Recent advances in structural technology for large deployable and erectable spacecraft

Ultra-low mass deployable and erectable truss structure designs for spacecraft are identified using computerized structural sizing techniques. Extremely slender strut proportions are shown to characterize minimum mass spacecraft which are designed for shuttle transport to orbit. Discrete element effects using a recently developed buckling theory for periodic lattice type structures are presented. An analysis of fabrication imperfection effects on the surface accuracy of four different antenna reflector structures is summarized. The tetrahedral truss has the greatest potential of the structures examined for application to accurate or large reflectors. A deployable module which can be efficiently transported is identified and shown to have significant potential for application to future antenna requirements. Investigations of erectable structure assembly are reviewed

Supersonic flutter of a thermally stressed flat panel with uniform edge loads

Supersonic flutter of thermally stressed flat panel with uniform edge load

Structural sizing considerations for large space structures

A number of missions for the space shuttle were proposed which involve placing large truss platforms on-orbit. These platforms range in size from tens of meters in span for reflector application to several thousand meters for solar power collector application. These proposed sizes and the operational requirements considered are unconventional in comparison to Earthbound structures and little information exists concerning efficient proportions of the structural elements forming the framework of the platforms. Such proportions are of major concern because they have a strong influence on the packaging efficiency and, thus, the transportation effectiveness of the shuttle. The present study is undertaken to: (1) identify efficient ranges of application of deployable and erectable platforms configured for shuttle transport to orbit, and (2) determine sensitivity to key parameters of minimum mass deployable and erectable platform designs

THE USE OF FILAMENTARY TARGETS TO PRODUCE PROLONGED SECONDARY-PARTICLE BEAMS IN THE BEVATRON

The foil technique for producing secondary-particle beams in a proton synchrotron is extended. Filamentary targets are described that are shown to produce secondaryparticle beams having almost arbitrary time duration and uniform intensity. The physical limitations imposed by available materials are discussed. (auth

The five basic protocols of cooperative learning in the classroom.

This study is to explore the effective use of the five basic protocols for oral discussion and debate as articulated by the National Council for the Social Studies, (NCSS, 1988), as a basis for promoting cooperative learning in Social Studies for grades three-six. Social Studies is especially suited to cooperative learning because it develops skills and processes for cooperative problem solving and the social participation skills. Children engage in discussion of social issues in the classrooms and in so doing grasp fully their social meaning and complexity. And, it is in this setting that cooperative learning is especially appropriate, since discussion is a prime means of developing and teaching thinking and analytical skills. This study was conducted in two stages: (1) Sixteen administrative interviews; and, (2) Nonparticipatory direct observations of 786 children. During these observations, every child observed the following five basic protocols as articulated by the National Council for the Social Studies (NCSS, 1988). They are: (1) Giving one\u27s ideas; (2) Listening to the ideas of others; (3) Planning one\u27s work with the group; (4) Presenting the group project; and, (5) Discussing how the group worked. Moreover, these rules were adhered to during the classroom meetings and small groups. This author concludes that during the discussions and debates, these elementary school children were in fact demonstrating the six classifications of cognitive development according to Bloom\u27s Taxonomy of Educational Objectives: Knowledge, comprehension, analysis, application, synthesis, and evaluation as well as cooperative problem solving and metacognition. Furthermore, in this post-Cold War era, our world is becoming a world of increasing democratic nations, therefore, this author\u27s general conclusions that cooperative learning in the Social Studies is dress rehearsal at the elementary school level for the children\u27s adult community activism

