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THE GLOBAL GEOSPACE SCIENCE PROGRAM AND ITS INVESTIGATIONS
----------------------------------------------------------
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 (LANL). 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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