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  • General Chemistry  (63)
  • Spacecraft Design, Testing and Performance  (55)
  • 2015-2019  (23)
  • 2000-2004  (49)
  • 1975-1979  (44)
  • 1925-1929  (2)
  • 1
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    Update to Mars Ascent Vehicle Design for Human Exploration (2019)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Astronauts on a mission to Mars will require several vehicles working together to get to Mars orbit, descend to the surface of Mars, support them while theyre there, and return them to Earth. The Mars Ascent Vehicle (MAV) transports the crew off the surface of Mars to a waiting Earth return vehicle in Mars orbit and is a particularly influential part of the mission architecture because it sets performance requirements for the lander and in-space transportation vehicles. With this in mind, efforts have been made to minimize the MAV mass, and its impact on the other vehicles. A minimal mass MAV design using methane and in situ generated oxygen propellants was presented in 2015. Since that time, refinements have been made in most subsystems to incorporate findings from ongoing research into key technologies, improved understanding of environments and further analysis of design options. This paper presents an overview of the current MAV reference design used in NASAs human Mars mission studies, and includes a description of the operations, configuration, subsystem design, and a vehicle mass summary.
    Keywords: Spacecraft Design, Testing and Performance
    Type: MSFC-E-DAA-TN62438 , IEEE Aerospace Conference; Mar 02, 2019 - Mar 09, 2019; Big Sky, MT; United States
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    NASA TECHNICAL REPORTS
  • 2
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    Structural Design Considerations for a 50 kW-Class Solar Array for NASA's Asteroid Redirect Mission (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: NASA is planning an Asteroid Redirect Mission (ARM) to take place in the 2020s. To enable this multi-year mission, a 40 kW class solar electric propulsion (SEP) system powered by an advanced 50 kW class solar array will be required. Powered by the SEP module (SEPM), the ARM vehicle will travel to a large near-Earth asteroid, descend to its surface, capture a multi-metric ton (t) asteroid boulder, ascend from the surface and return to the Earth-moon system to ultimately place the ARM vehicle and its captured asteroid boulder into a stable distant orbit. During the years that follow, astronauts flying in the Orion multipurpose crew vehicle (MPCV) will dock with the ARM vehicle and conduct extra-vehicular activity (EVA) operations to explore and sample the asteroid boulder. This paper will review the top structural design considerations to successfully implement this 50 kW class solar array that must meet unprecedented performance levels. These considerations include beyond state-of-the-art metrics for specific mass, specific volume, deployed area, deployed solar array wing (SAW) keep in zone (KIZ), deployed strength and deployed frequency. Analytical and design results are presented that support definition of stowed KIZ and launch restraint interface definition. An offset boom is defined to meet the deployed SAW KIZ. The resulting parametric impact of the offset boom length on spacecraft moment of inertias and deployed SAW quasistatic and dynamic load cases are also presented. Load cases include ARM spacecraft thruster plume impingement, asteroid surface operations and Orion docking operations which drive the required SAW deployed strength and damping. The authors conclude that to support NASA's ARM power needs, an advanced SAW is required with mass performance better than 125 W/kg, stowed volume better than 40 kW/cu m, a deployed area of 200 sq m (100 sq m for each of two SAWs), a deployed SAW offset distance of nominally 3-4 m, a deployed SAW quasistatic strength of nominally 0.1 g in any direction, a deployed loading displacement under 2 m, a deployed fundamental frequency above 0.1 Hz and deployed damping of at least 1%. These parameters must be met on top of challenging mission environments and ground testing requirements unique to the ARM project.
    Keywords: Spacecraft Design, Testing and Performance
    Type: GRC-E-DAA-TN26878 , AIAA SciTech2016; Jan 04, 2016 - Jan 08, 2016; San Diego, CA; United States
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    NASA TECHNICAL REPORTS
  • 3
    Electronic Resource
    Electronic Resource
    Isomeric Tetrakis(dimethylamino)naphthalenes: Syntheses, Structure-Dependence of Basicities, Crystal Structures, and Physical Properties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1617-1622 
    Details
    ISSN: 1434-193X
    Keywords: Tetrakis(dimethylamino)naphthalenes ; Basicity ; Hydrogen bonds ; Cyclicvoltammetry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---For comparison to the recently described 2,3,6,7-tetrakis(dimethylamino)naphthalene (1) the three isomers 2,3, and 4 were synthesized. The basicities of this group of isomers are strongly dependent upon the different mutual orientations of the pairs of dimethylamino substituents: only the isomers 3 and, partially, 4, both with dimethylamino groups in adjacent peri-positions of the naphthalene, are strong “proton sponges”. For the isomers 1 and 2 with the same number and kind of twofold dimethylamino substituents in neighbouring ortho-positions, however, no significant basicity increase is observed. To explain this difference between the two groups of isomers it is suggested that in the ortho-pairs of 1 and 2 the C-N bonds diverge considerably, leading to an increased N···N distance and consequently to less stable [N···H···N]+ hydrogen bonds in contrast to the parallel C-N bonds in the peri-substituted isomers 3 and 4. X-ray crystal structure analyses of the bases and of some of the salts derived therefrom were solved and are discussed. Cyclic voltammetry indicates that 1 to 4 are strong electron donors, reacting easily to radical cations or dications which with suitable acids have been obtained as salts.
