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Pegasus/AIM preview

An air-launched Pegasus rocket will loft NASA's AIM satellite into orbit to study mysterious clouds at the edge of space. On the eve of launch, officials held these briefings from Vandenberg Air Force Base, California.

 Mission | Science

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NASA's twin STEREO spacecraft have made the first three-dimensional images of the Sun. Scientists unveil the images in this news conference held April 23.


Hubble turns 17

The Hubble Space Telescope was launched in April 1990, opening a new window on the universe that has revolutionized our understanding of the cosmos.

 Full report

Flight of Gemini 3

The first manned flight of Project Gemini launched on March 23, 1965 with pioneering astronauts Gus Grissom and John Young. Take a look back!


Apollo 9: Spider flies

Apollo 9 put the lunar landing module Spider through the stresses of spaceflight while orbiting Earth. This documentary looks back with astronauts Jim McDivitt, Dave Scott, and Rusty Schweickart.


Expedition 15 coverage
The Russian Soyuz spacecraft with Expedition 15 cosmonauts Fyodor Yurchikhin and Oleg Kotov, along with tourist Charles Simonyi, fly to the space station.

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STS-61: Fixing Hubble

One of the most daunting yet crucial human spaceflights occurred in December 1993 as the crew of shuttle Endeavour embarked on a mission to repair the Hubble Space Telescope.


STS-51: Crew report

Narrating a highlights film from their STS-51 mission, the astronauts from Discovery's September 1993 flight describe launching an advanced communications satellite and a German telescope.


The Flight of Apollo 7

This documentary looks back at Apollo 7, the first manned flight of the Apollo program. Apollo 7 was designated as the essential engineering test of the spacecraft before the ambitious lunar missions could be attempted.


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Satellite to unveil secrets of Earth's highest clouds

Posted: April 25, 2007

NASA has launched a clue-seeking satellite to track eerily mysterious clouds at the threshold of space that some scientists believe are the harbingers of global climate change.

The Aeronomy of Ice in the Mesosphere mission, or AIM for short, sailed to its observation perch 375 miles above the planet Wednesday atop an air-launched Pegasus XL rocket.

File image of Pegasus rocket. Credit: NASA
A modified L-1011 jet hauled the winged booster off the coast of California to conduct the launch at a precise point over the Pacific Ocean. The aircraft departed Vandenberg Air Force Base with the plan of releasing the 55-foot-long rocket at 2026 GMT (4:26 p.m. EDT; 1:26 p.m. local).

The 58-minute countdown proceeded without a hitch as the Orbital Sciences-built rocket and satellite were prepped for launch. After receiving a "go" from the control center, the L-1011 pilot pushed a button to cast free the 50,000-pound Pegasus. Remarkably, the drop occurred just 3.7 seconds from the time engineers had calculated before the jet took off.

"Our launch pad is moving at close to 500 mph. So that's not too bad," NASA launch manager Omar Baez joked.

The three-stage solid-propellant rocket thundered southward to reach a circular orbit around the poles that will give AIM the best view of strange night-shining clouds, the focus of the $140 million mission.

The 440-pound satellite was released from the third stage motor about 10 minutes into the flight, marking the 24th successful Pegasus mission in a row.

"This has been a very happy launch without a doubt. Everyone is walking around with grins," NASA spokesman George Diller said.

AIM will spend two years studying polar mesospheric clouds to decipher their basic formation and why their characteristics have been changing. The silvery-blue clouds have intrigued skywatchers since the 19th century. But in recent times scientists say the wispy - yet complex - clouds have become more frequent, brighter and appearing further away from the poles.

"We are exploring clouds literally on the edge of space - 50 miles above the Earth's surface. In that region the air is 100,000 times dryer than it is the Sahara desert. The pressure is extreme low - 1/100,000th of the pressure at the Earth's surface," said Jim Russell, the AIM principal investigator from Hampton University, the first historically black college to lead a NASA science mission.

Polar mesospheric clouds form during each polar region's summer months in the coldest place in the atmosphere. Credit: Hampton University
They are called noctilucent, or night-shining, since the thin clouds usually can't be seen in daylight. They become visible at night when illuminated by sunlight from just below the horizon.

"Because each cloud is high above the Earth's surface, an observer standing on the ground in darkness will still see these bright, shiny clouds because the Sun is still reflecting off of them," Russell said.

"The clouds have not always been with us as far as we can tell from looking at past observations. They were first reported in the late 1800s shortly after eruption of the Krakatoa volcano," added Mary Mellott, NASA's AIM program scientist.

"They do capture the imagination," Russell said. "They are very variable. They show dynamics. You see all these ripples in them, which we're trying to understand. And really a picture is indeed in this case worth more than 1,000 words because it's hard to describe the clouds and their beauty."

AIM carries three instruments:

  • Cloud Imaging and Particle Size is a camera package to make panoramic images of the clouds
  • Solar Occultation for Ice Experiment is an instrument to look at the reduction of the Sun's rays by the atmosphere to determine the size and density of particles in the clouds, along with the temperature, water vapor levels and chemistry
  • Cosmic Dust Experiment to measure the amount of space dust entering the atmosphere

Previous satellites have made limited measurements of polar mesospheric clouds. But AIM is the first craft dedicated to studying them.

"We got just enough information to pique our interest to try and understand more about them," Russell said. "Now, AIM has a right mix of instruments to be able to answer the question of why these changes are occurring."

Artist's concept of AIM. Credit: NASA
Those changes may be a signal of broader issues for the Earth's environment. Some scientists speculate that the clouds could be related to increases in carbon dioxide and methane emissions as a result of human activities.

"There appears to be connection between the clouds and global change," Russell said. "These clouds are changing and they are changing in ways we don't understand. They are getting brighter, there are more of them than ever before and we're seeing them at lower latitudes than ever before. And all of these things suggest some kind of connection with global change. One plausible explanation is that CO2 buildup in the atmosphere is causing the atmosphere to cool, causing more favorable conditions for the clouds form."

While such carbon dioxide buildup near the Earth's surface creates a warming, the opposite occurs higher in the atmosphere.

Following an in-space checkout period, AIM should begin its work in about a month. The prime observing time for the northern hemisphere is mid-May through mid-August and mid-November through mid-March for the southern hemisphere.

AIM's mission of exploration began with a tribute to the victims of last week's Virginia Tech tragedy. Memorial decals were placed on the Pegasus rocket to honor those who lost their lives.

The deputy principal investigator on the AIM science team, Scott Bailey, is a professor at the school.

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