Impact Cratering Theory and Modeling for the Deep Impact Mission: From Mission Planning to Data Analysis

The cratering event produced by the Deep Impact mission is a unique experimental opportunity, beyond the capability of Earth-based laboratories with regard to the impacting energy, target material, space environment, and extremely low-gravity field. Consequently, impact cratering theory and modeling play an important role in this mission, from initial inception to final data analysis. Experimentally derived impact cratering scaling laws provide us with our best estimates for the crater diameter, depth, and formation time: critical in the mission planning stage for producing the flight plan and instrument specifications. Cratering theory has strongly influenced the impactor design, producing a probe that should produce the largest possible crater on the surface of Tempel 1 under a wide range of scenarios. Numerical hydrocode modeling allows us to estimate the volume and thermodynamic characteristics of the material vaporized in the early stages of the impact. Hydrocode modeling will also aid us in understanding the observed crater excavation process, especially in the area of impacts into porous materials. Finally, experimentally derived ejecta scaling laws and modeling provide us with a means to predict and analyze the observed behavior of the material launched from the comet during crater excavation, and may provide us with a unique means of estimating the magnitude of the comet’s gravity field and by extension the mass and density of comet Tempel 1.     

The x-ray cluster baryon crisis

Nucleosynthesis in the standard hot big bang cosmology offers a successful account of the production of the light nuclides during the early evolution of the Universe. Consistency among the predicted and observed abundances of D,³He,⁴He and⁷Li leads to restrictive lower and upper bounds to the present density of nucleons. In particular, the upper bound ensures that nucleons cannot account for more than a small fraction (<0.06h ₅₀ ^–2 ) of the mass in a critical density (Einstein-de Sitter) Universe. In contrast, x-ray observations of rich clusters of galaxies suggest strongly that baryons (in hot gas) contribute a significant fraction of the total cluster mass (0.2h ₅₀ ^–3/2 ). If, indeed, clusters do provide a fair sample of the mass in the Universe, this crisis forces us to consider other ways of mitigating it, including the politically incorrect possibility that <1. The options, including magnetic or turbulent pressure, clumping and non-zero space curvature and/or cosmological constant, are discussed.     

Operational life improvement of SSME high-pressure turbopumps

The current Space Shuttle Main Engine Phase I engine has demonstrated excellent flight performance at power levels up to 104% of rated power level. Early certification testing at 109% power level showed the operational life of the high pressure turbopumps to be limited. A development program, Phase II, has been under way since 1983 to increase the operational life and provide additional margin. The history of the SSME Phase I engine and the design and results of the SSME Phase II Program are presented. Operational life limits and high-maintenance areas of the high-pressure turbopumps are identified. The Phase II design improvements, supporting analyses, and test results are described. The formal certification test program is discussed. Modifications have been made to the high-pressure fuel turbopump to reduce turbine operating temperature, to extend the life of the first- and second-stage turbine blades, and to reduce sheet metal maintenance. Modifications have been made to the high-pressure oxidizer turbopump to improve bearing life and to eliminate subsynchronous whirl. These are discussed in detail, as is the design and use of special instrumentation to provide for rapid evaluation of merit.     

RPS strategies to enable NASA''s next decade robotic Mars missions

NASA's proposed roadmap for robotic Mars exploration over the next decade is influenced by science goals, technology needs and budgetary considerations. These requirements could introduce potential changes to the succession of missions, resulting in both technology feed forward and heritage. For long duration robotic surface missions at locations, where solar power generation is not feasible or limited, Radioisotope Power Systems (RPS) could be considered. Thus, RPSs could provide enabling power technologies for some of these missions, covering a power range from 10s of milliwatts to potentially a kilowatt or even higher. Currently, NASA and DoE with their industry partners are developing two RPSs, both generating about 110 W(e) at BOL. These systems will be made available as early as 2009. The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG)—with static power conversion—was down-selected as a potential power source for the MSL mission. Development of small-RPSs is in a planning stage by NASA and DoE; potentially targeting both the 10s of milliwatts and 10s of watts power ranges. If developed, Radioisotope Heat Unit (RHU) based systems—generating 10s to 100s of milliwatts—could power small adjunct elements on larger missions, while the GPHS module-based systems—each generating 10s of watts—could be stacked to provide the required power levels on MER class surface assets. MMRTGs and Stirling Radioisotope Generators (SRGs) could power MSL class or larger missions. Advanced Radioisotope Power Systems (ARPS) with higher specific powers and increased power conversion efficiencies could enhance or even enable missions towards the second half of the next decade. This study examines the available power system options and power selection strategies in line with the proposed mission lineup, and identifies the benefits and utility of the various options for each of the next decade launch opportunities.     

Modeling international cooperation for space exploration

Space exploration into the twenty-first century is contingent upon the ability of states to forge an appropriate vehicle for international cooperation. A theoretical framework that explains international cooperation in space exploration is proposed. This framework encompasses scientific, technological, political, and economic initial conditions, state and nonstate political actors, and models of cooperation that explain how initial conditions and actors interact to realize cooperative outcomes. It is hypothesized that the prevailing initial conditions favor certain political actors over others which, in turn, promote a specific model of cooperation. Cooperative policy outcomes are examined and assessed vis-à-vis case studies of cooperation in space exploration. On this basis, policy recommendations that engender effective cooperative outcomes in space exploration are suggested.     

