5/05/93:  HUNTRESS TESTIMONY ON OBSERVATIONS OF NEAR-EARTH OBJECTS


Statement of

Dr. Wesley T. Huntress, Jr.
Associate Administrator for Space Science 
National Aeronautics and Space Administration

before the 
Subcommittee on Space 
Committee on Science, Space and Technology 
House of Representatives

March 24, 1993




Mr. Chairman and Members of the Subcommittee:

I am pleased to have the opportunity to appear before this Subcommittee today
to report on NASA's plans for continuing our observations of Near-Earth Objects
(NEOs) and to detail our reaction to the two workshops chaired by David
Morrison (NEO Detection Workshop), and John Rather (NEO Interception Workshop),
who testified earlier.

On behalf of NASA, I would like to take this opportunity to publicly thank both
Drs. Morrison and Rather for their efforts in support of these workshops.
These two individuals, along with the many scientists who participated in the
two studies, worked hard to explore the complex issues surrounding NEOs. They
have provided NASA and the Congress with important insights into the
characteristics of these intriguing celestial bodies and a better understanding
of the potential threat they pose for life here on Earth.

NASA's expertise lies in the scientific study of asteroids and comets.  Our
decades of ground-based study of these objects show that many of them have
remained largely unchanged since the early periods after the formation of the
solar system 4.6 billion years ago.  They serve as fossils of a distant time,
when the solar system was very different from what it is today.  By studying
asteroids and comets we hope to enhance our understanding of the solar system
as a whole, and to gain new insights into questions about how the solar system
evolved.  We also hope to learn how many of these small bodies (asteroids and
comets) happen to be in orbits that are not circular, as in the main asteroid
belt, but in fact cross the orbit of Earth.

However, NASA's expertise does not extend into issues surrounding how to alter
the trajectory of a Near-Earth Object that might potentially threaten the
Earth, which was the focus of the NEO Interception Workshop. I will defer to my
colleagues in the Departments of Defense and Energy on those topics, and will
limit my remarks to the subject of the NEO Detection Workshop.

NEO DETECTION WORKSHOP RESULTS

The participants in the NEO Detection Workshop published "The Spaceguard
Survey," a report which confirms that Near-Earth Objects could pose a threat to
life should a large NEO collide with the Earth. The workshop participants
examined the likelihood of a major collision and the potential effects that
could result.  They concluded that while the probability of such an event
appears quite small, the consequences can be so catastrophic that a focused,
systematic approach to studying these objects appears prudent.

The participants also concluded that the necessary technology is available for
greatly increasing the rate of detecting NEOs. They also recommended greatly
increasing our capabilities for follow-on observations needed to identify the
orbit, and to assess the probable size and composition, of each newly detected
NEO.

I should emphasize here that NASA knows of no asteroid or comet that is
currently on a collision course with the Earth. As best we can tell, no large
object is likely to strike the Earth anytime in the next several hundred years.
Our ability to predict the exact location of a celestial object more than a few
hundred years in advance is somewhat limited given current technology and
understanding.  Nevertheless, it is likely that we would identify a potentially
threatening NEO, in the size range that could potentially cause catastrophic
changes in the Earth's environment (i.e. greater than 1 kilometer in diameter),
several decades in advance of a close approach to the Earth. Even in the less
likely event of a long period comet, we believe we should have at least 18
months to 2 years to react.

While the threat of a catastrophic collision is not imminent for the objects we
know about, we believe that a systematic approach to studying asteroids and
comets, especially those that pass relatively close to the Earth, makes good
sense.  We have been working to improve our existing detection programs and to
focus additional attention on this issue.  Our efforts encompass increased
detection activities using existing ground-based observatories, as well as a
renewed focus on space-based flight programs that will enhance our general
knowledge of asteroids and comets.

