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OCR for page 101
Approved, Continuing, and
Previously Recommended
Programs
AS emphasized in Chapter 2, the achievement of the goals for as-
tronomical research presented in Chapter 3 depends heavily on the
maintenance of support for approved and continuing programs; these,
together with programs previously recommended in other National
Academy of Sciences reports for implementation in fiscal year 1982
and earlier, form the base of present and planned resources from
which the recommendations of the Astronomy Survey Committee
proceed. Their role in the research of the 1980's is discussed below
in the following order, which carries no implication of priority:
A. Space Telescope and the associated Space Telescope Science
Institute;
B. Second-generation instrumentation for Space Telescope;
C. The Gamma Ray Observatory;
D. Level-of-effort observational programs within the National
Aeronautics and Space Administration:
· The NASA Explorer satellite program, with a substantial aug-
mentation,
· Research with balloons, aircraft, and sounding rockets, at
enhanced levels of support, and
· The Spacelab program, reaffirming NASA'S original strong
commitment to research with the Space Shuttle;
E. Two major astrophysics facilities for Spacelab:
· The Shuttle Infrared Telescope Facility (STRTF) and
101
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102
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
· The Solar Optical Telescope (SOT);
F. Facilities for the detection of solar neutrinos;
G. Federal grants in support of basic astronomical research at U.S.
. . .
unlverslhes;
H. Programs at the National Astronomy Centers; and
I. The 25-Meter Millimeter-Wave Radio Telescope.
The remainder of the present chapter illustrates the role that these
programs will play in addressing the major scientific problems of the
coming decade.
A. SPACE TELESCOPE AND THE ASSOCIATED SPACE TELESCOPE
SCIENCE INSTITUTE
The Astronomy Survey Committee regards Space Telescope (ST)
as a project of extreme importance for all of astronomy and rec-
ommends that NASA complete its development and place it into
operation at the earliest possible date. This facility will represent
one of the most momentous advances in astronomical instru-
mentation since Galileo's first telescope.
The launch of ST, now planned for 1985, will provide the first
permanent optical observatory in space. This facility, carrying a
2.4-m telescope of superb optical quality, will take full advan-
tage of the benefits of observing above the Earth's atmosphere:
sharp images unaffected by clouds or atmospheric turbulence,
elimination of airglow, and extension of the spectral range into
the ultraviolet (uv) and near-infrared wavelength regions. ST will
be the first orbiting telescope large enough to carry out studies
of extragalactic objects at the limits of the observable Universe.
The first complement of instruments on ST will obtain digital
photometric images over the wavelength range 1200-12000 A,
spectra from 1200 to 8000 ~ with a large range of resolutions,
and visible and uv photometry with fast time resolution. The
European Space Agency will provide one of these instruments as
part of a planned international collaboration in the ST program.
The results of ST will profoundly affect every branch of as-
tronomy. Identification and photometry of stars fainter than the
twenty-seventh magnitude in the visible and uv regions will
revolutionize extragalactic astronomy. Studies of stellar popula-
tions down to the main sequence can be made in nearby galax-
ies and in almost all of the globular clusters of our Galaxy. Bright
stars suitable as distance indicators can be observed individually
OCR for page 103
Approved, Continuing, and Previously Recommended Programs 103
,~
in galaxies out to the Virgo cluster, allowing the cosmic expan-
sion to be studied with unprecedented accuracy. The high an-
gular resolution of ST will permit morphological classification of
galaxies with red shifts up to order unity, allowing direct stud-
ies of the evolution of galaxies over the past 5 billion to 8 bil-
lion years. What kinds of galaxies may be associated with qua-
sars is likely to be determined from an analysis of ST images. The
question of whether some galaxies harbor giant black holes in
their nuclei may be settled. Galactic astronomy will utilize the
ability to measure the very faint stars in globular clusters and the
Galactic bulge to determine, for example, the mass function of
star formation in various regions of the Galaxy. The imaging ca-
pability of ST will also open an important new range of investi-
gations within the solar system; for example, diffraction-limited
images at high spatial resolution will permit detailed views of the
structure and dynamics of atmospheric circulation on other
planets.
