Sequence of the 16S rRNA gene from the thermoacidophilic archaebacterium Sulfolobus solfataricus and its evolutionary implications
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Olsen, G. J.↗
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Mass distribution and evolutionary scheme for central stars of planetary nebulae
IUE data and a distance measuring method that considered central stars in optically thick nebulae were used to examine mass distributions of planetary nebulae. Other data such as spectral type, spatial and kinematic characteristics, etc., were studied to derive relationships between population type and mass distribution. A central star mass range of at least 0.55 solar mass was obtained. Stars with masses of at least 0.64 solar mass, concentrated in the galactic disk, originated from 1.5 solar mass stars. Low mass nuclei originated in old disk or halo populations and evolved from 1.0 solar mass objects. A mass-loss parameter value of 1/3 was calculated for red giants, implying that white dwarfs evolve from stars of under 5 solar masses. Mass distributions around planetary nuclei were concluded to follow patterns associated with the individual mass.
Heap, Sara R.↗
Galilean satellites - Evolutionary paths in deep resonance
While the Laplace resonance among the three inner Galilean satellites possesses stable configurations where the mean motions taken by pairs are in nearly 2:1 ratios, or 'deep resonance', the current satellite configuration is unstable near this exact commensurability. There is presently noted, however, a continuous path of stable conditions branching toward deep resonance which furnishes a track for the tidal evolution of the system and renders scenarios involving (probably episodic) evolution from deep resonance viable; this eliminates the requirement for rapid tidal dissipation of Jupiter by the alternative equilibrium hypothesis.
Greenberg, Richard↗
An evolutionary communications scenario for Mars exploration
As Mars exploration grows in complexity with time, the corresponding communication needs will grow in variety and complexity also. From initial Earth/Mars links, further needs will arise for complete surface connectivity for the provision of navigation, position location, and voice, data, and video communications services among multiple Mars bases and remote exploration sites. This paper addresses the likely required communication functions over the first few decades of Martian exploration and postulates systems for providing these services. Required technologies are identified and development requirements indicated.
Stevenson, Steven M.↗
Evolutionary Space Station infrastructure
This paper discusses the approach to Space Station evolution planning and the preliminary analysis of options for the evolution of the infrastructure. The approach emphasizes the analysis of evolution paths, driven by specific user requirements, and evolution modes, i.e., the infrastructure required to support the evolution paths. The objective is to determine the near-term actions that must be taken to protect the future options. These include the identification of evolution 'hooks and scars' on the baseline Space Station and the establishment of an evolution advanced development program. The near term emphasis of the evolution planning is on methods of increasing the efficiency and productivity of the Space Station and on requirements to support new initiatives currently being studied by NASA.
Diaz, Alphonso V.↗
Manned Mars mission accomodation by the evolutionary Space Station
It is shown that an unmanned launch capability of about 90 metric tons to the Space Station altitude and inclination is required to support the buildup of the manned Mars mission. The paper presents details of the assembly sequence including the analysis and conceptual design of additional truss and other facilities required at the Space Station. It is noted that the The Critical Evaluation Task Force configuration (dual keel) can evolve to accommodate the Mars space vehicle buildup.
Pritchard, E. Brian↗
Telescope structures - An evolutionary overview
A development history is presented for telescope structural support materials, design concepts, equatorial and altazimuthal orientational preferences, and mechanical control system structural realizations. In the course of 50 years after Galileo, the basic configurations of all reflecting telescopes was set for the subsequent 300 years: these were the Cassegrain, Gregorian, and Newtonian designs. The challenge of making a lightweight ribbed pyrex glass primary mirror for the 5-m Palomar telescope was met by von Karman's use of finite element analysis. Attention is given to the prospects for a 20-m deployable space-based reflecting telescope.
