Small Solar System Body Mitigation: A Realist’s Approach

Kurzfassung

The common approach towards asteroid mitigation concept building is to, more or less explicitly, assume ample warning time before impact and, implicitly, an enlightened research and development funding environment. Without mentioning, both are expected to allow for the design and implementation of highly advanced mitigation methods which often require similarly advanced infrastructures and space transportation systems. History has shown that grandiose schemes, at least in the free world and open societies, will stay on the drawing board unless there is a clear and present, urgent and overwhelming societal need that more than warrants the associated grandiose expenditures. The missile and Moon races of the 1950s and 1960s are no exception to this rule. They however indicate what is possible in space once such a need is perceived. It can therefore be expected that no significant investment into small body mitigation efforts will ever be made prior to the discovery of a hazardous body and the subsequent robust confirmation of a very high likelihood of a dangerous impact. This reaction pattern is confirmed by several predicted and actual close encounters of Near Earth Asteroids (NEA) with our planet, some of which were expected to have a significant chance of colliding with it, most notably (99942) Apophis. Analysis of the orbits of these and other small bodies with respect to the Earth’s orbit show that the warning time before impact is subject to serious natural limits, set by synodic periods, actual perturbations, and observational and modelling uncertainties. The practical warning time window, starting from the discovery and certain recognition of a very likely impactor, is of the order of a few years to very few decades at most. Within these few years, a real and massive, integrated interplanetary spaceflight and ground observation campaign has to be mounted and lead to a successful conclusion. The necessary activities, often to be conducted in parallel, include target analysis, design, testing, launch, cruise phase, interception, mitigation effects application, effects accumulation time, and effects assessment. Therefore the question is whether a threatening small body can be mitigated on warning, without a prior standing investment, by commercially available and surplus space technology alone. It is shown that in most cases, a mitigation campaign with a comfortable chance of success against PHA-class objects can be designed using presently available space assets and spacecraft designs, only. The present space infrastructure faces a challenge when confronted with larger, km-scale objects. Smaller objects are easier to mitigate, but have in recent years been shown to carry considerable hazards, and are less likely to be detected in time for successful mitigation. Recommendations are made to improve the overall situation. Many of these measures result in considerable synergy effects for astronomy and affordable scientific interplanetary spaceflight. It is shown that all suggested measures are cost-effective investments, although some well exceed present efforts in the respective fields of work.