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Setting Priorities for Space Research: Opportunities and Imperatives (Chapter 2)
Setting Priorities for Space Research
Opportunities and Imperatives
2
The U.S. Space Research Program:
Accomplishments, Prospects, Lessons
Space research concentrates on observations or experiments that are
effective means of obtaining essential information, including studies of the Earth and
its environment, solar and space physics, solar system characteristics, astronomy,
life sciences, and fundamental physics. Each of these fields is in a different state of
maturity: astronomy, earth sciences, planetary sciences, and space physics reach
back to the very origins of the space program, whereas life sciences and
microgravity sciences are just now emerging as longer missions offer increased
opportunities for research.
The following pages summarize briefly the accomplishments and status of
U.S. space research. The summary is not meant to be exhaustive but rather to
provide a glimpse of what has been achieved in our space program, some ideas of
REPORT MENU
opportunities that remain, and a constructive evaluation of what we have learned
NOTICE
about program management.
MEMBERSHIP
PREFACE
SUMMARY
CHAPTER 1
CHAPTER 2 SELECTED DISCOVERIES AND ACCOMPLISHMENTS OF THE
CHAPTER 3
U.S. SPACE RESEARCH PROGRAM
CHAPTER 4
CHAPTER 5
In only 30 years, space research has brought forth a rich array of expanded
knowledge and understanding in all areas of space science and applications. Major
discoveries have been made as we moved outside the Earth's atmosphere, found a
new view of our home planet, and left behind such features of our environment as
the physiological effect of gravity.
From our new vantage point, we have achieved significant understanding of
many fundamental processes in the cosmos, solar system, Earth, and even our own
bodies. Our constant search for origins has been aided by space observations
providing new insights into the formation of the universe, the Earth, other planets,
and life as we know it. Through new eyes, we see an unexpected complexity in
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structure and processes over a vast range of spatial scales. Closer to home, we
have gained a deeper appreciation for the intricate interactions between humans
and the Earth. In some areas, we have gained substantial practical applications of
new knowledge and techniques.
Scientific research in space has provided answers to many questions and
stimulated even more. We have learned much about larger issues such as
What is in our worlds?
How do our worlds work?
How did our worlds come to be?
How do our worlds evolve?
How do we affect and how are we affected by our worlds?
These questions are used as organizing themes in the following brief review
of the major accomplishments of the space sciences over the past 30 years.
Discovery—What Is in Our Worlds?
We discover the wonders of the universe by extending our senses with
sophisticated instruments. In space, our instruments attain a unique perspective
from which to observe the Earth below and the cosmos above. Exotic objects, such
as gamma-ray bursters and braided rings, and global physical processes, such as
the ubiquitous mesoscale eddies in ocean currents, were revealed by the unique
capabilities of space instrumentation. New discoveries almost always stimulate new
investigations that require new sensory capabilities and lead to further discovery.
Complete worldwide patterns revealing the extent and variability of
important features and phenomena on the Earth have been assembled.
Atmospheric trace species (e.g., ozone, carbon monoxide, particulates, and many
others) were sampled only at isolated locations until just a decade ago. Now with
observations from space we can begin to piece together global budgets of these
important chemicals. Satellites have produced images showing the location and
seasonal movement of ecosystem boundaries. GEOS-3 produced the first
realization of the global geoid over the oceans, and Magsat mapped the Earth's
magnetic field. Landsat has contributed the first global view of geologic structures.
Landsat and other Earth remote sensing satellites provide abstracted information on
regions of the world that were unmapped 20 years ago. Since 1960, weather
patterns have been mapped by satellites and now represent a major tool in weather
forecasting and its interpretation to millions of television viewers. Mineral and oil
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deposits are located and mapped with the aid of Landsat and SPOT.
Solar system probes have discovered new planetary bodies and
unexpected phenomena throughout the solar system. The Voyager missions
discovered new moons and rings around the giant planets that had not been
detected from the Earth. The Voyagers also discovered active volcanism on Io,
bizarre and unexpected tectonics on icy satellites, a tenuous atmosphere and
massive nitrogen polar caps on Triton, tilted and shifted magnetic fields on Uranus
and Neptune, and other previously undetected phenomena. These discoveries and
the accompanying images from planetary explorers stimulated wide public interest in
the science and exploration of space.
Space is not a void, but is occupied by complex plasmas. One of the
first Earth satellites discovered the Van Allen radiation belts in 1958. Continuing
exploration with spacecraft revolutionized our view of the Earth's environment above
200-km altitude. We have discovered much about the molecular complexity of
interstellar and circumstellar environments. We now know that there is a region
above the ionosphere consisting of an electrically conducting plasma permeated by
the Earth's magnetic field. It is called the magnetosphere because its structure and
many of its processes are controlled by the magnetic field. We have learned that
other planets possess magnetospheres and that the Sun has a magnetosphere
consisting of a hot (about one million degrees Kelvin), magnetized plasma flow (the
solar wind) extending beyond the orbits of the planets and filling interplanetary
space, forming a distinct cavity—the heliosphere—in the nearby interstellar medium.
