission to visit the distant planet Pluto and frozen objects in the Kuiper Belt is explained by the project's managers and scientists in this NASA news conference from the agency's Washington headquarters on Dec. 19.

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Hubble Space Telescope
Scientists marvel at the achievements made by the orbiting Hubble Space Telescope in this produced movie looking at the crown jewel observatory that has served as our window on the universe.

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Protecting astronauts, craft from 'killer electrons'
EUROPEAN SPACE AGENCY NEWS RELEASE
Posted: January 1, 2006

ESA's Cluster mission has revealed a new creation mechanism of 'killer electrons' - highly energetic electrons that are responsible for damaging satellites and posing a serious hazard to astronauts.

Over the past five years, a series of discoveries by the multi-spacecraft Cluster mission have significantly enhanced our knowledge of how, where and under which conditions these killer electrons are created in Earth's magnetosphere.

Early satellite measurements in the 1950s revealed the existence of two permanent rings of energetic particles around Earth.

Usually called the 'Van Allen radiation belts', they are filled with particles trapped by Earth's magnetic field. Observations showed that the inner belt contains a fairly stable population of protons, while the outer belt is mainly composed of electrons in a more variable quantity.

Some of the outer belt electrons can be accelerated to very high energies, and it is these 'killer electrons' that can penetrate thick shielding and damage sensitive satellite electronics. This intense radiation environment is also a threat to astronauts.

For a long time scientists have been trying to explain why the number of charged particles inside the belts vary so much. Our major breakthrough came when two rare space storms occurred almost back-to-back in October and November 2003.

During the storms, part of the Van Allen radiation belt was drained of electrons and then reformed much closer to the Earth in a region usually thought to be relatively safe for satellites.

When the radiation belts reformed they did not increase according to a long-held theory of particle acceleration, called 'radial diffusion'. Radial diffusion theory treats Earth's magnetic field lines as being like elastic bands.

If the bands are plucked, they wobble. If they wobble at the same rate as the particles drifting around the Earth then the particles can be driven across the magnetic field and accelerated. This process is driven by solar activity.

Instead, a team of European and American scientists led by Dr Richard Horne of the British Antarctic Survey, Oxford, UK, used data from Cluster and ground receivers in Antarctica to show that very low frequency waves can cause the particle acceleration and intensify the belts.

These waves, named 'chorus', are natural electromagnetic emissions in the audio frequency range. They consist of discrete elements of short duration (less than one second) that sound like the chorus of birds singing at sunrise. These waves are among the most intense in the outer magnetosphere.

The number of 'killer electrons' can increase by a factor of a thousand at the peak of a magnetic storm and in the following days. Intense solar activity can also push the outer belt much closer to Earth, therefore subjecting lower altitude satellites to a much harsher environment than they were designed for.

The radial diffusion theory is still valid in some geophysical conditions. Before this discovery, some scientists thought that chorus emissions were not sufficiently efficient to account for the reformation of the outer radiation belt. What Cluster has revealed is that in certain highly disturbed geophysical conditions, chorus emissions are sufficient.

Thanks to the unique multipoint measurements capability of Cluster, the characteristic dimensions of these chorus source regions have been estimated for the first time.

Typical dimensions have been found to be a few hundred kilometres in the direction perpendicular to the Earth's magnetic field and a few thousands of kilometres in the direction parallel to this.

However, the dimensions found so far are based on case studies. "Under disturbed magnetospheric conditions, the chorus source regions form long and narrow spaghetti-like objects. The question now is whether those very low perpendicular scales are a general property of the chorus mechanism, or just a special case of the analysed observations," said Ondrej Santolik, of Charles University, Prague, Czech Republic, and main author of this result.

Due to our increased reliance on space based technologies and communications, the understanding of how, under which conditions and where these killer electrons are created, especially during magnetic storm periods, is of great iimportance.