Electrolysis Propulsion for Spacecraft Applications

Electrolysis propulsion has been recognized over the last several decades as a viable option to meet many satellite and spacecraft propulsion requirements. This technology, however, was never used for in-space missions. In the same time frame, water based fuel cells have flown in a number of missions. These systems have many components similar to electrolysis propulsion systems. Recent advances in component technology include: lightweight tankage, water vapor feed electrolysis, fuel cell technology, and thrust chamber materials for propulsion. Taken together, these developments make propulsion and/or power using electrolysis/fuel cell technology very attractive as separate or integrated systems. A water electrolysis propulsion testbed was constructed and tested in a joint NASA/Hamilton Standard/Lawrence Livermore National Laboratories program to demonstrate these technology developments for propulsion. The results from these testbed experiments using a I-N thruster are presented. A concept to integrate a propulsion system and a fuel cell system into a unitized spacecraft propulsion and power system is outlined

Approximate Performance of Periodic Hypersonic Cruise Trajectories for Global Reach

This paper develops the analytical framework to compare the approximate performance of periodic hypersonic cruise trajectories with previously proposed hypersonic trajectory profiles for global reach. Specifically, range, \DeltaV and payload carrying capacity are evaluated for various trajectory types to illustrate the enhanced performance achieved by flying periodic hypersonic cruise trajectories with existing hypersonic vehicle aerodynamic, propulsion, and structures technology. Analytical results reveal that periodic hypersonic cruise trajectories achieve better fuel consumption savings over long distances (ß20,000 km) than other trajectory types proposed for high-speed flight. A 20+% improvement in fuel consumption savings is possible for a Mach 10 vehicle with a modest L/D=4, and a curve-fitted rocket-based combined cycle engine model. Nomenclature a = Speed of sound A = Area Research Engineer y Assistant Professor, Senior Member AIAA. z Graduate Research Assistant, Stude..

Approximate Performance of Periodic Hypersonic Cruise Trajectories for Global Reach

This paper develops the analytical framework to compare the approximate performance of periodic hypersonic cruise trajectories with previously proposed hypersonic trajectory profiles for global reach. Specifically, range, \DeltaV and payload carrying capacity are evaluated for various trajectory types to illustrate the enhanced performance achieved by flying periodic hypersonic cruise trajectories with existing hypersonic vehicle aerodynamic, propulsion, and structures technology. Analytical results reveal that periodic hypersonic cruise trajectories achieve better fuel consumption savings over long distances ( 20,000 km) than other trajectory types proposed for high-speed flight. A 20+% improvement in fuel consumption savings is possible for a Mach 10 vehicle with a modest L/D=4, and a curve-fitted rocket-based combined cycle engine model. Nomenclature a = Speed of sound A = Area A = Vector term c = Exhaust velocity CD = Drag coefficient CL = Lift coefficient D = Drag E = Range/Mass..

Fundamental Physics of Periodic Hypersonic Cruise Trajectories

This technical note attempts to illustrate some of the important features associated with periodic hypersonic cruise trajectories for global reach. These trajectories have been previously shown to have enhanced payload carrying capacity for global ranges. In addition, these trajectories have been shown to reduce the effective heat load of vehicles attempting to fly globally. This technical note attempts to provide some insight as to why these trajectories have better performance than other trajectory forms. Specifically, this note attempts to address the following items: ffl fuel consumption savings comparison of trajectory types ffl drag and heat load comparison of trajectory types ffl sensitivity of global reach performance to fuel mass fraction ffl global reach comparison of trajectory types with rocket propulsion Assistant Professor, Senior Member AIAA. y Graduate Research Student, Student Member AIAA. z Research Engineer Copyright c fl1998. All rights reserved. Nomenclat..