Instruments in space have now covered almost the entire
electromagnetic spectrum, prompting the discovery of new objects and new
environments impossible to see in any other way. Through spacecraft surveys
of the celestial sphere at X-ray, ultraviolet, and infrared wavelengths, we have
cataloged more than 250,000 objects, many of which can be seen only from
space. Observations from rockets and satellites revealed the first black hole
candidates by detecting the intense, variable X-rays created near the event horizons
of these exotic objects. The Vela satellites, designed to monitor gamma-rays from
clandestine nuclear tests, quickly discovered gamma-ray bursters, objects emitting
bursts of gamma-rays lasting only a few seconds, whose exact nature remains
undetermined after more than a decade of study. The first infrared sky survey
discovered large, solid particles in orbit around ordinary stars, presumably remnants
of an earlier era of planet formation, detectable only from space-borne telescopes
and suggesting that planetary systems like our own are common in the galaxy. As
each new window at X-ray, gamma-ray, and infrared wavelengths opened, new
phenomena appeared with characteristics difficult or impossible to sense in any
other way.
We have identified the earliest stages of star formation from their faint
infrared emission. We know that almost every type of star, normal and extraordinary,
loses mass through outflowing streams of matter at all stages of its evolution.
Galaxies that emit 99 percent of their light at infrared wavelengths, quasars with
strong X-ray emission, supernovae, novae, accretion disks around neutron stars,
and black holes have all been discovered or studied from space. Without spacecraft
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bearing scientific instruments, these phenomena would remain unknown.
Understanding Processes—How Do Our Worlds Work?
Manifestations of physical laws in the universe occur through physical and
chemical processes that transform and transfer material, energy, and momentum
throughout natural systems. Spacecraft missions enable us to study processes in a
number of ways impossible from the Earth's surface: by using wavelengths
absorbed by the atmosphere, by investigating celestial objects and phenomena at
close range or by direct sampling, and by gaining a global-scale view of terrestrial
processes. In many cases, spacecraft observation aims not just at understanding
how a particular process works. Rather, by examining systems not reproducible in a
laboratory, (e.g., planetary rings, magnetospheres, and atmospheres), space
investigations gain a deeper understanding of the underlying physical laws.
The first measurements of important and cyclical phenomena on
Earth have been made from space. The now famous antarctic ozone hole was
observed in 1984 and confirmed by satellite imagery from Nimbus-7. With satellite
measurements the spatial extent and magnitude of yearly changes were
established. The yearly movements of both the antarctic and the arctic icepacks
have now been tracked in a synoptic manner to reveal detailed patterns. We have
also observed El Niño events, the effects of volcanoes on the stratosphere, and,
even occasionally, human-caused pollution events. Tropical cyclones are now
tracked from their spawning grounds to their landfall, with important consequent
reduction in human disaster.
The view from space has provided a fundamental advance in
understanding of the structure and dynamics of the Earth system. Perhaps the
most pervasive accomplishment of the space age began in 1960 with the launch of
TIROS-1, the first weather satellite. The images pieced together from the first
several passes of the satellite dramatically confirmed a view of atmospheric
dynamics that previously had only been inferred. Now, every evening, televisions
throughout the world display the latest generation of satellite imagery of global and
regional weather systems. Since the launch of TIROS-1, no hurricane has touched
shore without being spotted and tracked well in advance. The combination of sea
surface temperature and chlorophyll fields confirmed the widespread ocean
phenomenon of mesoscale eddies, changing our thinking about energy transport in
the oceans. Ocean color observations, at first a curiosity recognized as useful only
by fishermen, are now regarded as an excellent means to map mesoscale
circulation patterns in the open ocean, especially where the temperature signal is
washed out by seasonally high or low temperatures. That oceanic mesoscale
features are widespread was firmly established by such measurements.
Understanding plate tectonics and the tectonics of other solid planets has
revolutionized the study of the solid Earth. Space-borne measurements have
contributed most spectacularly by establishing the rate at which plates move with
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respect to each other on the time scale of years and also by determining the geoid
(the shape of the Earth's figure) with tremendously improved accuracy. The geoid
relates to mass distribution in the Earth's interior and helps in showing how the
Earth's mantle is convecting. Altimetry from orbit has improved understanding of
both submarine topography and structure. Measurements from space have shown
how the length of the Earth's day responds to wind currents on annual time scales
and to interior movements on decennial scales. Precise distance measuring from
space is revolutionizing the way we look at sea level variation on decennial time
scales, and space-borne optical and infrared imagery has come to be essential in
the study of the geology and geophysics of the continents. The first radar
measurements from space show the enormous potential of that method, and
magnetic measurements have established, among other things, that ultimately we
can expect to monitor temporal variations in the Earth's main field from space on
time scales from seconds to decades and centuries.
Enormous diversity in the manifestations of physical laws and
processes on other worlds has been discovered through planetary
exploration. Solar system bodies are remarkably different in evolution, composition,
and dynamics. Voyager encounters with the giant planets revealed intricate and
unexpected complexity in the ring systems of Saturn, Uranus, and Neptune.