GROUND-BASED PROGRAMS

NASA has been supporting ground-based asteroid studies since 1973.  At that
time, we initiated funding for an effort by the U.S. Geological Survey to
examine photographic plates and use a 0.46 meter Schmidt telescope at the
Palomar Observatory in California to track and catalog asteroids.  The program
was subsequently expanded to include a parallel effort at the Jet Propulsion
Laboratory (JPL), in Pasadena, California, which also used a 0.46 meter Schmidt
telescope.  In addition, NASA is also funding observations using the 0.9 meter
"Space Watch" telescope operated by the University of Arizona which applies
CCDs to the search for NEOs. The rate of discovery worldwide is currently about
2 to 3 new NEOs a month, and altogether over 100 new NEOs have been discovered
in recent years.  These search programs have also discovered many more
asteroids and comets which do not pass close to Earth.

Critical to the effective study of NEOs is the rapid dissemination of
information about new discoveries.  As a result of the NEO Detection Workshop
held last year, an International NEO Watch Center has been established at JPL
to meet this need.  This clearinghouse will disseminate information on newly
discovered NEOs to the general scientific community in a timely manner in order
to facilitate follow-on observations at other observatories for the prompt and
accurate determination of the asteroid's orbital path.

Such follow-on observations are being funded directly by NASA, including
ongoing programs at JPL and the Smithsonian Astrophysical Observatory in
Cambridge, Massachusetts. Other follow-on observations are being conducted
using NASA's Goldstone radio telescope in California and the Arecibo
Observatory in Puerto Rico. One of the world's largest radio telescopes,
Arecibo's observing capability will be significantly improved as part of a
3-year upgrade, jointly funded by NASA and the National Science Foundation,
which operates the telescope.

Also following the recommendations of the NEO Detection Workshop, NASA has
initiated funding for three parallel efforts directed at dramatically
increasing the detection rate of NEOs. These parallel efforts consist of
focused instrument upgrade programs at three sites.  The primary goal of these
efforts is to make better use of existing digital technologies to automate the
detection process.  Most of the discoveries of NEOs to date have involved the
use of photographic plates; requiring a tedious, manpower-intensive and lengthy
analysis process.  By adding CCDs to replace the use of photographic plates, or
upgrading existing CCDs with more powerful ones, the process can be automated
and carried out much more rapidly and efficiently using computers.

Specifically, NASA is funding an upgrade to the "Space Watch" telescope,
replacing the existing 0.9 meter telescope mirror with a 1.8 meter mirror, and
upgrading the CCDs in use there.  Increasing the size of the telescope mirror
will better concentrate the light entering the telescope and will permit
astronomers to observe fainter objects.  The resulting increase in observing
power should result in a five-fold increase in the number of NEOs discovered at
this site.

NASA also is funding a modernization of the Lowell Observatory's existing
Schmitt telescope.  This 3-year program will upgrade the current CCDs to a
larger format, allowing more of the sky to be studied with each exposure.  It
is anticipated that this site alone should be capable of discovering
approximately 10 NEOs per month once the modernization program is completed; as
you recall, the detection rate world-wide is currently 2 to 3 per month, so
this would be a significant improvement.  NASA also is supporting JPL's efforts
to transfer its existing search program from an older Schmitt telescope located
on Mt. Palomar to a newer facility managed by the U.S. Air Force on the
Hawaiian island of Maui. The improved site will also make use of state-
of-the-art CCDs, and will greatly enhance the detection rate over the previous
site.  All three of these efforts receive funding support from the Departments
of Defense and Energy.

Finally, NASA is taking other steps to enhance the scientific understanding of
NEOs. We are increasing our funding support for laboratory studies at over a
dozen universities and NASA Centers on the physical and chemical
characteristics of NEOs. We are also funding a week-long summer program for
graduate students and recent Ph.D.'s on NEOs at the California Institute of
Technology.

SPACE-BASED PROGRAMS

In addition to ground-based programs, NASA has begun to focus our flight
program resources on comets and asteroids, including those that pass close to
the Earth. These include scientific observations of asteroids and comets using
the orbiting Hubble Space Telescope (HST) and International Ultraviolet
Explorer (IUE), as well as sounding rockets and the Kuiper Airborne Observatory
(KAO).  These observing programs span large portions of the electromagnetic
spectrum, allowing researchers to explore multiple characteristics of these
objects.

In addition, NASA has included asteroid flybys as part of our major outer solar
system missions.  Since these missions must pass through the main asteroid belt
to reach their desired destinations, we have always to plan into these missions
a close flyby of at least one asteroid, contingent on the availability of
sufficient propellant.