Meinel, Aden B.↗
Growth requirements for multidiscipline research and development on the evolutionary space station
The NASA Space Station Freedom is being designed to facilitate on-orbit evolution and growth to accommodate changing user needs and future options for U.S. space exploration. In support of the Space Station Freedom Program Preliminary Requirements Review, The Langley Space Station Office has identified a set of resource requirements for Station growth which is deemed adequate for the various evolution options. As part of that effort, analysis was performed to scope requirements for Space Station as an expanding, multidiscipline facility for scientific research, technology development and commercial production. This report describes the assumptions, approach and results of the study.
Meredith, Barry↗
Evolutionary growth for Space Station Freedom electrical power system
Over an operational lifetime of at least 30 yr, Space Station Freedom will encounter increased space station user requirements and advancing technologies. The space station electrical power system is designed with the flexibility to accommodate these emerging technologies and expert systems and is being designed with the necessary software hooks and hardware scars to accommodate increased growth demand. The electrical power system is planned to grow from the initial 75 kW up to 300 kW. The Phase 1 station will utilize photovoltaic arrays to produce the electrical power; however, for growth to 300 kW, solar dynamic power modules will be utilized. Pairs of 25 kW solar dynamic power modules will be added to the station to reach the power growth level. The addition of solar dynamic power in the growth phase places constraints in the initial space station systems such as guidance navigation and control, external thermal, truss structural stiffness, computational capabilities and storage which must be planned-in in order to facilitate the addition of the solar dynamic modules.
Marshall, Matthew F.↗
On black widow evolutionary scenarios for binary neutron stars
The scenario whereby the pulsar 1957 + 20 ablates its companion by soft gamma-ray synchrotron emission (Ruderman et al., 1988) is critically examined, with particular regard to how the outflowing material, beginning at photospheric temperatures, is heated through the cooling barrier to coronal temperatures. Assuming the conductivity to be at most the Spitzer value, this consideration is found to constrain the mass flux more than two orders of magnitude more severely than merely considering cooling near the sonic point. This would imply that the ablation scenario fails by a large margin, even if the emission from the pulsar is beamed along the orbital plane.
Eichler, David↗
Evolutionary models of the rotating sun
A new rotating stellar evolution code is developed and applied to the sun. A hydrostatic fully convective premain-sequence model is evolved to the age of the sun. As the model evolves, it accounts for angular-momentum loss via a magnetic wind and angular-momentum redistribution by rotationally induced instabilities. The resulting models have an oblateness in agreement with observed upper limits. The rotation curves show two main features: the outer layers exhibit minimal radial differential rotation, and a rapidly rotating central core is preserved. These basic features persist through a wide range of model parameters.
Pinsonneault, M. H.↗
Liquid rocket booster study. Volume 2, book 5, appendix 9: LRB alternate applications and evolutionary growth
The analyses performed in assessing the merit of the Liquid Rocket Booster concept for use in alternate applications such as for Shuttle C, for Standalone Expendable Launch Vehicles, and possibly for use with the Air Force's Advanced Launch System are presented. A comparison is also presented of the three LRB candidate designs, namely: (1) the LO2/LH2 pump fed, (2) the LO2/RP-1 pump fed, and (3) the LO2/RP-1 pressure fed propellant systems in terms of evolution along with design and cost factors, and other qualitative considerations. A further description is also presented of the recommended LRB standalone, core-to-orbit launch vehicle concept.
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Evolutionary space station fluids management strategies
Results are summarized for an 11-month study to define fluid storage and handling strategies and requirements for various specific mission case studies and their associated design impacts on the Space Station. There are a variety of fluid users which require a variety of fluids and use rates. Also, the cryogenic propellants required for NASA's STV, Planetary, and Code Z missions are enormous. The storage methods must accommodate fluids ranging from a high pressure gas or supercritical state fluid to a sub-cooled liquid (and superfluid helium). These requirements begin in the year 1994, reach a maximum of nearly 1800 metric tons in the year 2004, and trail off to the year 2018, as currently planned. It is conceivable that the cryogenic propellant needs for the STV and/or Lunar mission models will be met by LTCSF LH2/LO2 tanksets attached to the SS truss structure. Concepts and corresponding transfer and delivery operations have been presented for STV propellant provisioning from the SS. A growth orbit maneuvering vehicle (OMV) and associated servicing capability will be required to move tanksets from delivery launch vehicles to the SS or co-orbiting platforms. Also, appropriate changes to the software used for OMV operation are necessary to allow for the combined operation of the growth OMV. To support fluid management activities at the Space Station for the experimental payloads and propellant provisioning, there must be truss structure space allocated for fluid carriers and propellant tanksets, and substantial beam strengthening may be required. The Station must have two Mobile Remote Manipulator Systems (MRMS) and the growth OMV propellant handling operations for the STV at the SS. Propellant needs for the Planetary Initiatives and Code Z mission models will most likely be provided by co-orbiting propellant platform(s). Space Station impacts for Code Z mission fluid management activities will be minimal.