Understanding the morphology of the rings has required detailed, ongoing studies at
the forefront of gravitational dynamics. Much of this work has application to larger
astrophysical systems, making ring studies a testbed for understanding gravitational
dynamics.
Based on spacecraft observations, comparative studies of atmospheric
dynamics on terrestrial and giant planets reveal a much broader range of physical
conditions than those seen on the Earth, and outstanding problems remain that tax
our understanding of the fluid mechanics of atmospheres. These include the
maintenance of long-lived spot features on Jupiter, the origin of wind speed
distribution on giant planets, and the energy balance of the Venus thermosphere.
Tectonic processes occur on large and small bodies alike, and understanding both
the energy sources and the origin of particular features continues to be a challenge
long after they were identified by spacecraft. The thick atmosphere of Titan,
discovered by Voyager, appears to hide a wealth of chemical and dynamical
processes as complex as those on the Earth (including a methane "hydrological"
cycle). Triton was shown by Voyager to have a surface-atmosphere nitrogen
transport cycle akin to that of carbon dioxide on Mars, but with the added feature of
nitrogen geysers, for which no Martian analog exists.
Microgravity has pronounced effects on living systems. While plants
and animals, including humans, can survive in the space environment, there are
clear effects (including exposure to microgravity) that have pronounced impacts on
living systems. Seeds of higher plants germinate in space, and grow at least into
seedlings. Fertilized frog eggs have developed in space.
Understanding Origins—How Did Our Worlds Come to Be?
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In the broadest sense, we seek to understand where we came from and how
the natural world was formed. Questions about the origin of the universe, the
formation of the solar system, and the appearance of life have been central to space
research over the past three decades.
The cosmic background radiation seen from space is the signature
of the beginning of the universe. Cosmic background radiation is the oldest
remnant of the early universe directly detected today. Its spectrum and pattern on
the sky show us the most primitive state of matter and serve as the strongest
constraints on our theories of how galaxies formed after the Big Bang. Between the
discovery of cosmic background radiation in 1965 and 1990, observations from the
ground, from aircraft, and from balloons all provided estimates of the spectrum of
this very faint radiation. But the Cosmic Background Explorer (COBE), launched in
late 1989, measured the spectrum so accurately that it disproved a few key results
from the previous 10 years, and several hundred theoretical papers became
meaningless. Midway through its mission at the time of this writing, COBE has
already revolutionized our understanding of the early universe and promises the
greatest refinement to our knowledge of the cosmic background since its discovery
25 years ago.
Solar system exploration revealed intricate links between the
physical and chemical record of planetary bodies and the large-scale
processes of star and planet formation. Detailed Pioneer and Voyager studies of
the outer system have shown that Jupiter and Saturn contain cores of elements
heavier than hydrogen and helium, while Uranus and Neptune appear to be made of
such cores with a veneer of hydrogen and helium. It is now recognized that the
formation of these planets required accretion of ice and rock cores before gas was
added. This is distinctly different from the formation of stars and constrains the
evolution of the protoplanetary disk in a number of intriguing ways. The volatile
composition of outer solar system bodies, including comets, is now just beginning to
be elucidated and has a number of significant differences from the composition of
environments in giant molecular clouds. With such a record, it is becoming possible
to piece together a history of grain material from such clouds, through infall into the
protoplanetary nebula and accretion into solar system bodies. Further missions to
investigate in situ the less-evolved bodies of the solar system should clarify the
history of the material that eventually formed the planets and allow us to
characterize the formation of the solar system as a part of star formation and
galactic chemical evolution.
Study of the gravito-electrodynamics in "dusty plasmas" discovered
in Saturn's rings provided insight into the formation and evolution of the solar
system. Observations of spokes in Saturn's rings by Voyager highlighted the effect
of electromagnetic forces on charged dust particles. In a similar way, the interaction
of dust and plasmas in comets is believed to be a central element in understanding
the formation of comet tails. Such observations have given rise to the study of
gravito-electrodynamics in dust plasmas, which has important applications to the
understanding of the formation and evolution of the solar system.
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The search for life on Mars is of continuing scientific interest. While
signs of life were not found at the sample areas, evidence from Viking for past
climate change on Mars shifts the issue to whether life formed on Mars sometime in
the past and whether it exists in selected niches today. The answers to these
questions are of fundamental importance, since on the Earth the evidence is strong
that life heavily modified the Earth's environment in favor of continued habitability. If
life actually formed there, why did this not occur on Mars?
Understanding Change—How Do Our Worlds Evolve?
Scientific events often remind us that few things are constant. The universe
evolved from some primordial event or juncture and continues to evolve. Stars are
born and die. Our Sun changes both gradually and cyclically. Planets develop
climates, and then those climates change. We know from geologic records that the
Earth has changed and continues to change. Some changes can be seen only from
space by observations in new spectral ranges, by visiting our neighbors in the solar
system, and by viewing our w planet from the vantage point of Earth orbit.
