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WIND

artist concept of Wind in space
Credit: NASA

* Mission Overview

After its November 1, 1994, launch NASA's Wind satellite took up a vantage point between the Sun and the Earth, giving scientists a unique opportunity to study the enormous flow of energy and momentum known as the "solar wind". The main scientific goal of the mission is to measure the mass, momentum and energy of the solar wind that somehow is transferred into the space environment around the Earth. Onboard are the hot plasma and charged particles Three-Dimensional Plasma analyzer (3DP) experiment, the Transient Gamma-Ray Spectrometer (TGRS), the Magnetic Fields Instrument (MFI), the Plasma and Radio Waves (WAVES) experiment, the Solar Wind Experiment (SWE), the Energetic Particle Acceleration, Composition and Transport (EPACT) experiment, the Solar Wind and Suprathermal Ion Composition Studies (SWICS/STICS) experiment and the Gamma Ray Burst Detector (KONUS).

At first, the satellite had a lunar swingby orbit around the Earth. With the assistance of the Moon's gravitational field Wind's apogee was kept over the day hemisphere of the Earth and magnetospheric observations were made. Later in the mission, the Wind spacecraft was inserted into a special "halo" orbit in the solar wind upstream from the Earth, about the sunward Sun-Earth equilibrium point (L1). The satellite has a spin period of ~ 20 seconds, with the spin axis normal to the ecliptic.

* Instrumentation

TGRS

The Transient Gamma-Ray Spectrometer (TGRS) detects transient
gamma-ray burst events. The Principal Investigator is B. Teegarden. TGRS was intended to make the first high-resolution spectroscopic survey of cosmic gamma-ray bursts, and to make measurements of gamma-ray lines in solar flares. The detector covers the energy range 15 keV - 10 MeV, with an energy resolution of 2.0 keV @ 1.0 MeV (E/delta E = 500). The instrument was also designed to monitor the time variability of the 511 keV line emission from the galactic center, on time scales from ~2 days to >1 year.

The TGRS instrument consists of four assemblies: detector cooler assembly, pre-amp, and analog processing unit, all mounted on a tower on the +Z end of the spacecraft, and a digital processing unit mounted in the body of the spacecraft. The detector is a 215 cubic cm high purity n-type germanium crystal of dimensions: 6.7 cm (diameter) X 6.1 cm (length), radiatively cooled to 85 degrees K. The germanium serves as a reaction medium for incoming gamma rays, which, depending on their energy, are either stopped by or passed through the detector crystal. Particle energy and angle of incidence are calculated based on a number of primary and secondary interaction processes, including photoelectric, Compton, pair and bremsstrahlung radiation as well as the ionization energy losses of secondary electrons. A two-stage cooler surrounds the detector, providing a field of view of 170 degrees. Gamma-ray bursts and solar flares are expected to be detected at a frequency of several per week, with typical durations between 1 second and several minutes. Between bursts the instrument is maintained in a waiting mode, measuring background counting rates and energy spectra. When a burst or flare occurs, the instrument switches to a burst mode, where each event in the detector is pulse-height analyzed and time tagged in a burst memory. Then the instrument switches to a dump mode for reading out the burst memory. The experiment was a collaboration between NASA-Goddard Space Flight Center and the Centre e'Etudes Spatiales des Rayonnements/Toulouse.

KONUS

The Konus experiment provides omnidirectional and continuous coverage of cosmic gamma-ray transients. It is the first Russian scientific instrument to fly on an American satellite since space cooperation between the U.S. and Russia was resumed in 1987. The Principal Investigator (PI) is E. P. Mazets of the Ioffe Institute in St. Petersburg, Russia, and the Co-PI is T. L. Cline of Goddard. The instrument monitors cosmic gamma-ray bursts (GRBs), soft gamma repeaters (SGRs), solar flares, and other transients with the moderate energy resolution available from scintillation spectrometers. It provides event time profiles in three energy ranges, from 10 to 770 keV, with 64-millisecond time resolution. In addition, 2-millisecond resolution is provided during high-intensity portions of events. The instrument also monitors the gamma-ray and particle backgrounds continuously, except for interruptions to readout burst profiles.

The Konus instrument consists of two detectors and an electronics package from Russia, and an interface unit from Goddard. The two identical detectors are mounted on the top and bottom of the spacecraft aligned with the spin axis; the other two assemblies are in the spacecraft body. The sensors, copies of ones successfully flown on earlier Soviet COSMOS, VENERA and MIR missions, and similar to the spectroscopy modifications of the Compton-GRO BATSE, are scintillation crystal detectors of 200 cm2 area, shielded by Pb/Sn. Quasi-isotropic sensitivity is a result of the design and location of the two sensors. In interplanetary space far outside the Earth's magnetosphere, Konus has the advantages over Earth- orbiting GRB monitors of continuous coverage, uninterrupted by Earth occultation, and a steady background, undistorted by passages through the Earth's trapped radiation.

* Science

Konus is now providing (with the demise of Compton-GRO) the only full-time, high-sensitivity near-Earth vertex in the interplanetary GRB network (IPN). Along with Ulysses and the NEAR mission, Konus completes this IPN in a fully long-baseline geometry that enables GRB source determinations to arc-minute accuracy. In addition, comparisons of the event count rates from the two Konus detectors can provide a spacecraft spin elevation measurement that translates to an ecliptic latitude source locus. This broad feature, when other source determinations, such as from BeppoSAX or Rossi XTE, are absent, enables the resolution of the IPN source ring intersection redundancy.

The 1999-2000 Ulysses/NEAR/Konus IPN has localized a number of GRBs with adequate precision and with sufficient alert rapidity to enable counterpart studies that have produced redshifts and other valuable GRB-associated measurements. In addition to its GRB studies, Konus has contributed recent advances in the studies of other hard x-ray transients, i.e., soft gamma repeaters (SGRs), the giant August 1998 SGR flare, and the bursting pulsar. Like its sister experiment on GGS-Wind, TGRS, Konus has provided little evidence for the existence of narrow spectral features in gamma ray bursts.


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This page last updated: Thursday, 18-Oct-2007 15:43:13 EDT