Isotopes as clues to the origin and earliest differentiation history of the Earth.

Measurable variations in (182)W/(183)W, (142)Nd/(144)Nd, (129)Xe/(130)Xe and (136)XePu/(130)Xe in the Earth and meteorites provide a record of accretion and formation of the core, early crust and atmosphere. These variations are due to the decay of the now extinct nuclides (182)Hf, (146)Sm, (129)I and (244)Pu. The (l82)Hf-(182)W system is the best accretion and core-formation chronometer, which yields a mean time of Earth's formation of 10Myr, and a total time scale of 30Myr.

Atmospheric electromagnetic pulse propagation effects from thick targets in a terawatt laser target chamber.

Generation and effects of atmospherically propagated electromagnetic pulses (EMPs) initiated by photoelectrons ejected by the high density and temperature target surface plasmas from multiterawatt laser pulses are analyzed. These laser radiation pulse interactions can significantly increase noise levels, thereby obscuring data (sometimes totally) and may even damage sensitive probe and detection instrumentation. Noise effects from high energy density (approximately multiterawatt) laser pulses (approximately 300-400 ps pulse widths) interacting with thick approximately 1 mm) metallic and dielectric solid targets and dielectric-metallic powder mixtures are interpreted as transient resonance radiation associated with surface charge fluctuations on the target chamber that functions as a radiating antenna.

NEO impact projections.

The concept of a near-Earth object (NEO) impact projection metric (PM) based on the ratio of the observation time to the impact time, rho(t), for a projected NEO impact is developed. The PM can assist NEO mitigation decision-making that is based on the discontinuously changing cumulative impact probability and help mitigate false alarms of NEO impact with Earth that have undermined public perception toward the veracity of predicting NEO threats.

A dynamic metric for NEO hazard mitigation.

A dynamic metric for near-Earth object (NEO) hazard mitigation quantifies threats from potential NEO impacts with Earth in terms of energy required to perturb threatening NEO orbits to avoid collision. The required energy is based on NEO mass, anticipated velocity change to avoid collision, and the momentum coupling coefficient.

Assessing NEO hazard mitigation in terms of astrodynamics and propulsion systems requirements.

Uncertainties associated with assessing valid near-Earth object (NEO) threats and carrying out interception missions place unique and stringent burdens on designing mission architecture, astrodynamics, and spacecraft propulsion systems. A prime uncertainty is associated with the meaning of NEO orbit predictability regarding Earth impact. Analyses of past NEO orbits and impact probabilities indicate uncertainties in determining if a projected NEO threat will actually materialize within a given time frame.