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4. Supporting Research and Development
An essential objective of the 1980's is the development
of more powerful instrumental techniques that will
achieve major improvements in sensitivities and in
spectral and angular resolutions. Technical concepts
already exist to achieve these goals, but they need
extensive development before they are ready for space-
flight. Thus, a vigorous research and development pro-
gram with development flights on balloons and the Shuttle
is an essential part of the strategy for gamma-ray
astronomy in the 1980's.
VI I . COSMIC-RAY ASTRONOMY
A. Introduction
Cosmic rays constitute a suprathermal gas of energetic
charged particles that pervade the entire Galaxy. Con-
sisting mostly of protons, alpha particles, and other
bare nuclei of the elements with individual particle
energies from 106 eV up to at least 102° eV, they are
the only sample of matter from regions well outside the
solar system that we can examine in detail. High-energy
electrons, the source of Galactic synchrotron radio noise,
constitute about 1 percent of the total cosmic-ray flux.
Positrons and antiprotons produced in collisions of cosmic
rays with interstellar matter have also been observed.
m e astrophysical significance of cosmic rays stems
from two considerations. On the one hand, they carry in
the details of their composition and energy spectra inter-
esting and unique information about their sources and the
regions of space in which they have traveled; on the other
hand, they are an important astrophysical entity in them-
selves, having an energy density comparable with that of
the Galactic magnetic field and of the turbulent motion
of the interstellar gas. The pressure of the cosmic-ray
gas and its heating of the interstellar medium affect the
processes of star formation and influence the structure
and evolution of the Galaxy.
Observations of cosmic rays are made with a wide
variety of instruments each tailored to the character-
istics of a particular component and energy regime.
Among the most important technical developments in recent
years are instruments capable of resolving individual
elements and isotopes, measuring the abundances of the
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exceedingly rare heavy nuclei up to uranium, observing
high-energy electrons and positrons, and searching for
particles of antimatter. Small detectors have been flown
on satellites and space probes to investigate the prop-
erties of low-energy cosmic rays in the solar system from
the orbit of Mercury to beyond the orbit of Saturn. Large
and heavy instruments have been used at high altitudes in
balloon flights and in Earth orbit on the HEAD-3 satellite
to measure the composition and spectra of cosmic rays up
to energies of 101~ eV.
Very large arrays of detectors
on the ground have been used to study cosmic rays with
energies as high as 1012 eV through the observation of
showers of secondary particles produced in the atmosphere
It is believed that most cosmic rays originate in pro-
cesses associated with supernovae and are confined within
the Galaxy for millions of years by the Galactic magnetic
field. Some low-energy cosmic rays are produced within
the solar system in solar flares, in planetary magneto-
spheres, and in shock waves in the interplanetary medium.
The rare cosmic rays with energies above 1019 eV
probably originate outside our Galaxy.
Magnetic force twists the trajectories of cosmic rays
into helices around the lines of the magnetic field and
thereby destroys any simple relation between the distri-
bution of their arrival directions and the locations of
their sources. Information about the sources of cosmic
rays is therefore sought primarily from measurements of
their composition and energy spectra. For example, the
presence in the ultraheavy (Z greater than 28) cosmic rays
of nuclei that can only be produced by rapid sequential
absorption of free neutrons would indicate that they are
synthesized during the nuclear phase of a supernova
explosion. The isotopic compositions of the nuclei of
individual elements such as neon, magnesium, silicon,
sulfur, and iron can be related to the temperature,
density, and mixing during nucleosYnthesis.
-
The existenc
of a substantial difference between the compositions of
cosmic rays with energies below and above the critical
value near 1017 eV for magnetic confinement within the
Galaxy would support the hypothesis that cosmic rays of
very high energy have a different, and probably extra-
galactic, origin. m e unambiguous detection of any nuclei
of antimatter with Z greater than unity would be con-
vincing evidence for the existence of stars of antimatter
and would have profound implications for the origin of
the Universe and the nature of the fundamental forces.
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Solar flares and planetary magnetospheres are sources
of highly variable fluxes of low-energy cosmic rays within
the solar system. Measurements of their elemental and
isotopic abundances provide direct information about the
composition of material in other bodies in our solar
system and about the nature of the acceleration
mechanisms.