    Additional Material: 3 Ill.
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    Paper (German National Licenses)
  • 4
    Electronic Resource
    Electronic Resource
    Stable Heterotopic Noncovalent Resorcin[4]arene Assemblies (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1727-1734 
    Details
    ISSN: 1434-193X
    Keywords: Self-assembly ; Vapor-pressure osmometry ; Resorcin[4]arenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Resorcin[4]arene tetracarboxylic acids 5,6 (A) and resorcin[4]arene tetrapyridines 2,3 (P) self-assemble in chloroform solution to form stable heterotopic AP dimers. Data from NMR titration and dilution experiments, as well as from vapor-pressure osmometry (VPO), indicate that the AP dimer is formed with an association constant greater than 107 M-1. Solid-solution extraction experiments are indicative of the formation of a 2:1 trimer (A2P), while self-associated homotopic species (A2 and A3) can be detected by NMR and VPO. Analysis of the heterotopic noncovalent assembly process over a range of compositions shows that these other species are much less stable than the AP heterodimer, which is the exclusive species at an A/P concentration ratio of 1:1 (〉 99.7% of the total at 10 mM).
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Anionic Cyclizations of Pentynones and Hexynones: Access to Furan and Pyran Derivatives (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 527-538 
    Details
    ISSN: 1434-193X
    Keywords: Furans ; Pyrans ; Dihydropyran-2-ylidenes ; Ring closure ; Addition reaction ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---On treatment with base the pentynones 8a-f undergo anionic addition reactions of the resulting enolate species to the alkyne moiety and afford the 2,5-disubstituted furans 10a-f in yields ranging from 10-91%. The proposed mechanism involves the 2-methylene-dihydrofurans 11 as intermediates which tautomerize to yield the observed products. In the case of the α-picolyl derivative 8g both possible enolates 12 and 13 are formed which are subsequently transformed to the products 10g and 14g, respectively. Starting with the hexynones 9a-e an analogous reaction takes place with the formation of the pyran derivatives 15 and 16 in comparable yields. Under the same reaction conditions the n-butyl ketone 9f gives rise to two isomeric compounds, namely the 4H-pyran 16f and the cyclohexenone 17. This result is explained by assuming initial formation of two isomeric enolates which react either by O- or C-attack on the carbon-carbon triple bond.
    Additional Material: 5 Tab.
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    Paper (German National Licenses)
  • 6
    Electronic Resource
    Electronic Resource
    Replacement of the Cleavable Phosphodiester Bond of a Hammerhead Ribozyme Substrate by an Amide Linkage (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 633-638 
    Details
    ISSN: 1434-193X
    Keywords: Amide linkage ; Phosphodiester ; Hammerhead ribozyme ; Oligonucleotides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A nucleoside dimer in which the natural phosphodiester bond is replaced by an isosteric amide linkage has been prepared. This dimer analogue was subsequently incorporated chemically at the cleavage position of a hammerhead ribozyme substrate. Although the resulting substrate analogue exhibited a high affinity for the ribozyme as shown by gel retardation assays, the amide bond proved to be fully resistant to cleavage under standard conditions of ribozyme cleavage activity.
