John L. Remo

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

Measurable variations in 182W/183W, 142Nd/144Nd, 129Xe/130Xe and 136XePu/130Xe 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 182Hf, 146Sm, 129I and 244Pu. The l82Hf–182W system is the best accretion and core-formation chronometer, which yields a mean time of Earths formation of 10 Myr, and a total time scale of 30 Myr. New laser shock data at conditions comparable with those in the Earths deep mantle subsequent to the giant Moon-forming impact suggest that metal–silicate equilibration was rapid enough for the Hf–W chronometer to reliably record this time scale. The coupled 146Sm–147Sm chronometer is the best system for determining the initial silicate differentiation (magma ocean crystallization and proto-crust formation), which took place at ca 4.47 Ga or perhaps even earlier. The presence of a large 129Xe excess in the deep Earth is consistent with a very early atmosphere formation (as early as 30 Myr); however, the interpretation is complicated by the fact that most of the atmospheric Xe may be from a volatile-rich late veneer.

Neo interaction with nuclear radiation

Abstract This paper investigates one of several possible means of deflection of a large near-Earth object (NEO) on a potential collision course with Earth by means of modest velocity changes (ΔV ≈ 1–200 cm/s) applied to the NEO at perihelion. Given the present uncertainty in the geometry, topography and materials properties of the asteroids and/or comets, a deflection mechanism is required which is relatively insensitive to such details. Stand-off nuclear devices present an option to fulfill this criterion. Momentum can be transferred by several mechanisms: directly by means of the kinetic energy of the debris or, more efficiently, by ablation resulting from the absorption of X-rays. Thermonuclear devices additionally produce high energy neutrons. Using approximate models of the various types of NEO materials and tabulations from the literature, we construct effective X-ray and neutron mass absorption coefficients. The latter are incorporated into a simple model to calculate the impulse, and hence the velocity change imparted by the various nuclear products to all the NEO materials models.

NEO scientific and policy developments, 1995-2000

Abstract Scientific and policy developments in the field of Near-Earth Objects (NEOs) since the UN NEO conference in 1995 are briefly outlined. Some areas of research and discovery have exhibited considerable progress while others have languished. In particular, facilities in the southern hemisphere for discovery and tracking of NEOs are inadequate. Suggestions are made both at the scientific and technical levels as well as at the policy level to provide coordinated and coherent progress in developing a long-term approach to NEO hazard mitigation. The next step should be the establishment of a panel of international scientific experts on the subject.

Near-earth Resources

ABSTRACT: The technologies required to detect, track, categorize, and intercept objects in Earth‐impacting orbits can also provide access to their rich storehouse of materials. Mitigation of a clear and present near‐Earth object (NEO) threat to the Earth must provide the greatest assurance of success with the least risk to the planet. In some cases, mining a threatening NEO may become a viable alternative or supplement to a deflection or interception scenario. This converts the NEO threat to a near‐Earth resource. NEOs can supply materials for a wide range of operations both in space and on Earth, as they are thought to contain large amounts of water, carbon, structural metals, industrial feedstocks of many types, and precious metals. This wealth has low overhead for utilization in space; some known NEOs would require lower transportation energy expenditure than lunar resources. Mining a NEO inherently requires, among other things, altering the mass distribution of the body during exposure, removal, and processing of the ore. These processes can be tailored to facilitate deflection of the body from Earth impact by altering its orbital characteristics. The advantage of NEO mining is that it can mitigate the threat — the primary effort — while converting it into resources for space exploration. This additional effort, within an appropriate time scale, allows sequential mitigation of the NEO in a controlled manner while providing the resources contained within the NEO for use either in space or on Earth. Both goals, to be successful, will require maximum utilization of all sources of knowledge. The two most important are an extensive reconnaissance of the target NEO and the long history of terrestrial mining practice. This paper discusses how current mining technology might be adapted to mine NEOs, whether threatening or not. It summarizes our knowledge of NEO composition, physical properties, and mining and processing methods, and points out areas where further research, especially physical testing in space, is vital. The great potential of NEO resources and the successful mitigation of NEO threats will be best realized if their utilization is considered from the earliest planning of Earth‐NEO mitigations.

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. Effective solutions that minimize atmospheric EMP effects on internal and proximate electronic and electro-optical equipment external to the system based on systematic measurements using Moebius loop antennas, interpretations of signal periodicities, and dissipation indicators determining transient noise origin characteristics from target emissions are described. Analytic models for the effect of target chamber resonances and associated noise current and temperature in a probe diode laser are described.