Sweet Corn Plastic Mulch Comparison

Early sweet corn production is enhanced by use of clear plastic mulch. Some growers use this practice on their earliest plantings to gain a market advantage and higher price. In cool, wet springs the practice is highly profitable. In central and northern Iowa, the years with a yield advantage more than offset the costs for years with no gain. There are many color plastic choices with various advertised benefits such as increased soil temperature and reflective radiation that speeds plant growth and development. The sweet corn research is designed to evaluate a few color mulches that are reported to affect corn growth and development—specifically, the sugar content of the kernel at harvest. The blue is supposed to enhance photosynthesis and improve translocation of carbohydrates (sucrose) to the developing kernel. As sweet corn is harvested in the immature stage (as opposed to field corn) it is thought there might be a sugar boost (some Canadian work was indecisive). The mulches were manufactured using pigment resins of a proprietary nature that change the wavelength of reflective radiation – blue and red. Thus, we measured the reflective radiation to see if that is true. Some plastics are included that affect soil temperature more than reflective radiation (i.e, the olive and clear). Increasing soil temperature and resultant enhanced shoot growth and leaf surface area may have more to do with photosynthesis and sugar production than specific reflective radiation

Deployable and erectable concepts for large spacecraft

Computerized structural sizing techniques were used to determine structural proportions of minimum mass tetrahedral truss platforms designed for low Earth and geosynchronous orbit. Optimum (minimum mass) deployable and erectable, hexagonal shaped spacecraft are sized to satisfy multiple design requirements and constraints. Strut dimensions characterizing minimum mass designs are found to be significantly more slender than those conventionally used for structural applications. Comparison studies show that mass characteristics of deployable and erectable platforms are approximately equal and that the shuttle flights required by deployable trusses become excessive above certain critical stiffness values. Recent investigations of eractable strut assembly are reviewed. Initial erectable structure assembly experiments show that a pair of astronauts can achieve EVA assembly times of 2-5 min/strut and studies indicate that an automated assembler can achieve times of less than 1 min/strut for around the clock operation

Seasonal Habitat Use and Movements of Mountain Goats, Oreamnos americanus, in East-central British Columbia

To identify the potential for adverse effects of forest development on Mountain Goats (Oreamnos americanus), we documented the patterns of forest use by goats and the factors influencing goat habitat use. We used a combination of 15 very high frequency (VHF) and six global positioning system (GPS) radiocollars to document the distribution and movements of 21 (15 female, 6 male) goats from 1997 to 1999 in the mountains surrounding the Robson Valley in east-central British Columbia. Because canopy closure reduces the likelihood that a GPS receiver will obtain a location fix, we estimated that GPS collars underrepresented forest use by about 23%. Three goats used separate winter and summer ranges separated by 8–13 km, while most simply exhibited seasonal shifts in elevation. In winter, goats were more often at lower elevations, in commercial forest stands, on southerly aspects, and moved less each hour and over the course of the winter. Goat use declined in areas >500 m from escape terrain and goats were found lower in elevation from evening to dawn compared to daylight hours. Collared goats used high elevation licks, which were either within their home range, or in two cases, 6 and 14 km from their typical home range. We documented use of known mid-elevation mineral licks by three collared goats, but no use of known low elevation (valley bottom and lower slopes) mineral licks. Robson Valley goats appeared to be at relatively low risk from disturbances related to logging, because although forest use was documented during winter, it occurred primarily on high elevation, steep slopes where trees are currently of low commercial value, and goats made little use of low elevation mineral licks. We recommend that in this area a forested buffer of 500 m around cliffs be left to reduce the possibility of adverse effects on goats especially, on southerly aspects above 1300 m

The versatility of a truss mounted mobile transporter for in-space construction

The Mobile Transporter (MT) evolution from early erectable structures assembly activities is detailed. The MT operational features which are required to support astronauts performing on-orbit structure construction or spacecraft assembly functions are presented and discussed. Use of the MT to perform a variety of assembly functions is presented. Estimated EVA assembly times for a precision segmented reflector approximately 20 m in diameter are presented. The EVA/MT technique under study for construction of the reflector (and the entire spacecraft) is illustrated. Finally, the current status of development activities and test results involving the MT and Space Station structural assembly are presented

Efficient concepts for large erectable space structures

The status of Langley Research Center development of the nestable column concept is reviewed including results of member and truss component tests, and planned assembly studies. In addition, more recent studies of alternative member concepts are presented. Preliminary results on relative efficiency of several types of truss-type columns are compared and future test plans discussed