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productive program, which has been funded at a constant-
dollar level for two decades.
V. PROJECTIONS INTO THE FUTURE
We have divided this part of our report into three
sections: the impact of our recommendations on science
management and the changes likely to result; the growth
of our technical capabilities through the 1990's; and the
impact this growth will have on the structure of scien-
tific research and the major scientific opportunities
that will be exploited during the 1990's and beyond.
A. Management Considerations
The 1970's witnessed the concentration of most new,
ground-based observational capabilities into a few
National Astronomy Centers and the decline, in absolute
terms, of the health and vigor of major university and
private observatories. We have made recommendations that
we hope will help stem deterioration of university
research. We have suggested that federal funds be used
to stimulate state and private groups to increase support
of their own observatory facilities. Because of technical
developments, the cost of 2.5- to 5-m ground-based optical
telescopes has dropped substantially. For telescopes in
this size range the operating costs will, in 5-10 years,
exceed the construction costs, and we urge federal help
for university and private groups struggling to utilize
fully the telescope capabilities that are available to
them. In part, full implementation of our fifth major
recommendation, for instrumentation development, will help
maintain the vigor of university groups. Nonetheless,
the overall impact of our major recommendations will be
to continue the trend toward a concentration of major
facilities into the National Centers. This trend seems
unavoidable; some large universities, such as California,
Texas, and Arizona, may be able to attract sufficient
private support to build very large ground-based tale
scopes, but even they cannot afford the largest practical
ground-based facility, and no university or private group
is proposing to initiate a major space effort without
using federal funds.
We believe that the collecting area available to
ground-based optical/IA astronomy should be increased
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tenfold. ~
the scientific
We believe that this is necessary to exploit
__ ~_~ opportunities of the 1980's, as well as to
back up the space and radio programs. Technological
developments have made this recommendation both cost-
effective and timely. Nevertheless, in the more distant
future, we see an increasing development and reliance on
our national space capability. Already the solar-
astronomy program is overwhelmingly a space program. The
gains achievable in the IR, both from the use of cooled
telescopes and through the exploitation of wavelengths
that do not penetrate the Earth's atmosphere, are very
large. The major initiatives of the IR program in the
1980's will lie in space. ST will be one of the principal
instruments for optical astronomy in the 1980's through
the 1990's.
there will be a shift of emphasis from ground-based to
space observations. As the century ends we may well wit-
ness the last major construction of optical telescopes on
the ground. To be sure, these telescopes will continue
to be useful well into the twenty-first century, and oper-
ational support for them will be crucial, but space facil-
ities will gradually take over the role of ground-based
telescopes beyond the 1990's. For some decades, and per-
haps indefinitely, the management of such expensive space
facilities will be the province of government labora-
tories. m ese facilities must be open to qualified users
and, increasingly, to foreign participation. Financial
support, management participation, and observational use
by foreign scientists should be encouraged.
m ese changes will require that careful thought be
given to several management problems:
It is clear that. as space technology ripens,
1. The health of university science in the face of
continued erosion of competitive observational canabil-
~ ,
ities in state and private observatories by comparison
with those of the National Astronomy Centers and gov-
ernment laboratories.
2. m e need to ensure balanced programmatic approaches
to observational astronomy. In the past, the existence
of numerous independent observatories ensured a balance
of style and programs in astronomy. As the National
Centers grow in power at the expense of private and
university facilities, it is important that the appro-
priate review committees and time-assignment committees
appreciate and support the need for diversity.
3. Adequate access to facilities established with
major investments of national resources. These must be
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open to all qualified users. Thus, institutional staff
members, outside principal investigators, and others must
have their programs competitively reviewed by an impartial
committee. Foreign scientists should continue to have
access to major U.S. facilities and, as in the case of
the STScI, foreign participation in both the management
and financial underwriting of the program should be
encouraged.
4. Support of survey programs and other long-term
efforts. Astronomy progresses both by spectacular dis-
coveries and by painstakingly slow survey programs that
search for systematic relations, subtle effects, or
unusual objects. Both styles of research are essential
and, indeed, synergistic. As astronomy moves increasingly
into a national-facility mode, with observing time on
forefront facilities increasingly allocated by commit-
tees, it is essential that these committees have the
wisdom to support long-term survey programs in addition
to those that promise immediate results.
By making national facilities open to all qualified
users, it should be possible to implement a program
incorporating observations at the National Centers,
support observations using state and private observa-
tories, and instrumentation development in both the
universities and at the National Centers that would
ensure the health of university science while at the same
time providing the powerful facilities that will be
needed at the end of the century.
,
We see these management problems becoming acute only
toward the end of the decade, when projected programs
result in national observational facilities that com-
pletely dominate the field. The shift from ground-based
to space astronomy should raise the issue of the appro-
priate roles that NASA and NSF play in astronomy. The
division between ground-based and space work is becoming
increasingly artificial, and it would seem appropriate
for Congress to re-evaluate the roles played by these two
principal support agencies for astronomy.