Satellites now routinely document the extent of some major changes
in the planet Earth. Images from space document continuing change of the Earth's
surface. The expansion of arid regions (desertification) is now tracked in several
regions almost exclusively by satellite. Retreats of glaciers, deforestation and natural
movements of forest edges, and even changes in habitat are now tracked from
satellites in some locations. Space geodesy provides measurements of continental
drift and changes in sea level.
Climate change on the terrestrial planets Venus and Mars is
profound on long and short time scales. Mariner 9 and Viking orbiters and
landers have revealed the complexities of the Martian environment, with intricate
weather patterns on diurnal and seasonal time scales distinct from those of the
Earth. The absence of oceans and the presence of seasonal polar caps with which
the atmosphere is in equilibrium provide a different physical system in which to test
our understanding of climate from local to global scales. Viking and Mariner data
detected seasonal and permanent polar cap composition, pressure variations at two
ground sites, water vapor distribution, growth and decay of dust storms, and the
presence of dust devils and mesoscale cyclonic storm systems. Evidence for an
earlier, warmer climate on Mars based on Viking images of apparent river channels
and glacial and lake deposits is even more profound. The evolutionary sequence
leading from the warmer, wetter past climate to the present cold, dry climate is an
outstanding issue raised by spacecraft exploration of Mars. The climate of Venus
varies on the short term, as revealed by Pioneer Venus ultraviolet data showing a
decrease in sulfur dioxide abundance in the stratosphere. The high surface
temperatures on Venus, established firmly by spacecraft, constitute a dramatic
demonstration of greenhouse warming. Magellan images indicate that Venus has
had a violent, volcanically active history, the climatic implications of which have just
begun to be assessed.
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The solar energy flux is not constant, but varies with time. Using
knowledge gained over the past 30 years, we can now identify some of the physical
mechanisms linking the Sun to the near-Earth environment. Motions in the
convective layers of the Sun are believed to generate the magnetic field and solar
wind variations; these in turn affect the Earth's magnetosphere and regulate the
amount of plasma energy incident on the Earth's polar caps. Current research
suggests that small percentage changes (about 0.5 percent) in the total energy
output of the Sun (the solar constant) may influence short-term terrestrial climate.
The Earth and its space environment contain coupled phenomena that must be
studied as part of a system including the Sun and its plasma environment along with
the Earth's magnetosphere, atmosphere, oceans, and biota.
Understanding Human Interaction—How Do We Affect and
How Are We Affected by Our Worlds?
Space research is increasingly concerned with human activities. Information
from Earth-observing satellites documents how human activities, including
agriculture, forestation and deforestation, and the use of fossil fuels, are changing
the Earth's surface and the planetary environment. Such information is used in a
variety of applications to guide our activities. Spaceflight exposes humans to an
unfamiliar environment with weightlessness and the threat of lethal streams of
radiation, thus raising questions about human physiology that must be addressed to
ensure safe, long-duration spaceflight.
Satellite observations are important for following some human
impacts on the planet and are materially aiding many human endeavors. The
first nighttime picture of city lights provided from the Defense Military Satellite
Program (DMSP) was a stunning image. More recently, leaders of several
developing countries have been convinced by satellite imagery to control
deforestation in tropical rain forests. In general, it is possible to track land use
patterns on regional scales simply and easily with data from operational satellites.
Even day-to-day logistical operations are aided by both Landsat and the Global-
Positioning System (GPS), as dramatically demonstrated in Desert Storm operations
in 1990-1991.
People can live and work in microgravity for periods at least as long
as one year and can then return to the Earth and readapt to gravity. Perhaps
the most striking accomplishment of the U.S. space program is the discovery that
humans can work in space and on another body in the solar system and can travel
to another part of our solar system and return successfully. Experience gained by
the Soviets using their space station MIR has proven that humans can survive for up
to one year in space and successfully adapt to 1 g upon return to the Earth. Such
demonstrations have opened the way for human exploration beyond the Earth for
centuries to come.
Prior to the spaceflight of higher mammals, physiologists did not know
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whether humans could survive for a significant period in a gravity-free environment.
In microgravity, essentially all physiological systems are perturbed. Some systems,
such as the bone and muscle, vestibular, and cardiovascular systems, are affected
more than others, such as the gastrointestinal and urinary systems. Some systems,
including the vestibular, adapt in a few days, whereas bone resorption continues at
least for months and perhaps indefinitely.
Space plasmas can have a profound and sometimes disastrous
effect on spacecraft and humans. It is well established that many spacecraft
systems and subsystems exhibit anomalies, or even failures, under the influence of
magnetospheric substorms, geomagnetic storms, and solar flares. Processes such
as spacecraft charging and "single-event upsets" (due to highly ionizing energetic
particles) in processor memories make the day-today operation of space systems
difficult. Radiation from these events could be fatal to humans if adequate protection
is not provided.
PROSPECTS AND OPPORTUNITIES FOR SPACE RESEARCH
Almost every field touched by space science has planned missions or long-
term opportunities promising major advances in our scientific knowledge of the
universe near and far. The major missions have been thoroughly reviewed and
refined. And the flow of novel ideas and proposals for small projects in unexplored
areas continues as the scientific achievements of the last three decades stimulate
new questions. The following is a representative list and brief description of the
myriad of missions and initiatives that are under discussion or planned for launch.
