In Building 1555 at North Vandenberg Air Force Base, workers get ready to attach the overhead crane to the AIM spacecraft. AIM will be moved into an area where a partial deployment of the solar arrays on the spacecraft will take place. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 at North Vandenberg Air Force Base, workers lift the AIM spacecraft from its stand in order to move it into an area where a partial deployment of the solar arrays on the spacecraft will take place. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

ISS031-E-116058 (13 June 2012) --- Polar mesospheric clouds in the Northern Hemisphere are featured in this image photographed by an Expedition 31 crew member on the International Space Station. In both the Northern and Southern Hemisphere, during their respective late spring and early summer seasons, polar mesospheric clouds are at the peak of their visibility. Visible from the ground during twilight, aircraft in flight, and the International Space Station, they typically appear as delicate shining threads against the darkness of space?hence their other name of noctilucent or ?night-shining? clouds. On the same day this image was taken from the space station while it was passing over the night-darkened Tibetan Plateau, polar mesospheric clouds were also visible to aircraft flying above Canada. In addition to this still image, the space station crew took a time-lapse image sequence of polar mesospheric clouds several days earlier (June 5, 2012) while passing over western Asia; this is first such sequence of images of the phenomena taken from orbit. Polar mesospheric clouds form between 76-85 kilometers above the Earth?s surface, when there is sufficient water vapor at these high altitudes to freeze into ice crystals. The clouds are illuminated by the setting sun while the ground surface below is in darkness, lending them their night-shining properties. In addition to the illuminated tracery of polar mesospheric clouds trending across the center of the image, lower layers of the atmosphere are also illuminated; the lowest layer of the atmosphere, the stratosphere, is indicated by dim orange and red tones. While the exact cause of formation of polar mesospheric clouds is still debated?dust from meteors, global warming, and rocket exhaust have all been suggested as contributing factors?recent research suggests that changes in atmospheric gas composition or temperature has caused the clouds to become brighter over time.

ISS024-E-006136 (16 June 2010) --- Polar mesospheric clouds, illuminated by an orbital sunrise, are featured in this image photographed by an Expedition 24 crew member on the International Space Station. Polar mesospheric, or noctilucent (?night shining?), clouds are observed from both Earth?s surface and in orbit by crew members aboard the space station. They are called night-shining clouds as they are usually seen at twilight. Following the setting of the sun below the horizon and darkening of Earth?s surface, these high clouds are still briefly illuminated by sunlight. Occasionally the ISS orbital track becomes nearly parallel to Earth?s day/night terminator for a time, allowing polar mesospheric clouds to be visible to the crew at times other than the usual twilight due to the space station altitude. This unusual photograph shows polar mesospheric clouds illuminated by the rising, rather than setting, sun at center right. Low clouds on the horizon appear yellow and orange, while higher clouds and aerosols are illuminated a brilliant white. Polar mesospheric clouds appear as light blue ribbons extending across the top of the image. These clouds typically occur at high latitudes of both the Northern and Southern Hemispheres, and at fairly high altitudes of 76?85 kilometers (near the boundary between the mesosphere and thermosphere atmospheric layers). The ISS was located over the Greek island of Kos in the Aegean Sea (near the southwestern coastline of Turkey) when the image was taken at approximately midnight local time. The orbital complex was tracking northeastward, nearly parallel to the terminator, making it possible to observe an apparent ?sunrise? located almost due north. A similar unusual alignment of the ISS orbit track, terminator position, and seasonal position of Earth?s orbit around the sun allowed for striking imagery of polar mesospheric clouds over the Southern Hemisphere earlier this year.

ISS017-E-011603 (22 July 2008) --- Layers of Earth's atmosphere, brightly colored as the sun rises over central Asia, and Polar Mesospheric Clouds (also known as noctilucent clouds) are featured in this image photographed by an Expedition 17 crewmember on the International Space Station. The image was acquired in support of International Polar Year research.

