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Various topics relating to lunar evolution are discussed. The moon's ancient orbital history, geophysical and geochemical constraints favoring the capture hypothesis, the site of the lunar core, chemical and petrological constraints, dynamical constraints, and mathematical models are among the topics discussed.
The Gravity Recovery and Interior Laboratory (GRAIL) mission has provided lunar gravity with unprecedented accuracy and resolution. GRAIL has produced a high-resolution map of the lunar gravity field while also determining tidal response. We present the latest gravity field solution and its preliminary implications for the Moon's interior structure, exploring properties such as the mean density, moment of inertia of the solid Moon, and tidal potential Love number k2. Lunar structure includes a thin crust, a deep mantle, a fluid core, and a suspected solid inner core. An accurate Love number mainly improves knowledge of the fluid core and deep mantle. In the future GRAIL will search for evidence of tidal dissipation and a solid inner core.
To probe a planet's interior, seismology provides the most direct constraints on the variables that govern the dynamic properties of the body. However, the GRAIL (Gravity Recovery and Interior Laboratory) mission's high-resolution measurements of the lunar gravity field provide constraints on crustal thickness, mantle structure, core radius and stratification, and core state (solid vs. molten). These data complement seismic investigations, and joint interpretation permits improved constraints on the Moon's internal structure. Joint interpretation of disparate geophysical datasets helps reduce drawbacks that can result from analyzing them individually. The Apollo seismic network was situated on the lunar nearside surface in a roughly equilateral triangle having sides approximately 1000 km long, with stations 12/14 nearly co-located at one corner. Due to this limited geographical extent, near-surface ray coverage from moonquakes is low, but increase with depth. In comparison, gravity surveys and their resulting gravity anomaly maps have traditionally offered optimal resolution at crustal depths. Gravimetric maps and seismic data sets are therefor well suited to joint inversion, since the complementary information reduces inherent model ambiguity. We will perform a joint inversion of Apollo seismic delay times and gravity data collected by GRAIL lunar gravity mission, in order to recover seismic velocity and density as a function of latitude, longitude and depth within the Moon. We will relate density (rho) to seismic velocity (v) using a linear relationship that is allowed to be depth-dependent. The corresponding coefficient (B) can reflect a variety of material properties that vary with depth, including temperature and composition. The inversion seeks to recover the set of rho, v, and B perturbations that minimize (in a least-squares sense) the difference between the observed and calculated data.
The installation of seismometers on the Moon s surface during the Apollo era provided a wealth of information that transformed our understanding of lunar formation and evolution. Seismic events detected by the nearside network were used to constrain the structure of the Moon s crust and mantle down to a depth of about 1000 km. The presence of an attenuating region in the deepest interior has been inferred from the paucity of farside events, as well as other indirect geophysical measurements. Recent re-analyses of the Apollo data have tentatively identified this region as a lunar core, although its properties are not yet constrained. Here we present new modeling in support of seismic missions that plan to build upon the knowledge of the Moon s interior gathered by Apollo. We have devised a method in which individual events can be linked to a known cluster using the observed S-P arrival time differences and azimuth to only two stations. Events can be further identified using each cluster's unique occurrence time signature
Atmospheric mining in the outer solar system has been investigated as a means of fuel production for high energy propulsion and power. Fusion fuels such as Helium 3 (3He) and deuterium can be wrested from the atmospheres of Uranus and Neptune and either returned to Earth or used in-situ for energy production. Helium 3 and deuterium were the primary gases of interest with hydrogen being the primary propellant for nuclear thermal solid core and gas core rocket-based atmospheric flight. A series of analyses were undertaken to investigate resource capturing aspects of atmospheric mining in the outer solar system. This included the gas capturing rate, storage options, and different methods of direct use of the captured gases. While capturing 3He, large amounts of hydrogen and 4He are produced. With these two additional gases, the potential for fueling small and large fleets of additional exploration and exploitation vehicles exists. Analyses of orbital transfer vehicles (OTVs), landers, and in-situ resource utilization (ISRU) mining factories are included. Preliminary observations are presented on near-optimal selections of moon base orbital locations, OTV power levels, and OTV and lander rendezvous points. Aerospacecraft with closed cycle gas core propulsion are used to capture the 3He and deuterium from the outer planet atmospheres. Water ice on the outer planet moons has been identified as critical resources for refueling the moon landers and the nuclear electric OTVs. The numbers of interplanetary transfer vehicles (ITVs) and the launch vehicles will be presented. Preliminary design parameters for the ITVs and their payload limits will be assessed. The number of mining machines and their associated issues are addressed.
