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THE GLOBAL GEOSPACE SCIENCE PROGRAM AND ITS INVESTIGATIONS
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M. H. Acuna, K. W. Ogilvie, D. N. Baker*, S. A. Curtis,
D. H. Fairfield, W. H. Mish
NASA/ Goddard Space Flight Center,
Laboratory for Extraterrestrial Physics, Greenbelt, MD 20771
* Now at the Laboratory for Atmospheric and Space Physics,
University of Colorado, Boulder CO
Introduction
The Global Geospace Science Program (GGS) is designed to
improve greatly the understanding of the flow of energy, mass and
momentum in the solar-terrestrial environment with particular
emphasis on "geospace". GGS has as its primary scientific
objectives:
a) Measure the mass, momentum and energy flow and their time
variability throughout the solar wind-magnetosphere-
ionosphere system that comprises the geospace environment;
b) Improve the understanding of plasma processes that
control the collective behavior of various components of
geospace and trace their cause and effect relationships
through the system;
c) Assess the importance to the terrestrial environment of
variations in energy input to the atmosphere caused by
geospace plasma processes.
Early space probes like the Explorer and IMP series of satellites
and more recently ISEE (International Sun Earth Explorers),
Dynamics Explorer and AMPTE (Active Magnetospheric Particle
Tracer Explorer) carried out localized studies of these regions
but without the global emphasis of GGS. Geospace is defined as
the near-Earth space environment and it encompasses the regions
toward the Sun where the heliosphere is disturbed by the Earth's
magnetic field, as illustrated in Figure 1. Single spacecraft
missions have suffered in the past from the disadvantage that it
is extremely difficult to separate time dependent phenomena
(i.e., transient disturbances), from the spatial structures
encountered along the spacecraft trajectory (e.g., magnetospheric
boundaries). The spatial boundaries define several characteristic
regions in geospace which play different roles in the transport,
storage and evolution of mass, momentum and energy in the system.
Moreover, the integrated magnetospheric system responds with
poorly known cause-effect relationships to perturbations induced
by solar activity [see for example, Akasofu and Chapman, 1972;
Yamide and Slavin, 1986; Hargreaves, 1992].
Mass, momentum and energy are carried by the charged
particles that comprise the solar wind and some of these
particles can enter the Earth's magnetosphere. This coupling
between the Sun and the Earth has been known for many years as it
is best evidenced by the spectacular auroral phenomena which are
visible at high latitudes in the southern and northern
hemispheres [see Frank and Craven, 1988; Meng, Rycroft and Frank,
1989]. This complex energy chain, from the Sun's interior through
the corona, the interplanetary medium and the magnetosphere, and
its ultimate deposition in the Earth's atmosphere is illustrated
in Figure 2. Several spacecraft names are associated with the
blocks in the figure to indicate the missions that principally
address the particular region of solar-terrestrial space. The
overall study of this energy chain is a daunting task which
cannot be undertaken by a single nation alone. The recognition of
this fact led to the concept and development of the International
Solar Terrestrial Physics Program (ISTP), an international effort
designed to coordinate solar-terrestrial research in a
synergistic manner, taking advantages of the unique resources and
already planned space missions by the United States, Europe, and
Japan.
The Global Geospace Science Program is the US contribution
to the ISTP Science Initiative. It was designed to address the
goal of detailed understanding of the global features of the
geospace system by integrating a number of key elements in its
planning. First, the acquisition of coordinated and concurrent
data from spacecraft placed in key orbits that allow the
synergistically selected onboard instruments to sample
simultaneously the principal regions of geospace where energy and
momentum are transported and stored. These key regions are the
upstream interplanetary medium (WIND), the geomagnetic tail
(GEOTAIL, provided by Japan), the polar regions (POLAR) and the
equatorial magnetosphere (equatorial science, originally covered
by the EQUATOR spacecraft). Second, the incorporation for the
first time of theory and global models as an integral part of the
program, to allow the prompt and ready interpretation of the
spacecraft measurements. The third and final component of the GGS
Program is the development of a Central Data Handling Facility
(CDHF) for the purpose of processing, storing and distributing
the GGS data sets to the investigators in a rapid and cost
effective manner. This concept makes use of advanced data
processing, management and visualization tools which address the
problems experienced with previous mission data sets in this
area. The fundamental objective of obtaining a detailed
understanding of the global geospace system is therefore
facilitated as never before.
The US GGS Program is thus made up of the WIND and POLAR
spacecraft and instruments, theory and ground based
investigations and data sets obtained from equatorial spacecraft
operated by the National Oceanics and Atmospheric Administration
(NOAA) and the Los Alamos National Laboratory (LNAL). The NASA
GGS Program, the Solar Terrestrial Science Program (STSP) of the
European Space Agency (CLUSTER and SOHO spacecraft) and the
Japanese Institute of Space and Astronautical Science (ISAS),
(GEOTAIL spacecraft), are all part of the ISTP effort. Additional
contributions are planned from the former InterCosmos
organization (IKI) of Russia, and other international efforts
coordinated through the Inter-Agency Coordination Group (IACG).
The IACG was formed by NASA, ESA, ISAS and IKI to coordinate the
space missions to comet Halley in 1986. After successfully
accomplishing this task, the IACG selected the coordination of
solar-terrestrial research as its next objective (see article by
E. Whipple, this issue). The Max Planck Institute for
Extraterrestrial Physics in Germany is also planning to build and
launch a small spacecraft (EQUATOR-S) designed to support in-situ
equatorial measurements and recover some of the objectives
originally assigned to the EQUATOR spacecraft. Finally, and
although not a formal part of ISTP, significant data sets and
scientific contributions are also expected from the Solar
Terrestrial Energy Program (STEP), a program of the Scientific
Committee on Solar Terrestrial Physics endorsed by the
International Council of Scientific Unions (ICSU).
This issue describes the WIND and POLAR spacecraft, the
scientific experiments carried onboard, the Theoretical and
Ground Based investigations which constitute the US Global
Geospace Science Program and the ISTP Data Systems which support
the data acquisition and analysis effort. The scientific
instruments carried aboard the GEOTAIL spacecraft, an integral
part of the ISTP/GGS program supported by Japan and which was
launched on 24 July 1992, are described in the "Geotail Prelaunch
Report" [1992], while complete descriptions of the experiments
and investigator teams for the CLUSTER and SOHO spacecraft are
given in "CLUSTER: Mission Payload and Supporting Activities"
[1993] and "The SOHO Mission: Scientific and Technical Aspects of
the Instruments" [1988]. Tables I-V summarize the investigations,
Principal Investigators and Institutions associated with the GGS
Science Teams.