    Additional Material: 3 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Synthesis of a Biotinated Lipofullerene as a New Type of Transmembrane Anchor (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1173-1181 
    Details
    ISSN: 1434-193X
    Keywords: Biotin ; Fullerenes ; Membranes ; Nanostructures ; Reflectometric interference spectroscopy ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -As a prototype for a new class of lipid membrane components, the lipophilic fullerene derivative (so-called lipofullerene) 1 was synthesized and characterized. This mixed [1:5]-hexakisadduct consists of ten long alkyl chains within five didodecyl malonate addends and a linker malonate carrying a (+)-biotin unit as part of an amphiphilic spacer. The malonates are attached to the fullerene core in an octahedral addition pattern, which was achieved by two successive cyclopropanation sequences with the functional precursor malonate 8 and dodecyl malonate 10. The final step of the synthesis of 1 was the attachment of activated biotin 5 with the deprotected precursor 11. Binding experiments followed by reflectometric interference spectroscopy [RIfS] proved the capability of 1 to bind specifically the protein streptavidin (SA) through the biotin unit. The amphiphilic behavior of 1 was demonstrated by Langmuir Blodgett (LB) film investigations.
    Additional Material: 3 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Substituent Effects on Redox Properties and Photoinduced Electron Transfer in Isoxazolo-Fullerenes (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 455-465 
    Details
    ISSN: 1434-193X
    Keywords: Fullerenes ; Cycloadditions ; Donor-acceptor systems ; Cyclic voltammetry ; Photoinduced electron transfer ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The new C60 and C70 adducts 1b, 1d-1k, 1m, 6d, 7d, and 8d have been synthesized by [2+3] cycloadditions of the appropriate nitrile oxides. Variations in the distance and geometry of the donor and acceptor substituents are seen to have an influence on the redox behavior of the fullerene adducts in cyclic voltammetry experiments. The isoxazolo-fullerenes 1c, 1d, and 1i show shifts of about 30 mV or 40 mV to more negative values compared with the reference compound 1a. On the other hand, strong acceptor properties are detected in the case of compound 1e, which shows a positive shift of 30 mV relative to 1a. Moreover, time-resolved fluorescence spectroscopy has shown that upon excitation of the fullerene moiety in the polar solvent benzonitrile, an electron is transferred from the donor substituent to the first excited singlet state of the fullerene, thereby reducing the excited-state lifetime. Our data demonstrate that the electron-transfer rate in donor-substituted fullerenes can be controlled by the electron-donating property of the substituent as well as the electronic structure and/or length of the spacer used. The C70 regioisomers 6d, 7d, and 8d exhibit differences in their spectroscopic characteristics.
    Additional Material: 3 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Construction of Quaternary Stereocenters by Nickel-Catalysis of Asymmetric Michael Reactions (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 701-705 
    Details
    ISSN: 1434-193X
    Keywords: Asymmetric catalysis ; Catalysis ; Addition reactions ; N ligands ; Nickel ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Quaternary stereocenters were constructed with an enantioselectivity of up to 91% ee under aerobic conditions and at ambient temperature in the Michael reaction of β-dicarbonyl compounds and methyl vinyl ketone with Ni(OAc)2·4H2O and optically active trans-1,2-diaminocyclohexane as a chiral catalyst.
    Additional Material: 1 Tab.
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  • 10
    Electronic Resource
    Electronic Resource
    Chemical Synthesis of a Tetrasaccharide Fragment Related to the Exopolysaccharide of Arthrobacter sp. CE-17 (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 181-186 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Oligosaccharides ; Glycosylations ; Organic synthetic methods ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetrasaccharide 5-aminopentyl glycoside β-D-Manp-(1→4)-β-D-Glcp-(1→4)-α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NH2(22) related to the exopolysaccharide of Arthrobacter sp. CE-17 was synthesized by coupling of the properly protected disaccharide blocks β-D-Manp-(1→4)-β-D-Glcp-1-S-Ph (11) and α-L-Rhap-(1→3)-β-D-Glcp-1-O-(CH2)5NHZ (20). Building block 11 was obtained by intramolecular β-mannosylation of a malonyl-tethered disaccharide glycoside which was prepared from phenyl 4,6-O-benzylidene-1-thio-β-D-glucopyranoside (1) and ethyl 2,3,4-tri-O-benzyl-1-thio-α-D-mannopyranoside (5) in 5 steps. Building block 20 was obtained by coupling N-Z-protected 5-aminopentyl 2-O-benzyl-4,6-O-benzylidene-β-D-glucopyranoside (14) obtained from the non-benzylated counterpart 12 with ethyl 2,3-di-O-benzoyl-4-O-chloroacetyl-1-thio-α-L-rhamnopyranoside (18) obtained in 3 steps from ethyl 2,3-O-isopropylidene-1-thio-α-L-rhamnopyranoside (15).
    Additional Material: 1 Ill.
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