ISS028-E-020276 (2 Aug. 2011) --- This photograph of polar mesospheric clouds was acquired at an altitude of just over 202 nautical miles (about 322 kilometers) in the evening hours (03:19:54 Greenwich Mean Time) on Aug. 2, 2011, as the International Space Station was passing over the English Channel. The nadir coordinates of the station were 49.1 degrees north latitude and 5.5 degrees west longitude. Polar mesospheric clouds (also known as noctilucent, or ?night-shining? clouds) are transient, upper atmospheric phenomena that are usually observed in the summer months at high latitudes (greater than 50 degrees) of both the Northern and Southern Hemispheres. They appear bright and cloudlike while in deep twilight. They are illuminated by sunlight when the lower layers of the atmosphere are in the darkness of Earth?s shadow. The horizon of Earth appears at the bottom of the image, with some layers of the lower atmosphere already illuminated by the rising sun. The higher, bluish-colored clouds look much like wispy cirrus clouds, which can be found as high as 60,000 feet (18 kilometers) in the atmosphere. However noctilucent clouds, as seen here, are observed in the mesosphere at altitudes of 250,000 to 280,000 feet (about 76 to 85 kilometers). Astronaut observations of polar mesospheric clouds over northern Europe in the summer are not uncommon.

Earth Observation taken during a night pass by the Expedition 40 crew aboard the International Space Station (ISS). Folder lists this as: Polar Mesospheric Clouds over Canada.

Earth Observation taken during a night pass by the Expedition 40 crew aboard the International Space Station (ISS). Folder lists this as: Polar Mesospheric Clouds over Canada.

Earth Observation taken during a night pass by the Expedition 40 crew aboard the International Space Station (ISS). Folder lists this as: Polar Mesospheric Clouds over Canada.

ISS034-E-024622 (5 Jan. 2013) --- Polar mesospheric clouds over the South Pacific Ocean are featured in this image photographed by an Expedition 34 crew member on the International Space Station. Polar mesospheric clouds—also known as noctilucent, or “night shining” clouds—are formed 76 to 85 kilometers above Earth’s surface near the mesosphere-thermosphere boundary of the atmosphere, a region known as the mesopause. At these altitudes, water vapor can freeze into clouds of ice crystals. When the sun is below the horizon such that the ground is in darkness, these high clouds may still be illuminated—lending them their ethereal, “night shining” qualities. Noctilucent clouds have been observed from all human vantage points in both the Northern and Southern Hemispheres – from the surface, in aircraft, and in orbit from the space station—and tend to be most visible during the late spring and early summer seasons. Polar mesospheric clouds also are of interest to scientists studying the atmosphere. While some scientists seek to understand their mechanisms of formation, others have identified them as potential indicators of atmospheric changes resulting from increases in greenhouse gas concentrations. This photograph was taken when the station was over the Pacific Ocean south of French Polynesia. While most polar mesospheric cloud images are taken from the orbital complex with relatively short focal length lens to maximize the field of view, this image was taken with a long lens (400 mm) allowing for additional detail of the cloud forms to be seen. Below the brightly-lit noctilucent clouds in the center of the image, the pale orange band indicates the stratosphere.

ISS022-E-052281 (30 Jan. 2010) --- Polar mesospheric clouds over the Southern Hemisphere are featured in this image photographed by an Expedition 22 crew member on the International Space Station. This striking view shows polar mesospheric clouds (PMC) over the polar region of the Southern Hemisphere. These clouds occur over the high latitudes of both northern and southern hemispheres during their respective summer months at very high altitudes of approximately 76?85 kilometers. When present they are visible during twilight, when the clouds are illuminated by the sun while the ground surface below is in darkness. The International Space Station (ISS) orbit extends from latitude 52 North to latitude 52 South; combined with the highly oblique views through Earth?s atmosphere possible with hand-held imagery, the ISS is an ideal platform for documenting these transient, high altitude phenomena. Another NASA mission, the Aeronomy of Ice in the Mesosphere or AIM satellite, is dedicated to the study of PMC and is providing daily information about their formation, distribution, and variability. Polar mesospheric clouds are also known as noctilucent or night-shining clouds ? a property that is clearly visible in this photograph. The PMC exhibit thin, wispy light blue forms that contrast with the darkness of space above (upper right). Lower levels of cloud are strongly illuminated by the sun and appear light orange to white. Clouds closest to Earth?s surface are reddish-orange (center). The image was taken approximately 38 minutes after midnight Greenwich Mean Time (GMT) while the ISS was located over the southern Atlantic Ocean. At this time of year, the sun never sets over Antarctica but rather defines an arc across the local horizon, allowing PMC to be observed near local midnight.