B. Instrumentation in the 1990's
It is harder to foresee the developments in instrumenta-
tion than it is to recognize the problems that science
management will face 10 years from now. A major issue
will center around the successors to ST and the 15-m NTT.
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In the past, each step toward more aperture for attack-
ing the perceived forefront problems of the era has led
to the discovery of new classes of objects and the delin-
eation of whole new arrays of problems, unimagined and
unanticipated prior to the availability of those new
facilities. Furthermore, in view of the new design con-
cepts and lightweight materials now being tested, there
is no longer a clear upper limit on telescope size. It
is possible that, by the 1990's, one could contemplate
the construction of a 25-m telescope on the ground within
the constraints of available funding.
The question of how then to proceed is complicated,
however, by the possibility that a somewhat smaller
diffraction-limited telescope of 7- to 15-m aperture
could be put in space by that time. If the very large
development costs of space platforms, extended missions,
space-fabrication techniques, and cheaper (per kilogram)
launch vehicles are to be totally borne by astronomy, this
option is of course out of the question. Yet it seems
clear that these developments will proceed for other
reasons, and astronomy may benefit from these technical
developments. The present experience in the astronomical
community with space astronomy through IUE, Copernicus,
and the HEAD series of satellites has been outstanding e
The relatively high efficiency of use of observing time,
absence of weather problems, and high equipment reliabil-
ity, combined with the reduced background, better seeing,
and lack of atmospheric absorption (thus extended wave-
length coverage) available from space have been and will
continue to be great attractions. me additional experi-
ence to be provided to the astronomical community by ST
will be critical in evaluating the advantages of large
space versus (perhaps slightly larger) ground-based tele-
scopes in the coming decades. At present, the technology
for neither a 25-m ground-based telescope nor an extended-
mission space telescope in the 7- to 15-m class is avail-
able. It is, for example, not yet clear how the lack of
gravity can be used to best advantage in reducing the
weight (hence the cost) of a large space telescope, and
how much the weight can be lowered without compromising
the optical performance. We must encourage developments
in both directions, so that the successors to this com-
mittee may in 10 years make an intelligent, well-informed
choice on a giant telescope for the 1990's.
Two-dimensional detector development is being driven
by commercial applications and, while that development
does not place high weight on astronomical applications,
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nevertheless commercial demand will ensure a continued
major effort that will likely produce two-dimensional
detectors with nearly 100 percent quantum efficiency over
the entire spectral range, from 100 ~ to 1 Em. In
the IR region very great improvement over current
technology should result from the military effort.
High-efficiency coatings are needed to cover the
wavelength interval from 100 A out to 1 mm. As optical
sophistication increases in instrumentation, such coatings
will allow the optical designer the freedom of increasing
the number of reflections without paying a penalty in low
transmission. Bare aluminum has high reflectivity down
to 100 A, a soft x-ray wavelength that would allow use-
ful surveys for high-red-shift quasars using the large
collecting area of a normal-incidence reflector. High-
efficiency, two-dimensional detectors for this wavelength
region already exist and could be improved.
There are numbers of suggestions for constructing very
large, nonfilled optical arrays in space. A simple cross
100 m in extent, filled with 1-m mirror elements, could
be used as an interferometer at optical wavelengths. The
resolution of such an instrument would be about 5 X 10-9
red (10-3 arcsec). With such an instrument one would
be able to image the nearer stars with about the same
resolution that Galileo's telescope achieved on the Sun.
Starspots could easily be seen and monitored. me struc-
ture of quasars, contact binaries, and galactic nuclei
could all be studied.
X-ray and radio surveys have historically been used to
identify interesting objects for studies at optical wave-
lengths. However, there may well be other objects that
are not particularly unusual at these extreme wavelengths
but reveal their unusual nature at W. optical, or IR
wavelengths. The Crab pulsar is not a particularly bright
radio pulsar, for example. It may be possible to exploit
the darkness of the sky in space to devise survey instru-
ments that could automatically, using optical techniques,
detect unusual objects. An objective-prism survey using
a large, advanced COD array is a simple example of a pos-
sible instrument.
There are some beginning attempts to develop "smart"
detectors. Three-dimensional CCD arrays that could per-
form simple arithmetic operations before transferring the
processed picture to a computer might allow the develop-
ment of high-speed speckle processors. If such devices
could be built, it might also be possible to build very
large, diffraction-limited IR telescopes. By working at
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wavelengths for which speckle techniques are not photon
limited and the required surface accuracy of the primary
mirror is low, one might build a telescope using nonrigid
techniques (for instance, an inflatable structure).
