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CCNet-ESSAY, 7 February 2000
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NEOS, PLANETARY DEFENSE AND GOVERNMENT - A VIEW FROM THE PENTAGON
By Brigadier General S. Pete Worden <SimonP.Worden@pentagon.af.mil>
I'll begin my short CCNet-essay with a disclaimer. The US
Department of
Defense (DoD) has no official view on the Near-Earth Object (NEO)
hazard. We have agreed to assist the overall United States effort
led
by NASA with technology and observational support. Official
disclaimers
out of the way, I'll provide my personal views in the remainder
of the
essay.
For those readers who don't know me, I'm a US Air Force officer
with a
background as a research astronomer. Although I began as a solar
physicist my current research interests--in the few moments I
have time
to do research--are focused on NEOs and meteors. Most of my
recent work
for the Air Force has been in developing options to perform
selected
national security missions from and through space. In the past
decade I
was responsible for much of the US DoD work to develop small
satellites, microsatellites and reusable satellite launchers. The
1994
Clementine mission to the moon (originally intended to include an
asteroid flyby) was one of the my programs.
I will assume that most readers share in the view that NEOs have
and
will continue to play a central role in the evolution of life on
this
planet. I'll also assume that we more or less agree that we face
a
continuing threat from these objects. Most analyses focus on the
big
threats--objects which can threaten life globally and have the
potential to destroy or seriously damage our species. I for one
believe
we should pay more attention to the "Tunguska-class"
objects--100 meter
or so objects which can strike up to several times per century
with the
destructiveness of a nuclear weapon.
NEO discussions in the United States have, as I believe they have
everywhere, suffered from the fact that catastrophic NEO impacts
are so
rare and hence so unlikely to occur in our lifetimes. Whereas
people
may pay good money to see a movie thriller about asteroid strikes
or
read with great interest of the demise of the dinosaurs, a
once-every-few-tens-of-millions-of-years possibility is not real
to
most people. Decision makers simply are unwilling to spend scarce
resources on such an unlikely catastrophe--however terrible it
may be
or even if it is inevitable.
Conversely, I can show people evidence of real strikes inflicting
local
and regional damage less than a century ago. Even more compelling
are
the frequent kiloton-level detonations our early warning
satellites see
in the earth's atmosphere. These are threats the public and its
leaders
will take seriously. These are threats we can understand. And
these are
even threats we could mitigate, if required, without recourse to
nuclear technology.
Many of my colleagues in the US national security community have
advocated a proactive role for our community. They would have us
build
and demonstrate a NEO defense system--perhaps based on nuclear
weapons.
This is premature. What we need now is a full characterization of
first
the phenomenon and then the threat which it might entail. We need
to
know how many objects there are, where they are and when any
closely
approach the Earth. And we need to know the composition and
structure
of all classes of NEOs. This is where the US national security
establishment can play an important role.
Within the United States space community there is a growing
concern
over "space situational awareness." We are beginning to
understand that
it is essential to identify and track virtually everything in
earth
orbit. Some of these objects, down to a few centimeters in size,
present a potential threat to commercial and civil space
operations
such as the International Space Station. Commercial space
operations
exceeded government space operations for the first time in the
last few
years. We have begun the era of "global utilities" such
as the Global
Positioning System (GPS) in which our ways of life are becoming
critically dependent on space systems. All of these demand the
ability
to search essentially all of space near the earth about once
every few
hours and track up to 300,000 objects.
The US Department of Defense has a network of sensors that
perform this
function but in a limited capacity compared to what is desired.
We plan
on upgrading the system over the next decade or so--including
space-based sensors--to provide comprehensive search, detection
and
tracking of space objects. The LINEAR system which has been so
successful over the past year in detecting NEOs is a prototype of
our
next generation ground-based optical system. With relatively
simple
modifications to operations, our future space surveillance system
could
produce a comprehensive catalog of NEOs at little or no expense
to the
scientific community.
If the international community had to duplicate this network of
sensors, it would cost 100s of millions of dollars, if not
more.
Simple economics argue that this is a portion of the NEO problem
that
should be urged upon and given to the US Military. For this
reason I
believe the growing community of experts on the NEO threat should
not
direct their efforts to building and funding more ground-based
telescopes. Although I must caveat that not everyone in the DoD
is
as eager as am I to take on the NEO task!