The list is not exhaustive but illustrative of the many exciting opportunities that exist.
Earth Observing System (EOS). The EOS will make a range of
contributions to the scientific questions outlined in the federal Global Change
Research Program. For some key questions, such as the role of clouds in the
planetary radiation budget and in the global hydrologic cycle, EOS will provide
information essential to rapid advancement in understanding the planet. In other
areas, like the Earth's history, EOS will supplement information largely derived from
surface measurements (e.g., sequencing of landforms). In all, EOS is the
centerpiece of the measurement program for global change research. Instruments
proven for scientific purposes on EOS will be the next generation of operational
sensors to monitor our weather, land use, and changing environment.l
Specialized spaceflights for measuring earth processes—Earth
Probes. Not all of the important variables will be measured from EOS. A number of
special initiatives are planned as Earth Probes. These include Synthetic Aperture
Radar (SAR), the best hope for quantitative measurements of soil moisture and
vegetative mass; the Tropical Rainfall Measuring Mission (TRMM); the Sea-viewing
Wide Field-of-View Sensor (SeaWIFS), for studying oceanic biomass and
mesoscale circulation features; a scatterometer to investigate global wind fields over
the ocean; and new magnetic and gravity measurements.
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Geosynchronous platforms for Mission to Planet Earth. These
satellites will provide continuing detailed observations of a number of variables in
mid-latitude with temporal resolution of minutes (versus days). They will contribute to
studies of atmospheric dynamics, oceanic dynamics, atmospheric structure, water
vapor, surface features and vegetation, and many more processes. Some of these
satellites will provide all-weather observations by using microwave emissions.
Upper atmosphere composition and dynamics—UARS. Launched in
late 1991, the Upper Atmosphere Research Satellite (UARS) is to measure the key
constituents and key dynamic processes of the upper atmosphere on a global scale.
UARS will also contribute to studies of ozone depletion.
Ocean topography mission—TOPEX/Poseidon. Planned for a 1992
launch, the TOPEX/Poseidon spacecraft will resolve topography in order to measure
the variable component of oceanic circulation. In due course (with a gravity mission),
it will produce a quantitative measure of mean oceanic circulation.
Improved operational meteorological satellites. Continuing
improvements are planned for the U.S. series of weather satellites to enhance
observations of the horizontal and vertical structure of the atmosphere (mainly
temperature and water content) worldwide. These observations will contribute to
improved forecasts of large-scale weather patterns and significant weather events
affecting human activities.
Operational land observatories—Landsat. Many routine remote
sensing applications require continuing and consistent measurements. These have
been provided by Landsat, and more recently by SPOT. Applications include mineral
exploration, agriculture, and land use management.
Martian climatic processes—Mars Observer. The Mars observer will
provide a comprehensive remote sensing study of the surface and atmosphere, with
emphasis on climate change on a variety of scales.
Aeronomy of the Martian atmosphere—Mars Aeronomy Observer.
The Mars Aeronomy Observer will characterize the potential fields of the upper
Martian atmosphere, clarify the role of photochemistry, and study the dynamics of
the ionosphere.
Geophysics of the Martian surface—Mars penetrators. These
missions will install a network of seismometers, weather stations, and heat flow
experiments on the Martian surface and possibly perform simple geochemical
analyses.
Study of the Jovian System—Galileo. Galileo, now en route to Jupiter,
will deploy a probe to measure directly the composition and dynamics of the Jovian
atmosphere and will study in detail the satellites, atmosphere, and magnetosphere
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of the Jovian system.
Detailed geophysical surveys of the Galilean satellites—The Jupiter
Grand Tour. This nuclear electronic propulsion mission will orbit each individual
Galilean satellite, providing microwave and radar sounding of the subsurface. It will
deploy penetrators for surface geochemical analyses of selected satellites and
provide global remote sensing for each from the main spacecraft. It will determine
gravitational moments and hence the constraints on internal structure for each
satellite.
Origin and evolution of the outer solar system—CRAF/Cassini.
Planned for launches in the late 1990s, these missions will closely observe the
nucleus of a comet, deploy a probe into the atmosphere of Titan, and provide in-
depth physical and chemical studies of primitive bodies, Titan, and the Saturn
system. The surface atmosphere processes appear to be as rich and complex as
those on Earth but without the presence of life.
Neptune Orbiter and Probes—Triton penetrator and Pluto
flyby—Poseidon. This spacecraft will orbit Neptune and drop a probe to sample
gas abundance and atmospheric dynamics through and below the ammonium
hydrosulfide cloud layer. It will perform long-term atmospheric observations from
orbit. The orbiter will make repeated passes by Triton to determine surface
temperature distribution, volatile transport processes, gravitational moments (for
internal structure), and atmospheric composition for molecular abundances,
including noble gases. A companion probe to make the first flyby of the enigmatic
Pluto-Chalon system is also under study.
