WIND SPACECRAFT TO STUDY SOLAR BREEZE

The Mission

The orbiting Wind spacecraft is the first of two missions of the Global Geospace Science (GGS) initiative, which is the United States portion of a worldwide collaboration called the International Solar-Terrestrial Physics (ISTP) program. The aim of ISTP is to understand the physics of the behavior of the solar-terrestrial system in order to predict how the Earth's atmosphere will respond to changes in solar wind. GGS is being managed by the Goddard Space Flight Center in Greenbelt, Md., for the Office of Space Science at NASA Headquarters in Washington, D.C. Wind was launched November 1 1994 on a Delta II rocket from Cape Canaveral Air Station, Fla.

The second GGS satellite, Polar, was launched February 24, 1996. to measure the flow of plasma - a wind of electrified particles - within the Earth's magnetosphere, which is the region around the planet dominated by the Earth's magnetic field. These missions will perform simultaneous and closely coordinated measurements of the key regions of Earth's geospace, or space environment. Data also will be provided from missions in equatorial orbits. In addition, ground-based and theoretical investigations will be conducted.

In addition to GGS, another element of ISTP is the Collaborative Solar-Terrestrial Research (COSTAR) program. As part of COSTR, NASA is collaborating with the The Japanese and Europeans on three solar-terrestrial missions. The first was the Geotail satellite, provided by the Japanese Institute of Space and Astronautical Science (ISAS) and launched in July 1992 to explore the tail of the magnetosphere. Geotail will be followed by the Solar and Heliospheric Observatory (SOHO) and the four-spacecraft Plasma Turbulence Laboratory (CLUSTER) mission.

WIND SPACECRAFT

The Wind spacecraft will carry six U.S. instruments, one French instrument and the first Russian instrument ever to fly on an American satellite. The satellite will be put into a figure-eight orbit around the Earth with the assistance of the moon's gravitational field. The furthest point from the Earth on the orbit - the apogee - will be as far as 250 Earth radii (990,000 miles, or 1,600,000 kilometers). The closest point to Earth - the perigee - will be at least 4.5 Earth radii (18,000 miles, or 29,000 kilometers). Later, the Wind spacecraft will be inserted into a small circular orbit in the solar wind upstream from the Earth around the point where the gravity of the Earth and Sun are balanced (Approximately 990,000 miles or 1,6000,000 kilometers from the Earth).

The Science

Energy streams out from the Sun toward the Earth in a solar wind of electrified particles. Moving at a million miles per hour, this hot, ionized gas - called plasma - carries particles and magnetic fields from the Sun outward past the planets. The Earth is shielded from the full blast of these particles by its magnetosphere. The existence of the solar wind was first confirmed in the early 1960's by NASA's Mariner 2 spacecraft. Subsequent exploration of the Earth's geospace has revealed a dynamic and complex system of interacting plasma, magnetic fields and electrical currents.

The Wind mission is designed to measure properties of the solar wind before it reached the Earth. Wind first will take readings in the turbulent area where particles of the solar wind are reflected from a shock wave that forms when this wind encounters the Earth's magnetic field. This supersonic shock wave, known as the bow shock, occurs in front of the magnetosphere where the outward force of the compressed geomagnetic field is balanced by the force of the solar wind. Later, Wind will be repositioned in to a circular orbit between the Sun and the Earth to observe the solar wind before it intercepts the magnetosphere.

THE WIND INVESTIGATIONS

Radio and Plasma Waves (Waves), Dr. Mike Kaiser, GSFC - The Sun and the Earth's magnetosphere emit radio waves that affect particles in the interplanetary plasma and carry some of the energy flowing there. The Radio and Plasma Waves instrument will measure the properties of these waves and other wave modes of the plasma over a very wide frequency range.

Solar Wind Experiment (SWE), Dr. K. Ogilvie, NASA /Goddard Space Flight Center - SWE will measure ions and electrons in the solar wind and the foreshock regions at a rate of once per minute for ions and 20 times per minute for electrons. Measurements made in the foreshock are important for understanding the structure of the bow shock. From these measurements, the solar-wind velocity, density, temperature and heat flux can be deduced. Electron and ion velocity distributions should reveal properties of the flowing plasmas and their pivotal role in the transfer of mass, momentum and energy from the Sun to the Earth. Because the solar wind is an extension of the corona, from which it is accelerated, these measurements also assist in studies of the Sun.

