The concept of selecting materials for the design of separable parts of missiles with a property that ensures their rapid disposal by burning after the mission is completed is considered. The ...characteristics of incinerated materials are presented. The choice of materials based on the proximity of thermal and strength characteristics to existing structural materials used in the production of traditional head fairings is made.
•New fluoropolymer containing hydroxyl groups is developed with high coating stability.•Ignition characteristics of single Al-FCOS composite particles is carefully examined.•The new coatings greatly ...shortens the ignition delay of virgin Al particles.•Al-FCOS enhance the combustion intensity and efficiency of common solid propellant.•Combustion and agglomeration can be tuned by adjusting the new fluoropolymer content.
Fluorine-containing organic substances (FCOS) are often added to aluminized solid propellants to improve their ignition and combustion characteristics, but existing FCOS coatings tend to have poor mechanical strength, limiting their reliability in practical applications. In this experimental study, we investigate the effect of adding a new functionalized FCOS to aluminized solid propellants. Specifically we focus on the oxidation and ignition characteristics of Al-FCOS composite particles and on the combustion of fluorine-containing propellants. By altering the surface pre-ignition reaction, FCOS-modified particles are found to ignite more quickly and produce more gaseous products. For pressures above 5 MPa, adding FCOS can both increase and decrease the burning rate relative to a baseline Al propellant, depending on the precise Al-FCOS content used, with 8.5 wt% and 17 wt% Al-FCOS producing a higher and lower burning rate, respectively. Compared with the baseline Al propellant, the FCOS-modified propellants are found to produce smaller agglomerates. This shows that the ignition, combustion and agglomeration characteristics can be readily tuned by adjusting the content of the new functionalized fluoropolymer. These findings can help guide the development of FCOS additives for aluminized propellants in solid rocket motors.
Ammonium perchlorate (AP), the workhorse of oxidizers in solid rocket and missile propellants, exhibits various environmental issues resulting from the release of perchlorate into ground water, which ...have been directly linked to thyroid cancer. Furthermore, the generation of hydrochloric acid causes the depletion of the ozone layer and leads to high concentrations of acid rain. Nowadays, considerable efforts have been devoted to developing solid propellants using green oxidizers which demonstrate less hazards and environmentally friendly chlorine free combustion products. Although many candidates for AP replacement have been identified, most of them are far from being practically employed in real applications because of a number of severe difficulties, including cost. In this review, the potential green chemicals for use as oxidizers are highlighted and these reveal interesting physicochemical properties and performance. After a quick definition of green solid propellants and their main ingredients, the current status of AP propellants issues is discussed in light of possible substitution with potential green ingredients. Particular attention will be paid to the recent advances in the green oxidizers, their production and their characteristic properties. The advantages and shortcomings of various green oxidizers for specific and potential propellant uses are also discussed together with the attempts made to overcome these problems. As a consequence, efforts will certainly continue to seek AP alternatives and efficient green oxidizers for solid rocket propulsion in the near future.
Recent progress in the synthesis and modification of green oxidizers and their application in solid rocket propellant formulations during these last few decades are reviewed.
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•Many metals react with water to produce H2 on demand in exothermic reactions.•Metal-water combustion leads to higher energy density than batteries or H2 storage.•High-temperature ...metal-water flames maximize system power density.•Hot H2 from metal-water reactions is a promising fuel for compact power systems.
Metals are energy-dense fuels that can react exothermically with water to produce hydrogen, and this hydrogen is useful as a propellant for rockets and underwater vehicles or as a fuel for engines and fuel cells. Propulsion systems usually rely on high-temperature combustion (T>3000K) of metal-water propellants, while hydrogen-production systems typically employ low reactor temperatures (T<100°C). This paper reviews the current state of knowledge of both low-temperature and high-temperature metal-water reactions. Low-temperature reactions allow only the chemical energy contained in the hydrogen to be used, with the thermal energy released during the metal-water reaction being wasted. Metal-water propulsion systems typically make use of only the thermal energy of the metal-water reaction, with the hydrogen being exhausted to produce thrust. This paper proposes several novel applications of high-temperature metal-water combustion that allow the full chemical energy within the metal fuel to be harnessed, including high-speed air-breathing engines and high-power, compact, low-emissions power-generation systems. These technologies promise improved performance by maximizing the conversion of the chemical energy, stored within the metal fuel, into useful work at sufficient rates for high-power applications.
•The impact of ten leafy vegetables and the light intensity at harvest was explored.•Rocket vegetable leaf showed the highest proteins, P, K, Ca and nitrate contents.•Total phenols in red lettuce was ...high.•Proteins, K, Ca, Mg contents and antioxidant activities were enhanced at high PAR.
The nutritional composition of ten leafy vegetables (chicory, green lettuce, lamb’s lettuce, mizuna, red chard, red lettuce, rocket, spinach, Swiss chard, and tatsoi) and quality traits of the selected leafy vegetables in relation to the light intensity (low and high Photosynthetically Active Radiation; PAR) at time of harvest were determined. Irrespective of the light intensity at time of harvest, the highest leaf dry matter (DM), proteins, nitrate, P, K and Ca contents were observed in rocket followed by mizuna. The highest lipophilic antioxidant activity (LAA) was recorded in red lettuce and rocket, whereas ascorbic acid (AA) and total phenolic (TP) contents of red lettuce were higher compared to the other leafy vegetables. When leafy vegetables were harvested at low as opposed to high PAR, the leaf content was higher in DM, protein, K, Ca and Mg, hydrophilic antioxidant activity (HAA), and LAA by 12.5%, 10.0%, 12.6%, 23.7%, 14.1%, 11.9%, and 18.5%, respectively. The highest values in TP for chicory, green lettuce, lamb’s lettuce, mizuna, red chard, and red lettuce, were observed under high PAR.
