The CloudSat mission was selected under NASA's Earth System Science Pathfinder program in 1999. Overseen by NASA's Science Mission Directorate, the Earth System Science Pathfinder Program sponsors missions designed to address unique, specific, highly focused scientific issues, and to provide measurements required to support Earth science research. Missions selected in this program are small- to- medium-sized and are capable of being built, tested, and launched quickly. They support a variety of scientific objectives related to Earth science, including studies of the atmosphere, oceans, land surface, polar ice regions, and solid Earth.
CloudSat's primary mission is scheduled to continue for 22 months after launch in 2006, in order to allow more than one seasonal cycle to be observed, although radar lifetime data indicates that the radar is expected to operate for three years with a 99 percent probability.
Launch Site and Vehicle
CloudSat and CALIPSO were launched together from Space Launch Complex 2W at Vandenberg Air Force Base, California, on a two-stage Delta 7420-10C launch vehicle with a dual payload attachment fitting (DPAF). The Delta II launch vehicle has a history of more than 300 successful launches, with a 98 percent success rate. Delta II payload capabilities range from 2.7 to 5.8 metric tons (6,020 to 12,820 pounds) to low Earth orbit.
The Delta launch vehicle features a liquid-fueled first stage with four strap-on solid fuel boosters and a second-stage liquid-fueled engine. With its payloads, the vehicle stood 39 meters (128 feet) tall.
The first stage of the Delta II uses a Rocketdyne RS-27A main engine. The engine provides nearly 920,782 newtons (207,000 pounds) of thrust by reacting RP-1 fuel (thermally stable kerosene) with liquid oxygen. The four solid rocket motors are 102 centimeters (40 inches) in diameter and fueled with enough hydroxyl-terminated polybutadiene solid propellant to provide about 431,478 newtons (97,000 pounds) of thrust each.
The Delta's second stage is powered by a restartable Aerojet AJ10-118K engine, which produces about 42,703 newtons (9,600 pounds) of thrust. The engine uses a fuel called Aerozine 50, which is a mixture of hydrazine and dimethyl hydrazine, reacted with nitrogen tetroxide as an oxidizer.
Launch TimingUnlike spacecraft sent to other planets, comets or asteroids, the launches of Earth-orbiting satellites such as CloudSat and CALIPSO do not need to be timed based on the alignment of the planets. The launch date is based only on the readiness of the satellites, the Delta launch vehicle, and the launch range at Vandenberg Air Force Base.
Earth-orbiting satellites do, however, need to be launched during particular windows within any given 24-hour day in order to get into the proper orbit around Earth. CloudSat and CALIPSO were launched into a sun-synchronous orbit flying close to Earth's north and south poles. In order to achieve this orbit, the satellite could only be launched during a daily near-instantaneous launch window. On the actual launch date (28 April 2006), launch occurred at 3:02:16.721 AM PDT (10:02:16.721 UTC).
When the Delta II launches, its first-stage engine and its four strap-on boosters ignite at the moment of liftoff and the rocket rises vertically from the launch pad and then heads south over the Pacific Ocean. Sixty-four seconds after liftoff the strap-on boosters burn out and their spent casings are jettisoned approximately 83 seconds after liftoff.
About four minutes and 24 seconds into the flight, the main engine cuts off. About 14 seconds later, the second stage ignites, and five seconds later, the nose cone, or 'fairing' falls away. At about 11 minutes and 10 seconds after liftoff, the second-stage engine temporarily stops firing.
At about 59 minutes and 56 seconds after liftoff, the second stage restarts, burning 11 seconds before shutting down. At this point, the spacecraft with the second stage of the Delta still attached is in a circular parking orbit 695 kilometers (375 nautical miles) above Earth. CALIPSO spacecraft separation occurs approximately 62 minutes after liftoff, and CloudSat separates approximately 97 minutes after liftoff.
After separation, CloudSat deployed its solar arrays and pointed its mission instruments at Earth using three-axis attitude control. All sensors and units were checked, and about 34 days after launch, CloudSat was maneuvered into its operational circular, sun-synchronous orbit about 705 kilometers (438 miles) above Earth.