The spectroscopic capabilities of ST are equally impressive. Our
understanding of the interstellar medium, revolutionized by ob-
servations with the Copernicus satellite and rocket surveys of soft
x rays, will be further advanced by ST measurements down to
1200-A wavelength: new observations will be made at much
higher spectral resolution and in much more heavily obscured
regions all over the Galaxy. Most of the known quasars can be
studied spectroscopically in the uv region, permitting critical
comparisons of distant and nearby objects and the use of qua-
sars as probes of the intervening medium. In planetary astron-
omy, the w spectroscopic capability will permit searches for new
molecules in planetary atmospheres and comets and delineate
their structure. The surface chemistry of planets and asteroids can
also be explored.
The Committee strongly approves NASA'S commitment to oper-
ate and support ST through an associated but independent Space
Telescope Science Institute, which will include international par-
ticipation. The Institute will be responsible for the scientific di-
rection of ST, for data-reduction facilities, for education concern-
ing use of the instrumentation, and for meeting all research
expenses incurred by the ST user community; it will also be the
liaison between NASA and the scientific community on matters
concerning the management and improvement of this powerful
instrument.
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ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
B. SECOND-GENERATION INSTRUMENTATION FOR SPACE
TELESCOPE
Space Telescope is designed to employ interchangeable instru-
ments that can be replaced either in orbit or when ST iS re-
turned to Earth. Since ST should exploit all the benefits of the
latest technology, the Astronomy Survey Committee regards timely
upgrading as extremely important. Major changes that can cur-
rently be foreseen include improvements to the ST spectrographs
and the implementation of ST'S potential infrared capability. These
two changes are sufficiently important to merit further discus
slon.
Both of the first-generation spectrographs on ST employ Digi-
con detectors with one-dimensional diode arrays behind a pho-
tocathode. The power of a spectrograph can be increased dra-
matically through use of a two-dimensional detector; in an echelle
format, for example, a wide spectral range is then available in
one high-resolution exposure; for extended objects, spatial infor-
mation is then obtained along the entire slit image. It seems likely
that two-dimensional, charge-coupled-device-type detectors with
very low read-out noise and high uv sensitivity will become
available within a few years. This combination of two-dimen-
sional coverage with high quantum efficiency constitutes an up-
grading of very high priority.
Present ST instruments do not allow observations at wave-
lengths much longer than 1 ~m. Although the infrared region will
also be covered by the ERAS Explorer satellite and the powerful
SIRTF Shuttle facility, the large aperture of ST gives it a great
advantage in two crucial areas of scientific investigation. One is
imagery in the near infrared, for which detectors of high quan-
tum efficiency will almost certainly soon become available. The
other is high-resolution spectroscopy throughout those extensive
regions of the infrared to which the Earth's atmosphere is opaque;
this work requires the greater collecting area and angular reso-
lution of ST. Infrared capability in each of these areas is com-
plementary to both ground- and space-based programs and will
be valuable for a wide variety of critical programs ranging from
planetary science to cosmology. For example, since the expan-
sion of the Universe shifts the well-studied optical region into the
infrared for very distant objects, evolutionary studies of galaxies
cannot be complete without infrared data. The Committee there
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Approved, Continuing, and Previously Recommended Programs 105
fore recommends that NASA develop appropriate infrared instru-
ments to be flown aboard ST.
C. THE GAMMA RAY OBSERVATORY
The Astronomy Survey Committee believes that the Gamma Ray
Observatory (GRO) will yield results on high-energy processes that
will be of fundamental importance to the advance of astrophys-
ics during the coming decade. The 1979 report of the Space Sci-
ence Board's Committee on Space Astronomy and Astrophysics
(CSAA) recommended that GRO be the next new space-astronomy
mission beyond those already approved by Congress at that time
(A Strategy for Space Astronomy and Astrophysics for the 1980's, Na-
tional Academy of Sciences, Washington, D. C., 1979~. The Sur-
vey Committee joins with CSAA in endorsing this important fa-
cility and is pleased that GRO iS now an approved component of
the U.S. space-science program.
