Dolores Beasley Headquarters, Washington, DC August 7, 2000 (Phone: 202/358-1753) Susan Hendrix Goddard Space Flight Center, Greenbelt, MD (Phone: 301/286-7745) RELEASE: 00-118 REVISED - SECOND CLUSTER LAUNCH TO COMPLETE ON ORBIT QUARTET The two remaining Cluster spacecraft, set to launch later this week, will rendezvous in mid-August with their two sister ships, creating a fleet that will explore a vast but invisible magnetic ocean that surrounds our Earth. This mysterious region we know as the magnetic field holds off a million mile-per-hour solar wind, and it's where million-amp electric currents surge and ignite a show seen as the northern and southern lights. Lift-off for the second Cluster duo, named Rumba and Tango, is scheduled for 7:13 a.m. EDT on Wednesday, Aug. 9, aboard a Russian Soyuz rocket from Baikonur, Kazakhstan. "NASA and the U.S. scientific community are very excited and pleased with the first launch of Cluster spacecraft and eagerly await the second launch," said Larry Christensen, Cluster project manager at NASA's Goddard Space Flight Center, Greenbelt, MD. "This international mission will help us better understand a mysterious region of our space environment that can affect spacecraft and electrical power grids on Earth." The Earth's magnetic field, called the magnetosphere, is relentlessly blasted and energized by the solar wind, a stream of electrically charged particles that flows constantly from the Sun. During the next two years, as the solar wind buffets Earth's magnetic sea, the Cluster II fleet will penetrate its depths to see how the Earth's magnetosphere responds and interacts with solar wind particles. By flying in a tetrahedral - or triangular pyramid- formation, the Cluster quartet will study the physical processes that take place between about 11,800 miles (19,000 km) and nearly 74,000 miles (119,000 km) above Earth, providing scientists with the first thorough three-dimensional maps of this shadowy realm. The first Cluster pair, called Samba and Salsa, launched July 16, reached their parking elliptical orbit on July 21 after a complex series of maneuvers. They await the arrival of the sister spacecraft, Rumba and Tango, to achieve their final observational orbit. The space quartet will orbit at an apogee of more than 75,200 miles (121,098 km) and a perigee of nearly 10,500 miles (16,869 km) above Earth. Cluster will join the Solar and Heliospheric Observatory (SOHO) as the second cooperative solar- terrestrial project between NASA and the European Space Agency (ESA). In support of this ESA mission, NASA will provide project management and funding for the U.S. principal investigator and co-investigator hardware investigations, assist ESA managers with launch and early operations support, provide scheduling support, and transmit data from the Wide Band Data experiment on each spacecraft to the University of Iowa via NASA's Deep Space Network. For a listing of the instruments aboard Cluster, go to: You also can view a live webcast of the Aug. 9 launch from the ESA website at: - end -