High energy density laser interactions with planetary and astrophysical materials: methodology and data

Sandia National Laboratories NLS (1064 nm) and Z-Beamlet (527 nm) pulsed lasers @ ~ 100 GW/cm2 and 10 TW/cm2 were used to attain pressures at 20 - 525 GPa on a variety of metallic and mineral targets. A simple, inexpensive and innovative electro-optical real-time methodology monitored rear surface mechanical deformation and associated particle and shock wave velocities that differ considerably between metals and non-metals. A reference calibration metal (Aluminum) and a reference non-metal (graphite) were used to demonstrate the validity of this methodology. Normative equations of state and momentum coupling coefficients were obtained for dunite, carbonaceous meteorites, graphite, iron and nickel. These experimental results on inhomogeneous materials can be applied to a variety of high energy density interactions involving stellar and planetary material formation, dynamic interactions, geophysical models, space propulsion systems, orbital debris, materials processing, near-earth space (lunar and asteroid) resource recovery, and near-earth object mitigation models.

Propulsion options for missions to near-Earth objects

Abstract An analysis identifying opportunities for extending space propulsion capabilities to ranges around 1 AU from the Earth is presented to suggest an effective and practical response to critical scientific, mitigation, and commercial missions to near-Earth objects (NEOs). The approach developed, which is based on previous studies of flight in field-free space, provides a convenient and simple means of comparing deep space missions employing a variety of candidate advanced propulsion concepts. Three types of mission are considered: flyby, rendezvous, and round trip. Two classes of propulsion systems are considered: Type I, characterized by impulsive thrusters providing rapid acceleration to coast speed and Type II, characterized by slow but continuous acceleration with a short duration coast at final velocity. Consideration is focused on timely interception of NEOs approaching Earth well beyond cislunar range during a time period out to about 2020. It is shown such missions might be best accomplished by means of nuclear thermal or nuclear electric propulsion. Considering the development effort expended thus far on such systems, it is recommended that completing this effort is of paramount importance for ensuring future deep space performance capability.

Diffraction losses for symmetrically perturbed curved reflectors in open resonators.

The diffraction power losses for slightly tilted (perturbed) open resonator reflectors with both circular and rectangular apertures are computed for several tilt angles and reflector radii of curvature. Computational results indicate that the power losses increase monotonically with increasing tilt angle for stable systems, while for unstable systems the power losses are hardly affected by the tilt angle. At a given tilt angle, the perturbation generated power losses are negligible for the confocal case but become significant as the geometry of the system approaches that of the concentric or plane-parallel resonator and fluctuate about the unperturbed values for an unstable geometry. This last result may have applications for unstable laser design.

Plasma-driven Z-pinch X-ray loading and momentum coupling in meteorite and planetary materials

X-ray momentum coupling coefficients, C M , were determined by measuring stress waveforms in planetary materials subjected to impulsive radiation loading from the Sandia National Laboratories Z-machine. Velocity interferometry (VISAR) diagnostics provided equation-of-state data. Targets were iron and stone meteorites, magnesium-rich olivine (dunite) solid and powder (~5–300 μm), and Si, Al, and Fe calibration targets. Samples were ~1-mm thick and, except for Si, backed by LiF single-crystal windows. X-ray spectra combined thermal radiation (blackbody 170–237 eV) and line emissions from pinch materials (Cu, Ni, Al, or stainless steel). Target fluences of 0.4–1.7 kJ/cm 2 at intensities of 43–260GW/cm 2 produced plasma pressures of 2.6–12.4 GPa. The short (~5 ns) drive pulses gave rise to attenuating stress waves in the samples. The attenuating wave impulse is constant, allowing accurate C M measurements from rear-surface motion. C M was 1.9 − 3.1 × 10 −5 s/m for stony meteorites, 2.7 and 0.5 × 10 −5 s/m for solid and powdered dunite, 0.8 − 1.4 × 10 −5 s/m for iron meteorites, and 0.3, 1.8, and 2.7 × 10 −5 s/m respectively for Si, Fe, and Al calibration targets. Results are consistent with geometric scaling from recent laser hohlraum measurements. CTH hydrocode modeling of X-ray coupling to porous silica corroborated experimental measurements and supported extrapolations to other materials. CTH-modeled C M for porous materials was low and consistent with experimental results. Analytic modeling (BBAY) of X-ray radiation-induced momentum coupling to selected materials was also performed, often producing higher C M values than experimental results. Reasons for the higher values include neglect of solid ejecta mechanisms, turbulent mixing of heterogeneous phases, variances in heats of melt/vaporization, sample inhomogeneities, wave interactions at the sample/window boundary, and finite sample/window sizes. The measurements validate application of C M to (inhomogeneous) planetary materials from high-intensity soft X-ray radiation.

Mining Near‐Earth Resources

ABSTRACT: Mining the potentially vast storehouse of natural resources contained within near‐Earth objects (NEOs) could assist mitigation of the danger that a threatening object presents to life on Earth. Properly planned, NEO mining could provide a substantial basis for the exploration and development of space, in addition to providing important tools and opportunities for mitigating impact hazards.