By Brigadier General S. Pete Worden February 7 2000
I'll begin my short 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
From Louis Friedman
Pete Worden's essay is notable in that he explicitly rejects efforts to spend resources on mitigation, and correctly emphasizes the need for more knowledge. Going beyond this framework has led to a loss of credibility toward those whose advocate dealing with the NEO threat.
But clearly what Gen. Worden offers is a solution looking for a problem. He wants a mission for the DoD, and defines a rational one, based on the need for more knowledge about NEOs. The following statement from his essay is revealing, "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." One would normally think that the lack of catastrophic impacts is not something for the discussions to suffer, but something that would assist the discussions. Unless one want the threat to be a justification for a mission.
The motivation of trying to find a role for DoD should be carefully examined. We all can agree on increased observation programs (indeed The Planetary Society both funds private ones and advocates government programs), and on space missions of exploration. But astronomical observation programs and exploration missions are civil pursuits, not military ones -- and there should be no military mission defined here. So far, the military has agreed.
Military - civil cooperation is to be applauded. This was wisely stated in the founding act for a civil space agency. The LINEAR and other programs prove that. But encouraging military assets and cooperation in this civil endeavor is very different from defining a military mission. If a deterministic threat is ever identified so that defense of the world, or the country, is required then we can assign a military mission. But until then, making the search for knowledge about NEOs a military function will inhibit scientific and international cooperation, and turn the focus from astronomy and science to devices and exercises. It makes no more sense for the NEO threat to become a military mission, than it does for fighting the threat of global warming (maybe less, at least the global warming threat is a known one). Both need to be dealt with, but appropriately.
Louis Friedman Executive Director, The Planetary Society http://planetary.org
By Jonathan Tate, SPACEGUARD UK
As Brigadier General Worden started his essay with a disclaimer, I feel that I ought to do the same, although as a mere Major I am significantly lower in the food chain than he is! Suffice to say that the British Ministry of Defence has no official view on the Near-Earth Object (NEO) hazard, and has made it clear to the author that it considers this hazard outside its remit ("shut up and go away"). However, the Department of Trade and Industry has taken the responsibility upon itself, and this, in itself, is something of a triumph!
Over the past couple of years the concerns of parts the NEO community have begun to shift from the threat posed by the "traditional" one kilometre or larger objects to the 50 to 500 metre objects that are capable of inflicting local or regional damage. This shift in emphasis seems to be, at least in part, the result of a number of factors:
* The recent, and continuing success of detection programmes such as LINEAR and Spacewatch in detecting unprecedented numbers of the larger NEOs, and a substantial number of smaller ones. These increasing detection rates, coupled with well publicised estimates that appear to have reduced the number of large threatening objects are beginning to engender the hope that we will soon have the situation as it pertains to these larger objects under control.
* Emerging technology makes the detection of smaller, dimmer objects increasingly practical.
* The realisation that small impacts can have hitherto unrecognised effects on the environment and the infrastructure on which our civilisation depends.
* An increasing understanding of the rate at which small impacts occur.
* And finally, over the past few years it has become clear, despite the best efforts of many, that the NEO community is unlikely to be able to grip funding agencies (particularly governments) with a threat that occurs only on timescales of hundreds of thousands of years.
While these are all good arguments to shift the centre of gravity of our proposals and work, the fact remains that the main threat posed to the physical well being of our species (and that of all of the others as well) comes from the rare, globally threatening impacts. The arguments put forward in the middle of the last decade still hold water.
The speed at which research is advancing in all aspects of this subject is staggering, in theoretical studies, hardware and software development, and in the integration of other disciplines into the overall picture. We should also not forget the changes being made in the public perception of the impact hazard. Each advance, in whatever sphere, changes our overall perception of the threat to a greater or lesser extent. However, we should not lose sight of the fact that, as far as detection is concerned, we are far from achieving our goal with the larger objects. True, we may see the light at the end of the tunnel, but thereís a long way to daylight yet. Some members of the public and the press are getting the idea that the scientists have the problem licked. This is dangerous and should be discouraged. Some statements that have appeared recently tread a perilous line between comforting optimism and irresponsibility.
It is also worth remembering that detection, while being the sexy end of the market, is of little or no value unless there is the back up support of follow-up observations, characterisation, physical and dynamical studies etc, etc. These areas are barely keeping up with current detection rates, and will be severely pressured by furtherincreases.
All of this is not to say that we shouldn't be raising a large red flag over the smaller object threat. All of the factors that I mentioned above apply, but we still do not have the levels of funding that allow us to concentrate on anything but the primary threat. However, to use the threat from smaller objects as a trigger for additional funding is both appropriate and to be encouraged. The one thing that has become abundantly clear in the UK is that we are not going to achieve a full-blown, all encompassing programme overnight. We have to attack the problem incrementally, based on current research and the political and financial realities of the moment. If additional or independent resources should become available, or when our survey of the larger objects reaches an acceptable level of completeness, then we should shift the emphasis to smaller objects. We may, of course, be overtaken by events, in which case the problems of funding might disappear anyway.
We should be anything but complacent about the "Tunguska" type of event. Indeed, such events pose a clear and present danger to every part of the globe, but we must be very careful about complacency over the ever-present threat of a globally threatening catastrophe.
On a slightly separate issue, I was a little surprised to read some of the things in Louis Friedman's comment. Firstly, he implies that discussion of methods to prevent a catastrophic NEO collision has led to a loss of credibility for the NEO community. I fear that, as far as the public are concerned (who pay for science, after all) precisely the opposite is true. They cannot see any point in detecting, tracking and studying NEOs unless there is something that we can do about the hazard! I have heard the concept of study without planning for mitigatory action described as "scientific masturbation" -- and that by a politician.
I was also a bit surprised by the arguments against military involvement in the search for NEOs. The question of whether the NEO problem is one of research or defence has been well aired over the years, and here is not the place to retread the old paths. I do not see Brigadier Worden's proposal as a solution looking for a problem, but even if it is, if the DoD is indeed willing to search for a role, better this than some other things that I can think of. There are certainly drawbacks to military involvement in essentially civil programmes, but the military have skills that civilians can have difficulty with and resources that can be of great value. Also, the "mainstream" scientific community, certainly in UK, has a really hard time viewing NEO survey as "pure research". In my original paper (that was submitted to the British Ministry of Defence) I pointed out that the Government of the United Kingdom has been charged, by the Crown, with the defence of the realm. This duty has been distilled into three National Defence Roles:
Defence Role 1 - To ensure the protection and security of the United Kingdom and its dependent territories, even when there is no immediate external threat.
Defence Role 2 - To ensure against any major external threat to the United Kingdom and its allies.
Defence Role 3 - To contribute to promoting the United Kingdom's wider security interests through the maintenance of international peace and security.
It should be noted that there is no definition or limitation on possible threats to the United Kingdom explicit in these tasks. You will see that, for the UK at least, there need be no "mission search" -- it's already implicit in the MOD Mission Statement.
I think it is imprudent to be dismissive of military involvement at this early stage -- they (we) have C3I systems, hardware and wetware that are ideally suited to search programmes and the essential task of planetary defence. NEOs are not just objects of sterile scientific interest -- the public demands security and that means defence against threats internal and external. We are burying our heads in the sand if we think that we needn't worry about mitigation.
Jay Tate Spaceguard UK