308 research outputs found
Synthesis of optically clear polymeric materials for high temperature windows
A polymer has been developed that has excellent potential for use as windows in spacecraft as well as conventional aircraft. This polymer, phenolphthalein polycarbonate, has outstanding thermal properties, e.g., in place of melting or burning, it produces an insulating charred foam that closes off transmission of radiant heat through the window. This fact, coupled with an oxygen index of 0.43 and a 177 C tensile strength of 58 mega Newtons/sq m, makes this polymer a prime candidate for further development. Pilot plant preparation in a 20 gallon Pfaudler kettle was accomplished and large test specimens were prepared for evaluations
Guidance, Navigation, and Control for Agile Small Spacecraft with Articulating Solar Arrays
Payload operations for small satellites are often impacted by the need to allocate time for modifying the attitude to perform power generation or orbit maneuvering. A typical small satellite design would consist of a single rigid body with body-mounted solar cells, making the power generation subject to the spacecraftâs attitude. Often to achieve the high power generation that is required to enable the payload function, the attitude must be specifically set to maximize the solar cell area facing the Sun, which typically means diverting it from an attitude that is useful for payload operations for some period of time. At the scale of modern global constellations, these downtimes in the payload operation schedule can greatly reduce the overall capability of the system. By including deployable, articulating solar arrays in the design of small spacecraft, array pointing can be decoupled from the mainpayload pointing operations. With these pieces decoupled, payload operations can proceed uninterrupted while the articulating arrays ensure sufficient power generation. In this paper, the dynamic equations of the multibody system are derived, and guidance, navigation, and control (GNC) considerations are presented for achieving decoupled attitude and articulation objectives. Results from simulation of a sample mission show that agile target tracking attitude maneuvers can be performed together with array solar tracking with negligible impact on overall payload pointing performance
Adsorption of malachite green and alizarin red s dyes using fe-btc metal organic framework as adsorbent
Synthetic organic dyes are widely used in various industrial sectors but are also among the most harmful water pollutants. In the last decade, significant efforts have been made to develop improved materials for the removal of dyes from water, in particular, on nanostructured adsorbent materials. Metal organic frameworks (MOFs) are an attractive class of hybrid nanostructured materials with an extremely wide range of applications including adsorption. In the present work, an iron-based Fe-BTC MOF, prepared according to a rapid, aqueous-based procedure, was used as an adsorbent for the removal of alizarin red S (ARS) and malachite green (MG) dyes from water. The synthesized material was characterized in detail, while the adsorption of the dyes was monitored by UV-Vis spectroscopy. An optimal adsorption pH of 4, likely due to the establishment of favor-able interactions between dyes and Fe-BTC, was found. At this pH and at a temperature of 298 K, adsorption equilibrium was reached in less than 30 min following a pseudo-second order kinetics, with kâ of 4.29 Ă 10â3 and 3.98 Ă 10â2 gâmgâ1 minâ1 for ARS and MG, respectively. The adsorption isotherm followed the Langmuir model with maximal adsorption capacities of 80 mgâgâ1 (ARS) and 177 mgâgâ1 (MG), and KL of 9.30â103 Lâmgâ1 (ARS) and 51.56â103 Lâmgâ1 (MG)
Chaoticity and Shell Effects in the Nearest-Neighbor Distributions
Statistics of the single-particle levels in a deformed Woods-Saxon potential
is analyzed in terms of the Poisson and Wigner nearest-neighbor distributions
for several deformations and multipolarities of its surface distortions. We
found the significant differences of all the distributions with a fixed value
of the angular momentum projection of the particle, more closely to the Wigner
distribution, in contrast to the full spectra with Poisson-like behavior.