At Vandenberg Air Force Base in California, the Orbital Sciences Pegasus XL rocket is ready for mating to the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

The mated Pegasus XL rocket - AIM spacecraft is moved onto a transporter in Building 1655 at Vandenberg Air Force Base in California. The launch vehicle will be transferred to a waiting Orbital Sciences Stargazer L-1011 aircraft for launch. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- At Vandenberg Air Force Base in California, the Orbital Sciences Pegasus XL rocket is ready for mating to the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

At North Vandenberg Air Force Base in California, the AIM spacecraft is prepared for its move to the clean room for testing. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- At North Vandenberg Air Force Base in California, the AIM spacecraft is prepared for its move to the clean room for testing. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

At Vandenberg Air Force Base in California, a technician mates the AIM spacecraft, at left, to the Orbital Sciences Pegasus XL rocket, at right. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- The mated Pegasus XL rocket - AIM spacecraft is secured onto a transporter at Vandenberg Air Force Base in California. The rocket will be transferred to a waiting Orbital Sciences Stargazer L-1011 aircraft for launch. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch is scheduled for April 25.

At Vandenberg Air Force Base in California, technicians prepare to mate the AIM spacecraft (at left) to the SoftRide isolation system on the Orbital Sciences Pegasus XL rocket. The Cosmic Dust Experiment surfaces can be clearly seen as 12 rectangular areas on the aft portion of the spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- In Building 1555 on North Vandenberg Air Force Base in California, technicians lower the AIM spacecraft onto a moveable stand. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

The mated Pegasus XL rocket - AIM spacecraft is secured onto a transporter at Vandenberg Air Force Base in California. The rocket will be transferred to a waiting Orbital Sciences Stargazer L-1011 aircraft for launch. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- At Vandenberg Air Force Base in California, a technician mates the AIM spacecraft, at left, to the Orbital Sciences Pegasus XL rocket, at right. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- At Vandenberg Air Force Base in California, the third stage of the Orbital Sciences Pegasus XL rocket is being mated to the AIM spacecraft, at right. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- In Building 1555 on North Vandenberg Air Force Base in California, technicians work on the separation system to be mated to the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

The mated Pegasus XL rocket - AIM spacecraft leaves Building 1655 at Vandenberg Air Force Base in California. The rocket will be transferred to a waiting Orbital Sciences Stargazer L-1011 aircraft for launch. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- In Building 1555 on North Vandenberg Air Force Base in California, technicians work on the separation system to be mated to the AIM spacecraft, hovering above it. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- In Building 1555 on North Vandenberg Air Force Base in California, technicians lower the spacecraft handling fixture around the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- In Building 1555 on North Vandenberg Air Force Base in California, technicians maneuver the spacecraft handling fixture toward the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- In Building 1555 on North Vandenberg Air Force Base in California, technicians roll the AIM spacecraft back under the protective clean tent. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians move a mobile stand toward the AIM spacecraft suspended via a crane at left. . AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians lift the AIM spacecraft via the spacecraft handling fixture attached to it. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

At North Vandenberg Air Force Base in California, the AIM spacecraft has been rotated to horizontal prior to its move to the clean room for testing. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians work on the separation system to be mated to the AIM spacecraft, hovering above it. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians lower the AIM spacecraft onto a moveable stand. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside a clean room at Vandenberg Air Force Base in California, NASA's Aeronomy of Ice in the Mesosphere, or AIM, spacecraft is weighed. AIM is the seventh Small Explorers mission under NASA's Explorer Program. The program provides frequent flight opportunities for world-class scientific investigations from space within heliophysics and astrophysics. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- The mated Pegasus XL rocket - AIM spacecraft leaves Building 1655 at Vandenberg Air Force Base in California. The rocket will be transferred to a waiting Orbital Sciences Stargazer L-1011 aircraft for launch. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch is scheduled for April 25.

At Vandenberg Air Force Base in California, the third stage of the Orbital Sciences Pegasus XL rocket is being mated to the AIM spacecraft, at right. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians maneuver the spacecraft handling fixture toward the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

At North Vandenberg Air Force Base in California, the AIM spacecraft is moved into a clean room for testing. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians work on the separation system to be mated to the AIM spacecraft, hovering above it. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Flight simulation No. 3 is on the schedule for the Pegasus XL launch vehicle, seen here in Building 1555 on North Vandenberg Air Force Base in California. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- At Vandenberg Air Force Base in California, workers perform a fit check mating the AIM spacecraft to the Orbital Sciences Pegasus XL rocket. Red covers are in place to protect the Cosmic Dust Experiment instrument. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