Charged particles are accelerated by electric fields
induced by changing magnetic fields. The latter are
caused, in turn, by collective motions of plasma or other
conductors, such as rotating stars and planets, in which
the current sources of the magnetic field are located O A
necessary condition for this process to produce cosmic
rays is that the density of plasma in the region of
acceleration be low enough so that the particles gain
energy faster from the induced electric field than they
lose it in collisions. This condition evidently occurs
throughout the Universe under a variety of circumstances.
Much discussed cases are the outer layers of an exploding
supernova remnant and interstellar shock waves. Informa-
tion about the acceleration mechanisms can be derived
from measurements of the energy spectra of individual
components of cosmic rays. Particularly important is the
range above 1011 eV/nucleon in which the spectra observed
at Earth are not appreciably distorted by effects of the
solar wind and relative abundances are apparently changed
very little by interactions with interstellar matter.
More specific information can be gained from measurements
of the isotopic composition. For instance, the mean time
between the nucleosynthesis of cosmic-ray nuclei and their
acceleration to relativistic energies can be derived from
measurements of the abundances of radioactive nuclides
that decay by K-electron capture. Only those nuclides
are present that were accelerated and stripped of their
K-electrons by Coulomb collisions before they decayed.
Cosmic rays interact with interstellar matter, with
the magnetic field that controls their motions, and with
photons of starlight and the microwave background. The
average thickness, or pathlength, of the matter traversed
before escape from the Galaxy is determined from measure-
ments of the relative abundances of the secondary cosmic
rays produced in these interactions, such as the nuclei
produced by fragmentation of heavier nuclei in collisions
with interstellar matter. If one also determines the
average containment time, for instance through measure-
ments of the abundances of various radioactive isotopes,
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one can find the average density of the matter in the
regions traversed by cosmic rays.
Cosmic-ray electrons with energies above 1013 eV,
spiraling along magnetic-field lines in the Galactic
disk, lose most of their energy within a few hundred
parsecs owing to synchrotron emission and inverse Compton
scattering with the microwave background radiation. Thus
the shape of the energy spectrum of electrons in this
energy range is a sensitive indicator of the distribution
in distance of the sources of cosmic-ray electrons. Simi-
lar considerations apply to the interpretation of the
energy spectrum of cosmic-ray nuclei above the threshold
for photodisintegration by collisions with photons of the
microwave background. m is threshhold is near 1019 eV.
While cosmic-ray nuclei with energies above this thresh-
old almost certainly originate outside the Galaxy, their
mean free path before photodisintegration is short com-
pared with the Hubble distance so that the shape of their
spectrum must be influenced by the spatial distribution
of their sources.
Interstellar matter is ionized and heated by cosmic
rays that lose energy by Coulomb collisions. This may
have significant effects on the evolution of molecular
clouds and star formation. The importance of this effect
depends critically on the flux of Galactic cosmic rays at
very low energy. This flux is still unknown, because low-
energy cosmic rays are swept out of the solar system by
the solar magnetic field moving outward with the solar
wind. A direct measurement could be made only by a deep
space probe that leaves the solar cavity.
B. Progress during the 1970's
1. Instrumentation and Vehicles
.
During the 1970ts balloon experiments were the principal
and almost exclusive source of new information about the
composition and energy spectra of Galactic cosmic rays at
energies above 1 GeV per nucleon. At lower energies
absorption and production of secondaries in the Earth's
atmosphere limit the usefulness of balloon observations.
Balloon experiments also played an essential role in the
development of instrumentation for subsequent observations
from space vehicles. Substantial progress was made in
increasing the capabilities of balloon vehicles in regard
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to reliability' loads, and duration and in improving the
quality of support facilities and data recovery. Typical
flights carried payloads of 1000 or 2000 kg to altitudes
above 40 km for about 1 day.
Space experiments extended the range of cosmic-ray
measurements to lower energies and yielded data of a
precision limited only by counting statistics. The
Interplanetary Monitoring Platform (IMP)-5, -6, -7, and
-8, the Orbiting Geophysical Observatory (OGO)-5 and -6
and International Sun Earth Explorer (ISEE)-1 and -3
carried instruments outside the Earth's magnetosphere to
measure the elemental and isotopic composition and the
energy spectra of low-energy (E less than 109 eV/nucleon)
cosmic rays from Galactic and solar system sources. In-
struments on solar satellites and deep space probes, which
include Pioneer-10 and -11, Mariner-10, Helios-1 and -2
and Voyager-1 and -2, measured the composition and spectra
of cosmic rays over a wide range of heliocentric distances
and surveyed the particle populations and acceleration
phenomena in the magnetospheres of Jupiter and Saturn.