Important shell effects are observed in the nearest neighbor spacing
distributions, the larger the smaller deformations of the surface
multipolarities.Comment: 10 pages and 9 figure
Hydroxyapatite thick films as pressure sensors
Electrical properties of hydroxyapatite (HA) in the form of screen printed thick films that can be used as a biocompatible coating for bone and dental implants are reported. In particular, piezo- and pyroelectric behaviour of these films suggest that they can be used to promote faster healing of bones and prevent rejection of implants. Moreover, the reversible pressure-induced changes in their electrical characteristics can be employed for real-time in vivo pressure sensors implantable simultaneously, for example, with knee or hip prosthesis. The additional advantage of HA in the form of screen-printed thick films is that, due to the technologyâs versatility, it can be produced on flexible substrate in any shape and size to suit the needs of various patients
A Review of the MLAS Parachute Systems
The NASA Engineering and Safety Center (NESC) is developing the Max Launch Abort System (MLAS) as a risk-mitigation design should problems arise with the baseline Orion spacecraft launch abort design. The Max in MLAS is dedicated to Max Faget, the renowned NASA spacecraft designer. The MLAS flight test vehicle consists of boost skirt, coast skirt and the MLAS fairing which houses a full scale boilerplate Orion Crew Module (CM). The objective of the flight test is to prove that the CM can be released from the MLAS fairing during pad abort conditions without detrimental recontact between the CM and fairing, achieving performance similar to the Orion launch abort system. The boost and coast skirts provide the necessary thrust and stability to achieve the flight test conditions and are released prior to the test -- much like the Little Joe booster was used in the Apollo Launch Escape System tests. To achieve the test objective, two parachutes are deployed from the fairing to reorient the CM/fairing to a heatshield first orientation. The parachutes then provide the force necessary to reduce the total angle of attack and body angular rates required for safe release of the CM from the fairing. A secondary test objective after CM release from the fairing is to investigate the removal of the CM forward bay cover (FBC) with CM drogue parachutes for the purpose of attempting to synchronously deploying a set of CM main parachutes. Although multiple parachute deployments are used in the MLAS flight test vehicle to complete its objective, there are only two parachute types employed in the flight test. Five of the nine parachutes used for MLAS are 27.6 ft D(sub 0) ribbon parachutes, and the remaining four are standard G-12 cargo parachutes. This paper presents an overview of the 27.6 ft D(sub 0) ribbon parachute system employed on the MLAS flight test vehicle for coast skirt separation, fairing reorientation, and as drogue parachutes for the CM after separation from the fairing. Discussion will include: the process used to select this design, previously proven as a spin/stall recovery parachute; descriptions of all components of the parachute system; the minor modifications necessary to adapt the parachute to the MLAS program; the techniques used to analyze the parachute for the multiple roles it performs; a discussion of the rigging techniques used to interface the parachute system to the vehicle; and a brief description of how the evolution of the program affected parachute usage and analysis. An overview of the Objective system, rationale for the MLAS approach and the future of the program will also be presented. We hope to have flight test results to report at the time of the Conference Presentation
Aberrant Development of Thymocytes in Mice Lacking Laminin-2
In previous in vitro studies, we proposed a role for the extracellular matrix component, laminin-
2, and its integrin receptor, VLA-6, in thymocyte development. The characterization of
two dystrophic mouse strains with different defects in laminin-2 allowed us to examine this
proposal in vivo. Mice deficient in laminin-2, dy/dy, show a significant reduction in thymus
size and number of thymocytes compared to normal littermates. These mice also exhibited
apparent alterations of thymic architecture. Examination of the CD4/CD8 populations in dy/dy
thymi showed large relative increases in the DN (CD4-CD8-) and SP (CD4+CD8-,
CD4-CD8+) populations and a significant decrease in the DP (CD4+CD8+) population. Further
examination of the DN population for CD44 and CD25 expression showed a remarkable
decrease in the more mature pre-T cell populations. Analysis of apoptosis in situ, and by flow
cytometry, in dy/dy thymi revealed a significant increase in apoptotic DN thymocytes in the
capsule and subcapsular regions. Interestingly, thymocyte development appeared to proceed
normally in dystrophic mice expressing a mutant form of laminin-2, dy2J, as well as, in fetal
and neonatal dy/dy mice. We propose that laminin-2 plays an active role in thymocyte development
by delivering cell survival and differentiation signals at specific stages of development
in young adult mice
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