The WIND and POLAR spacecraft and their orbits
WIND and POLAR are cylindrical, spinning spacecraft of
traditional design which will be launched by DELTA II vehicles
from the Cape Canaveral Air Force Station, Florida, and the
Western Space and Missile Center in Vandenberg, California,
respectively. WIND spins at 20 RPM to allow the instruments to
sample the ambient charged particle distribution function with
good time resolution while POLAR spins at 10 RPM to accommodate
the requirements of a despun platform where visual, ultraviolet
and X-ray wavelength imagers and specialized charged particle
instruments are mounted [see papers by Frank et.al.; Torr et.
al.; Imhof et. al., this issue]. Both spacecraft have been
implemented with stringent electrostatic, magnetic and
electromagnetic constraints to minimize potential interference
with the sensitive measurements carried out by the scientific
instruments. The spacecraft record the science and engineering
data on magnetic tape recorders which are then played back to the
ground during tracking passes. There is no requirement for either
spacecraft to provide real time science data; however, they can
be operated in this mode for limited periods of time when ground
tracking facilities are available. This capability is important
if the WIND spacecraft is to be used as an early detection and
warning system for disturbances induced by solar activity, a
desired objective of the Forecast Center of NOAA's Space
Environmental Laboratory. Detailed engineering design features of
the WIND and POLAR spacecraft and their subsystems are given in
the article by Harten and Clark, this issue.
The initial orbit selected for WIND is based on a general
class of orbits commonly called "double lunar swing-by"
[Farquhar, 1991] due to the fact that the gravitational
attraction of the Moon is used through periodic encounters with
the spacecraft to maintain the semimajor axis of the orbit
roughly aligned with the Earth-Sun direction during the entire
mission. The WIND orbit is illustrated in Figure 3 and was
selected by the Science Team for the purpose of providing a
radial mapping of the interplanetary medium and the Earth's
foreshock region by the onboard instruments at the beginning of
the WIND mission. After a preselected time has elapsed (6-12
months), the WIND spacecraft will be placed in a "halo" orbit
around the Lagrangian point (L1) between the Earth and the Sun
[Farquhar, 1970] utilizing the onboard propulsion system which
has a total delta-V capability in excess of 500 meters/sec. The
halo orbit was used in the recent past to maintain the ISEE-3
spacecraft at the Lagrangian point to act as an upstream monitor
of solar wind conditions, [Ogilvie et. al., 1978] and is intended
as well for ESA's SOHO spacecraft since it allows continuous
remote sensing of the Sun's corona and photosphere without
periodic perturbations induced by the rotation of the Earth as in
ground based observatories. The double lunar swingby technique
has also been used by the GEOTAIL spacecraft to maintain its
orbit apogee continuously in the geomagnetic tail, as shown in
Figure 4 .
For scientific reasons which are related to the ability to
predict conditions at the Earth's orbit based on observations
carried out at the L1 point, it is desired that the semiaxes of
the final halo orbit achieved be as small as possible. However,
the minimum distance is bounded by a limit dictated by
communications requirements such that ground-based antennas
tracking the spacecraft do not have to point close to the Sun
which is a very powerful noise radio source and would interfere
with command and data acquisition functions. An additional
constraint that must be satisfied by the double lunar swingby
orbit is that eclipse-induced shadows must not last for more than
90 minutes at any time during the prime mission in order to
maintain thermal and power design constraints on the GGS
instruments and spacecraft. To maximize the performance of the
onboard scientific instruments and the communication system, the
WIND spin axis will be maintained perpendicular to the ecliptic
plane to within ñ 1 degree. Particular attention was placed on
building a magnetic, electrostatic and electromagnetically clean
spacecraft. The accurate measurement of very low energy plasmas
and weak electric and magnetic fields imposes significant system
level requirements on the spacecraft due to the sensitivity of
the science instruments. All exterior surfaces including thermal
blankets, solar cells and control paints are conductive to ensure
the equipotential behavior of the spacecraft as well as an
excellent Faraday shield for electric field radiation shielding.
Long booms place the magnetometers and search coil sensors away
from the main spacecraft body to reduce interference to a
minimum.
The POLAR spacecraft is similar in design to WIND except for
the addition of a despun platform and a real time data rate
capability that is an order of magnitude greater (56 KB/sec.), as
required to support the imaging investigations. POLAR will be
placed in a 90 degree inclination, elliptical orbit with a 9 Re
apogee and a 1.8 Re perigee, as shown in Figure 5. Initially and
during the prime mission, the orbit apogee will be located over
the north polar regions but with a small (10 degrees or less)
southward tilt towards the Earth-Sun line. This is required by
the visible, ultraviolet and X-ray imaging experiments carried
onboard [Torr et. al.; Frank et. al.; Imhof et. al., this issue]
whose prime objectives are to acquire images and carry out a
quantitative assessment of the energy deposited in the auroral
region. Over the life of the POLAR mission, orbital mechanics
will cause the orbital line of apsides to precess slowly to
higher latitudes, swing over the north pole and continue
southward. However, the perigee altitude is sufficiently high
such that the maximum precession rate is less than 10
degrees/year. Like WIND, POLAR carries a propulsion system with
500 meters/sec delta-V maximum capability. This system will be
used to perform attitude re-orientation maneuvers every six
months and to raise the initial injection perigee from a few
hundred kilometers to the 1.8 Re desired by the Science Team to
sample the auroral particle acceleration region. The attitude
maneuvers are required because the POLAR spin axis will be placed
normal to the orbit plane to allow the imagers to view the high
latitude regions almost continuously, and to enable the particle
instruments to map the complete charged particles distribution
function, including the loss cone [Roederer, 1970]. As the Sun
angle changes during the year, the amount of power generated by
the solar array will vary. To maintain adequate power margins and
to satisfy the thermal requirement that the despun platform not
be exposed to the sun for extended periods of time, the POLAR
spacecraft spin axis orientation will be "flipped" 180 degrees
every six months using the onboard propulsion system.
The Science Instruments
The complement of instruments and investigations associated
with the GGS Program and summarized in Tables I-V are
representative of the state-of-the-art in the field of
experimental and theoretical space and magnetospheric physics
research. These investigations were competitively selected by
NASA in 1980 in response to an Announcement of Opportunity for
the then planned Origin of Plasmas in the Earth's Neighborhood
(OPEN) program which would have involved four spacecraft
strategically placed in the four key geospace regions discussed
earlier . The evolution of the OPEN program into an international
collaboration caused the reorganization of several selected
science teams and also led to the decision to replace some of the
spacecraft and instruments with contributions from international
partners like the Institute of Space and Astronautical Science in
Japan who provided the GEOTAIL spacecraft . In addition, budget
and schedule limitations led NASA to delete the EQUATOR
spacecraft and its investigations originally proposed for the
OPEN program, and the decision to utilize data from existing,
orbiting spacecraft and ground-based measurements in its place.
Other significant changes for the science experiments
involved the POLAR despun platform. Initially it was conceived as
a two-axis despun system to allow imaging as well as the
positioning of narrow field of view particle detectors along the
ambient magnetic field line thus making possible the mapping of
the corresponding charged particle loss cone. However, power,
mass and other design considerations led to the simplified
single-axis despun platform currently implemented in this
spacecraft.
The evolution of the technology of imaging charged particle
detectors during the long period between investigation selection
and the start of the implementation phase introduced new elements
in the development of the GGS instruments. To recover the science
capability lost with the single axis despun platform design and
to bring the instrumentation to "world class science" levels,
major design updates and science enhancements were allowed by the
GGS Project Officein almost all GGS experiments immediately
following the selection of the prime contractor in 1988. Not only
additional new technology detectors were incorporated in the
instruments, but advanced data processing techniques were added
to their data processing units made possible by technological
developments and devices which were non-existent or high risk at
the time of investigation selection. Similar "enhancements" were
implemented in the ground based and theoretical investigations as
well.