Skylab, at the beginning of the decade, carried plastic
track detectors in Earth orbit to measure the composition
of the rare ultraheavy nuclei. At the end of the decade
the third of the High Energy Astronomical Observatories,
HEAD-3, was launched with heavy instruments to measure
the mean isotopic composition of the cosmic-ray nuclei up
to iron and the elemental composition beyond iron. Simi-
lar measurements were undertaken with the British
Explorer-class satellite, Ariel VI.
Large air-shower detectors were operated on the ground
in several countries to measure the energy spectrum, arri-
val directions, and composition of the very rare cosmic
rays in the region above 1017 eV where a transition may
occur from Galactic to extragalactic sources. Novel
approaches to the measurement of ultra-high-energy cosmic
rays were taken in developing the "Fly's Eye" detector,
designed to record the fluorescent light emitted along
the trajectory of an air shower in the atmosphere, and
the Homestake mine installation, which detects high-energy
muons produced by interactions of primary cosmic-ray
nuclei with air atoms near the top of the atmosphere.
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2. Scientific Accomplishments
a. Elemental Composition and Energy Spectra (Z up
through 28):
Precise measurements of the elemental composition
have been made up to energies of approximately 10
GeV/nucleon, and exploratory composition measurements
have been performed to about 100 GeV/nucleon. mese
measurements led to the discovery that the elemental
composition of cosmic rays is strikingly similar to the
of solar system material. On the other hand several
characteristic deviations from the solar-system abundances
have been found, and these deviations have led to these
important conclusions:
(i) The abundances of the secondary cosmic rays around
1 GeV/nucleon imply an average pathlength in interstellar
matter of 7 g/cm before escape from the Galaxy.
(ii) The average pathlength, and perhaps the
containment time, decrease with increasing energy. Around
100 GeV/nucleon, the average pathlength may be as small
as l g/cm2, a most surprising result whose interpreta-
tion is currently a subject of intense study.
(iii) Heavy elements are relatively more abundant in
cosmic rays than in the solar system, possibly owing to
the greater ease with which high-, atoms can be ionized
prior to acceleration.
An "anomalous component" of cosmic rays with very low
energies of about 10 MeV/nucleon or less has been dis-
covered. Its most likely origin is neutral atoms of
interstellar matter, photoionized in the neighborhood of
the Sun and accelerated by magnetohydrodynamic turbulence
in the solar cavity.
The composition of cosmic rays above 1012 eV is essen-
tially unknown. However, measurements of the energy spec-
trum were extended to about 1012 eV. Above 3 X 10 eV
the spectrum begins to fall off more rapidly, possibly
owing to a higher rate of leakage from the Galaxy. Above
1019 eV this trend reverses, and a small but significant
anisotropy in the distribution of arrival direction is
apparently present. It is likely that the origins of the
particles above 1019 are extra-galactic, but the nature
and location of their sources are unknown.
b. Ultraheavy Nuclei with Z Greater Than 28
Before 1979 only very limited data were available on
the extremely rare ultraheavy nuclei. The situation
changed after HEAD-3 and Ariel VI were launched. The in-
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struments aboard these spacecraft were capable of resolv-
ing, for the first time, the more abundant elements with
nuclear charges up to those of the actinide elements.
The preliminary data were not sufficient to establish
definitely whether there exists an overabundance of heavy
reprocess elements such as platinum and the actinides, as
expected for supernova material. In the region of lower
nuclear charges (Z up to 40) the elemental composition is
clearly not dominated by the products of reprocess nucleo-
synthesis, and the difference between cosmic-ray and
solar-system abundances are roughly correlated with the
values of the first ionization potentials.
c. Isotopic Composition
Recent investigations of low-energy cosmic rays have
resolved individual isotopes of the elements from hydrogen
to iron and have yielded information that cannot be
derived from measurements of elemental abundances alone.
For example, the neutron-rich isotopes of neon, magnesium,
and silicon are significantly overabundant compared with
solar-system material. This is clear evidence that
cosmic-ray matter has a nucleosynthetic history that is
different from that of solar-system material. Another
example is the low abundance of the radioactive isotope
1OBe (half-life = 1-5 X 106 years) around 200 MeV/nucleon,
which implies that the cosmic-ray containment time is
about 10 years, much longer than previously assumed.
