|
|
GGS-WIND
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.
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 (http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/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.
Konus (http://lheawww.gsfc.nasa.gov/docs/gamcosray/legr/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.
[Gallery] (http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/images/wind_images.html)
[Publications] (http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/biblio/wind_biblio.html)
|