Enthusiasm grows for the next generation satellite, the so-called
"microsatellite." These are 100 kilogram-class
satellites costing about
$5-10M US to build and an equivalent amount to launch. Leading
the
world in the development of these microsatellites are a number of
European groups. Their rapid progress has been enabled by the
capacity
of the Ariane IV and V launchers to carry as auxiliary payloads
up to
eight microsatellites into a GEO transfer orbit at a cost of
about $1
million per satellite. NASA, US academic institutions and US
aerospace
companies have begun efforts to develop microsatellites for space
science and planetary exploration missions.
Similarly, the DoD is beginning the development of similar small
size
microsatellites for servicing and re-fueling larger mission
satellites.
These microsatellites should allow for low-cost missions to a
wide
range of NEOs--including missions to fully characterize their
structure
and possibly bring back samples to earth. Microsatellite missions
can
also assist in the surveillance and cataloguing of NEOs as there
is
some doubt that sensors based on the earth or in earth orbit can
detect
all of the potentially threatening objects. Microsatellites
internal to
the earths orbit--perhaps in a Venus-type orbit--could provide a
low-cost solution. This is potentially another task for low-cost
microsatellites. The NEO research community community will have
access
to both low-cost spacecraft and low-cost launch. In addition to
Ariane,
the United States Air Force is putting a similar auxiliary
microsatellite adapter on our new EELV (Evolved Expendable Launch
Vehicle) launch systems.
What then should we do? What role should the US Government, and
specifically the US DoD play in what everyone agrees is an
international concern? I believe we in the US DoD can and should
agree
to modify our space surveillance systems to identify and track
all
potentially threatening NEOs--probably down to about the 100
meter
class. In parallel, in situ studies of NEOs using low-cost
microsatellite missions should begin immediately. These missions
can
and should involve NASA, ESA, other European space agencies as
well as
the US DoD. These missions can use new technology to rendezvous,
inspect, sample, and even impact NEOs to study their composition
and
structure. With an estimated cost of about $10-20M per mission,
including data reduction and launch, this is an affordable
program.
Here is where I would focus the growth of official interest in
NEOs as
evidenced by the recent UK decision to stand up a formal program.
And finally, I would propose focusing on the very small end of
NEOs--100 meters diameter or less. At any given time there are
probably
tens of objects 10 meters or larger in cislunar space. These are
easily
accessible to the low-cost microsatellite mission.
Should we worry now about mitigating the NEO hazard? I would say
no,
until a bona fide threat emerges. This will avoid much of the
political
consternation that has arisen in the past from nuclear weapon
experts
advocating weapons retention and even testing in space. After
all, we
can't reliably divert an NEO until we know much more about
its
structure. This we'll get from a decade of dedicated
microsatellite
missions. Some of these missions may even have as a side
experiment
moving very small (10-50 meter class) NEOs by impacting them.
This
could give us much of the necessary experience should a true
threat
emerge in the near future.
Another benefit of a focused international NEO space mission
suite is
public awareness and enthusiasm. From a scientific standpoint,
these
are primordial objects--the stuff of which we were made. People
throughout the world, as well as the entire scientific community,
will
truly embrace such an exciting endeavor. Moreover, space
visionaries
often look to the NEOs as the raw material of eventual space
industrialization. We originally chose the title
"Clementine" for the
1994 lunar and NEO probe launched by the DoD for this purpose. An
old
American song about a frontier miner's daughter, Clementine, was
the
origin of the mission's name. We hoped to evoke not only the
spirit of
the frontier but also to leverage the appeal that valuable lunar
and
asteroid mineral resources might have.
In summary, I believe we have an opportunity to harness public
interest, government attention and existing expertise on the NEO
problem. An objective program should have two complementary
parts.
First, to detect and to catalog virtually all threatening
objects.
This can be considerably easier and cheaper if the US DoD can be
persuaded to adopt it as part of its current space surveillance
mission. Second, we should mount a modest, low-cost program to
fully
characterize the composition and structure of all classes of
NEOs. The
latter can and should be an international effort involving space
agencies around the world. When, and not until, we find a likely
threat
is the time to work hard on mitigation.
S. Pete Worden, Brigadier General (sel), USAF
Deputy Director for Command and Control
Headquarters, United States Air Force
The Pentagon, Washington, DC USA
e-mail: spw21oct@erols.com
SimonP.Worden@pentagon.af.mil
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