Compensating for Cryogenic Propellant Boiloff for a Cargo Mission to Mars

A previous work by the authors (Architecture Study for a Fuel Depot Supplied from Lunar Resources – AIAA 2016-5306) examined architectures for a fuel depot supplied from lunar ice deposits. The study recommended a fuel depot be located at Earth-Moon L1. The study used three design reference missions in the formulation of candidate architectures – among them a Mars Cargo Vehicle (MCV). Each vehicle used 60 layers of multi-layer insulation (MLI) to minimize the boiloff of cryogenic propellants. Boiloff was shown to not be a driver in architecture selection, but it was noted that reducing the number of layers of MLI from 60 to 30 reduced the MLI mass by almost 4,000 kg, but the predicted boiloff only increased about 2,000 kg. This suggested that further investigation was needed to determine the optimum balance between MLI mass, predicted boiloff, and the mass of propellant needed to compensate for that boiloff. While holding the payload mass constant, this paper uses the Modified Lockheed Model to calculate predicted boiloff, and uses multiple iterations of the classic rocket equation to determine how much propellant will be needed to compensate for boiloff over a 288-day mission to Mars

Achievements and Perspectives in the Breeding of Temperate Grasses and Legumes

This paper will focus on a historical perspective on cool season forage production, plant breeding methods for cool season forages, major cool season forage selection criteria, some examples of significant achievements, and a future perspective. Topics similar to ours have been discussed at recent previous meeting of this Congress (Humphreys, 1997; Van Wijk et al., 1993); however, we will strive to avoid “plowing the same ground twice”. In an attempt to prevent duplication of content with other sections of this Congress, only limited attention will be given to genetic resource acquisition and conservation. Additionally, alfalfa (Medicago sativa L.), one of the primary temperate forage legumes, will generally not be discussed, since a full paper by Dr. Bouton will be presented in another session

Marker-Assisted Selection for Fibre Concentration in Smooth Bromegrass

The concentration of neutral detergent fibre is the best single laboratory predictor of voluntary intake potential in forage crops. However, the assay of thousands of plant samples for NDF selection in a breeding program requires a large amount of labour and time, potentially increasing cycle time and reducing the rate of progress. A previous study (Diaby and Casler, 2005) identified 16 random amplified polymorphic DNA (RAPD) markers that were strongly associated with NDF concentration in one or more of four smooth bromegrass (Bromus inermis Leyss) populations. The objective of this study was to validate these associations by implementing marker-assisted selection for these 16 RAPD markers

Forage Yield and Economic Losses Associated with the Brown-Midrib Trait in Sudangrass

Brown-midrib genes increase digestibility due to reduced lignification in sudangrass, Sorghum bicolor subsp. drummondii (Nees ex Steud.) de Wet & Harlan. Brown-midrib lines are known to be low in forage yield potential, but this reduction in forage yield has not been previously quantified. The objectives of this study were to quantify the increase in forage quality and decrease in forage yield and to provide an economic assessment of this dichotomy. Piper and Greenleaf (normal leaves) were compared with their brown-midrib counterparts and four highly selected brown-midrib (FG) lines at two locations for 2 yr. Brown-midrib lines averaged 9.0% lower in lignin and 7.2% higher in in vitro fiber digestibility than normal lines. The reduction in first-harvest forage yield was highly variable across germplasms and locations. Greenleaf and the FG lines showed severe forage yield reductions in Wisconsin but not in Nebraska, whereas forage yield of Piper was uniformly reduced across locations. Reduced tillering and plant height of the brown-midrib plants appeared to be mechanisms for reducing forage yield. The brown-midrib phenotype of sudangrass, caused by the homozygous condition of the bmr-6 allele, appears to be environmentally sensitive, particularly limiting production in cooler and shorter growing seasons. Conversely, uniform reductions in second-harvest forage yield suggested a fundamental limitation to regrowth potential associated with the brown-midrib phenotype. Predicted net returns from feeding sudangrass hay were similar for first-harvest normal and brown-midrib lines, but severely depressed for brown-midrib lines in second harvest, due to the severe yield reductions

Genetic modification of lignin concentration affects fitness of perennial herbaceous plants

Populations of four perennial herbaceous species that were genetically modified for altered lignin content (or associated forage digestibility) by conventional plant breeding were evaluated for two agricultural fitness traits, plant survival and plant biomass, in three Northcentral USA environments for more than 4 years. Reduced lignin concentration or increased digestibility resulted in increased winter mortality in two of four species and reduced biomass in one species. Results from other experiment indicate that these apparent genetic correlations may be ephemeral, suggesting that selection for fitness can be successful within high-digestibility or low-lignin germplasm. Results indicate that perennial plants genetically engineered with altered lignin concentration or composition for use in livestock, pulp and paper, or bioenergy production should be evaluated for fitness in field environments prior to use in agriculture

