The third stage of the Orbital Sciences Pegasus XL rocket is bei

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.