This and the known average pathlength imply that cosmic
rays are confined in low-density regions of interstellar
space (with about 0.2 atom/cm3) or perhaps the galactic
halo.
d. Cosmic-Ray Electrons and Positrons
The observations of cosmic-ray electrons and posi-
trons lead to the following conclusions:
(i) The energy spectrum of electrons above about 30
GeV is steeper than that of all cosmic-ray nuclei. At-
tributing this effect to the influence of Compton- and
synchrotron-energy losses in interstellar space, one finds
the containment time of cosmic-ray electrons in the Galaxy
to be of the order of 107 years, in good agreement with
the containment time of cosmic-ray nuclei derived from
the measurements of 1OBe.
(ii) In the energy range 1-30 GeV, positrons have an
intensity much smaller than that of negative electrons.
Since positrons and negative electrons are produced in
nearly equal numbers as a result of high-energy inter-
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actions of cosmic-ray nuclei with interstellar matter,
this observation shows that only a small fraction of the
cosmic-ray electrons arise from such interactions.
(iii) Electrons observed near Earth at low energies
(less than 50 MeV) include not only particles of inter-
stellar and solar origin but also, and perhaps mostly,
particles that originate in the magnetosphere of Jupiter.
Scientific Goals for the 1980's
Cosmic-ray research has reached the stage where it is now
possible to make definitive measurements that bear on the
origins of cosmic rays and on the interplay between cosmic
rays, interstellar matter, and fields. The following
observations are major goals of the 1980's.
1. Isotopic Composition from Hydrogen through Nickel
A detailed comparison of the abundances of cosmic-ray
isotopes with the solar-system abundances will provide
critical information on the nucleosynthetic history of
the material that becomes cosmic rays and, by comparison,
a new perspective on the origin of the solar system.
Particularly important are the abundances of the neutron-
rich isotopes of neon, magnesium, silicon, sulfur, iron,
and nickel, all of which are sensitive to circumstances
of the initial phase of a supernova explosion.
Information about the Galactic containment time of cos-
mic rays can be derived from measurements of the relative
abundances of radioactive isotopes. It is important that
the abundances of a wide variety of isotopes be investi-
gated in order to decide whether all cosmic-ray species
experience the same propagation history. The measure-
ments must cover a large energy range corresponding to a
wide range of relativistic time dilations.
2. Elemental Composition of the Ultraheavy Nuclei
The elemental composition in the range of atomic numbers
above Z = 26 yields clues to the processes of nucleosyn-
thesis and acceleration of cosmic rays. Precise abun-
dance measurements should be made of individual elements
including the rare odd-, elements. Even more valuable
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information could be derived from measurements of their
isotopic abundances, but the technical problems of such
measurements are severe.
The relative abundances of interstellar secondaries of
ultraheavy nuclei (Z values in the ranges 41-49 and
67-75) provide a particularly sensitive measure of the
pathlength distribution of cosmic rays at short path-
lengths since their interaction cross sections are much
larger than those of the lighter cosmic rays. The radio-
active actinide elements are potentially useful as chro-
nometers for estimating the time elapsed since their
nucleosynthesis.
3. Elemental Composition at High Energies
The composition and the individual energy spectra of the
major cosmic-ray components should be determined in direct
measurements up to energies of at least 104 GeV/nucleon.
As noted above, the average pathlength of cosmic-ray
nuclei at these high energies is probably less than 1
g/cm2. Thus abundance changes due to interstellar
spallation are almost negligible, and the measurements
will yield direct information on the elemental compo-
sition at the acceleration site. These measurements will
also reveal how the average pathlength depends on energy
and thereby cast new light on the confinement of cosmic
rays in the Galaxy. The range of direct measurements
should overlap the ultra-high-energy range of air-shower
measurements in order to achieve an effective cross-
calibration of the measurement techniques.
4. Energy Spectrum of Electrons at High Energies
The energy spectrum of cosmic-ray electrons should be
measured up to at least 104 GeV. Such measurements
will provide information on the possible existence of
cosmic-ray sources closer than about 1 kiloparsec. They
will also yield more precise information on the contain-
ment time of Galactic cosmic-ray electrons. Measurement
of the positron spectrum is of special importance because
the input spectrum of positrons can be calculated from
knowledge of the interstellar nuclear collisions in which
they arise. Currently available positron data do not yet
cover the energy region above 30 GeV, where radiative
energy losses are significant.