The Gravity Recovery and Interior Laboratory (GRAIL) mission [1] has provided lunar gravity with unprecedented accuracy and resolution. GRAIL has produced a high-resolution map of the lunar gravity field [2,3] while also determining tidal response. We present the latest gravity field solution and its preliminary implications for the Moon's interior structure, exploring properties such as the mean density, moment of inertia of the solid Moon, and tidal potential Love number k(sub 2). Lunar structure includes a thin crust, a thick mantle layer, a fluid outer core, and a suspected solid inner core. An accurate Love number mainly improves knowledge of the fluid core and deep mantle. In the future, we will search for evidence of tidal dissipation and a solid inner core using GRAIL data.
Apollo 11 bulk and core tube fines and rock cosmic ray tracks, discussing material history and corpuscular radiation flux and energy spectra near moon
This paper describes Lambert and Kepler algorithms designed to be the core of an autonomous rendezvous guidance system for an onboard computer. Applications include robotic and piloted missions to the moon and planets. Flight software must be compact, fast, and totally reliable. Although high accuracy is not essential for flight, in double precision these algorithms are accurate to at least 14 places almost everywhere. Both are universal; they apply to elliptic, parabolic, hyperbolic, and even rectilinear trajectories. The algorithms are improvements to those published by Battin (1987).
A space generic open avionics architecture created for NASA is described. It will serve as the basis for entities in spacecraft core avionics, capable of being tailored by NASA for future space program avionics ranging from small vehicles such as Moon ascent/descent vehicles to large ones such as Mars transfer vehicles or orbiting stations. The standard consists of: (1) a system architecture; (2) a generic processing hardware architecture; (3) a six class architecture interface model; (4) a system services functional subsystem architectural model; and (5) an operations control functional subsystem architectural model.
Atmospheric mining in the outer solar system has been investigated as a means of fuel production for high energy propulsion and power. Fusion fuels such as Helium 3 (3He) and deuterium can be wrested from the atmospheres of Uranus and Neptune and either returned to Earth or used in-situ for energy production. Helium 3 and deuterium were the primary gases of interest with hydrogen being the primary propellant for nuclear thermal solid core and gas core rocket-based atmospheric flight. A series of analyses were undertaken to investigate resource capturing aspects of atmospheric mining in the outer solar system. This included the gas capturing rate, storage options, and different methods of direct use of the captured gases. While capturing 3He, large amounts of hydrogen and 4He are produced. With these two additional gases, the potential for fueling small and large fleets of additional exploration and exploitation vehicles exists. Analyses of orbital transfer vehicles (OTVs), landers, and in-situ resource utilization (ISRU) mining factories are included. Preliminary observations are presented on near-optimal selections of moon base orbital locations, OTV power levels, and OTV and lander rendezvous points. Aerospacecraft with closed cycle gas core propulsion are used to capture the 3He and deuterium from the outer planet atmospheres. Water ice on the outer planet moons has been identified as critical resources for refueling the moon landers and the nuclear electric OTVs. Outer planet moon mining issues are addressed. The issues include the mass fraction of water ice on the moon’s surface, the volume of the mined regolith-water ice matter, and the time to capture the water ice.