Improved Performance of Sub-Optimal Periodic Hypersonic Cruise Trajectories for Long Range

This work investigates periodic flight trajectories to achieve optimal fuel savings for long-range hypersonic flight. A model of the aerodynamic and scramjet propulsion characteristics for a hypersonic lifting body configuration, is used to study enhanced fuel savings over steady-state cruise. Parameterized forms of undamped and damped periodic profiles are evaluated for their ability to achieve long-range. By enforcing continuity between multiple periods, optimal long-range solutions are developed. These piecewise solutions for long-range provide insight into the behavior of optimal periodic trajectories for hypersonic flight. Specifically, this work compares the benefits of undamped and damped periodic hypersonic cruise trajectories for long-range. Nomenclature a = Speed of sound A e = Engine inlet area Aw = Wing area an , bn = Scalar fourier series expansion constants CD = Drag coefficient CDo = Zero-lift drag coefficient CL = Lift coefficient C Lo = Zero angle of attack lift coef..

Coronal Heating as Determined by the Solar Flare Frequency Distribution Obtained by Aggregating Case Studies

Flare frequency distributions represent a key approach to addressing one of the largest problems in solar and stellar physics: determining the mechanism that counter-intuitively heats coronae to temperatures that are orders of magnitude hotter than the corresponding photospheres. It is widely accepted that the magnetic field is responsible for the heating, but there are two competing mechanisms that could explain it: nanoflares or Alfv\'en waves. To date, neither can be directly observed. Nanoflares are, by definition, extremely small, but their aggregate energy release could represent a substantial heating mechanism, presuming they are sufficiently abundant. One way to test this presumption is via the flare frequency distribution, which describes how often flares of various energies occur. If the slope of the power law fitting the flare frequency distribution is above a critical threshold, $\alpha=2$ as established in prior literature, then there should be a sufficient abundance of nanoflares to explain coronal heating. We performed $>$600 case studies of solar flares, made possible by an unprecedented number of data analysts via three semesters of an undergraduate physics laboratory course. This allowed us to include two crucial, but nontrivial, analysis methods: pre-flare baseline subtraction and computation of the flare energy, which requires determining flare start and stop times. We aggregated the results of these analyses into a statistical study to determine that $\alpha = 1.63 \pm 0.03$. This is below the critical threshold, suggesting that Alfv\'en waves are an important driver of coronal heating.Comment: 1,002 authors, 14 pages, 4 figures, 3 tables, published by The Astrophysical Journal on 2023-05-09, volume 948, page 7

Preoperative nasopharyngeal swab testing and postoperative pulmonary complications in patients undergoing elective surgery during the SARS-CoV-2 pandemic.

BACKGROUND: Surgical services are preparing to scale up in areas affected by COVID-19. This study aimed to evaluate the association between preoperative SARS-CoV-2 testing and postoperative pulmonary complications in patients undergoing elective cancer surgery. METHODS: This international cohort study included adult patients undergoing elective surgery for cancer in areas affected by SARS-CoV-2 up to 19 April 2020. Patients suspected of SARS-CoV-2 infection before operation were excluded. The primary outcome measure was postoperative pulmonary complications at 30 days after surgery. Preoperative testing strategies were adjusted for confounding using mixed-effects models. RESULTS: Of 8784 patients (432 hospitals, 53 countries), 2303 patients (26.2 per cent) underwent preoperative testing: 1458 (16.6 per cent) had a swab test, 521 (5.9 per cent) CT only, and 324 (3.7 per cent) swab and CT. Pulmonary complications occurred in 3.9 per cent, whereas SARS-CoV-2 infection was confirmed in 2.6 per cent. After risk adjustment, having at least one negative preoperative nasopharyngeal swab test (adjusted odds ratio 0.68, 95 per cent confidence interval 0.68 to 0.98; P = 0.040) was associated with a lower rate of pulmonary complications. Swab testing was beneficial before major surgery and in areas with a high 14-day SARS-CoV-2 case notification rate, but not before minor surgery or in low-risk areas. To prevent one pulmonary complication, the number needed to swab test before major or minor surgery was 18 and 48 respectively in high-risk areas, and 73 and 387 in low-risk areas. CONCLUSION: Preoperative nasopharyngeal swab testing was beneficial before major surgery and in high SARS-CoV-2 risk areas. There was no proven benefit of swab testing before minor surgery in low-risk areas