The GGS instruments cover a very large dynamic range of
measurement capability in the areas of electromagnetic fields,
plasma and energetic particles, global auroral imaging and cosmic
and gamma ray bursts. The applicable spectral coverage and
dynamic ranges are summarized in Figure 6. The requirement to
acquire simultaneous data from several spacecraft as a requisite
for scientific success led to a strategy of overlap coverage in
particle instruments and partial and full redundancy in imaging
and electric and magnetic field detectors to prevent catastrophic
single point failure modes. In addition, several technological
factors drove the conceptual design of the instruments. First and
foremost was the ready availability for spaceflight use of
microprocessors and memory devices. In contrast, while ISEE3
contained a single microprocessor based instrument with a total
of 512 bytes of storage, the average GGS instrument incorporates
at least two microprocessors and several tens of kilobytes of
memory. Thus the concepts of "microprocessor control" and "flight
software" took a whole new dimension, allowing an unprecedented
versatility in the achievement of desired performance
characteristics and in the operational philosophy for the GGS
science instruments. Second and distinct from previous
spacecraft, WIND, POLAR and GEOTAIL are operated in the "store
and dump mode". This implies that there exist long periods of
time (e.g., 24 hours for WIND) when the spacecraft are not in
contact with the ground controllers and the instruments must be
designed to "safe" themselves if any anomaly occurs. This
requirement for autonomous response to faults was not present in
previous missions of this type.
The following papers describe the instruments in detail as
well as their outstanding performance characteristics which are
expected to yield data of unprecedented scope and quality
essential to accomplish the GGS science objectives. The global
GGS data sets and the specialized ISTP contributions, interpreted
in the framework provided by the models and theoretical
investigations, are expected to lead to the detailed
understanding of the global geospace system behavior as well as
that of many incomplete and poorly known phenomena such as
magnetic field line merging and reconnection, the triggering
mechanisms for magnetospheric substorms and the production of the
aurora that results from energization and flow of charged
particles throughout the magnetosphere [Dyer, 1972; McCormac,
1976]. Significant contributions will also be made to the study
of the bow shock and solar wind flow past the Earth, and how all
of the above phenomena are controlled by the interplanetary
medium and ultimately by the Sun [Yamide and Slavin, 1986;
Hargreaves, 1992].
The heritage of the GGS instruments and science team is
extensive, beginning with the earliest spaceflight instruments
developed for upper atmosphere, ionosphere and magnetosphere
research. Each instrument represents the latest contribution of
small, dedicated research groups associated with universities,
industry and government laboratories. In contrast to the large
orbiting laboratory class spacecraft, the majority of the GGS
instruments are built "in-house" and with the direct
participation of the investigators and team members involved.
This implementation mode, prevalent during the early years of the
space program evolved significantly with the advent of very
large, observatory class spacecraft, with the attending increase
in complexity in terms of documentation and management
requirements. The long duration of the implementation phase of
the GGS instruments (14+ years) introduced many new elements
which affected significantly the cost and risk associated with
each investigation. However, the instruments described in this
issue illustrate the extraordinary efforts carried out by the GGS
investigators in overcoming these very difficult challenges. The
outstanding contributions of the large number of engineers,
scientists, mathematicians, data analysts, instrument managers,
software specialists and innumerable other personnel that make a
complex program like GGS a success, are evidenced throughout the
papers in the papers in this issue.
The Central Data Handling Facility and
Science Planing and Operations Facility
As mentioned in the introduction and in parallel with the
integration and test of the spacecraft and flight instruments,
imaginative science planning and instrument operations tools,
data analysis and visualization concepts are being developed to
complement the measurements and promote the efficient
interpretation and analysis of the data. These concepts involve
ideas and products derived from a strong interaction among
modellers, theoreticians, experimentalist and data processing
specialists. These are described in detail in this issue in the
papers by Ashour-Abdalla et. al., Papadopoulos et.al., Hudson et.
al. Mish et.al. where new concepts and data products such as
"mission oriented theory", "theory projects", "key parameters",
"science planning tools", and others are described.
The successful achievement of the science objectives of GGS
depends critically on the ultimate ability to acquire, process
and analyze vast amounts of data from very sophisticated and
complex instruments which may interact strongly with the carrier
spacecraft. This difficult problem has been recognized for many
years and addressed in a variety of ways with increasing success.
One of the elements that has proven to be of high value is the
prompt generation of medium time resolution, summary data sets
which can be used as general indexes to the more general, high
time resolution data. Typical examples of these data sets are the
Dynamics Explorer "data pool tapes", Voyager "summary tapes",
AMPTE's "summary data tapes", etc. These data products allow the
rapid assessment and selection of intervals of high scientific
interest for further detailed study. This approach is driven by
the fact that the typical ratio of data volume analyzed in detail
to the total data volume generated is usually small. For the
design of the GGS system, this ratio was estimated at a ten
percent average over the total investigation complement. This
fraction has been organized in terms of "Key Parameters" selected
for each investigation from recommendations of the Science
Working Group and Principal Investigators. These data have a
typical time resolution of 1 to 3 minutes and reflect fundamental
geophysical parameters and time series associated with each
investigation. A summary of the GGS Key Parameters for each GGS
investigation is given elsewhere in this issue in the paper by
Mish et. al.,. It is extremely important to note that these Key
Parameters are uncalibrated, utilize "predict" orbit and attitude
data rather than actual, processed values and hence cannot be
used for formal scientific work. Their fundamental utility lies
in the fact that they are processed immediately following data
reception at NASA's Goddard Space Flight Center and made
available for scientific assessment within 48 hours of
acquisition. Thus, a prompt analysis of the Key Parameters can be
used to respond to changing geophysical conditions or solar
events, reconfigure the operating modes of the science
instruments and evaluate potential high interest periods for
further study. A secondary, engineering function of the Key
Parameters is to provide a quick assessment of the performance of
the instruments and to observe their operating modes for
consistency with the primary science goals of the mission.
The organization that has the responsibility of processing
the data acquired by the GSFC Data Capture Facility (DCF) into
Key Parameters and other data products for distribution to the
GGS Investigators, is the Stanley Shawhan Central Data Handling
Facility, named after the late, first Director of NASA's Space
Physics Division. A block diagram of this facility and its
functional interfaces is shown in Figure 7. It operates
fundamentally as a "black box" where raw data are processed
routinely under central direction and configuration control into
key parameters and level zero data products that are distributed
to the ISTP/GGS investigators for processing at their Remote Data
Analysis Facilities (RDAF's). Detailed descriptions of the
functional blocks and data products are given in the paper by
Mish et. al., this issue.in almost all GGS experiments
The responsibility for coordinating the science operations
of the GGS instruments is handled by the Science Planning and
Operations Facility (SPOF) under the direction of the GGS Project
Scientists and the Science Working Group. This facility receives,
analyzes and coordinates the commands requested to be sent to the
instruments by the investigators with the purpose of identifying
and resolving science conflicts. Engineering evaluation,
instrument health monitoring and conflict resolution are carried
out at the Project Operations and Control Center (POCC). The
proposed instrument configuration and operational modes are
formatted into short and long range "Science Operation Plans"
which are evaluated for consistency with the GGS science
objectives to insure conflict-free operation of the instruments.