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A smaller scale manned Mars evolutionary program
This paper describes a concept for a manned Mars mission in which the parameters and trajectories are chosen to minimize the initial mass in earth orbit. The concept permits ready evolution from an initial modes step to full Mars surface operations. It uses a new heavy lift launch vehicle concept, the Shuttle Z.
Bekey, Ivan↗
An evolutionary communications scenario for Mars exploration
As Mars exploration grows in complexity with time, the corresponding communication needs will grow in variety and complexity also. From initial Earth/Mars links, further needs will arise for complete surface connectivity for the provision of navigation, position location, and voice, data, and video communications services among multiple Mars bases and remote exploration sites. This paper addresses the likely required communication functions over the first few decades of Martian exploration and postulates systems for providing these services. Required technologies are identified and development requirements indicated.
Stevenson, Steven M.↗
A surface systems architecture for an evolutionary lunar base
The NASA Office of Exploration has completed a Systems Engineering and Integration effort to define a point design for an evolving lunar base that supports substantial science, exploration, and resource production objectives. This study addressed systems level design; element requirements and conceptual designs; assessments of precursor and technology needs, and operations concepts. The central base is assumed to be located equatorially on the lunar nearside north of the crater Moltke in Mare Tranquillitatis. The study considers an aggressive case with three main phases. The initial Man-Tended Phase establishes basic enabling facilities that include a modular habitat that periodically houses a crew of four. During the Experimental Phase the base becomes permanently manned with the construction of a larger habitat that provides augmented workshop and laboratory volumes and housing for crew. The Operational Phase expands base capabilities to a substantially mature level while reducing reliance on earth.
Roberts, Barney B.↗
Evolutionary growth for Space Station Freedom electrical power system
Over an operational lifetime of at least 30 yr, Space Station Freedom will encounter increased Space Station user requirements and advancing technologies. The Space Station electrical power system is designed with the flexibility to accommodate these emerging technologies and expert systems and is being designed with the necessary software hooks and hardware scars to accommodate increased growth demand. The electrical power system is planned to grow from the initial 75 kW up to 300 kW. The Phase 1 station will utilize photovoltaic arrays to produce the electrical power; however, for growth to 300 kW, solar dynamic power modules will be utilized. Pairs of 25 kW solar dynamic power modules will be added to the station to reach the power growth level. The addition of solar dynamic power in the growth phase places constraints in the initial Space Station systems such as guidance, navigation, and control, external thermal, truss structural stiffness, computational capabilities and storage, which must be planned-in, in order to facilitate the addition of the solar dynamic modules.
Marshall, Matthew Fisk↗
The evolutionary sequence of planetary nebulae
A first-order solution to the problem of nebular evolution is presented and used to construct photoionization models with the correct ionized gas geometry with respect to the central star. The models are used to investigate the evolution of the central star in terms of a 'transformed' H-R diagram in which H-beta luminosity replaces stellar luminosity and the nebular excitation class takes the place of stellar effective temperature. It is shown that the optically thick PN in the Magellanic Clouds behave as ram-pressure confined H II regions trapped between the shocked remnants of AGB wind and the high-velocity stellar wind of the PN nuclei.
Dopita, M. A.↗