Gamma-ray astronomy permits the study of energy transfor-
mations in critically important processes, such as cosmic explo-
sions, acceleration and interactions of high-energy particles,
gravitational accretion by superdense objects, nucleosynthesis in
stars, and matter-antimatter annihilation. Because gamma rays
have high penetrating power, they can reach the Earth from parts
of the Universe whose optical or low-energy x-ray emission may
be obscured by intervening matter, such as the center of our own
Galaxy and the central regions of active galaxies.
Observations with GRO will address many important astro-
nomical questions. The SAS-2 satellite and, in Europe, the COS-B
satellite have demonstrated the rich character of the diffuse Gal-
actic radiation, believed to be a result of cosmic-ray interactions
with the interstellar medium. Observations of this emission on a
finer scale with GRO will help to determine the origin and dy-
namic-pressure effects of cosmic rays, to identify large concen-
trations of interstellar gas, and to study Galactic structure.
Numbers of discrete gamma-ray sources have been detected in
previous surveys. While some of these are associated with known
supernova remnants and pulsars, others have not yet been
identified at longer wavelengths and may thus represent a new
class of objects. Additional gamma-ray observations are required
to clarify why some sources are more complex than anticipated.
The Vela pulsar, for example, exhibits two gamma-ray pulses per
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106
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
cycle, while only one pulse occurs in the radio region; more-
over, neither gamma-ray pulse is in phase with the radio pulse.
Another puzzle is a strong source in the general direction of the
Galactic center, which is indicative of pair annihilation; further
observations are needed to investigate the nature of this source.
GRO can obtain information relevant to nucleosynthesis by de-
tecting nuclear-decay gamma-ray lines of recently synthesized
elements in our own and other nearby galaxies. In the most in-
tense sources it may be possible to record line profiles, from
which one can infer the current rate of heavy-element produc-
tion and information relevant to the densities, temperatures, and
flow velocities in supernova remnants. Regions in which mas-
sive stars are forming may be found through observations of the
lines of isotopes such as 26A1.
GRO will permit the study of cosmic gamma-ray bursts with
much greater sensitivity and energy resolution than provided by
any previous or other currently planned mission, thus shedding
new light upon the nature of gamma-ray burst sources.
GRO will also obtain detailed information on the spatial uni-
formity and energy spectrum of the diffuse extragalactic gamma
radiation, providing clues to its origin. Since gamma radiation
may reflect most directly the primary emission process in active
galaxies, GRO observations will contribute to an improved under-
standing of these objects. Studies of time variability at gamma-ray
(and other) wavelengths will yield insight into the active vol-
umes and associated energy densities. High-energy gamma rays
may also be observed from nearby normal galaxies; if so, GRO
data will furnish information on the distributions of cosmic rays
and matter in such galaxies as well.
The Committee agrees with CSAA that the continued develop-
ment and timely launch of GRO iS essential to the pursuit of these
important scientific objectives during the coming decade.
~ {Jet 1
D. LEVEL-OF-EFFORT OBSERVATIONAL PROGRAMS WITHIN THE
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
NASA has developed three modes for carrying out observational
space astronomy within level-of-effort programs: the Explorer
program; balloons, aircraft, and sounding rockets; and the
Spacelab program. Each of these modes provides a highly effec-
tive and in some cases unique mechanism to address particular
observational problems in astronomy and to test instrument con
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Approved, Continuing, and Previously Recommended Programs 107
cepts employing state-of-the-art technology. The Astronomy Sur-
vey Committee regards these level-of-effort programs as the
backbone of observational space astronomy and astrophysics for
the 1980's. The Committee therefore urges the continued, vigor-
ous support of the Explorer program and of research with bal-
loons, aircraft, and rockets, together with a speedy reaffirmation
of NASA'S original strong commitment to the Spacelab program.
