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Uncertainty in Electric Propulsion Erosion Measurements
Get PDFUncertainty in erosion rates as measured by different methods is discussed and quantified. The work focuses on case studies from components on the Hall Effect Rocket with Magnetic Shielding (HERMeS) Hall thruster, but the methods can be extended for many electric propulsion applications. The primary method used for evaluating erosion is non-contact profilometry of masked and exposed components. Accurate quantification of the erosion rates of components is critical to determining lifetime and is therefore critical to mission planning purposes
Rotational and Translational Velocity and Acceleration Thresholds for the Onset of Cybersickness in Virtual Reality
Get PDFThis paper determined rotational and translational velocity and acceleration thresholds for the onset of cybersickness. Cybersickness causes discomfort and discourages the widespread use of virtual reality systems for both recreational and professional use. Visual motion or optic flow is known to be one of the main causes of cybersickness due to the sensory conflict it creates with the vestibular system. The aim of this experiment is to detect rotational and translational velocity and acceleration thresholds that cause the onset of cybersickness. Participants were exposed to a moving particle field in virtual reality for a few seconds per run. The field moved in different directions (longitudinal, lateral, roll, and yaw), with different velocity profiles (steady and accelerating), and different densities. Using a staircase procedure, that controlled the speed or acceleration of the field, we detected the threshold at which participant started to feel temporary symptoms of cybersickness. The optic flow was quantified for each motion type and by modifying the number of features, the same amount of optic flow was present in each scene. Having the same optic flow in each scene allows a direct comparison of the thresholds. The results show that the velocity and acceleration thresholds for rotational optic flow were significantly lower than for translational optic flow. The thresholds suggestively decreased with the decreasing particle density of the scene. Finally, it was found that all the rotational and translational thresholds strongly correlate with each other. While the mean values of the thresholds could be used as guidelines to develop virtual reality applications, the high variability between individuals implies that the individual tuning of motion controls would be more effective to reduce cybersickness while minimizing the impact on the experience of immersion
Space Mission Concept Design at the NASA Ames Mission Design Center (MDC)
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NASAs Laser Communications Relay Demonstration Mission Leaves Goddard Space Flight Center
Get PDFOn Jan. 22, 2020, the Laser Communications Relay Demonstration (LCRD) flight payload was delivered to Northrop Grummans facility in Sterling, Virginia. There the payload will be integrated onto the U.S. Air Forces Space Test Program Satellite 6 (STPSat-6) and prepared for launch. LCRD will be NASAs first end-to-end optical relay, sending and receiving data from missions in space to mission control on Earth
PCB Quality Metrics that Drive Reliability (PD 18)
Get PDFRisk based technology infusion is a deliberate and systematic process which defines the analysis and communication methodology by which new technology is applied and integrated into existing and new designs, identifies technology development needs based on trends analysis and facilitates the identification of shortfalls against performance objectives. This presentation at IPC Works Asia Aerospace 2019 Events provides the audience a snapshot of quality variations in printed wiring board quality, as assessed, using experiences in processing and risk analysis of PWB structural integrity coupons. The presentation will focus on printed wiring board quality metrics used, the relative type and number of non-conformances observed and trend analysis using statistical methods. Trend analysis shows the top five non-conformances observed across PWB suppliers, the root cause(s) behind these non-conformance and suggestions of mitigation plans. The trends will then be matched with the current state of the PWB supplier base and its challenges and opportunities. The presentation further discusses the risk based SMA approaches and methods being applied at GSFC for evaluating candidate printed wiring board technologies which promote the adoption of higher throughput and faster processing technology for GSFC missions
Feeding Ten Billion People Is Possible Within Four Terrestrial Planetary Boundaries
No full textGlobal agriculture puts heavy pressure on planetary boundaries, posing the challenge to achieve future food security without compromising Earth system resilience. On the basis of process-detailed, spatially explicit representation of four interlinked planetary boundaries (biosphere integrity, land-system change, freshwater use, nitrogen flows) and agricultural systems in an internally consistent model framework, we here show that almost half of current global food production depends on planetary boundary transgressions. Hotspot regions, mainly in Asia, even face simultaneous transgression of multiple underlying local boundaries. If these boundaries were strictly respected, the present food system could provide a balanced diet (2,355 kcal per capita per day) for 3.4 billion people only. However, as we also demonstrate, transformation towards more sustainable production and consumption patterns could support 10.2 billion people within the planetary boundaries analysed. Key prerequisites are spatially redistributed cropland, improved waternutrient management, food waste reduction and dietary changes.