After this process is completed, the results are passed to the
Project Operations Control Center where the final "command loads"
are assembled for transmission to the spacecraft at the
appropriate times and subsequent execution. To perform the
functions of science coordination, conflict resolution and key
parameter quality monitoring the SPOF has its disposal a number
of specially developed tools in the form of geophysical data
bases and models, orbit visualization and analysis software, and
interactive key parameter display software. The tools, data
products and software utilized by the SPOF have been designed to
follow the general guidelines recommended by the Inter-Agency
Consultative Group (IACG), mentioned earlier in this paper, to
promote standardization and common format throughout ISTP
missions. Further descriptions of these systems and facilities
are also given in the Whipple and Mish et. al. papers in this
issue.
Acknowledgements
On behalf of the GGS investigators, we would like to express
our appreciation to NASA, ESA and ISAS which have made the GGS,
STSP and GEOTAIL programs possible, to the GGS Project Manager
J.Hrastar for his unrelenting efforts to make the project a
success, to W. Worrall and the staff of the CDHF and SPOF
organizations for their outstanding efforts on the ground data
system, and to the countless other personnel that have
contributed over the last 14 years to this program. The
outstanding coordination efforts of the National Space Science
Data Center and the IACG through its Working Groups in the areas
of science campaigns, the promotion of common methods, formats,
data products and standards, electronic data communication, etc.
is hereby recognized and appreciated.
Figure Captions
Figure 1 - The Earth's geospace environment. The interaction of
the solar wind with the Earth's magnetic field creates a
supersonic shock wave and a magnetospheric cavity bounded by the
indicated surfaces. The orbits of the GGS spacecraft are designed
to provide coverage of key regions of geospace.
Figure 2 - The solar-terrestrial energy chain. The Sun's energy
flows from the interior through the photosphere, corona and
interplanetary medium to the vicinity of the Earth where it
interacts with the geomagnetic field and atmosphere.
Figure 3 - The selected orbit for the WIND spacecraft. Periodic
encounters with the Moon are used to maintain the apogee near the
Earth-Sun line ("double lunar swing-by's"). The final orbit is a
"halo" orbit around the L1 libration point.
Figure 4 - The GEOTAIL orbit is similar to the WIND orbit except
that lunar swingby maneuvers are used to maintain the apogee
inside the geomagnetic tail. The initial orbit reached distances
in excess of 200 Re. In the fall of 1994 the apogee of the
GEOTAIL orbit will be reduced to approximately 30 Re.
Figure 5 - The POLAR spacecraft orbit. This orbit was selected as
a compromise among conflicting requirements by imaging and
charged particle investigations.
Figure 6 - The measurements, spectral coverage and dynamic range
of the GGS flight instruments. Significant overlap redundancy
exists among similar classes of experiments.
Figure 7 - Overview of the ISTP/GGS ground data system showing
the serial flow of data from the spacecraft, receipt by the Deep
Space Network on to the Data Capture Facility, the Central Data
Handling Facility, the Data Distribution Facility and finally to
the individual PI Teams for processing at the Remote Data
Analysis Facilities and the NSSDC. Also shown is the Science
Planning and Operations Facility, an off-line facility where the
science planning is coordinated.
Tables I - WIND Investigations and Institutions
Table II - POLAR Investigations and Institutions
Table III - GEOTAIL Investigations and Institutions
Table IV - Ground Based Investigations and Institutions
Table V - Theory and Modeling Investigations and Institutions
References:
Akasofu, S.I. and S. Chapman, "Solar Terrestrial Physics", Oxford
University Press, 1972.
"CLUSTER: Mission, Payload and Supporting Activities", ESA
SP-1159, March 1993.
Dyer, 1972 - "Critical Problems of Magnetospheric Physics",
Proceedings of the Joint COSPAR/IAGA/URSI Symposium, Madrid,
Spain, E. R. Dyer, editor, 1972.
Farquhar, R. W., " A new Trajectory Concept for Exploring the
Earth's geomagnetic Tail", Journal of Guidance and Control,
April, 1991
Farquhar, R. W., "The Control and Use of Libration Point
Satellites", NASA Technical Report TR-R346, September 1970
Frank, L.A. and J. D. Craven, "Imaging results from Dynamics
Explorer I", Rev. Geophys. 26, 249, 1988.
"GEOTAIL Pre-Launch Report", Institute of Space and Astronautical
Science, SES-TD-92-007SY, April 1992.
J.K. Hargreaves, "The Solar Terrestrial Environment", Cambridge
University Press, 1992
B. M. McCormac, "Magnetospheric Particles and Fields", D. Reidel
Publishing Co., Dordrecht-Holland, 1976
Meng, C.I., M. J. Rycroft and L. A. Frank, "Auroral Physics",
Cambridge University Press, 1989.
Ogilvie, K. W., A. Durney and T. von Rosenvinge, "Description of
the Experimental Investigations and Instruments for the ISEE
Spacecraft", IEEE Trans. Geoscience Electronics, GE-16, No. 3,
1978.
"The SOHO Mission: Scientific and Technical Aspects of the
Instruments", ESA SP-1104, November 1988.
Roederer, J. G., "Dynamics of Geomagnetically Trapped Radiation",
Springer-Verlag, New York, 1970
Yamide, Y and J. A. Slavin, "Solar Wind-Magnetosphere Coupling",
D. Reidel Publishing Co., Dordrecht-Holland, 1986
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Spacecraft: Geotail Brief Description
The Geotail mission will measure global energy flow and transformation
in the magnetotail to increase understanding of fundamental
magnetospheric processes. This will include the physics of the
magnetopause, the plasma sheet, and reconnection and neutral line
formation, i.e., the mechanisms of input, transport, storage, release
and conversion of energy in the magnetotail. Geotail, together with Wind,
Polar, SOHO, and Cluster projects, constitute a cooperative
scientific satellite project designated the International Solar
Terrestrial Physics (ISTP) program which aims at gaining improved
understanding of the physics of solar terrestrial relations.
Geotail is a spin-stabilized spacecraft utilizing mechanically despun
antennas with a design lifetime of about four years. The nominal spin
rate of the spacecraft is about 20 rpm around a spin axis maintained
between 85 and 89 deg to the ecliptic plane. Geotail is cylindrical,
approximately 2.2 m in diameter and 1.6 m high with body-mounted solar
cells. Geotail also has a back-up battery subsystem which operates
when the spacecraft is in the Earth's shadow (limited to 2 hrs).
Real-time telemetry data transmitted in X-band are received at the
Usuda Deep Space Center (UDSC) in Japan. There are two tape recorders
on board, each with a capacity of 450 Mbit which allows daily 24-hour
data coverage and are collected in playback mode by the NASA Deep
Space Network (DSN). The Geotail mission is divided into two phases.
During the 2-year initial phase, the orbit apogee is kept on the
nightside of the Earth by using the Moon's gravity in a series of
double-lunar-swing-by maneuvers that result in the spacecraft spending
most of its time in the distant magnetotail (maximum apogee about 200
Earth radii) with a period varying from one to four months. During the
second phase the apogee will be reduced to 30 Earth radii to study the
near-Earth neutral line formation.