Intensive geological and biological studies of sites on Mars—Mars
Rover and Sample Return. Mars Rover is being planned to conduct detailed, on-
site geological and biological investigations of portions of the Martian surface. It will
search for microfossils and return selected samples to the Earth for comprehensive
laboratory studies.
Detailed atmospheric and surface chemical analysis for
Venus—Venus Probe. The Venus Probe will determine the isotopic and chemical
composition of the atmosphere, resolving ambiguities from previous experiments. It
will characterize the geochemistry of uplands and plains sites on the surface.
Comet Sample Return—Rosetta. Rosetta is intended to collect a
sample of a comet nucleus from at least 1-meter depth, in order to understand
further the ice-volatile component. The sample will be preserved and returned to the
Earth for laboratory study.
Global mapping of the lunar surface—Lunar Observer. The Lunar
Observer will characterize the crustal composition of the Moon, place lunar samples
in global context, and search for ice in the polar regions of the Moon.
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Composition and properties of a sample of asteroids—Multiple
Asteroid Rendezvous Mission. This mission is intended to yield observations of
remotely sensed asteroid surface composition as a function of heliocentric distance.
Exploration of the universe through new windows—The Great
Observatories. The major components of the planned astronomical satellites for the
next decade are NASA's Great Observatories, four orbiting platforms for
observations in different wavelength bands. The first of these, the Hubble Space
Telescope (HST) now flying, was designed to improve the resolution, sensitivity, and
wavelength range of ultraviolet and visual observations beyond anything available
from the ground. With modifications to its camera optics to compensate for spherical
aberration induced by construction errors, it should achieve this full resolution by
1993. The Advanced X-ray Astronomy Facility (AXAF) will increase the capabilities
of X-ray observations by several orders of magnitude over any previously available,
allowing study of accretion disks around black holes, quasars, and the diffuse X-rays
from distant clusters of galaxies. The Gamma-ray Observatory (GRO) is designed to
study the exotic gamma-ray bursters as well as the matter-antimatter annihilation
seen toward the center of the galaxy. The Space Infrared Telescope Facility (SIRTF)
will cover the entire infrared spectrum from 1 micron to almost 1 millimeter,
searching for dark matter in the form of brown dwarfs, the birth of new planetary
systems around young stars, and the first generation of galaxies created after the
Big Bang.
Other astronomical missions. A suite of other missions is equally
important for exploration of emissions impossible to study from the ground. The
Extreme Ultraviolet Explorer (EUVE), the X-ray Timing Explorer (XTE), and the
Submillimeter Wave Astronomy satellite are three examples among many. These
special-purpose satellites will further extend our capabilities by providing, for
example, high spectral resolution in special bands, wide field coverage, special
timing capability to detect rapid variables and accurately measure their periods,
polarization properties of light, particle detectors for cosmic rays, and specialized
instruments to follow up new discoveries with the Great Observatories. Suborbital
observations, including the Stratospheric Observatory for Infrared Astronomy
(SOFIA) measurements from aircraft, are essential complements to the spacecraft
missions. They not only provide unique capabilities, but also aid space instrument
designers by allowing quick turnaround and hands-on development of novel
techniques.
Moon-based instruments. Multiple-telescope interferometers in Earth
orbit or on the Moon promise to improve the angular resolution for visual and
infrared observations by several orders of magnitude. At this time, spacecraft
interferometers, both for imaging and for astrometry, represent one of the logical
next steps for instrument development. It is widely believed that advances from this
technique alone could revolutionize our view of the universe with resolution fine
enough to image surfaces of nearby stars and probe to the event horizons of
massive black holes in the nuclei of distant galaxies.
International Solar-Terrestrial Physics (ISTP) Program. A constellation
of several Earth-orbiting satellites will be launched during the 1990s by the United
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States, Japan, Europe (through the European Space Agency) and the [former]
USSR. The overall scientific objective of ISTP is to develop a comprehensive, global
understanding of the generation and flow of energy from the Sun, through the
interplanetary medium, and into the Earth's space environment. The improved
knowledge will have practical applications in understanding and forecasting radio
and power interruptions from solar events.
Orbiting Solar Laboratory (OSL). The OSL is intended to provide high-
spatial-resolution measurements of temperatures, densities, velocities, magnetic
fields, and chemical abundances in the solar atmosphere to determine the
fundamental processes responsible for plasma heating and the transport of mass
and energy between different levels of the solar atmosphere.
Solar Probe. This spacecraft will pass through the outer regions of the
Sun's corona, carrying out in situ measurements of plasma, fields, and energetic
particles in the solar wind acceleration region.
Imaging Super Cluster (ISC). Two spacecraft in highly elliptical polar
and equatorial Earth orbits will employ photon, energetic neutral atom (ENA), and
radio-wave imaging techniques to provide images of the Earth's radiation belts (Van
Allen belts) and magnetotail. A cluster of four spacecraft will be actively maneuvered
throughout the magnetotail to make simultaneous in situ plasma and field
measurements.