The Explorer Program
The Explorer program has been one of the most productive and cost-
effective elements of the NASA space-science program. Its level-of-
effort character has encouraged both frugal management and rela-
tively rapid response to newly perceived scientific opportunities,
providing a highly effective mechanism to exploit new observational
techniques, to explore newly accessible wavelength intervals, or to
study a particular class of objects. Nearly all of the branches of space
astronomy have had or will soon have their beginnings in Explorer
missions. For example, the present International Ultraviolet Explorer
(lUE) program has provided essentially all of the intermediate-reso-
lution uv spectra available to the world of astronomy. The future
astronomy Explorers now under development or planned give prom-
ise of continuing this high level of pioneering achievement:
· The Infrared Astronomy Satellite THRASH, a project based on in-
ternational collaboration, will provide a detailed and comprehensive
reconnaissance of those components of the Universe that radiate
most strongly at relatively low temperatures (100-1000 K). Millions
of sources that emit substantially in the 10-100-m wavelength range
should be detected and their positions determined by ERAS, providing
a wealth of material for an initial survey of regions of active star
formation as well as of the brightest extragalactic sources. ERAS will
also be able to determine the surface composition of thousands of
asteroids within the solar system.
· The Cosmic Background Explorer (COBE) will make definitive
measurements of the 3 K cosmic background radiation, now generally
accepted to be a relic of the radiation generated in the big bang. COBE
will test this conclusion through precise measurements of the inten-
sity throughout the spectrum and of the anisotropy of the radiation.
Deviations from isotropy on the largest angular scales reflect the
motion of our Galaxy with respect to the large-scale structure of the
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108
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
Universe, while deviations on angular scales of the order of 10° carry
unique information about the inhomogeneity of the early Universe.
· The Extreme Ultraviolet Explorer (EUVE) will open for study an-
other major region of the electromagnetic spectrum, from 100 to 912
wavelength (from soft x rays to the uv region below the Lyman
limit), a primary objective being the completion of an unbiased, all-
sky survey of sources of EUV radiation. EUVE iS expected to reveal a
large number of new sources with temperatures in the range 105-
106 K, furnish broadband spectral information on many other already
known sources, and provide new information on the structure and
ionization state of the interstellar medium over a wide range of
distances from the Sun. This mission can also yield new information
about the Jovian magnetosphere and cometary atmospheres.
· The X-Ray Timing Explorer (XTE) will provide important new
opportunities for observations of variability in x-ray sources on time
scales ranging from milliseconds to years. The scientific objectives
of this mission include investigations of the mass, magnetic moment,
and internal structure of neutron stars and degenerate dwarfs; the
physics of accretion disks, plasmas, and stellar magnetospheres; the
geometry of source emission regions; the nature and evolution of
normal stars, through studies of mass loss; the nature of variable
sources, such as x-ray bursters and transient x-ray sources; and the
underlying physics and emission mechanisms in compact extraga-
lactic objects.
The Committee endorses the above mission concepts, which have
been carefully studied and highly recommended by other review
groups. Our concern is primarily for the future of this highly pro-
ductive program. We believe that it is vitally important for NASA to
maintain a strong Explorer program; over the past decade, however,
inflation and other factors have doubled the dollar cost charged to
the Explorer budget for the same real level of effort. The Committee
therefore recommends an augmentation to the Explorer program to
restore it at least to the level of effort of the previous decade. Such
an augmentation will ensure not only the timely flights of the mis-
sions described above but also opportunities for pursuit of many
other exciting new scientific objectives, as discussed in Chapter 6.
Balloons, Aircraft, and Sounding Rockets
The balloon, aircraft, and sounding-rocket programs have been vi-
tally important to the progress of astronomy and to the development
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Approved, Continuing, and Previously Recommended Programs 109
and testing of new detector systems later used on satellites. The
Greenstein report recommended a doubling of support for balloons,
rockets, and aircraft; balloon research has received strong support
by the Balloon Study Committee of the Geophysics Research Board
(The Use of Balloons for Physics and Astronomy, National Academy of
Sciences, Washington, D.C., 1976~; and balloons, aircraft, and rockets
have been supported by CSAA in its recent report (`A Strategy for Space
Astronomy and Astrophysics for the 1980's, National Academy of Sci-
ences, Washington, D.C., 1979~. Unfortunately, funding for such
programs has not grown, although the need is ever more acute. The
present Committee supports a vigorous effort in all three areas during
the 1980's to encourage innovative experiments and to obtain promptly
the initial scientific results from recently developed instruments.