Geotail CPI Brief Description
------------------------------
The objective of this investigation is to make comprehensive
observations of the three-dimensional velocity distribution functions
of electrons and positive ions, with identification of ion species.
The instrument contains three sets of quadrispherical analyzers with
channel electron multipliers. These three obtain three-dimensional
measurements for hot plasma and solar wind electrons, for solar wind
ions, and for positive-ion composition measurements. The positive-ion
composition measurement includes five miniature imaging mass
spectrometers at the exit aperture of the analyzer, and covers masses
from 1 to 550 u/Q at 100 eV, and 1 to 55 u/Q at 10 keV. The hot
plasma analyzer measures electrons and ions in the range 1-50,000
eV/Q. The solar wind analyzer measures ions from 150 to 7,000 eV/Q.
Sequencing of the energy analyzers and mass spectrometers, and other
control functions, are provided by two microprocessors.
caveat supplied by Bill Patterson on 25 August 1994:
There are problems with some Hot Plasma parameters, particularly the
HP average energy and the densities. These parameters will be
recomputed and there will be better definitions of the HP parameters
in the skeleton table in a new version. The Solar Wind parameters
appear to be generally ok.
Geotail EFD Brief Description
------------------------------
The objectives of this investigation are studies of (1) the large
scale configuration of the electric field in the magnetotail, (2) tail
electric field variations during substorms, (3) the electric field in
the plasma sheet, (4) the electric field near the magnetopause and in
the plasma mantle at locations tailward of those covered by similar
measurements on ISEE 1, (5) micropulsation and low frequency wave
measurements at frequencies covering the local gyrofrequency (<1Hz)
and lower hybrid frequency (<10Hz) in the tail, (6) plasma density as
deduced from measurement of the floating potential of the spacecraft,
and (7) electric field comparisons (with the aid of the other
spacecraft in the ISTP program) at different points along the same
magnetic field line, at different points along a common boundary, or
in different regions of the magnetosphere. The instrument consists of
two orthogonal double probes, each of which is a pair of separated
spheres on wire booms that are located in the satellite spin plane and
whose difference of potential is measured. The separation distances
between the pair of sensors are variable and as great as 160 m
tip-to-tip. One operating mode involves length ratios of the two
antennas of about 2:1 in order to verify instrument operation through
showing that the electric field signature is proportional to the boom
length. A second reason for two pairs of wire booms in the satellite
spin plane is the requirement for measurements having a time
resolution far better than the satellite spin period.
Geotail EPIC Brief Description
------------------------------
The principal objective of the EPIC (energetic particle and ion
composition) investigation is to explore the distant magnetotail
region and obtain information on the origin, transport, storage,
acceleration and dynamics of suprathermal and non-thermal particle
populations. The instrument performs three-dimensional distribution
measurements by using both total energy (LEMS -- low energy
composition system) and velocity/composition detectors (ICS - ion
composition system), measuring ions and electrons with energies >20
keV, and ions with energy >8 keV/nucleon, respectively. Composition
measurements are made by using a thin foil time-of-flight technique
which resolves the H and He isotopes, and provides elemental
resolution up to approximately argon. The instrument also measures
the non-thermal components to 6 MeV for protons, 480 keV for
electrons, and 400 keV/nucleon for ions with Z>2. Directional
measurements with a time resolution <1 s are possible.
GEOTAIL EPIC KP Data Caveat
--------------------------
1. Prior to March 8, 1993, the >34keV electron anisotropy parameters a1, a2,
phi1, and phi2 are not useable. After this date, all electron intensity and
anisotropy data are not useable due to EPIC key parameter software
calibration problems.
2. A small subset of the ICS key parameters are not correct because the EPIC
KP software failed to recognize when the instrument was in a reduced
aperture or calibration mode. Please contact Dr. Richard McEntire at
richard_mcentire@jhuapl.edu or (301)953-5410 or Dr. Tony Lui at
anthony_lui@jhuapl.edu or (301)953-6000, ext. 8407 to verify whether
your periods of interest are affected.
3. In periods of low flux, the 96-second averaging interval is insufficient
for calculating meaningful anisotropy measurements. Large values of a1
and a2 and random values of phi1 and phi2 result.
4. Not all aspects of the STICS key parameters have been fully validated.
5. Several miscellaneous corrections are needed to the EPIC KP CDF file meta
information:
a) The range of all phi1 and phi2 anisotropy parameters should be -pi to
+pi, not 0.0 to 2pi.
b) The range of all a1 and a2 anisotropy parameters should be 0.0 to 2.1,
not 0.0 to 2.0.
c) The lower bounds of the two STICS proton differential intensity energy
bands are not correct. For the given center values of 9.38 and 22.86
keV, the minus values to specify the lower limits of the bands should be
0.11 keV and 0.27 keV, respectively, not 0.3 keV and 0.0 keV,
respectively.
Stewart Nylund (ISTP::NYLUND)
Geotail HEP Brief Description
------------------------------
There are three scientific objectives to be studied by this
investigation: (1) plasma dynamics in the geomagnetic tail, (2) solar
flare particle acceleration and propagation, and (3) the origin, lifetime
and propagation of cosmic ray particles. There are five instruments that
make up this investigation: Low-energy particle Detector (LD), Burst
Detector (BD), Medium-energy Isotope detectors (MI-1 and MI-2), and High
energy Isotope detector (HI). LD and BD are mainly dedicated to
magnetospheric studies. MI and HI concentrate on solar flare and cosmic
ray studies. The LD sensor system consists of three identical Imaging Ion
Mass spectrometers which use time-of-flight/energy measurement, and
covers 180 degrees in polar angle over the energy range 20--300 keV for
electrons, 2 keV--1.5 MeV for protons, and 2 keV--1.5 MeV per charge for
ions. LD provides distribution of electrons and ions with complete
coverage of the unit sphere in phase space, and electron and proton flux
in 4 azimuth sectors, helium and oxygen flux at an azimuth of 0 degrees.
The BD sensor consists of three delta-E x E telescopes which identify
particles by their energy loss and residual energy over the energy range
0.12--2.5 MeV for electrons, 0.7--35 MeV for protons, and 0.7--140 MeV
for helium. The three telescopes each have an opening angle of 30 degrees
by 45 degrees with look directions of 30, 90, and 150 degrees to the spin
axis. BD provides count rates for high energy electrons, protons and
helium, as well as electron and proton fluxes in four 90 degree azimuth
bins. The MI and HI instruments are all silicon semiconductor detector
telescopes utilizing the well-known dE/dx x E algorithm for isotope
identification: mass and nuclear charge. The MI instrument measures
elemental and isotopic compositions of solar energetic particles and
energetic particles in the heliosphere with 2<Z<28 in the energy range
2.4--80 MeV/nucleon, and measures the elemental composition of solar
energetic particles heavier than iron. The HI instrument also measures
elemental and isotopic compositions of solar energetic particles and
galactic cosmic rays with 2<Z<28 in the energy range 10--210 MeV/nucleon.
