CubeSat Active Thermal Control via Microvascular Carbon Fiber Channel Radiator

Small spacecraft rarely have space for any thermal control subsystems and often must perform operations in “burst” mode as a result. The few spacecraft who do have control rely on low-complexity thermal control systems which conduct heat to the bus structure and then radiate the heat away. These simplistic techniques are sufficient for low power missions in Low Earth Orbit (LEO) but are not capable of dumping the heat produced in new mission profiles that are in development. This is due to small spacecraft incorporating increasingly advanced subsystems which have difficult thermal control requirements such as propulsion systems or high-power antennas. The University of Illinois at Urbana-Champaign, in partnership with NASA Ames Research Center, is developing a thermal control system for small spacecraft. This control system uses a deployable radiator panel made from carbon fiber with micro-vascular circulatory system for coolant. This paper is a follow-up on the previous year’s SmallSat conference. A bench prototype of the thermal control subsystem was designed and built. The prototype underwent a range of thermal and vibration tests at NASA Ames. Test results and lessons learned are presented. Moving forward, test conclusions will require some design parameters to be changed and the subsystem will reach TRL 6 by the end of the two-year program

Rearrangement of Retinogeniculate Projection Patterns after Eye-Specific Segregation in Mice

It has been of interest whether and when the rearrangement of neuronal circuits can be induced after projection patterns are formed during development. Earlier studies using cats reported that the rearrangement of retinogeniculate projections could be induced even after eye-specific segregation has occurred, but detailed and quantitative characterization of this rearrangement has been lacking. Here we delineate the structural changes of retinogeniculate projections in the C57BL/6 mouse in response to monocular enucleation (ME) after eye-specific segregation. When ME was performed after eye-specific segregation, rearrangement of retinogeniculate axons in the dorsal lateral geniculate nucleus (dLGN) was observed within 5 days. Although this rearrangement was observed both along the dorsomedial-ventrolateral and outer-inner axes in the dLGN, it occurred more rapidly along the outer-inner axis. We also examined the critical period for this rearrangement and found that the rearrangement became almost absent by the beginning of the critical period for ocular dominance plasticity in the primary visual cortex. Taken together, our findings serve as a framework for the assessment of phenotypes of genetically altered mouse strains as well as provide insights into the mechanisms underlying the rearrangement of retinogeniculate projections

The C-Terminal 88 Amino Acids of the Sendai Virus P Protein Have Multiple Functions Separable by Mutation

The Sendai virus P-L polymerase complex binds the NP-encapsidated nucleocapsid (NC) template through a P-NP interaction. To identify P amino acids responsible for binding we performed site-directed mutagenesis on the C-terminal 88 amino acids in the NC binding domain. The mutant P proteins expressed from plasmids were assayed for viral RNA synthesis and for various protein-protein interactions. All the mutants formed P oligomers and bound to L protein. While two mutants, JT3 and JT8, retained all P functions at or near the levels of wild-type (wt) P, three others—JT4, JT6, and JT9—were completely defective for both transcription and genome replication in vitro. Each of the inactive mutants retained significant NC binding but had a different spectrum of other binding interactions and activities, suggesting that the NC binding domain also affects the catalytic function of the polymerase. NC binding was inhibited by combinations of the inactive mutations. The remaining P mutants were active in transcription but defective in various aspects of genome replication. Some P mutants were defective in NP(0) binding and abolished the reconstitution of replication from separate P-L and NP(0)-P complexes. In some of these cases the coexpression of the wt polymerase with the mutant NP(0)-P complex could rescue the defect in replication, suggesting an interaction between these complexes. For some P mutants replication occurred in vivo, but not in vitro, suggesting that the intact cell is providing an unknown function that cannot be reproduced in extracts of cells. Thus, the C-terminal region of P is complex and possesses multiple functions besides NC binding that can be separated by mutation

CHARMM-GUI Membrane Builder for Mixed Bilayers and Its Application to Yeast Membranes

The CHARMM-GUI Membrane Builder (http://www.charmm-gui.org/input/membrane), an intuitive, straightforward, web-based graphical user interface, was expanded to automate the building process of heterogeneous lipid bilayers, with or without a protein and with support for up to 32 different lipid types. The efficacy of these new features was tested by building and simulating lipid bilayers that resemble yeast membranes, composed of cholesterol, dipalmitoylphosphatidylcholine, dioleoylphosphatidylcholine, palmitoyloleoylphosphatidylethanolamine, palmitoyloleoylphosphatidylamine, and palmitoyloleoylphosphatidylserine. Four membranes with varying concentrations of cholesterol and phospholipids were simulated, for a total of 170 ns at 303.15 K. Unsaturated phospholipid chain concentration had the largest influence on membrane properties, such as average lipid surface area, density profiles, deuterium order parameters, and cholesterol tilt angle. Simulations with a high concentration of unsaturated chains (73%, membraneunsat) resulted in a significant increase in lipid surface area and a decrease in deuterium order parameters, compared with membranes with a high concentration of saturated chains (60–63%, membranesat). The average tilt angle of cholesterol with respect to bilayer normal was largest, and the distribution was significantly broader for membraneunsat. Moreover, short-lived cholesterol orientations parallel to the membrane surface existed only for membraneunsat. The membranesat simulations were in a liquid-ordered state, and agree with similar experimental cholesterol-containing membranes

Microvascular Composite Radiators for Small Spacecraft Thermal Management Systems

Small spacecraft have typically relied on thermal control systems in which waste heat is simply conducted though structural elements to the surface where it is radiated away. This simplistic approach is adequate for low-complexity missions to LEO, but increasingly complex mission profiles are being proposed including missions to deep space locations which present a harsher thermal environment as well as incorporating advanced capabilities which have challenging thermal control requirements such as cryogenically cooled sensors or propulsion systems. The University of Illinois at Urbana-Champaign, in partnership with NASA Ames Research Center, is developing a thermal control system for small spacecraft utilizing a deployable radiator made of a micro-vascular composite material, through which a coolant can be circulated. These microvascular composite radiators contain tiny channels, as small as 100 micrometer diameter, which can only be manufactured using a novel fabrication technique developed at the University of Illinois, the Vaporization of Sacrificial Components (VaSC). Early mission concepts were evaluated to determine the design guidelines for the cooling system definition. Moving forward, thermal vacuum testing of the prototype will raise the TRL to 6 by the end of the two year development program

A moonlighting metabolic protein influences repair at DNA double-stranded breaks

Catalytically active proteins with divergent dual functions are often described as ‘moonlighting’. In this work we characterize a new, chromatin-based function of Lys20, a moonlighting protein that is well known for its role in metabolism. Lys20 was initially described as homocitrate synthase (HCS), the first enzyme in the lysine biosynthetic pathway in yeast. Its nuclear localization led to the discovery of a key role for Lys20 in DNA damage repair through its interaction with the MYST family histone acetyltransferase Esa1. Overexpression of Lys20 promotes suppression of DNA damage sensitivity of esa1 mutants. In this work, by taking advantage of LYS20 mutants that are active in repair but not in lysine biosynthesis, the mechanism of suppression of esa1 was characterized. First we analyzed the chromatin landscape of esa1 cells, finding impaired histone acetylation and eviction. Lys20 was recruited to sites of DNA damage, and its overexpression promoted enhanced recruitment of the INO80 remodeling complex to restore normal histone eviction at the damage sites. This study improves understanding of the evolutionary, structural and biological relevance of independent activities in a moonlighting protein and links metabolism to DNA damage repair