CCNet-ESSAY, 7 February 2000


By Brigadier General S. Pete Worden <>

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

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


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