HEP operates continuously with no change in allocated bit rate. LD has
two operational modes: normal and burst. Burst mode is an internal high
speed mode which does not change the data output. BD has four operational
modes for calculating energy spectra for electrons, protons, and helium:
16 sectors in 1 spin (time high resolution mode), 8 sectors in 32 spins
(energy high resolution mode), 8 sectors in 2 spins, and 16 sectors in 4
spins. MI and HI have only one operational mode.
Geotail LEP Brief Description
------------------------------
The objective of this experiment is to observe plasma and energetic
electrons and ions in the terrestrial magnetosphere and in the
interplanetary medium. The LEP consists of three sensors: LEP-EA, LEP-SW,
and LEP-MS, with common electronics (LEP-E). LEP-EA measures
three-dimensional velocity distributions of hot plasma in the
magnetosphere. EA consists of two nested sets of quadrispherical
electrostatic analyzers. The inner analyzer measures electrons in the
energy range from 6--36 eV, and the outer one measures positive ions from
7 eV/Q to 42 keV/Q. The field of view for each quadrispherical analyzer
covers 10 degrees by 145 degrees, where the longer dimension is parallel to
the satellite spin axis. LEP-SW measures three-dimensional velocity
distributions of solar wind ions in the energy range from 0.1--8 keV/Q with
a 270 degree spherical electrostatic analyzer with a field of view of
5 degrees by 60 degrees. LEP-MS is an energetic ion mass spectrometer,
which provides three-dimensional determinations of the ion composition in
32 steps over the energy range of 0--25 keV/Q. All sensors operate
continuously as long as the spacecraft power budget can allow, except for
the orbit/attitude maneuvering operation. When spacecraft power budget is
not sufficient to fully operate the instruments, priority is given to
LEP-EA and LEP-E.
Geotail MGF Brief Description
------------------------------
The objective of this experiment is to measure the magnetic field
variation of the magnetotail in the frequency below 50 Hz. The MGF
experiment consists of dual three-axis fluxgate magnetometers and a
three-axis search coil magnetometer. Triad fluxgate sensors, which
utilize a ring core geometry, are installed at the end and middle of a
6 m deployable mast. Three search coils are mounted approximately
one-half of the way out on another 6 m boom together with search coils
for the VLF wave in the PWI system. The fluxgate magnetometers are of
standard design and consist of an amplifier, filter, phase sensitive
detector, integrator, and a voltage-current convertor. The fluxgate
magnetometers operate in seven dynamic ranges to cover various regions
of the Earth's magnetosphere and the solar wind: +/-16 nT, +/-64 nT,
+/-256 nT, +/-1024 nT, +/-4096 nT, +/-16384 nT, and +/-65536 nT, and
supply 16 vectors/sec. The search coil magnetometer system consists of
three sensors, preamplifier, amplifier, filter, multiplexer, and an
A/D converter. The search coil magnetometers operate in a frequency
range of 0.5 kHz to 1 kHz, and supply 128 vectors/sec. The fluxgate
magnetometer operates in both real time and record modes, while the
search coil data are used only in real time mode.
Geotail PWI Brief Description
------------------------------
The objective of this investigation is to determine the dynamic
behavior of the plasma trapped in the earth's magnetosphere, i.e.,
toroidal and poloidal currents, oscillations and waves in the plasmas,
ion entrance and exit via the ionosphere and solar wind, and the
extent of the plasmasheath. The instrument measures electric fields
over the range 0.5 Hz to 400 kHz, and magnetic fields over the range 1
Hz to 10 kHz. Triaxial magnetic search coils are utilized in addition
to a pair of electric dipole antennas. The instrument contains two
sweep-frequency receivers (12 Hz to 400 kHz and 12 Hz to 6.25 kHz), a
multichannel analyzer (5.6 Hz to 311 kHz for the electric antenna and
5.6 Hz to 1.0 kHz for the magnetic coils), a low frequency waveform
receiver (0.01 to 10 Hz), and a wideband waveform receiver (10 Hz to
16 kHz).
---------------------------------------------------------------------------
Spacecraft: IMP-8 Brief Description:
Updated May 6, 1994
IMP 8 (Explorer 50), the last satellite of the IMP series,
was launched October 26, 1973. It is a drum-shaped spacecraft,
135.6 cm across and 157.4 cm high, instrumented for
interplanetary, magnetotail, and magnetospheric boundaries studies
of cosmic rays, energetic solar particles, plasma, and
electric and magnetic fields. Its initial orbit was more
elliptical than intended, with apogee and perigee distances of
about 45 and 25 earth radii. Its eccentricity decreased after
launch. Its orbital inclination varies between 0 deg and about
55 deg with a periodicity of several years. The spacecraft spin
axis is close to being normal to the ecliptic plane, and the spin
rate is approximately 23 rpm. The data telemetry rate is 1600
bps. The spacecraft is in the solar wind for 7 to 8 days of
every 12.2 day orbit. Telemetry coverage was 90% in the early
years, but only 50-70% through most of the 1980's and into the
1990's. The telemetry is VHF and the spacecraft is tracked by
Wallops Island, VA; Redu, Belgium; Tasmania Australia; Santiago
Chile; and Hawaii. The objectives of the extended IMP-8
operations are similar to the original goals with emphasis on
providing solar wind parameters as input for magnetospheric
studies and as a 1-AU baseline for deep space studies, and to
continue solar cycle variation studies with a single set of
well-calibrated and understood instruments.
Imp-8 MAG Brief Description
------------------------------
This experiment consists of a boom-mounted triaxial fluxgate
magnetometer designed to study the interplanetary, geomagnetic
tail, and boundary magnetic fields. Each sensor has three
dynamic ranges of plus or minus 12, plus or minus 36, and plus or
minus 108 nT. The instrument provides a "detail" sample rate of
3.125 vectors/s. The experiment operated normally from launch
until mid-1975. On July 11, 1975, because of a range change
problem, the experiment operation was frozen into the 36-nT
range. The digitization accuracy in this range is about plus or
minus 0.14 nT. On March 23, 1978, the sensor flipper failed.
After that time, alternative methods of Z-axis sensor zero-level
determination were required. Key Parameters for the Magnetometer
investigation are computed within the ISTP/CDHF for a week of data
at a time. Generally Key Parameter availability lags real time by
about 14 days.
The PI is Dr. Ronald Lepping, Code 696, Goddard Space Flight
Center, Greenbelt MD, 20771; email rpl@leprpl.gsfc.nasa.gov and
should be contacted before use of these data.
Imp-8 PLA Brief Description
------------------------------
A modulated-grid, split-collector-plate Faraday cup, is used to
study the positive ions and electrons in the solar wind,
transition region, and magnetotail. Parameters derived on a
routine basis are proton velocity, number density, and temperature
(most probable thermal speed).
The collector plate split is perpendicular to the spacecraft spin
axis in order to measure the flow angle of the ions in a
meridional plane; the flow angle in the spacecraft equatorial
plane is determined from the fluxes measured as the spacecraft
rotates.
Electrons are measured using 21 logarithmically-spaced energy
windows covering the energy/charge range between 23 and 1935
volts. Positive ions are studied using 24 energy windows covering
the range between 50 and 7000 volts.