The effective solid propellant burning rate in a rocket depends on surface area and propellant composition. Currently, the surface area geometry in a rocket is limited to what can be practically cast ...using molds, etc. Additive manufacturing (AM) could allow the production of unique propellant grain geometries, however printing propellants with high solids loadings and viscosities is not readily possible using currently available printers. A new AM direct write system developed recently in our laboratory, is capable of printing visibly low-void propellants with high end mix viscosities into highly resolved geometries. The system was used to print ammonium perchlorate (AP) composite propellants at 85% solids loading using hydroxyl-terminated polybutadiene (HTPB) and a UV-curable polyurethane binder. The change in HTPB propellant viscosity with time after mixing was measured and the microstructure of the strands was evaluated with X-ray tomography scans. The burning rate of printed and cast strands was measured to compare the quality of the strands at high pressure, since propellants with significant voids should catastrophically fail due to flame spreading. The printed samples burned in a planar fashion up to pressures of 10.34 MPa with consistent rates that were comparable to the cast propellants. The HTPB propellant used was not optimized and showed some porosity due to gas generation, but strands printed with the UV binder exhibited extremely low porosity. A strand printed with no gaps in one half and gaps in the other failed catastrophically where intended at high pressure, demonstrating the ability to spatially grade propellants. This new system can produce adequate strands of composite propellant with high solids loadings without the addition of solvents, special binders (low viscosity, thermal softening, etc.), or restricting use to formulations with lower viscosities, and enables the fabrication of complex propellant grain geometries.
The computational design of transmembrane proteins with more than one membrane-spanning region remains a major challenge. We report the design of transmembrane monomers, homodimers, trimers, and ...tetramers with 76 to 215 residue subunits containing two to four membrane-spanning regions and up to 860 total residues that adopt the target oligomerization state in detergent solution. The designed proteins localize to the plasma membrane in bacteria and in mammalian cells, and magnetic tweezer unfolding experiments in the membrane indicate that they are very stable. Crystal structures of the designed dimer and tetramer-a rocket-shaped structure with a wide cytoplasmic base that funnels into eight transmembrane helices-are very close to the design models. Our results pave the way for the design of multispan membrane proteins with new functions.
The combustion of ammonium perchlorate (AP) in a polymer binder matrix of hydroxyl-terminated-polybutadiene (HTPB) is reviewed, covering the experimental and modeling approaches explored for over a ...half-century. AP is capable of self-deflagration and is a propellant in its own right as ammonia and perchloric acid decompose at the surface to sustain a flame in the gas-phase with an adiabatic flame temperature of roughly 1400 K. AP also has unique low temperature decomposition behavior and burning characteristics as a function of pressure attributed to the importance of condensed phase reactions. A polymer, most commonly HTPB, is used to bind AP crystals within a solid matrix and impart desired mechanical properties and additional fuel for inclusion in a solid rocket motor. Aside from providing an additional fuel source for the decomposing AP, the HTPB introduces diffusion flames into the system, which have the advantage of decreasing the combustion instability of the AP monopropellant. The objective of this paper is to review the critical physical processes of AP/HTPB propellant combustion and to explore the different experimental and computational avenues used to shed light on such a complex phenomenon. Experimental diagnostics and the simulation of solid propellant combustion have progressed immensely over the years with the introduction of more advanced laser diagnostics and imaging techniques, as well as an increase in computational resources and processing power available for computations; additional physics can now be modeled that would have otherwise been impossible to include before. A recommendation on future research is given based on the current state of the art.
Mit dem Drachen ins All
Physik in unserer Zeit,
07/2020, Letnik:
51, Številka:
4
Journal Article
Am 30. Mai starteten erstmals nach dem Ende der Shuttle‐Ära vor neun Jahren amerikanische Astronauten wieder mit einem eigenen Raumschiff ins All. Einen Tag später dockten sie an der Internationalen ...Raumstation ISS an. Die beiden Astronauten Robert Behnken und Douglas Hurley werden einige Wochen dort bleiben. Die Rakete, eine Falcon 9, und das Raumschiff Crew Dragon hat das private Raumfahrtunternehmen SpaceX gebaut. Weitere Missionen werden folgen.
Reactive molecular dynamics (MD) simulation makes it possible to study the reaction mechanism of complex reaction systems at the atomic level. However, the analysis of MD trajectories which contain ...thousands of species and reaction pathways has become a major obstacle to the application of reactive MD simulation in large-scale systems. Here, we report the development and application of the Reaction Network Generator (ReacNetGenerator) method. It can automatically extract the reaction network from the reaction trajectory without any predefined reaction coordinates and elementary reaction steps. Molecular species can be automatically identified from the cartesian coordinates of atoms and the hidden Markov model is used to filter the trajectory noises which makes the analysis process easier and more accurate. The ReacNetGenerator has been successfully used to analyze the reactive MD trajectories of the combustion of methane and 4-component surrogate fuel for rocket propellant 3 (RP-3), and it has great advantages in terms of efficiency and accuracy compared to traditional manual analysis.
The ReacNetGenerator program can automatically extract reaction information from the reactive MD trajectory and construct reaction networks.
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