Adoption of the Sustainable Development Goals by all nations
in 2015 is the first ever commitment to a world development
path that safeguards the stability of the Earth system
as a prerequisite for meeting universal human standards1. The longstanding
challenge of achieving food security through sustainable
agriculture is particularly acute in this context as world agriculture
is a leading cause for the current transgressions of multiple planetary
boundaries (PBs) globally and regionally25. The PB framework
is a comprehensive scientific attempt to synoptically define
our planets biogeophysical limits to anthropogenic interference. It
suggests bounds to nine interacting processes that together delineate
a Holocene-like Earth system state. The Holocene is chosen as
the reference state as it is the only period known to provide a safe
operating space for a world population of several billion people,
and according to a precautionary principle, the PBs are set in sufficient
distance from processes that may critically undermine Earth
system resilience and global sustainability. A challenging question,
thus, is whether human development goals such as food security
can be met while maintaining multiple PBs along with their subglobal
manifestations.
Further PB transgressions could jeopardize the chances of providing
sufficient food for a world population projected to be wealthier
and reach >9 billion by 2050. This conundrum portrays a tradeoff
between Earths biophysical carrying capacity and humankinds rising
food demand, calling in response for radical rethinking of food
production and consumption patterns69. Yield gap closures, avoidance
of excessive input use, shifts towards less resource-demanding
diets, food waste reductions and efficient international trade are
crucial options for sustainably increasing the food supply1015. For
example, enhancing water-use efficiency on irrigated and rain-fed
farms can triple or quadruple crop yields in low-performing systems,
suggesting possible global gains of >20% (ref. 16). Even higher gains
appear feasible through globally optimized configurations of the
land-use pattern17, and cutting food losses by half could generate
food for another billion people18. Thus, collective large-scale implementation
of such options could sustain food for a further growing
world population19. Yet achieving this within a safe operating space
as defined by PBs requires not only a halt to but actually a reversal
of existing PB transgressions. Previous studies suggest that such a
reconciliation might be possible, but these were based on aggregate
representations of PBs (not accounting for the spatial patterns
of limits, transgressions and interactions) or considered only one
boundary in isolation17,2023.
Here, we systematically quantify to what extent current food production
depends on local to global transgressions of the PBs for biosphere
integrity, land-system change, freshwater use and nitrogen
(N) flows, along with the potential of a range of solutions to avoid
these transgressions and still increase food supply (Table 1). To this
end, we configured an internally consistent process-based model of
the terrestrial biosphere including agriculture (LPJmL) with multiple
spatially distributed PBs and their interactions. LPJmL is among
the longest-established and best-evaluated biosphere models, showing
robust performance regarding simulation of, for example, carbon,
water and crop yield dynamics (Supplementary Figs. 1 and 2
and Supplementary Table 1; see ref. 24 for a comprehensive benchmarking
and Supplementary Methods for more detail on model
evaluations). In principle following established definitions4, we
refine the computation of some PBs with respect to their regional
patterns and interactions (Methods), providing globally gridded
precautionary limits to human interference with the Earth system at
a level of great detail. In particular, we account for the evidence that
many PBs need to be represented spatially explicitly4 to cover thei
NASA ETR Quiet Zone Probe Study
Get PDFThe NASA Langley Research Centers Experimental Test Range is an indoor anechoic compact range far field test facility used to conduct antenna and electromagnetic radiation measurements. The Experimental Test Range was designed to simulate far field illumination in the facility test volume over a broad band of frequencies by collimating the RF energy from the 26 ft by 26 ft parabolic reflector. The quality of the antenna and radiation measurements are dependent on the uniformity of the far field plane wave generated by the compact range reflector. While this facility is going through several upgrades, this report describes an assessment of the far field plane wave conducted after resurfacing the primary reflector to improve performance and extend the range of frequencies for which this facility can operate. This assessment addresses far field uniformity probe data measured in the test volume across the facility operational frequency bands
Contribution of Infiltration Process Uncertainty on the Simulation of Terrestrial Water and Energy Budgets
Get PDFThe infiltration step is the major forking point of precipitation partition in land surface models, which plays a more significant role than canopy interception for simulating water and energy budgets.In this study, we found significant differences in water and energy-related outputs amount JULES, Noah, Noah-MP, and VIC. The differences are directly or indirectly related to the infiltration components in the models. Those differences add uncertainties to the applications of land surface models. Thorough evaluations are needed to determine the reliability of infiltration schemes used in these models
