Abstract :
The greatest natural threat to the long-term survivability of mankind is an asteroid or comet impact with the Earth. SHIELD is an architectural concept for a comprehensive Earth defense system designed to discover, catalog, calculate orbits of near-Earth objects, and to deflect potential impactors. SHIELD consists of Sentries, Soldiers, and an Earth Control Center. Sentries are spacecraft designed to search and locate NEOs of all types. Sentries maximize the lead-time for a potential impact, which simplifies the task of the Soldiers to deflect the object. Sentry spacecraft determine the orbit of each object, and compare it with the onboard database of known NEOs. The results are kept in a distributed space-Earth database. Soldier spacecraft deflect or disperse the potential impactor. Several mitigation methods have been compared by their specific impulse. Each technique requires some development to be feasible. These techniques can be categorized into “rendezvous” in which the Soldier physically lands on the NEO and “intercept”. The required number of Soldiers and their locations has been examined. SHIELD has clearly shown that an Earth-protection system is practical and that a full system could be built within a few years. Indeed, very capable Sentries can be launched today.