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5. The Composition and Origins of Ultra-High-Energy
Cosmic Rays
The origin of cosmic-ray particles with energies above
1018 eV remains a central problem of high-energy astro-
physics that can only be approached through the detection
and analysis of the very large showers that such particles
produce in the atmosphere. Better knowledge of shower
development and accurate calibrations of detectors are
needed to improve the reliability with which the energy
and composition of the ultra-high-energy primaries are
deduced from observations of showers. Years of exposure
time with detectors of the largest attainable effective
collecting areas will be required in order to obtain
adequate statistical accuracy in the measurement of the
spectrum and the distribution in arrival directions.
6. Low-Energy Cosmic Rays (<300 MeV/Nucleon) in
Interstellar Space
The contribution of low-energy cosmic rays to heating the
interstellar gas and the effects they have on the struc-
ture of the Galaxy should be studied by measurements out-
side the heliosphere. Direct measurements can be made
only with a deep-space probe that leaves the solar system.
7. Solar-System Cosmic Rays
Measurements of energetic particles originating in the
solar system are of fundamental importance in the effort
to gain a better understanding of the processes of par-
ticle acceleration and propagation in less accessible
regions of the cosmos. Such measurements may also reveal
subtle differences in the isotopic composition between
solar cosmic rays and terrestrial material and thereby
cast new light on the origin and history of the solar
system. In order to distinguish clearly between temporal
and spatial variations the measurements must be made
simultaneously at widely separated locations in the solar
system and over several solar cycles.
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D. Inventory of Present or Approved Resources
1. Small Satellites and Space Probes
Several spacecraft or deep-space probes with small
cosmic-ray detectors aboard are expected to remain active
into the 1980's. Detectors on ISEE-1 and -3 will con-
tinue to measure the low-energy elemental composition and
low-energy electrons in interplanetary space and provide
the isotopic composition of the more abundant nuclides.
Detectors on the deep-space probes Pioneer-10 and -11,
and Voyager-1 and -2 will measure Galactic, solar, and
planetary cosmic rays at very large distances from the
Sun, and thereby probe the particle population and the
solar modulation mechanisms in regions not pre- viously
explored. During the next decade, these missions will
reach distances out to 30 astronomical units (AU).
The International Solar Polar Mission (ISPM), as
originally approved, would be the first spacecraft to
carry cosmic-ray and energetic-particle detectors far
outside the ecliptic plane and over the poles of the
Sun. It would thus explore fluxes and composition of
particles from interstellar space and from the Sun in
those parts of the solar system where no direct measure-
ments could ever before be made.
2. Large Spacecraft
HEAD-3 carried two large cosmic-ray detectors to measure
the elemental composition of the more abundant ultraheavy
cosmic rays and to measure the mean mass, i.e., the iso-
topic mix of the elements around a few GeV/nucleon. This
mission ceased operation in 1981.
3. Space Shuttle
m e Space Shuttle can carry very large and heavy detec-
tors. Unfortunately, the exposure times will be limited
initially to only about 1 week. Nonetheless, experiments
approved for Spacelab flights in the early 1980's will
address key questions of cosmic-ray astrophysics. They
will extend measurements of the elemental composition and
energy spectra of the more abundant cosmic-ray species
into the TeV/nucleon range, and they will provide informa-
tion on the interactions of high-energy heavy nuclei at
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energies far above those currently attainable at accel
Orators.
4. Balloons
High-altitude balloons have been important vehicles for
cosmic-ray measurements and will continue to be vitally
important to development of the field. The balloon pro-
gram is, however, severely underfunded. Its full poten-
tial could be realized with an increase in funds in
amounts that are small compared with the costs of space
missions.
5. Air-Shower Detectors
Ground-based observations of the extremely energetic cos-
mic radiation will be pursued at several installations.
In particular, the first phases of the Fly's Eye project
is nearly completed and will provide pioneering data
during the next few years.