The instrument has three operating modes. The tracking mode
yields the best time resolution which is about 1 minute. A single
energy window is used during a spacecraft rotation. The ion
spectrum is obtained in eight spacecraft revolutions using a
subset of the energy windows that track the peak of the solar
wind. In this mode, fluxes are measured during 11.25-degree
sectors of the spacecraft spin while the instrument is looking
within the 90 degree sector centered on the sun direction and
during 45 degree sectors for the remainder of the rotation. The
other modes yield a spectrum using all 24 windows (with the same
angular sectors described above) or a spectrum that results from
integrating the observed fluxes over 45 degree sectors for the
entire spacecraft rotation.
Electron data are obtained in all modes, but are not usually
analyzed.
Parameters derived on a routine basis are proton velocity, number
density, and temperature (most probable thermal speed). Those
parameters are obtained from a non-linear, least-squares fit to
the observed fluxes using a convected, isotropic Maxwellian model.
Key Parameters for the Plasma instrument are computed at MIT using
Level Zero data that are staged to the ISTP/CDHF approximately two
weeks after being received on Earth. Thus the plasma instrument's
Key Parameters lag real time by something greater than 2 weeks,
but less than four.
The PI is Dr. Alan Lazarus, Room 37-687, MIT, Cambridge, MA,
02139; email: ajl@space.mit.edu and he should be contacted early
in the process before use of these data for publication or at a
conference.
---------------------------------------------------------------------------
Spacecraft: LANL Brief Description:
This spacecraft is part of a continuing series of classified
spacecraft. The three spacecraft USA 39 (89-046A), USA 65 (90-095A),
and USA 75 (91-080B) replace an earlier constellation of geosynchronous
orbit spacecraft. These three were positioned at longitudes of
approximately 195, 8, and 72 degrees, respectively, as of February 20,
1992. Each spacecraft carries two instruments whose data are available
for magnetospheric research: the Magnetospheric Plasma Analyzer (MPA)
and the Synchronous Orbit Particle Analyzer (SOPA). The article by
McComas et al., ``Magnetospheric plasma analyzer: Initial three-spacecraft
observations from geosynchronous orbit,'' (J. Geophys. Res., 98, No. A8,
p. 13453, 1993) gives more information. It also declares: ``Recently, the
MPA and SOPA data sets have become part of the International Solar
Terrestrial Physics (ISTP) program with the inclusion of key parameter
data in the ISTP Central Data Handling Facility (CDHF). These data should
provide a valuable adjunct to ISTP science, particularly in light of the
lack of a dedicated `Equator' spacecraft, in addition to providing new
information about the geosynchronous environment in their own right.''
LANL MPA Brief Description
------------------------------
The Magnetospheric Plasma Analyzer (MPA) was designed to minimize
weight, power, and volume while providing comprehensive measurements
of plasma conditions. Similar instruments are on board all three of
the constellation of geosynchronous spacecraft 89-046A, 90-095A, and
91-080B. The MPA consists of a single electrostatic analyzer (ESA)
coupled to an array of channel electron multipliers, and it measures
three-dimensional energy/charge distributions of both ions and electrons
in a range of ~1 eV/q to >40 KeV/q. For use at this orbit, the
instrument was designed for high sensitivity with moderate energy and
angular resolutions. The ESA is composed of a set of spherical plates
such that the bending angle from the center of the entrance aperture is
a constant 60 degrees, independent of the polar angle of entry.
Electrons and ions are analyzed alternately with this single ESA. After
leaving the ESA, the particles are accelerated into an array of six
spiral-configuration channel electron multipliers (CEMs). Each CEM
covers a separate polar angle field of view (FOV). The FOVs are
fan-shaped and centered at +/- 11.5, 34.5, and 57.5 degrees polar
angle, where 90 degrees is the spin axis direction (actively controlled
to point to the center of the earth). Three-dimensional measurements are
obtained by using spacecraft rotation, at a nominal 6 rpm, to sweep the
FOV through the full 360 degree range of spacecraft azimuth angle while
recording counts in the six polar angle FOVs. Measurements are made in
standard cycles at each of 24 angles (15 degree spacing) in azimuth
during each 10 s spacecraft revolution. Approximately 92% of the unit
sphere is observed by the MPA. Normal instrument operation is composed
of five types of cycles arranged in an eight-cycle sequence that repeats
every 86 s. This provides both two-dimensional and three-dimensional
distributions, with varying resolutions. For more details of the
instrument, see the paper by S. J. Bame et al., Rev. Sci. Instrum., 64,
(4), pp. 1026-1033, 1993.
LANL SOPA Brief Description
------------------------------
The Synchronous Orbit Particle Analyzer (SOPA) consists of three nearly
identical silicon solid state detector telescopes, pointed at 30, 90,
and 120 degrees to the satellite's earth-centered spin axis. Similar
instruments are on board all three of the constellation of geosynchronous
spacecraft 89-046A, 90-095A, and 91-080B. The working end of the telescope
consists of a very thin front silicon detector, D1, followed by a thick
back detector, D2. The D1 sensors are mounted with the thin aluminum
contact out. The thinner than usual Al contact was chosen to minimize the
entrance deadlayer to allow as low a proton threshold as possible.
Measurements show that the deadlayer is approximately 30 micrograms/cm**2.
The detector stack is surrounded, except for the aperture, by passive
low-Z (aluminum) and high-A (copper) shielding, which excludes
side-penetrating protons up to about 65 MeV and electrons up to 6 MeV.
The front collimator baffle is designed to require at least two-fold
scattering of particles not in the acceptance angle of the detector to
encounter the D1 detector. This provides an extremely sharp angular
cutoff of incident particles. The full acceptance angle of the telescopes
is about 11 degrees. Each telescope has a geometrical factor of
8.49 E-4 cm**2 sr for ions, and 1.09 E-3 cm**2 sr for low-energy
electrons. A single rotation requires about 10 s, and in that time,
64 cuts of the unit sphere are taken by the three telescopes in a certain
pattern. Passive cooling keeps the telescope temperatures within the range
-15 to +5 C. In this range, essentially all of the noise associated with
leakage current in the surface barrier detectors is eliminated. Even so,
the high capacitance of the D1 sensors (~500 pF) requires setting the
first energy threshold relatively high. The numerous thresholds and logic
channels (including anti-coincidence) result in identification of
differential fluxes of protons from 50 KeV to 50 MeV. Differential
fluxes of electrons are determined from 50 KeV to 1.5 MeV, with integral
flux above 1.5 MeV. The differential flux range for alpha particles is
0.5--1.3 MeV; for CNO, 1.5--3.55 MeV; for carbon, 5.0--13 MeV; for
nitrogen, 6.0--14 MeV; and for oxygen, 7.2--15 MeV. Integral ion fluxes
are determined for sulphur above 8 MeV, and for bromine above 15 MeV. A
sun sensor with three collimators that overlap the fields-of-view of the
three telescopes provides input to tag the pulse pairs that are
potentially contaminated by sun-generated pulses from D1. For more details
of the instrument, see the paper by R. D. Belian et al., J. Geophys. Res.,
97, A11, pp. 16897-16906, 1992, from which this information was obtained.
LANL/MPA KP Data Caveat
----------------------
The MPA KP data values are preliminary and have a number of problems which
will be corrected when we revise our algorithms and re-process the data.
However, that could be a while in coming. It is to be understood that the MPA
data set contains very preliminary values (not publishable!) and any
investigators interested in using them should contact us before embarking
on any extensive study using them.
