Ranger (spacecraft) - astronomy.

Ranger (spacecraft) - astronomy. I INTRODUCTION Ranger (spacecraft), series of nine, unpiloted, United States space probes, launched from 1961 to 1965, designed for exploration of the moon. The National Aeronautics and Space Administration (NASA) designed the Ranger program to test management techniques, procedures, and technology necessary for later lunar and interplanetary probes. Early Ranger probes were equipped with scientific instruments to study space between the moon and the earth. Later probes in the series were designed for lunar impact, in which television cameras transmitted detailed images of the moon's surface before the spacecraft crashed into the moon. Ranger was also expected to improve upon the disappointing performance of early U.S. Pioneer lunar probes. The Ranger program was spurred by the Union of Soviet Socialist Republics (USSR), which launched Luna 2 in 1959, the first spacecraft to impact the moon. II SPACECRAFT Rangers 1 and 2 were intended for basic flight testing of spacecraft systems and space study. Weighing about 306 kg (about 820 lb), Rangers 1 and 2 carried a high gain antenna that swung out from under the bus, or main body, for data transmission back to the earth. A tower housed the low gain antenna and scientific instruments. Two solar panels (see Solar Energy) provided electrical power for the main spacecraft battery. Attitude control was maintained by nitrogen gas jets, which kept the solar panels continuously facing the sun and the high gain antenna directed toward the earth. Rangers 3, 4, and 5 were designed for lunar impact and for transmitting pictures just prior to crashing. In addition, these Rangers were equipped with instruments, such as a seismometer (see Seismology: Means of Study) that ejected from the spacecraft bus and crash-landed onto the lunar surface to study so-called moonquakes (like earthquakes on the earth). Rangers 3, 4, and 5 weighed about 330 to 345 kg (about 880 to 925 lb). The cameras included two 25-mm wide-angle and four 75-mm telephoto lenses. The first five Ranger probes failed in some way, so project officials simplified the next Ranger missions in hopes of a better success rate. They eliminated all scientific experiments except for the cameras for Ranger 6, 7, 8, and 9. Each of these later craft weighed about 365 kg (about 805 lb). All nine Rangers were launched using an Atlas-Agena B rocket, a military intercontinental ballistic missile. The Ranger probes communicated with ground control through tracking stations at Goldstone, California; Johannesburg, South Africa; and Woomera, Australia. III MISSIONS Ranger 1 was launched on August 23, 1961. The craft encountered problems almost immediately when its Agena rocket failed to boost the probe into an orbit suitable for effective spacecraft operations. Ranger 1 reentered the earth's atmosphere and disintegrated seven days later. Ranger 2 was launched on November 18, 1961. This flight also failed as another rocket malfunction sent the craft tumbling back to the earth after two days in an ineffective low orbit. Ranger 3, designed for lunar impact, was launched on January 26, 1962. Another rocket engine malfunction caused the probe to miss the moon and go into orbit around the sun. Ranger 4 was launched on April 23, 1962. Though successful in reaching the moon and crashing on its surface, the probe's central computer failed, rendering all scientific instruments and cameras inoperative. Lift-off for Ranger 5 was on October 18, 1962. An on-board power failure caused the probe to miss the moon and enter solar orbit. Ranger 6 was launched on January 30, 1964. Lunar impact was achieved but no images could be transmitted. Success finally came to the project after Ranger 7's launch on July 28, 1964. On July 31, the probe transmitted over 4000 close-up pictures of the Mare Vaporum (Sea of Clouds) region of the moon before impact. Ranger 8, launched on February 17, 1965, repeated Ranger 7's success. Before impact on Mare Tranqillitas (Sea of Tranquillity), the probe transmitted over 7000 pictures. Ranger 9 was launched on March 21, 1965. Three days later, it transmitted over 5500 images before impact in the Alphonsus crater. Despite its early failures, Project Ranger provided NASA with the technology and expertise for launching and operating later robotic space probes, including the Surveyor and Lunar Orbiter lunar projects of 1966 to 1968. Ranger also gathered valuable information regarding surface features of the moon, which proved useful to the Apollo program, America's piloted lunar landing effort. Contributed By: Mark E. Kahn Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.