The question of whether the Earth ever passed through a magma ocean stage is of considerable interest. Geochemical evidence strongly suggests that the Moon had a magma ocean and the evidence is mounting that the same was true for Mars. Analyses of martian (SNC) meteorites have yielded insights into the differentiation history of Mars, and consequently, it is interesting to compare that planet to the Earth. Three primary features of Mars contrast strongly to those of the Earth: (i) the extremely ancient ages of the martian core, mantle, and crust (about 4.55 b.y.); (ii) the highly depleted nature of the martian mantle; and (iii) the extreme ranges of Nd isotopic compositions that arise within the crust and depleted mantle. The easiest way to explain the ages and diverse isotopic compositions of martian basalts is to postulate that Mars had an early magma ocean. Cumulates of this magma ocean were later remelted to form the SNC meteorite suite and some of these melts assimilated crustal materials enriched in incompatible elements. The REE pattern of the crust assimilated by these SNC magmas was LREE enriched. If this pattern is typical of the crust as a whole, the martian crust is probably similar in composition to melts generated by small degrees of partial melting (about 5%) of a primitive source. Higher degrees of partial melting would cause the crustal LREE pattern to be essentially flat. In the context of a magma ocean model, where large degrees of partial melting presumably prevailed, the crust would have to be dominated by late-stage, LREE-enriched residual liquids. Regardless of the exact physical setting, Nd and W isotopic evidence indicates that martian geochemical reservoirs must have formed early and that they have not been efficiently remixed since. The important point is that in both the Moon and Mars we see evidence of a magma ocean phase and that we recognize it as such. Several lines of theoretical inference point to an early Earth that was also hot and, perhaps, mostly molten. The Giant Impact hypothesis for the origin of the Moon offers a tremendous input of thermal energy and the same could be true for core formation. And current solar system models favor the formation of a limited number of large (about 1000 km) planetesimals that, upon accreting to Earth, would cause great heating, being lesser versions of the Giant Impact. Several lines of geochemical evidence do not favor this hot early Earth scenario. (i) Terrestrial man-tle xenoliths are sometimes nearly chondritic in their major element compositions, suggesting that these rocks have never been much molten. Large degrees of partial melting probably promote differentiation rather than homogenization. (ii) Unlike the case of Mars, the continental crust probably did not form as a highly fractionated residual liquid from a magma ocean (about 99% crystallization), but, rather, formed in multiple steps. [The simplest model for the formation of continental crust is complicated: (a) about 10% melting of a primitive mantle, making basalt; (b) hydrothermal alteration of that basalt, converting it to greenstone; and (c) 10% partial melting of that greenstone, producing tonalite.] This model is reinforced by the recent observation from old (about 4.1 b.y.) zircons that the early crust formed from an undepleted mantle having a chondritic Lu/Hf ratio. (iii) If the mantle were once differentiated by a magma ocean, the mantle xenolith suite requires that it subsequently be homogenized. The Os isotopic compositions of fertile spinel lherzolites place constraints on the timing of that homogenization. The Os isotopic composition of spinel lherzolites approaches that of chondrites and correlates with elements such as Lu and Al. As Lu and Al concentrations approach those of the primitive mantle, Os isotopic compositions approach chondritic. The Re and Os in these xenoliths were probably added as a late veneer. Thus, the mantle that received the late veneer must have been nearly chondritic in terms of its major elements (excluding Fe). If the mantle that the veneer was mixed into was not al-ready homogenized, then Os isotopes should not correlate with incompatible elements such as Al. Consequently, either early differentiation of the mantle did not occur or the homogenization of this differentiation must have occurred before the late veneer was added. The timing of the late veneer is itself uncertain but presumably postdated core formation at about 4.45 b.y. and did not postdate the 3.8-3.9 b.y. late bombardment of the Moon. This timing based on siderophile elements is consistent with the Hf isotopic evidence cited above. If the Earth, Moon and Mars had magma oceans, the Earth subsequently rehomogenized whereas the Moon and Mars did not. The simplest solution to this observation is that homogenization of igneous differentiates was never necessary on Earth, either because the hypothetical magma ocean never occurred or because this event did not produce mantle differentiation.
Various theories regarding lunar and Mercurian magnetic properties are discussed in terms of the thermal evolutions of these bodies. In particular, the extinct dynamo, the primordial field of external origin, local mechanisms, and the active dynamo hypotheses are reviewed. The theory involving magnetization by an internal dynamo is applied to Mercury, noting that it implies the existence of a molten metallic core, or shell. Possible sources of the energy required for core differentiation are discussed, including accretional heating, long-lived radioactive isotopes, and other radioactive heat sources. Thermal processes which might keep the core molten are suggested along with processes permitting the flow of heat through the mantle. Conclusions suggested by the dynamo hypothesis are reviewed in terms of current models of the thermal evolution of Mercury and the moon.