Ionosphere-Thermosphere-Magnetosphere Coupler (ITMC). A
constellation of several Earth-orbiting satellites will investigate the physical,
chemical, dynamic, radiative, and energetic processes that couple the ionosphere-
thermosphere-magnetosphere system with the heliosphere and outer
magnetosphere above and the stratosphere below.
Mercury Orbiter (MEO). Two spacecraft with instruments to observe
plasmas and fields and with solar physics and planetology experiments will fly in
polar orbit around Mercury. The mission will map the magnetic structure and plasma
environment of Mercury, investigate apparent substorm processes, and study the
transfer of mass and energy from the solar wind.
High-Energy Solar Physics (HESP) Mission. This mission will acquire
high-resolution imaging and spectroscopy of high-energy radiations during solar
maximum. Sub-arc-second imaging and high-resolution gamma-ray spectroscopy
will provide simultaneous photospheric and coronal imaging.
Long-duration human exposure to microgravity. The effects of
microgravity on physiological systems that have evolved in the constant and
ubiquitous presence of gravity provide rich opportunities for research. Understanding
of the processes of physiological systems is facilitated by the study of perturbed
systems, and the reduction of gravity provides such an effect. Much remains to be
discovered and understood. Such studies are a necessary prelude to defining
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limiting physiological factors for long voyages in space. Experiments need to be
conducted in microgravity for at least as long as the contemplated voyage.
Human productivity in space. We do not know whether crew members
can withstand the effects of long-duration space missions of several years or more.
Much basic and applied research is necessary to ascertain whether spaceship
design and programming of activities can enhance the safety, efficiency, and
accomplishments of crews on long-duration missions. The social effects of long-term
confinement are unknown, but such confinement can be provided on the Earth. Very-
long-term studies will be required. These should be started several decades before a
long-term human mission is designed in detail. As with EOS, practical applications
are likely to develop quickly based on the improved measurements and the
enhanced understanding they generate.
Effects at varying gravity-space-based centrifuge. Variable speed
centrifuges in space will permit quantitative assessment of effects of different
accelerations on physiological functions. Studies at 1 g either on the Earth or in a
centrifuge in space would provide control states for comparison with microgravity
environments. A centrifuge large enough to provide a living environment for crew
members would permit determination of the extent to which constant acceleration
can prevent or attenuate the physiological disturbances in space, especially those of
bone and muscle. Even prolonged vigorous exercise has, at most, only limited
effectiveness in microgravity.
Reproduction in microgravity. Prolonged sojourns in space will provide
the opportunity to determine whether sequential generations of higher plants and
animals will occur in the absence of gravity.
Table 2.1 shows how many of these and other initiatives and programs
contribute in a major way to addressing the five questions used above in this chapter
to organize the exposition of past accomplishments of the U.S. space research
program. Major missions and smaller missions, of course, contribute to many
questions simultaneously. Other initiatives often focus on just one of these areas.
The scientific potential of the planned programs is tremendous. They are well
planned and have been reviewed by scientists at many different levels, each group
reaffirming their worth to science. When the small, less visible programs and the
unseen opportunities that will arise from rapid advances in technology and scientific
understanding are added to this list, the prospects are far greater than the support
that will be available.
As this list of prospects demonstrates, we must grapple with choices
between large projects and small, between projects in different fields, and between
support for mature fields versus support for untested ideas. To succeed in space
research, we must push forward with new missions while reinvesting in human
resources and the technology base necessary to maintain vigorous scientific
enterprise.
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TABLE 2.1 Major Contributions of Future Initiatives and Programs to the "Large
Questions"
Major Contributions
Understand-
Initiatives Understand- Understand- Understand- ing Human
and Programs Discovery ing Processes ing Origins ing Change Interaction
RESEARCH AND X X X X X
ANALYSIS BASE
MISSION TO PLANET EARTH
EOS X X X X
Earth Probes X X
Geosynchronous X
platforms
UARS X X X X
TOPEX/ Poseidon X
Upgraded X
meteorological satellites
Landsat/SPOT X X X X
PLANETARY AND LUNAR EXPLORATION
Mars Observer, Mars X X
Aeronomy Observer,
and Mars penetrators
CRAF X X X
Cassini X X X X
Galileo X X X
Poseidon X X X X
Mars Rober and Sample X X X
Return
Venus Probe X X
Rosetta X X
Lunar Observer X X
ASTRONOMY AND ASTROPHYSICS
Great Observatories X X X X
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OTHER ASTRONOMICAL MISSIONS
EUVE X X
Submillimeter wave X X
astronomy
XTE X X X
Moon-based imaging X X X X
interferometry
Grand Tour Cluster X X
SPACE PLASMA PHYSICS
International Solar X X X
Terrestrial Physics
(ISTP) Program
Orbiting Solar X X X
Laboratory (OSL)
Solar Probe X X X X
Mesosphere Lower X X X
Thermosphere (TIMED)
Inner Magnetosphere X X
Imager (IMI)
Ionosphere- X X X
Thermosphere-
Magnetosphere Coupler
(ITMC)
Mercury Orbiter (MEO) X X
High-Energy Solar X X X
Physics (HESP)
BIOLOGICAL SYSTEMS IN SPACE
LifeSat X X
Spacelabs/Space X X
Shuttle
Space Station X X
LESSONS LEARNED
Many lessons are available from more than 30 years of experience in flying
space research missions. Here they are coalesced into a few specific statements
offered as guidance for the future:
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Routine access to space is of utmost importance to scientific
research in space. Unfortunately, this does need to be said because space
research has suffered from restricted access to space. Launch vehicles should be
appropriate for the mission and should reliably achieve the needed orbit and launch
date.