The best example of this strategy is the Galileo mission, which passes through
the asteroid belt twice during its 6-year journey to Jupiter. Galileo's first
asteroid flyby was successfully completed in October 1991, when it passed
within 1600 kilometers (1000 miles) of the asteroid 951 Gaspra. The powerful
instruments on Galileo surveyed Gaspra for several hours, providing scientists
with their first-ever close up views of an asteroid.  A small, heavily-cratered
object, Gaspra has shown that asteroids are as interesting up close as they
appeared from afar.  A second asteroid flyby will occur later this year in
August, when Galileo will pass within 3200 kilometers (2000 miles) of a larger
asteroid, 243 Ida.

NASA currently is working on two other flight missions that will focus on
asteroids, either as primary or secondary targets for study.  These missions
are NASA's proposed Near- Earth Asteroid Rendezvous (NEAR) mission and the
"Clementine" mission which is being developed in cooperation with the U.S.
Department of Defense (DoD).  Each mission will provide the opportunity for
extended observations of a near-Earth asteroid, greatly enhancing our
understanding of these objects and their origins.

NEAR is planned as a Discovery-class mission.  The Discovery program is a
proposed series of low-cost planetary missions, with very focused science
objectives, similar to NASA's existing Explorer and Earth Probes programs.  The
NEAR mission is currently being studied by the Applied Physics Laboratory (APL)
at Johns Hopkins University under contract to NASA. It will be designed to
spend a full year shadowing an asteroid and providing detailed data about its
composition and characteristics.  NEAR will determine the bulk properties of
the asteroid, including its size, volume, mass, gravity field, and spin rate.
It will also collect data on surface properties such as mineralogical
composition, and the shapes of surface features like craters, ridges and
fissures.  Other science objectives include determining the distribution of
mass within the asteroid, studying the interactions between gases, dust, and
the solar wind in the vicinity of the asteroid, and determining whether or not
it possesses a magnetic field.

The Clementine mission is being managed by DoD as a test of spacecraft
subsystems and detectors.  A few years ago, when DoD considered sending this
mission into deep space, they sought NASA's advice in determining which objects
should be studied, and which instruments would be most appropriate for studying
them.  NASA has been working closely with DoD to maximize the science return
from this mission, and to match their desire to understand target recognition
techniques with our desire to understand more about the Moon and near-Earth
asteroids.

Clementine is scheduled to be launched in January 1994 on a trajectory that
will take it into lunar orbit.  Clementine will spend approximately 2 months
mapping the Moon and studying its surface.  It will then be redirected toward a
flyby of a near- Earth asteroid, 1620 Geographos, in late August 1994.
Geographos will make its closest approach to Earth late in August, and
Clementine will complete its flyby shortly thereafter.  The exact distance of
the flyby will likely be less than 100 kilometers (approximately 62 miles), the
closest any spacecraft has ever come to an asteroid.  Coupled with data from
the Galileo flybys of Gaspra and Ida, Clementine will provide a strong data set
on asteroids from which to interpret various ground-based and space-based
observations.

SUMMARY

The program I have laid out for you today takes a very balanced and reasoned
approach to the study of NEOs.

% NASA is expanding our support for existing ground- based search activities

% NASA is funding the automation of ground-based search activities through
computer upgrades and enhancements at a number of sites

% NASA has established an international NEO information clearinghouse at JPL

% NASA is expanding our support for follow-on observations and upgrading
facilities particularly well adapted for these orbit determination studies

% NASA is focusing our space-based programs on asteroids and comets:

-- Using existing orbital and airborne observatories to study comets and
asteroids (HST, IUE, KAO and sounding rockets)

-- Making use of our outer solar system missions for asteroid flybys (Galileo)

-- Developing two missions specifically focused on enhanced understanding of
NEOs (NEAR and Clementine)

We feel this approach reflects the need to systematically and prudently
increase the detection rate of NEOs, and to enhance our understanding of these
objects.  Our goal is to increase the rate at which we discover and catalog
these objects to several per week, while simultaneously expanding our
scientific knowledge about the role they play in solar system evolution and the
emergence of life.  We look forward to working with the Committee to make all
of this possible.

Thank you.