Magnetic Field Investigation (MFI), Dr. R. Lepping, NASA/Goddard Space Flight Center - MFI will investigate the structure, intensity and fluctuations of the interplanetary magnetic field, which influence the transport of energy and the acceleration of particles in the solar wind. The magnetic field measurements from MFI are especially important to the interpretation of other data from Wind.

Energetic Particle Acceleration, Composition, and Transport (EPACT), Dr. T. von Rosenvinge, NASA/Goddard Space Flight Center - The EPACT investigation will measure properties of high-energy ions in the solar wind. This direct sampling of solar matter is a way to study events on the solar surface and the incorporation of solar material into the solar wind. Because of their distinctive high charge, solar-wind ions can be used as tracers for the transfer and flow of particles from the solar wind into the magnetosphere. EPACT also will provide information on shock waves in the interplanetary medium.

Solar Wind and Suprathermal Ion Composition and Mass Measurements (SMS), Dr. G. Gloeckler, University of Maryland - This investigation will determine the abundance, velocity, spectra, temperature and thermal speeds of solar-wind ions. The SMS instruments will enable the isotopes of many elements to be studied. These ion studies, along with the EPACT and other plasma investigations, will provide additional analysis of the events on the solar surface. This investigation will add to our knowledge of how the solar wind is formed and accelerated from the solar surface into the interplanetary medium.

Three-Dimensional Plasma Analyzer and Energetic Particle Analyzer (3-D Plasma), Dr. R. Lin, University of California at Berkeley - This investigation will measure ions and electrons with energies above that of the solar wind and into the energetic particle range. It will study particles upstream of the bow shock and in the foreshock region, as well as the transient particles emitted by the Sun during solar particle events following solar flares. In addition, this instrument will cover the energy gap between the SWE and EPACT instruments.

Transient Gamma-Ray Spectrometer(TGRS), Dr. B. Teegarden, NASA/Goddard Space Flight Center - TGRS will observe transient gamma-ray events. It will make the first high-resolution spectroscopic survey of cosmic gamma-ray lines in solar flares. The causes of the transient events, which occur at great distances from the Earth, represent one of the intriguing mysteries of present-day astrophysics.

Russian Gamma-Ray Spectrometer (KONUS), Dr. E. Mazets, Ioffe Institute, Russia and T. Kline, NASA/Goddard Space Flight Center - Konus will perform gamma-ray burst studies similar to the TGRS studies, but at lower resolution with broader coverage. When their data are combined, they provide coverage of the full sky. Konus also will perform event detection and measure time history. The Konus investigation is the first Russian instrument to fly on an American satellite.

The Wind Spacecraft and Mission Operations

Wind is a spin-stabilized (20 rpm) cylinder-shaped spacecraft measuring 7.87 feet (2.4 meters) in diameter and 5.91 feet (1.8 meters) in height. The dry weight of the spacecraft is 1,973 pounds (895 kilograms), with an additional 662 pounds (300 kilometers) of hydrazine propellant for orbit and attitude control. The minimum design life of Wind is three years.

Several NASA and NASA/Goddard Space Flight Center facilities will play key roles in the collection and dissemination of Wind science data. The NASA Deep Space Network will be used to command the spacecraft and collect Wind data via radio link. At Goddard, raw data will be processed, organized and stored. The Central Data Handling Facility will produce "key parameters" that will serve as a guide to the much larger volume of raw data. Detailed analysis of the data will be performed by investigators using their own computers at their sites, sharing the data through NASA Science Internet connections in the United States, Japan and Europe.

Management

Office of Space Science, NASA Headquarters, Washington, D.C.
W.T. Huddleston, program manager, Space Physics Division
Dr. Robert Carovillano, program scientist, Space Physics Division

NASA/Goddard Space Flight Center, Greenbelt, Md.
Joe Dezio, project manager, Flight Projects Directorate
Dr. M. Acuna, project scientist, Space Sciences Directorate