E. Recommendations for the 1980's
Broad progress in cosmic-ray astronomy requires a wide
variety of observations. Of central importance to the
field in the 1980's are long exposures of large instru-
ments in near-Earth orbit and high-sensitivity isotopic
composition measurements on spacecraft beyond the inter-
ference of the Earth's magnetosphere. Experiments on cur-
rently active satellites and space probes should be fully
utilized, and future planetary missions should be equipped
with appropriate particle detectors. Instrumentation
development and exploratory measurements on balloon vehi-
cles must be continued. Progress at the highest energies
requires the further development of air-shower
installations.
1. The Cosmic-RaY Platform
Definitive measurements in several important areas of
cosmic-ray astronomy require exposures of massive (1000-
5000 kg) detectors with large collection areas (1-30 m2
sr) in Earth orbit for periods of at least 1 year. Such
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instruments can be developed and tested and will yield
important preliminary results in Spacelab flights. How-
ever, the long exposures required for definitive measure-
ments could be provided by a relatively simple Cosmic-Ray
Platform (CRP) that is launched, maintained, and refur-
bished by the Shuttle Transportation System. The CRP
does not need accurate celestial pointing. It should be
able to carry one or two instruments and should be usable
in either near-equatorial or high-inclination orbits. In
typical missions, each individual instrument will be
developed and supported by a group of invest) gators and
institutions. Launch opportunities should exist at 1- to
2-year intervals, starting in the mid-1980's.
The following investigations promise the most impor-
tant scientific returns and should therefore be given
highest priority:
(a) Measurements of the composition of cosmic rays up
to very high energies (104-105 GeV/nucleon).
(b) Detailed composition measurements of ultraheavy
cosmic rays, with resolution of individual elements and,
perhaps, isotopes.
(c) Precise measurements of the isotopic composition
from hydrogen to iron at energies up to several
GeV/nucleon.
The experimental techniques to perform these measure-
ments are currently available. In several cases, they
have been verified on balloons or on HEA0-3 or are under
development for Spacelab flights.
2. Missions outside the Magnetosphere
We recommend that an Advanced Interplanetary Explorer be
launched in the mid-1980's and that opportunities be made
available to fly cosmic-ray instruments on this and other
interplanetary spacecraft. Such spacecraft provide long-
term (about 3 years) exposures outside the magnetosphere
for detectors of modest size and cost. Highest priority
should be given to detailed measurements of the isotopic
composition of cosmic rays at low energies (1 GeV/nucleon)
and of solar-flare-accelerated particles. Other scien-
tific objectives include measurement of the elemental
composition at low energies, detailed studies of the
anomalous component, and investigations of particles of
interplanetary origin. Simultaneous measurements at
different locations in the heliosphere and over a long
period of time are necessary. These measurements will
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require detectors with geometrical factors of about 100
cm2 sr (1 to 2 orders of magnitude larger than previous
instruments) and good mass resolution (0.2 AMU) over the
energy region from well below 1 MeV/nucleon to 1000
MeV/nucleon. The appropriate technology is at hand, and
the expected scientific return is large.
3. Deep-Space Missions
The study of the low-energy interstellar cosmic rays
requires the operation of detectors outside the solar
system to avoid the perturbing effects of the solar
wind. During the 1980's Pioneer-10 will be beyond 20 AU
from the Sun, Pioneer-ll will have passed Saturn, and the
Voyagers will be traveling between 10 AU and 30 AU. The
ISPM probes will be passing over both polar regions of
the Sun at distances somewhat over 1 AU. In order to
realize the astronomy objectives of these investigations,
it is vital that collection of data from these missions
by the Deep Space Network continue through 1990. Fur-
thermore, in order to distinguish temporal from spatial
variations, simultaneous measurements are needed near 1
AU.
Opportunities for deep-space observations on future
outer planetary missions should be utilized in order to
enhance the probability that a properly functioning
spacecraft will eventually leave the region of solar
modulation, even though the time required for the journey
significantly exceeds nominal mission and spacecraft
design lifetimes.
4. Balloons
High-altitude balloons have been exceedingly successful
carriers of cosmic-ray instrumentation in the past, and
they will continue to be important in the 1980's. They
provide the means to develop and optimize innovative
experimental approaches at relatively low cost and with
rapid turnaround. Techniques to fly heavy payloads for
weeks or months have been proposed. Their development
should be supported along with the conventional balloon
program. It is extremely important that adequate suppor
be made available not only for the development of new
instrumentation techniques but also for a broad range of
basic experimental and theoretical studies.
Representative terms from entire chapter:
elemental composition