Rubber-mirror technology with small adjustable reimaging
mirrors is a different approach to the problem of
constructing large, low-surface-accuracy mirrors that
feed a system that is ultimately diffraction limited.
Looking forward to the 1990's, we should consider novel
ways of obtaining astronomical information not possible
from the ground or even from Earth orbit. For example,
studies suggest that it may be feasible to launch an
instrumented spacecraft into an eccentric orbit about the
Sun with perihelion near 4 solar radii and that the
experiments on this proposed "Star Probe" mission should
be able to survive encounter and transmit back data.
Among the important questions that could be addressed in
this way are the fine structure of the solar surface and
corona (at a resolution of a few kilometers), the In situ
plasma properties and wind speeds at all levels of the
corona down to the temperature maximum, energetic-
particle distributions, and the acceleration mechanism of
the solar wind. Precise tracking of the Star Probe will
also provide information on the distribution of mass and
angular momentum in the Sun and should provide high-
accuracy tests of General Relativity. We should keep in
mind that each planetary-encounter mission has provided
totally unexpected and exciting information and that the
Star Probe would provide our only opportunity to study a
star at close range in the foreseeable future.
It seems quite certain that we are in a revolutionary
period for classical astrometry.
Already parallax tech-
niques have undergone a tenfold improvement in precision.
Electronic focal-plane systems will be greatly improved
in the 1980's. The ultimate accuracy has not yet been
determined, but it is clear that astrometry will make
major new impacts on astrophysics and open new fields,
such as the search for extrasolar planets.
C. The Direction of Scientific Research in the 1990's
It is clear from the developments of the past several
decades that astronomy is an explosively expanding
science. New discoveries pile on top of each other with
bewildering frequency. That old lady Urania, the muse of
astronomy, is showing us that she is divinely unpredict-
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able. We must not presume that we can accurately forecast
future developments. But we can project the likely capa-
bilities that will become available as the century ends
and note the fields that will be affected by these techno-
logical initiatives.
The instrumental initiatives discussed earlier will
lead to the following major changes in capability.
1. Large Gains in Angular Resolution
During the 1980's, ST will routinely give a tenfold im-
provement in angular resolution by comparison with that
usually available from the ground. Large arrays in space,
launched in the 1990's, will be capable of bettering the
ST resolution by an additional factor of 100. To appreci-
ate the significance of this improvement one must recall
that the introduction of the telescope in the seventeenth
century improved the resolution capability of the human
eye by about the same factor of 100. For ground-based
observations, angular resolution was then, as now, limited
by the turbulence of the Earth's atmosphere. Above the
atmosphere there seems to be no limit, except for the
practical limits imposed by our ability to construct ever-
larger instruments while maintaining high dimensional
accuracy. Existing NASA, industry, and university studies
are optimistic about our ability to achieve very high
angular resolution in space. We now seem to have within
our grasp the ability to end the 300-year hiatus on major
improvements in optical resolution.
The improvements in angular resolution can have major
impact on three fundamentally different fields of astron-
omy: positional astronomy for measurements of the spatial
relationship of (usually unresolved) astronomical objects;
the mapping of previously unresolved objects that happened
to lie just below our current resolution capability; and
the separation and detailed study of phenomena that are
now blended into confusing background sources.
It seems quite likely that high angular resolution
will lead directly to exciting new discoveries and open
new fields of research that are not now even imagined.
We can now resolve the disk of the Sun, and we can infer
the surface appearance of other stars, but we have not
yet "seen" starspots on another star. Milliarcsecond
resolution will resolve the disks of nearby giant stars.
In the far W. the contrast between starspots and the
disks of late-type stars will be large.
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There is no galactic nucleus of any type that is close
enough for us to probe with high spatial resolution using
current optical techniques. The nuclei of galaxies are
bright; there is some evidence that some galactic nuclei
contain black holes. An increase of a factor of 1000 in
angular resolution, together with a spectroscopic radial-
velocity capability, would probably settle this issue.
High angular resolution will also allow us to penetrate
deeply into crowded fields. Do x-ray-emitting globular
clusters hide black holes in their centers? Radial-
velocity studies of stars near the centers may provide an
. .
answer. In any case, from where does the x-ray emission
originate? Deep- W photographs would do much to clarify
the situation.
The diameter and structure of bright planetary nebulas
in the Local Group of galaxies could be studied with very
high resolution. Differences in excitation class and
abundances will be better understood when we can resolve
the nebular envelope.
High-spatial-resolution imaging and spectroscopy of
the Sun during the 1980's has the potential of resolving
the fundamental structures defined by the filamentary but
strong magnetic fields. When this occurs, the Sun will
indeed become a plasma astrophysics laboratory, in which
we will see for the first time how magnetic fields and
plasmas interact to yield such phenomena as heating on
slow and rapid time scales, flares, and wind acceleration.