The balloon program has been of particular value to infrared, x-
ray, gamma-ray, and cosmic-ray astrophysics, yielding important
contributions to the study of cosmic rays, energetic x-ray spectra,
low-energy gamma-ray bursts, gamma radiation from the Galactic
center, and far-infrared emission from ionized H ~ regions. Balloon
detector systems were prototypes for instruments on HEAo-3 and
SAS-2 and for several of those planned for COBE, Spacelab, and GRO.
The balloon program will continue to provide important new sci-
entific results and permit new instruments to be tested in an envi-
ronment similar to that of space. In order to remain productive, this
program should receive an augmentation in funding to compensate
for inflation, to provide larger balloons for heavier instruments, and
to develop a new balloon system to allow flights of longer duration.
The NASA aircraft program-including the U2 aircraft, the Lear let
Observatory, and especially the Kuiper Airborne Observatory (KAO:
has achieved scientific results of great importance, including the first
observations of far-infrared emission from other galaxies; an impor-
tant series of infrared observations of our own Galactic center; the
study of internal energy sources in Jupiter, Saturn, and Neptune;
the probing of interstellar molecular clouds and ionized regions in
new ways; a primary role in the discovery of rings around Uranus;
and studies of water vapor in the atmosphere of Jupiter and of
sulfuric acid droplets in the clouds of Venus. The KAO and Lear let
Observatory not only continue to serve as test facilities for many of
the research instruments and techniques being developed for space-
science applications but also provide the reconnaissance of the field
necessary for future major missions. For example, first-generation
instrumentation for far-infrared and submillimeter-wavelength spec-
troscopy is now being used on KAO to probe the spectral lines that
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ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
are believed to govern the energy balance in the bulk of the inter-
stellar medium. The full potential of these aircraft observatories un-
fortunately has not been achieved because of a lack of funds for
operations and personnel. A substantial increase in funding should
be provided for KAO operations in particular, not only to compensate
for increased fuel costs but also to permit the greater numbers of
flights required for a more intensive and hence more efficient use of
this outstanding facility.
The U.S. sounding-rocket program has played a key role in ad-
vancing the frontiers of x-ray, ultraviolet, and infrared astronomy,
with achievements including the discovery of the first cosmic x-ray
source (Sco X-1), discovery of x-ray pulsations from the Crab pulsar,
the first measurement of the uv spectrum of a nearby quasar, the
first soft x-ray sky survey, and the first ~20-~m all-sky survey, which
yielded new information about classes of previously unobserved in-
frared sources. Sounding rockets will continue to provide economical
and effective means for developing new instruments, for testing new
observational techniques, and for exploratory investigations. A strong
sounding-rocket program should therefore be maintained. The Com-
mittee also endorses the extension of observing time for rocket pay-
loads through their placement in temporary orbit by the Space Shuttle
as part of NASA'S Experiment of Opportunity Program (EOP).
The Spacelab Program
The Spacelab program will provide new flight opportunities for large
payloads that require servicing and will facilitate observational pro-
grams demanding higher altitudes or flights of longer duration than
. . . ~ . . ~ . . ~ ~ . ~ . ~
can ne achieved by aircraft or balloons. Spacelab flights will be par-
ticularly suitable for those facilities (both large and small) that can
gather substantial quantities of data within the relatively short initial
flights of the Space Shuttle; the Solar Optical Telescope and Shuttle
Infrared Telescope Facility described in Section E below are examples.
On its recent report, cited in the preceding section, CSAA recom-
mended a vigorous program of astronomy and astrophysics on Spacelab
with an annual level of effort exceeding that of a typical moderate
~ . .
c. .ass mission.
It is therefore of serious concern that funding for Spacelab exper-
iments and facilities has not yet reached substantial levels; support
for experiments that have already been approved has been signifi
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Approved, Continuing, and Previously Recommended Programs 111
cantly reduced, and the selection of additional PI experiments has
been deferred. The Committee is cognizant of the programmatic and
technical problems that have contributed to these decisions. How-
ever, now that flights of the Space Shuttle have begun, we urge
NASA to re-establish its original strong commitment to a vigorous
Spacelab program as soon as possible.