C-band FET power amplifier for TWTA replacement

The technology of gallium arsenide field-effect transistors has advanced to the point where these devices can serve to replace traveling wave tubes in spaceborne communication transponders.This paper describes interim results of a C-band FET amplifier which is currently being developed by RCA for INTELSAT. The FETA is designed to provide a 6-W output with an efficiency greater than 25%, and a backed-off 1.5-W output level with low distortion and efficiency of 13%.The third order intermodulation ($\text{C}\text{I}$) of a FETA at saturation is typically 15 dB as compared to 10 dB for a TWTA. At 10 dB input power back-off the $\text{C}\text{I}$ improves to 24 dB while that of a TWTA is only 16 dB.We fabricated a breadboard 5-W FETA which demonstrates that a linear operation can be achieved at an output level of 1.5 W with 10% efficiency. By contrast the efficiency of a typical 5 W TWTA in the same linear region is no greater than 3–5%.     

Humans to Mars: a feasibility and cost-benefit analysis

Mars is a compelling astrobiological target, and a human mission would provide an opportunity to collect immense amounts of scientific data. Exploration alone, however, cannot justify the increased risk. Instead, three factors drive a human mission: economics, education, and exploration. A human mission has a unique potential to inspire the next generation of young people to enter critically needed science and engineering disciplines. A mission is economically feasible, and the research and development program put in place for a human mission would propel growth in related high-technology industries. The main hurdles are human physiological responses to 1–2 years of radiation and microgravity exposure. However, enabling technologies are sufficiently mature in these areas that they can be developed within a few decade timescale. Hence, the decision of whether or not to undertake a human mission to Mars is a political decision, and thus, educational and economic benefits are the crucial factors.     

Ozone concentrations and ultraviolet fluxes on Earth-like planets around other stars

Coupled radiative-convective/photochemical modeling was performed for Earth-like planets orbiting different types of stars (the Sun as a G2V, an F2V, and a K2V star). O(2) concentrations between 1 and 10(-5) times the present atmospheric level (PAL) were simulated. The results were used to calculate visible/near-IR and thermal-IR spectra, along with surface UV fluxes and relative dose rates for erythema and DNA damage. For the spectral resolution and sensitivity currently planned for the first generation of terrestrial planet detection and characterization missions, we find that O(2) should be observable remotely in the visible for atmospheres containing at least 10(-2) PAL of O(2). O(3) should be visible in the thermal-IR for atmospheres containing at least 10(-3) PAL of O(2). CH(4) is not expected to be observable in 1 PAL O(2) atmospheres like that of modern Earth, but it might be observable at thermal-IR wavelengths in "mid-Proterozoic-type" atmospheres containing approximately 10(-1) PAL of O(2). Thus, the simultaneous detection of both O(3) and CH(4) - considered to be a reliable indication of life - is within the realm of possibility. High-O(2) planets orbiting K2V and F2V stars are both better protected from surface UV radiation than is modern Earth. For the F2V case the high intrinsic UV luminosity of the star is more than offset by the much thicker ozone layer. At O(2) levels below approximately 10(-2) PAL, planets around all three types of stars are subject to high surface UV fluxes, with the F2V planet exhibiting the most biologically dangerous radiation environment. Thus, while advanced life is theoretically possible on high-O(2) planets around F stars, it is not obvious that it would evolve as it did on Earth.     

A narratological approach to interpreting and designing interstellar messages

Contemporary narratology (narrative theory) offers a useful framework for interpreting interstellar messages that have already been sent to potential extraterrestrial recipients, as well as for designing messages that may be transmitted in the future. In this paper, narratological concepts are used to analyze in depth a single interstellar message sequence, elucidating methods by which various parts of speech (nouns, verbs, adjectives, and adverbs) can be paired with pictures to describe the human body in motion. The concept of focalization is applied to the message sequence's use of isolation and magnification, which highlight the structure and function of the human body and its constituent parts. The challenges of interpreting gaps within narratives, as well as the setting in which events occur, are considered. The importance of closure in providing a fitting end to narratives is examined, and the plausibility of creating images that could be interpreted correctly by extraterrestrial intelligence is assessed. Narratological concepts examined here, as well as additional aspects of narrative, provide important resources for future work in interpreting and designing interstellar messages.     

Microwave Radiometric Sensing for Air Navigation

This paper discusses the results of an analytic study of the feasibility of using microwave radiometry as a technique for navigation data sensing in Army aircraft. The study included a review of Army aircraft characteristics and navigation requirements. Various means of sensing passively aircraft velocity, altitude, and velocity-altitude ratio were considered. While there appears to be no practical method for direct measurement of either velocity or altitude separately, it does appear possible to measure velocity-altitude ratio by comparing radiometric signals received from the terrain along the aircraft ground track. When combined with a radar altimeter, such a sensor could yield navigation data compatible with Army aircraft requirements. Microwave radiometry may also be the basis for direction sensing (to known landmarks) in high-flying aircraft or satellites.