Pegasus XL launches with AIM spacecraft

NASA’s Launch Services Program at Kennedy Space Center, Florida, is managing the AIM launch, and Orbital Sciences Corporation is conducting launch services. The previous Pegasus mission was with ST-5, which successfully launched on March 22, 2006.

With all the interest surrounding SpaceX’s Falcon I launch vehicle of late, many forget that Pegasus was the world’s first privately developed space launch vehicle. Its maiden 1990 mission marked the first all-new, unmanned space launch vehicle developed in the US in more than 20 years.

Other landmarks included the Pegasus being the first winged vehicle to accelerate to eight times the speed of sound, and the first air-launched rocket to place satellites into orbit, using its carrier aircraft as an ‘air breathing reusable first stage.’

The three-stage Pegasus is used by commercial, government and international customers to deploy small satellites weighing up to 1,000 pounds into low-Earth orbit.

Pegasus is carried aloft by the ‘Stargazer’ L-1011 aircraft to approximately 40,000 feet over open ocean, where it is released and then free-falls in a horizontal position for five seconds before igniting its first stage rocket motor. With the aerodynamic lift generated by its unique delta-shaped wing, Pegasus typically delivers satellites into orbit in a little over 10 minutes, which it has done 37 times before, carrying 78 satellites in the process.

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.

‘These clouds are indicators of conditions in the upper reaches of the Earth’s atmosphere, and are an important link in the chain of processes that result in the deposition of solar energy into Earth’s atmosphere,’ said Mary Mellott, AIM program scientist, NASA Headquarters, Washington.

‘AIM will provide an understanding of how and why these clouds form, an important contribution toward the NASA goals of understanding the fundamental physical processes of our space environment and how the habitability of planets is affected by the interaction of planetary magnetic fields and atmospheres with solar variability.’

The clouds are noctilucent, meaning they can be seen from the ground only at night, when they are illuminated by sunlight no longer visible from the Earth’s surface. The brightest of these clouds are now known to be primarily composed of water ice.

Their seasonal lifecycle is controlled by complex interactions between temperature, water vapor, solar activity, atmospheric chemistry and small particles on which the cloud crystals form. Human-induced factors such as carbon dioxide cause a warming in the lower atmosphere but a cooling in the mesosphere.

The clouds form in the coldest part of the Earth’s atmosphere at the summer season in the polar regions. In the northern hemisphere they begin appearing in mid-May and last through mid-August, in the southern hemisphere beginning mid-November and lasting through mid-March.

‘The occurrence of these clouds at the edge of space and what causes them to vary is not understood,’ said AIM principal investigator James Russell III, Hampton University.

‘One theory is that the cloud particles grow on ‘seeds’ of meteoric dust or dust lofted up from below. AIM will provide the comprehensive data needed to test current theories for cloud formation or develop new ones, and allow researchers to build tools to predict how they will change in the future.’

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.

‘This Small Explorer mission is a good example of the huge science returns we can get for a relatively small cost investment,’ said Vicki Elsbernd, program executive for the AIM mission, NASA Headquarters.