The Spacelab program will also facilitate the development of large
instruments designed to make initial observations on Shuttle flights
and later to be placed in orbit to carry out more comprehensive
scientific programs, possibly aboard a long-duration space platform.
The augmentation of Spacelab capability by such a space platform
would allow the Shuttle to realize its full potential as a scientific tool.
We therefore support NASA plans for the development of a long-
duration space platform operated in conjunction with Spacelab and
the Shuttle (see Appendix A, Statement Concerning a Space Plat-
form). We furthermore endorse the pursuit of means to extend the
observing time available to rocket-sized payloads through the de-
velopment of a standard module that will allow such payloads to be
placed in temporary orbit during Spacelab missions, without incur-
ring the substantial costs of an active Shuttle interface, such as may
be required for larger payloads.
The Committee also encourages the development of a Solar Shuttle
Facility, composed of several advanced facility-class instruments, to
be used in a coordinated group on the Space Shuttle. These instru-
ments will obtain data critical to an understanding of the fundamental
plasma processes underlying cyclic activity and transient high-energy
phenomena on the Sun and other stars; their development should
proceed as part of the ongoing Spacelab program, with the Solar
Optical Telescope (SOT) as the first such instrument. A plan for the
addition of succeeding instruments is expected to emerge from the
recommendations of other advisory groups, particularly the cssP.
Among the other instruments proposed for inclusion are a Solar Soft
X-Ray Telescope Facility (SSXTF), a Grazing Incidence Solar Telescope
(GRIST, selected for advanced study by the European Space Agency),
and a Pinhole/Occulter Facility for hard x-ray imaging and for the
study of the corona at high resolution (currently under study by
NASA). Still other solar instruments-such as those for EM and gamma-
ray observations and for specialized observations of the extended
corona, long-period photospheric oscillations, and large-scale circu-
lation should be considered for development as PI instruments or
as additional facilities within the Spacelab program.
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2
ASTRONOMY AND ASTROPHYSICS FOR THE 1980's
E. TWO MAJOR ASTROPHYSICS FACILITIES FOR SPACELAB
The Astronomy Survey Committee endorses both the Shuttle In-
frared Telescope Facility (SIRTF) and the Solar Optical Telescope
(SOT) as the first major astrophysics facilities planned for Space-
lab; the order of the following discussion carries no implication
of priority.
The Shuttle Infrared Telescope Facility (SIRTF)
The proposed SIRTF will be the cornerstone of research in infrared
astronomy during the 1980's. The Astronomy Survey Committee joins
with the Space Science Board's Committee on Space Astronomy And
Astrophysics (A Strategy for Space Astronomy and Astrophysics for the
1980's, National Academy of Sciences, Washington, D.C., 1979) in
recommending this facility as the first major infrared telescope in
space.
STRTF will permit investigations over the enormous range of wave-
lengths from 2 to 300 ~m. For some important types of observations
it will, because of its cryogenically cooled optics, yield a sensitivity
gain of 1000 over the largest existing ground-based and airborne
infrared telescopes; this gain in sensitivity is so large that it is not
unreasonable to expect that SIRTF will make important and unex-
pected discoveries. The multiple, interchangeable focal-plane instru-
ments planned for SIRTF will moreover greatly increase our ability to
explore the evolution of distant extragalactic sources, the physical
properties and chemical composition of molecular clouds and regions
of star formation, the nature of cometary nuclei and asteroids, and
the structure of planetary atmospheres. For example, STRTF will be
able to detect infrared sources at the limits of the observable Universe;
on one Shuttle flight, it could gather information on sources of both
large and small red shift, thus permitting a comparison of the en-
ergetics of quasars and galaxies at the earliest epochs of the Universe
with those at the present epoch. Because of its relatively wide field
of view, SIRTF will also be able to carry out efficient surveys of infrared
sources that will help to optimize the observing programs of larger
instruments, such as the New Technology Telescope (NTT), the VERB
Array, and a Large Deployable Reflector (LDR) in space, which have
narrower fields of view.
STRTF should be an early and frequently flown payload on Shuttle
sortie missions. It has such high sensitivity that very extensive in-
frared observations can be accomplished even within the relatively