NASA's Aeronomy of Ice in the Mesosphere, or AIM, spacecraft arrives in a clean room at Vandenberg Air Force Base in California. AIM is the seventh Small Explorers mission under NASA's Explorer Program. The program provides frequent flight opportunities for world-class scientific investigations from space within heliophysics and astrophysics. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- In Building 1555 on North Vandenberg Air Force Base in California, technicians lift the AIM spacecraft via the spacecraft handling fixture attached to it. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians roll the AIM spacecraft back under the protective clean tent. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians work on the separation system to be mated to the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians lower the spacecraft handling fixture around the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- At North Vandenberg Air Force Base in California, the AIM spacecraft is moved into a clean room for testing. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- The mated Pegasus XL rocket - AIM spacecraft is moved onto a transporter in Building 1655 at Vandenberg Air Force Base in California. The launch vehicle will be transferred to a waiting Orbital Sciences Stargazer L-1011 aircraft for launch. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- At Vandenberg Air Force Base in California, technicians prepare to mate the AIM spacecraft (at left) to the SoftRide isolation system on the Orbital Sciences Pegasus XL rocket. The Cosmic Dust Experiment surfaces can be clearly seen as 12 rectangular areas on the aft portion of the spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch from the Pegasus XL rocket is scheduled for April 25.

At Vandenberg Air Force Base in California, technicians prepare the AIM spacecraft for fairing installation. The fairing is a molded structure that fits around the spacecraft and forms an aerodynamically smooth nose cone, protecting the spacecraft during launch. Launch will be from a Pegasus XL rocket, carried and released by Orbital Sciences L-1011 jet aircraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians look over the spacecraft handling fixture that will be used to lift the AIM spacecraft. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians carry the separation system, at left, toward the AIM spacecraft hovering above the stand at right. AIM, which stands for Aeronomy of Ice in the Mesosphere, is being prepared for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

ISS017-E-011632 (22 July 2008) --- Polar Mesospheric Clouds (also known as noctilucent clouds) are transient, upper atmospheric phenomena observed usually in the summer months at high latitudes (greater than 50 degrees) of both the Northern and Southern Hemispheres. They are bright and cloudlike in appearance while in deep twilight. They are illuminated by sunlight when the lower layers of the atmosphere are in the darkness of the Earth's shadow. This image was acquired at an altitude of just over 200 miles in the pre-dawn hours of July 22, 2008 as the International Space Station was passing over western Mongolia in central Asia. The dark horizon of the Earth appears below with some layers of the lower atmosphere already illuminated. The higher, bluish-colored clouds look much like wispy cirrus clouds which can be found in the troposphere as high as 60,000 feet. However noctilucent clouds, as seen here, are observed in the mesosphere at altitudes of 250,000 to 280,000 feet. Astronaut observations of Polar Mesospheric Clouds (PMC) over northern Asia in June and July are not uncommon. The Expedition 17 crew of the International Space Station acquired this image, and more, in support of research for the International Polar Year. Some researchers link increased observations of PMC to changes in global climate; PMC have been the subject of extensive observation and research from space by the Swedish satellite Odin launched in 2001 and more recently by NASA's Aeronomy of Ice in the Mesosphere (AIM) satellite system beginning in 2007.