The space program should minimize its reliance on a single launch
capability. The main example of a failure to follow this principle is the forcing of all
payloads onto the Shuttle. However, scientific research programs should also avoid
excessive reliance on large, complex spacecraft. Space research requires a balance
of large and small missions. The following two lessons are related to this one.
Build spacecraft with robustness and flexibility. The Voyager
spacecraft operated beyond their lifetimes, permitting scientifically exciting extended
missions to Uranus and Neptune. Relatively inexpensive upgrades to Earth-based
communication antennas maximized the data return from these most distant planets.
Do not force scientific activities into an inappropriate approach. A
prime example is the forcing of Hubble onto the Shuttle, with the consequence that it
was required to operate in low Earth orbit and to be "man rated." These
requirements diminished its scientific effectiveness, raised its costs, and increased
its operational complexity by large factors.
In almost all cases of interest, space-based scientific investigations
must be complemented by other observations. For example, in the Earth
sciences, surface verification of space measurements is essential. The Great
Observatories cannot make all needed observations: the light-gathering capacity of
large ground-based telescopes is needed for spectroscopy.
For the lifetime of scientific programs, scientists should be
intimately involved with the instruments making the observations. This lesson
has several implications. For example, the principal investigator of the Solar
Mesosphere Explorer was intimately involved with its development and operation
and that was seen as contributing strongly to its scientific, schedule, and budget
success. Another implication is that there must be continuous efforts to make data
readily available to the scientists who will use it. An unfortunate example of the
failure to do this is the filtering (by data management algorithm) of data on ozone
concentrations, which delayed discovery of the antarctic ozone hole. A positive
example of successful efforts to make data available is the unplanned use of
Advanced Very High Resolution Radiometer (AVHRR) data to determine a global
vegetation index. These data were intended only for cloud images and sea surface
temperature maps.
Adequately fund data analysis. Seasat is an example of a program that
had grossly inadequate funding for data analysis, and the result was great delay of
scientific results. A positive example is found in astronomy, where funds are
available to do research using archived data. When proposals to use a certain data
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base are no longer being submitted, then those data probably have been adequately
exploited for the time being.
There is a need for more accountability in project management. The
Earth Radiation Budget Experiment (ERBE) is an example in which two centers had
partial responsibility for a project. It was badly managed until responsibility was
clarified. On the other hand, the Upper Atmosphere Research Satellite (UARS)
project was not started until responsibilities were clear. In addition, the UARS
managers made a careful cost estimate at the beginning, and the project has
remained within that budget. Because the ultimate purpose is scientific research,
one way to ensure accountability in science missions is to put scientists in charge.
Another caveat with respect to project management accountability is that promises
must be linked to reality. A primary example of the failure to do this was the claim
that the Shuttle could be expected to fly 50 missions per year.
Multiyear funding of basic research supporting spaceflight activities
is essential. The development of new concepts and the exploitation of observations
from space missions are both multiyear efforts and usually involve graduate students
working on dissertations. Annual proposals and multiple grants take time and effort
away from research and seriously impede progress.
Basic research is a good investment. The fruits of space research are
harvested by analysis of observations and modeling, efforts that reveal new
opportunities for observation. When resources are severely limited, the best value is
obtained from basic research, as supported by the research and analysis program,
because it maintains the vigor of scientific research and education and provides the
foundation for future scientific progress.
Consensus works. When a community can say with one voice what
needs to be done, it can have great force in budget and program planning. Two
examples are the sequence of astronomy survey reports2 and the report of the
federal Committee on Earth Sciences setting forth a national global change research
program.3
NOTES
1. For additional National Research Council discussions on EOS, see Space
Studies Board, "Space Studies Board Position on the NASA Earth Observing
System" (unpublished report issued July 10, 1991) and the 1990 report of the Panel
to Review the FY 1991 Global Change Research Program, The U.S. Global Change
Research Program: An Assessment of FY 1991 Plans (National Academy Press,
Washington, D.C., 1990).
2. See, for example, the two most recent such surveys (National Academy
Press, Washington, D.C.): Astronomy Survey Committee, Astronomy and
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Setting Priorities for Space Research: Opportunities and Imperatives (Chapter 2)
Astrophysics for the 1980's (1982); Astronomy and Astrophysics Survey Committee,
Board on Physics and Astronomy, The Decade of Discovery in Astronomy and
Astrophysics (1991).
3. Committee on Earth Sciences. 1989. Our Changing Planet: A U.S.
Strategy for Global Change Research, a report to accompany the U.S. President's
Fiscal Year 1990 Budget.
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