The benefit of these studies to theoretical astrophysics
is incalculable.
High-resolution spectroscopic capability will pro-
foundly affect the studies of planets in our solar system.
We will be able to monitor weather patterns in their
atmospheres and study structural and chemical composition
changes on their surfaces. The Landsat and weather satel-
lites have demonstrated the importance of remote sensing
for geology and for an understanding of the Earth's global
weather patterns. Their planetary counterparts will be
able, for example, to monitor volcanic activity on
Jupiter's satellite To.
Astrometry will be revolutionized by ultrahigh angular
resolution. It will be possible to measure directly the
distances to all objects in our Galaxy. Planets orbiting
nearby stars will be detectable from the irregular motions
of these stars. It might even be possible to detect
planets using direct-imaging techniques.
m ese examples illustrate only the easily imagined uses
of very high angular resolution. The real excitement will
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result from discoveries that we cannot now expect or pre-
dict. This was the case for Galileo's telescope, the
extension to our vision provided by x-ray and radio tech-
niques, and the improvement in resolution afforded by
deep-space planetary probes.
2. Increased Light-Gathering Power
m is report calls for a substantial improvement in tele-
scope light-gathering power during the 1980's. me 15-m
NTT will collect nine times more photons per second than
the 5-m Hale telescope on Mt. Palomar. Its spectroscopic
capabilities, if located on an excellent site and equipped
with the most sensitive instruments and detectors, will
surpass by several orders of magnitude the capabilities
of the 1970's.
In space it might be possible, using rubber-mirror
techniques, to correct imperfections in a giant primary
mirror and thus to erect very large space telescopes that
would be nearly diffraction limited. While we have not
yet developed the technology to deploy telescopes that
would exceed by an order of magnitude the light-gathering
power of a 15-m telescope, we are at a point where we
could begin to think along these lines, and we might be
able to construct such telescopes by the end of the
1990's.
Spectroscopy is the key to understanding the physics
of astronomical objects. By increasing the light-
gathering power of a telescope, we are able to study
sources that are increasingly faint, either because they
are only weak emitters of light or because they are veiled
by interstellar dust clouds. Spectroscopic studies of
such objects probe the very frontiers of the physical
Universe, the birth and death of stars, the evolution of
galactic systems, and the physical conditions that lead
to the phenomena we call quasars, pulsars, x-ray binaries,
and black holes.
3. Increased Capability for Study of Objects with Low
Surface Brightness
Space telescopes, operating in the absence of veiling
glare from atmospheric airglow, lend themselves naturally
to the studies of low surface brightness phenomena.
Already, ground-based telescopes, using modern fine-
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grained emulsions and working at dark sites, have dis-
covered very low surface brightness plumes, bridges, jets,
and halos associated with relatively nearby galaxies. Are
these structures composed of stars, dust, or gas? Do some
of them reveal a physical connection between objects of
very different red shift? Are we seeing the remains of
the protogalactic cloud from which the galaxy collapsed,
or are we seeing material that was ejected during a period
of high nuclear activity? Are they the remains of an
ancient galactic collision?
Since many of these sources are so faint (about magni-
tude 30/arcsec2) as to be virtually undetectable, it
seems a hopeless task to obtain slit spectra of them;
however, it would be useful to obtain broadband colors.
The spectral range free of terrestrial atmospheric emis-
sion is quite narrow, extending only from about 4500 to
6500 A. In space, where there are no atmospheric prob-
lems, it would be possible to obtain images in the vacuum-
W, in the green, and in the near-IA, where the spectra
of late-type stars reach their maximum luminosity.
It would be of great interest to establish the occur-
rence of such phenomena as a function of age of the
object. We know that faint halos are associated with
nearby Galaxies. Are they present with the same fre-
, ,
quency and structure at a time when the Universe was only
half as old as it is now? It should be possible to
detect such halos at large red shift using high-sensi-
tivity panoramic detectors with a telescope having high
spatial resolution. We know that some of the brighter
clouds are emission nebulas. From space they should be
very bright at red-shifted Lyman-alpha wavelengths. Such
nebulas have been found in the radio lobes of the nearby
radio galaxy Centaurus A; are they also present in the
much more distance source Cygnus A?
Within our own Galactic system and neighborhood, there
are sources that would be better understood if we had an
improved ability to detect low surface brightness objects.
Some supernova remnants are very faint. Old planetary
nebulas expand and fade from view; high Galactic latitude
clouds only shine weakly with reflected Galactic light.
Interferometric techniques can study some of these
sources, particularly if strong W lines are present, but
they must be found and mapped. With high spatial resolu-
tion these "Galactic" studies can be extended to all the
galaxies of the Local Group. It would be particularly
interesting to detect optical nebulosity, or faint blue
stars, corresponding to the radio detection of a
Magellanic Stream.
Representative terms from entire chapter:
low surface