S117-E-06998 (10 June 2007) --- Polar Mesospheric Clouds are featured in this image photographed by a STS-117 crewmember onboard Space Shuttle Atlantis. Sometimes in the summertime in the far northern (or southern) latitudes, high in the Earth's atmosphere at the edge of space, thin silvery clouds form and are observed just after sunset. These high clouds, occurring at altitudes of about 80 kilometers (50 miles), are called Polar Mesospheric Clouds (PMC) or noctilucent clouds, and are the subject of new studies to determine whether their occurrence is related to global climate change. Observations over the past few years suggest that PMC are now observed more frequently and at lower latitudes than historical observations. Several studies related to the International Polar Year (IPY), and the AIM (Aeronomy of Ice in the Mesosphere) spacecraft are underway to collect relevant data on the chemistry and physics of the mesosphere that might explain the occurrence of PMC. Astronauts in orbiting spacecraft frequently observe PMC over Canada, northern Europe and Asia during June, July and August. While PMC also occur over the high latitudes in the southern hemisphere in December, January and February, astronaut observations of southern PMC are less frequent. Earlier in June 2007, the shuttle crew visiting the International Space Station observed spectacular PMC over north-central Asia. This image was taken looking north while the shuttle and station were docking and flying over the border between western China, Mongolia and Kazakhstan. The red-to-dark region at the bottom of the image is the dense part of the Earth's atmosphere. Because this image was taken with a long lens (180mm), the entire profile of the Earth's limb is not captured. To support IPY research over the next 2 years, station crewmembers will be looking for and documenting PMC in both hemispheres.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, two of the solar array panels on the AIM spacecraft are deployed for testing. Inside are the instruments that will study polar mesospheric clouds located at the edge of space. The AIM spacecraft will fly three instruments designed to study those clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, two of the solar array panels on the AIM spacecraft are deployed for testing. Inside are the instruments that will study polar mesospheric clouds located at the edge of space. The AIM spacecraft will fly three instruments designed to study those clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, two of the solar array panels on the AIM spacecraft are deployed for testing. Inside are the instruments that will study polar mesospheric clouds located at the edge of space. The AIM spacecraft will fly three instruments designed to study those clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, two of the solar array panels on the AIM spacecraft are deployed for testing. Inside are the instruments that will study polar mesospheric clouds located at the edge of space. The AIM spacecraft will fly three instruments designed to study those clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, two of the solar array panels on the AIM spacecraft are deployed for testing. Inside are the instruments that will study polar mesospheric clouds located at the edge of space. The AIM spacecraft will fly three instruments designed to study those clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, two of the solar array panels on the AIM spacecraft are deployed for testing. Inside are the instruments that will study polar mesospheric clouds located at the edge of space. The AIM spacecraft will fly three instruments designed to study those clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In Building 1555 at North Vandenberg Air Force Base, workers lower the AIM spacecraft onto a moveable base. AIM will be moved into an area where a partial deployment of the solar arrays on the spacecraft will take place.The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 at North Vandenberg Air Force Base, workers roll the AIM spacecraft into the "tent" where a partial deployment of the solar arrays on the spacecraft will take place. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians look at an area of the AIM spacecraft. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- Inside the clean-room 'tent' of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians look at part of the AIM spacecraft. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians look at part of the AIM spacecraft. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, a technician places a star tracker cover on the AIM spacecraft during testing of the solar array panel deployment. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians work on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians place a star tracker cover on the AIM spacecraft during testing of the solar array panel deployment. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians look at an area of the AIM spacecraft. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians place a star tracker cover on the AIM spacecraft during testing of the solar array panel deployment. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In Building 1555 at North Vandenberg Air Force Base, workers roll the AIM spacecraft into the "tent" where a partial deployment of the solar arrays on the spacecraft will take place. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, a star tracker cover is ready for placement on the AIM spacecraft during testing of the solar array panel deployment. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. AIM will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

KENNEDY SPACE CENTER, FLA. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, a technician places a star tracker cover on the AIM spacecraft during testing of the solar array panel deployment. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians prepare the AIM spacecraft for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In a clean-room environment at North Vandenberg Air Force Base, technicians work on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

VANDENBERG AIR FORCE BASE, CALIF. -- In a clean-room environment at North Vandenberg Air Force Base, technicians remove covers from instruments in the AIM spacecraft while solar panels are partially deployed. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians prepare the AIM spacecraft for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians prepare the AIM spacecraft for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

Inside the clean-room "tent" of Building 1555 at North Vandenberg Air Force Base, technicians in bunny suits prepare for the solar array deployment on the AIM spacecraft. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 at North Vandenberg Air Force Base, workers prepare the area where a partial deployment of the solar arrays on the AIM spacecraft will take place. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to the Pegasus XL during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.

In Building 1555 on North Vandenberg Air Force Base in California, technicians prepare the AIM spacecraft for integrated testing and a flight simulation. The AIM spacecraft will fly three instruments designed to study polar mesospheric clouds located at the edge of space, 50 miles above the Earth's surface in the coldest part of the planet's atmosphere. The mission's primary goal is to explain why these clouds form and what has caused them to become brighter and more numerous and appear at lower latitudes in recent years. AIM's results will provide the basis for the study of long-term variability in the mesospheric climate and its relationship to global climate change. AIM is scheduled to be mated to its launch vehicle, Orbital Sciences' Pegasus XL, during the second week of April, after which final inspections will be conducted. Launch is scheduled for April 25.