A general theory of the rotation of solid bodies in the solar system leads to the following conclusions: No special initial conditions on the primordial rotation states of most tidally evolved bodies are necessary to account for their present rotation. The possible exception is the rotation of Venus, which must have been initially retrograde unless a liquid core-solid mantle interaction or an accelerating atmospheric tide could dominate the ordinary gravitational tides. Tides eventually drive all bodies in precessing orbits to 'Cassini states', where the spin vector, normal to the orbit and normal to the invariable plane remain coplanar as the first two precess about the latter. The constant obliquity in this configuration, together with the lowest order gravitational harmonics and the amplitude of the physical libration allows the determination of the central condensation and the extent of a liquid-core for Mercury. Criteria for the existence of observable amplitudes of the free wobble, free precession and libration of the moon are established which do not exclude current, non-zero values.
The chemical compositions of lunar rocks and soils are examined, taking into account sulfur abundances and distributions in mare basalts and their source magmas, lithophile trace and major elements in Apollo 16 and 17 lunar samples, the role of vaporization processes in lunar rock formation, chemical studies of the lunar regolith with emphasis on zirconium and hafnium, a model for the lunar anorthositic gabbro, and trace-element chemistry and reducing capacity of size fractions from the Apollo 16 regolith. Other topics considered are related to lunar chronology, volatile meteoritic elements, isotopic studies, light element geochemistry, and agglutinates and regolith processes. Attention is given to meteoritic material in four terrestrial meteorite craters, the state of meteoritic material on the moon, volatile elements in Allende inclusions, oxygen isotope fractionation in Apollo 17 rocks, cosmogenic isotope production in Apollo deep-core samples, and the effects of exposure conditions on cosmic-ray records in lunar rocks.
Twelve polished thin sections from Apollo 17 drive tube 76001 have been studied by optical petrography. The entire core is found to be mature showing little variation in depth, which is consistent with a depositional model involving slow downslope movement of the regolith by mass wasting. However, within the core some major differences are preserved between two stratigraphic units. Unit A (20-31 cm depth) is enriched in gabbroic anorthosite relative to unit B (0-20 cm depth), while unit B is enriched in KREEPY noritic breccias relative to unit A. This observation is interpreted in terms of a stratigraphy for North Massif involving a noritic breccia unit overlying a unit enriched in gabbroic anorthosite. Pronounced differences between the highland/mare ratios in drive tube 76001 and the Apollo 17 drill core separated by only 3.5 km demonstrate the relative inefficiency of lateral transport as a regolith mixing mechanism on the moon.
The earliest metal phases to crystallize from the least-fabricated low Ti mare basalts contain about 30% Ni and 2 to 7% of Co. Experimental investigations of partitioning of Ni and Co between primitive lunar basaltic magmas and metal phases are currently in progress. Preliminary results show that the metal phase crystallizing near the liquidus of Green Glass (185 ppm Ni, 70 ppm Co) would contain about 40% Ni and 2.3% Co. It seems, therefore, that if a lunar core does exist, as suggested by the results of (2), it is relatively rich in Ni (30-40%) and Co (2-7%). This composition presents a remarkable contrast to that of the Earth's core which is estimated to contain about 6% Ni and 0.3% Co. Explanations for the differing densities of Earth and Moon are imvestigated.
Radio Doppler data from four encounters of the Galileo spacecraft with the jovian moon Europa have been used to refine models of Europa's interior. Europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice-liquid outer shell, but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice-liquid shell. The size of a metallic core is uncertain because of its unknown composition, but it could be as large as about 50 percent of Europa's radius. The thickness of Europa's outer shell of water ice-liquid must lie in the range of about 80 to 170 kilometers.
NASA Marshall Space Flight Center (MSFC) is currently at work developing hardware and systems for the Ares I rocket that will send future astronauts into orbit. Built on cutting-edge launch technologies, evolved powerful Apollo and Space Shuttle propulsion elements, and decades of NASA spaceflight experience, Ares I is the essential core of a safe, reliable, cost-effective space transportation system -- one that will carry crewed missions back to the moon, on to Mars and out into the solar system. Ares I is an in-line, two-stage rocket configuration topped by the Orion crew vehicle and its launch abort system. In addition to the vehicle's primary mission -carrying crews of four to six astronauts to Earth orbit --Ares I may also use its 25-ton payload capacity to deliver resources and supplies to the International Space Station, or to "park" payloads in orbit for retrieval by other spacecraft bound for the moon or other destinations. Crew transportation to the International Space Station is planned to begin no later than 2014. The first lunar excursion is scheduled for the 2020 timeframe. This paper presents the challenges in designing the Ares I upper stage for reliability and safety while minimizing weight and maximizing performance.