Registration of WS4U and WS8U Switchgrass Germplasms

Two upland switchgrass (Panicum virgatum L.) germplasm pools, WS4U (Reg. no. GP-92, PI 639191) and WS8U (Reg. no. GP-93, PI 639192), were released cooperatively on 18 July 2002 by the University of Wisconsin, University of Nebraska, and the USDA-ARS, Lincoln, NE. These germplasms were developed as source material to be used in developing cultivars with increased biomass yield and geographic adaptation for bioenergy production in USDA hardiness zones 3 and 4 in the northern USA and similar geographic regions of southern Canada. WS4U is a tetraploid (2n = 4x = 36) and WS8U is an octoploid (2n = 8x = 72)

Forage Yield and Economic Losses Associated with the Brown-Midrib Trait in Sudangrass

Brown-midrib genes increase digestibility due to reduced lignification in sudangrass, Sorghum bicolor subsp. drummondii (Nees ex Steud.) de Wet & Harlan. Brown-midrib lines are known to be low in forage yield potential, but this reduction in forage yield has not been previously quantified. The objectives of this study were to quantify the increase in forage quality and decrease in forage yield and to provide an economic assessment of this dichotomy. Piper and Greenleaf (normal leaves) were compared with their brown-midrib counterparts and four highly selected brown-midrib (FG) lines at two locations for 2 yr. Brown-midrib lines averaged 9.0% lower in lignin and 7.2% higher in in vitro fiber digestibility than normal lines. The reduction in first-harvest forage yield was highly variable across germplasms and locations. Greenleaf and the FG lines showed severe forage yield reductions in Wisconsin but not in Nebraska, whereas forage yield of Piper was uniformly reduced across locations. Reduced tillering and plant height of the brown-midrib plants appeared to be mechanisms for reducing forage yield. The brown-midrib phenotype of sudangrass, caused by the homozygous condition of the bmr-6 allele, appears to be environmentally sensitive, particularly limiting production in cooler and shorter growing seasons. Conversely, uniform reductions in second-harvest forage yield suggested a fundamental limitation to regrowth potential associated with the brown-midrib phenotype. Predicted net returns from feeding sudangrass hay were similar for first-harvest normal and brown-midrib lines, but severely depressed for brown-midrib lines in second harvest, due to the severe yield reductions

Latitudinal Adaptation of Switchgrass Populations

Switchgrass (Panicum virgatum L.) is a widely adapted warm-season perennial that has considerable potential as a biofuel crop. Evolutionary processes and environmental factors have combined to create considerable ecotypic differentiation in switchgrass. The objective of this study was to determine the nature of population x location interaction for switchgrass, quantifying potential differences in latitudinal adaptation of switchgrass populations. Twenty populations were evaluated for biofuel and agronomic traits for 2 yr at five locations ranging from 36 to 46° N lat. Biomass yield, survival, and plant height had considerable population x location interaction, much of which (53-65%) could be attributed to the linear effect of latitude and to germplasm groups (Northern Upland, Southern Upland, Northern Lowland, and Southern Lowland). Differences among populations were consistent across locations for maturity, dry matter, and lodging. Increasingly later maturity and the more rapid stem elongation rate of more southern-origin ecotypes (mainly lowland cytotypes) resulted in high biomass yield potential, reduced dry matter concentration, and longer retention of photosynthetically active tissue at more southern locations. Conversely, increasing cold tolerance of more northern-origin ecotypes (mainly upland cytotypes) resulted in higher survival, stand longevity, and sustained biomass yields at more northern locations, allowing switchgrass to thrive at cold, northern latitudes. Although cytotype explained much of the variation among populations and the population x location interaction, ecotypic differentiation within cytotypes accounted for considerable variation in adaption of switchgrass populations

Selection Signatures in Four Lignin Genes from Switchgrass Populations Divergently Selected for \u3ci\u3eIn Vitro\u3c/i\u3e Dry Matter Digestibility

Switchgrass is undergoing development as a dedicated cellulosic bioenergy crop. Fermentation of lignocellulosic biomass to ethanol in a bioenergy system or to volatile fatty acids in a livestock production system is strongly and negatively influenced by lignification of cell walls. This study detects specific loci that exhibit selection signatures across switchgrass breeding populations that differ in in vitro dry matter digestibility (IVDMD), ethanol yield, and lignin concentration. Allele frequency changes in candidate genes were used to detect loci under selection. Out of the 183 polymorphisms identified in the four candidate genes, twenty-five loci in the intron regions and four loci in coding regions were found to display a selection signature. All loci in the coding regions are synonymous substitutions. Selection in both directions were observed on polymorphisms that appeared to be under selection. Genetic diversity and linkage disequilibrium within the candidate genes were low. The recurrent divergent selection caused excessive moderate allele frequencies in the cycle 3 reduced lignin population as compared to the base population. This study provides valuable insight on genetic changes occurring in short-term selection in the polyploid populations, and discovered potential markers for breeding switchgrass with improved biomass quality