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The ISTP program promises progress through the 1990s and beyond with measurements that will provide first comprehensive, quantitative assessment of how energy is transferred and stored in the solar-terrestrial environment. From that assessment, scientists the world over will gain not only a deeper understanding of the physical processes that shape our environment, but also the information necessary to model it on a global scale. NASA, the European Space Agency (ESA) and Japan's Institute of Space and Astronautical Science (ISAS) are collaborating with scientists and technicians from 18 countries and more than 100 institutions to build on our understanding of solarterrestrial processes.
The program is managed by NASA's Goddard Space Flight Center in Greenbelt, Md., for the Office of Space Science at NASA Headquarters in Washington, D.C.
The scientific objectives of ISTP are to develop a comprehensive, global understanding of the flow of energy from the Sun through the Sun's space environment through the heliosphere to the Earth's space environment, or geospace. In developing this understanding, ISTP participants expect to define the cause-and-effect relationships between the physical processes that link different regions of this dynamic environment.
The program includes five spaceflight missions Wind, Polar, Geotail, SOHO and Cluster with one or more spacecraft provided by each agency and a data networking system to make the collected data base accessible to the worldwide science community.
Global Geospace Science (GGS) is the phase of ISTP that will focus on the global flow of energy from the solar wind which are high-energy particles emitted by the Sun through the three regions of geospace: the magnetosphere (the outermost region of geospace), the ionosphere (the area above the Earth's atmosphere) and the atmosphere. The GGS program is a subset of ISTP. GGS will provide the Wind and Polar satellites and use data from the Geotail satellite to perform measurements in key geospace regions.
The magnetosphere begins about 380 miles (611 kilometers) above the Earth's surface. The ionosphere extends above the atmosphere to the magnetosphere, beginning about 25 miles (40 kilometers) above the surface.
The GGS program has four main objectives:
While past programs have advanced understanding of geospace components individually, an understanding of this region as a whole requires a planned program of simultaneous observations. These observations need to be keyed to a global assessment of the production, transfer, storage and dissipation of energy throughout geospace. GGS is a comprehensive, quantitative study of the solar-terrestrial energy chain. The GGS spacecraft will make measurements of key geospace phenomena such as solar wind and the geomagnetic tail region.
Each of the GGS spacecraft will be launched by NASA on Delta II rockets. Each will carry a liquid propulsion system to maneuver the spacecraft to its final mission orbit and permit attitude control and stationkeeping during the mission lifetime of at least three years. The Wind and Polar satellites are provided by NASA. Geotail is provided by ISAS. The GGS spacecraft will be positioned in different regions of the magnetosphere to provide measurements and data on processes that occur from interactions between the Sun and Earth. They are designed to monitor the cause and effect of events at the Sun that trickle down into the Earth's atmosphere.
All of the ISTP spacecraft are scheduled to be launched by 1996.
WIND: Launched in November 1994, Wind is provided by NASA and has a payload instrumentation from NASA, ESA and the former Soviet Union. Wind will use lunar swingby orbit adjustments to measure properties of the solar wind plasma before it reaches the Earth. It also will observe the volume of geospace called foreshock, where turbulence is produced by particles reflected from the interaction of the solar wind as it approaches the Earth's magnetic field. One of the eight instruments aboard Wind will be Konus, a Russian research instrument designed to detect gammaray bursts. Konus is the first instrument from the former Soviet Union to fly on a NASA spacecraft.
POLAR: Scheduled for launch in December 1995, Polar will measure energy input to the Earth's polar regions. It will provide complete coverage of the inner magnetosphere, obtain global images of the polar aurora and provide complementary data to the Upper Atmosphere Research Satellite (UARS).
Polar also will measure high-latitude solar wind entry and ionospheric plasma entry, plus energy deposition into the aurora - upper atmosphere. The Polar spacecraft is designed to have onboard interconnection of instrumentation for electronic communication. This important feature makes it possible to share data efficiently among the instruments by using sophisticated onboard computers. The spacecraft will contain 11 instruments.
ESA's Contribution
The remaining spacecraft represent ESA's contribution to the program, referred to as the Collaborative SolarTerrestrial Science Research (COSTR) program. ESA is responsible for system design and spacecraft development. COSTR provides the NASA contributing elements to the Geotail, Solar and Heliospheric Observatory (SOHO) and Cluster missions. The instrumentation, mission operations, launch and network support will be shared by NASA and ESA. The spacecraft involved in this phase are:
GEOTAIL: In July 1992, Geotail was the first ISTP spacecraft to be launched. The satellite was built by ISAS and launched by NASA. Geotail measures the flow of energy and its transformation in the magnetotail created by the interaction between the solar wind and the Earth. Geotail also determines, in detail, the overall plasma characteristics of the distant geomagnetic tail - a cometlike tail of plasma millions of miles long created by the solar wind. Following a year of deep-tail observations, an orbit-adjust engine will be used to place Geotail in a neartail orbit to identify regions of explosive plasma transformations. There are seven instruments aboard this spacecraft.
SOHO: The Solar and Heliospheric Observatory (SOHO) spacecraft will study the physical processes taking place in the Sun's corona and changes in the Sun's interior by conducting remote sensing observations in visible, ultraviolet and extreme ultraviolet light. Its scheduled launch date is November 1995. SOHO will carry 12 U.S. and European instruments. SOHO also is expected to probe the interior structure of the Sun and investigate its outer layers to better understand the energy deposit and acceleration of plasma and particles into the solar wind. SOHO will conduct investigations through a process known as helioseismology, which studies the Sun's internal dynamics and structure by observing oscillations vibrations of the Sun's surface.
CLUSTER: Set to be launched in December 1995, Cluster is a set of four spacecraft developed by ESA. Cluster will be placed in a polar orbit that will take the spacecraft through key regions of geospace. The Cluster mission will provide information on small-scale structure and on plasma turbulence throughout the polar and middle magnetosphere, as well as in the solar wind. Cluster will determine the small-scale structure of the solar wind flow around the Earth and use the fourspacecraft configuration to determine the threedimensional shape and dynamics of magnetic structures.
The countries involved with ISTP through spacecraft development and scientific investigations are: Australia, Austria, Belgium, Canada, England, Finland, France, Germany, Greece, Holland, Ireland, Italy, Japan, Norway, Sweden, Switzerland, United States and the former Soviet Union .
NASA/Goddard Space Flight Center, Greenbelt, Md.
Joe Dezio, GGS project manager, Flight Projects Directorate
K. Sizemore, ISTP project manager, Flight Projects Directorate
Dr. M. Acuna, GGS project scientist, Space Sciences Directorate
Last Revised: 29 August 1995