Michelle Thomsen (S:ESSDP1::thomsen)
---------------------------------------------------------------------------
Spacecraft: GOES 6 (7) Brief Description:
GOES 6 was the eighth in a series of NASA-developed, NOAA-operated,
geosynchronous, and operational spacecraft. The spin-stabilized
spacecraft carried (1) a visible infrared spin-scan radiometer (VISSR)
atmospheric sounder (VAS) to provide high-quality day/night cloudcover
data, to take radiance-derived temperatures of the earth/atmosphere
system, and to determine atmospheric temperature and water vapor
content at various levels, (2) a meteorological data collection system
to relay processed data from central weather facilities to regional
stations equipped with APT and to collect and retransmit data from
remotely located earth-based platforms, and (3) a space environment
monitor (SEM) system to measure proton, electron, and solar X-ray
fluxes and magnetic fields. The cylindrically shaped spacecraft
measured 190.5 cm in diameter and 230 cm in length, exclusive of a
magnetometer that extended an additional 83 cm beyond the cylindrical
shell. The primary structural members were a honeycombed equipment
shelf and a thrust tube. The VISSR telescope, which was mounted on
the equipment shelf, viewed the earth through a special aperture in
the side of the spacecraft. A support structure extended radially
from the thrust tube and was affixed to the solar panels, which formed
the outer wall of the spacecraft to provide the primary source of
electrical power. Located in the annulus-shaped space between the
thrust tube and the solar panels were stationkeeping and dynamics
control equipment, batteries, and most of the SEM equipment. Proper
spacecraft attitude and spin rate (approximately 100 rpm) were
maintained by two separate sets of jet thrusters mounted around the
spacecraft equator and activated by ground command. The spacecraft
used both UHF-band and S-band frequencies in its telemetry and command
subsystem. A low-power VHF transponder provided telemetry and command
during launch and then served as a backup for the primary subsystem
once the spacecraft attained synchronous orbit. GOES 6 was moved from
its 135 deg W position to a more central 98 deg W position when GOES 5
failed on July 29, 1984.
GOES-6 (7) EPS Brief Description
------------------------------
The energetic particle monitor consisted of three detector assemblies,
each covering limited regions of the overall energy spectrum. The
first two detector assemblies monitored protons in seven energy ranges
between 0.8 and 500 MeV, and alpha particles in six ranges from 4 to
>400 MeV. There was also one channel for the measurement of electrons
in the >=500 keV range. The third detector, the high energy proton
and alpha detector (HEPAD), monitored protons in four energy ranges
above 370 MeV and alpha particles in two energy ranges above 640
MeV/nucleon.
GOES-6 (7) MAG Brief Description
------------------------------
not available at this time.
GOES 6 and 7 KP Data Caveat
---------------------------
1. There are several difficulties with some of the
present GOES KP data; however, even with these limitations, the
data can be useful for such activities as event detection and
understanding the level of disturbance of the geomagnetic field.
It is to be understood that this data cannot be published or
presented without the PI's authorization.
2. In addition to comments imbedded in the CDF's regarding data
quality, some additional comments regarding the data are provided
below.
(the following quality information was provided by Dr. Howard J. Singer,
Acting Chief Geospace Branch, NOAA R/E/SE 303-497-6959) :
GOES 6 - Magnetometer
A variety of malfunctions of the spin plane components (He
and Hn) of this instrument have occurred since at least September
1992. These data are useful for detecting a variety of disturbances
in the space environment, but the actual field values are not to be
trusted. The parallel, or spin axis, component (Hp) of the field
appears to be unaffected by the spacecraft or instrument
difficulties; however, the offset of this component is difficult to
calibrate and questionable. Interpretation of the data is also
complicated by the fact that the GOES 6 spacecraft orbit has
become more inclined to the equatorial plane than is typical of the
GOES satellites.
GOES 7 - Magnetometer
The GOES 7 magnetometer transverse components (He and
Hn) failed on May 2, 1993. At this time an offset also appeared in
the spin axis component. This offset was removed on May 18,
1993; however as with GOES 6, the absolute value of the spin axis
component also has uncertainties.
(the following quality information was provided by Dr. Herb Sauer
NOAA R/E/SE 303-497-3681) :
Energetic Particle Detectors
The GOES E1 and P1 channels were designed to measure the
geostationary flux of electrons of energy E>2 MeV and protons of
energy E such that .6 < E < 4.2 MeV. Because of radiation damage
to the GOES-6 E1 detector, these data are not included in the
data-set. The GOES -7 electron detector also responds to protons
of energy E > 80 MeV. Therefore, during solar energetic particle
events, the electron data are often compromised to the extent that
they may primarily represent the detector response to energetic
protons. GOES-7 particle detector data is missing during an
eclipse and for approximately the following 4 hours.
Finally, the geomagnetic cutoff at geostationary orbit is of the
order of 1 MeV, which is within the energy range of the P1
channel. Therefore, the flux observed during a solar energetic
particle event by channel P1 is a composite of trapped protons at
the lower channel energies and event protons which reach the
satellite from sources outside the magnetosphere.
---------------------------------------------------------------------------
Ground Based Experiment: Dual Auroral Radar Network (DARN)
The Dual Auroral Radar Network (DARN) is one of the
Ground-Based Instruments (GBI) of the ISTP/GGS project. As
it is currently configured, DARN consists of 6 independent
radar systems. Each radar is briefly described below
(moving from East to West):
1. STARE
The Scandinavian Twin Auroral Radar Experiment. This
is a VHF radar system which uses two radars observing a
common volume to determine plasma drift velocities in
the ionospheric E-region. The two radars are located
in Finland and Norway. The institutions involved are
the Finnish Meteorological Institute and the Max Planck
Institut f$r Aeronomie.
2. SABRE
The SABRE radar is a single VHF radar located at Wick,
Scotland. It is similar to the STARE radars, but uses
only a single radar rather than a pair. The radar is
operated by the Univ. of Leicester, UK.
3. Goose Bay HF radar
The Goose Bay radar is an HF radar located in Goose
Bay, Labrador. It observes the ionospheric plasma
drift velocities in both the E and F-Regions. It is
operated by the Applied Physics Laboratory.
4. SHERPA
The SHERPA radar is an HF radar similar to the Goose
Bay radar. It is located in Schefferville, Quebec.
Its field of view partially overlaps that of the Goose
Bay radar, and it is possible to determine 2-D plasma
velocity vectors in some cases, by using the data from
the 2 radars. However, unlike STARE, the 2 radars
operate independently. SHERPA is operated by CNRS in
France.
5. BARS
The Bistatic Auroral Radars System is one component of
the Canadian CANOPUS system. It is a dual VHF radar
system similar to STARE and observes plasma drift
velocities in the E-region.
6. Halley Station radar
The Halley radar is located at Halley station
Antarctica. It is an HF radar virtually identical to
the Goose Bay radar, and its field of view is
magnetically conjugate to that of the Goose Bay radar.
The Halley radar is operated by the British Antarctic
Survey. The combined observations from Halley and
Goose Bay form the Polar Anglo-American Conjugate
Experiment (PACE).
----------------------------------------------------------------------