Derated ion thruster design issues

Preliminary activities to develop and refine a lightweight 30 cm engineering model ion thruster are discussed. The approach is to develop a 'derated' ion thruster capable of performing both auxiliary and primary propulsion roles over an input power range of at least 0.5 to 5.0 kilo-W. Design modifications to a baseline thruster to reduce mass and volume are discussed. Performance data over an order of magnitude input power range are presented, with emphasis on the performance impact of engine throttling. Thruster design modifications to optimize performance over specific power envelopes are discussed. Additionally, lifetime estimates based on wear test measurements are made for the operation envelope of the engine

Performance of 10-kW class xenon ion thrusters

Presented are performance data for laboratory and engineering model 30 cm-diameter ion thrusters operated with xenon propellant over a range of input power levels from approximately 2 to 20 kW. Also presented are preliminary performance results obtained from laboratory model 50 cm-diameter cusp- and divergent-field ion thrusters operating with both 30 cm- amd 50 cm-diameter ion optics up to a 20 kW input power. These data include values of discharge chamber propellant and power efficiencies, as well as values of specific impulse, thruster efficiency, thrust and power. The operation of the 30 cm- and 50 cm-diameter ion optics are also discussed

High power ion thruster performance

The ion thruster is one of several forms of space electric propulsion being considered for use on future SP-100-based missions. One possible major mission ground rule is the use of a single Space Shuttle launch. Thus, the mass in orbit at the reactor activation altitude would be limited by the Shuttle mass constraints. When the spacecraft subsystem masses are subtracted from this available mass limit, a maximum propellant mass may be calculated. Knowing the characteristics of each type of electric thruster allows maximum values of total impulse, mission velocity increment, and thrusting time to be calculated. Because ion thrusters easily operate at high values of efficiency (60 to 70%) and specific impulse (3000 to 5000 sec), they can impart large values of total impulse to a spacecraft. They also can be operated with separate control of the propellant flow rate and exhaust velocity. This paper presents values of demonstrated and projected performance of high power ion thrusters used in an analysis of electric propulsion for an SP-100 based mission

Approach Considerations in Aircraft with High-Lift Propeller Systems

NASA's research into distributed electric propulsion (DEP) includes the design and development of the X-57 Maxwell aircraft. This aircraft has two distinct types of DEP: wingtip propellers and high-lift propellers. This paper focuses on the unique opportunities and challenges that the high-lift propellers--i.e., the small diameter propellers distributed upstream of the wing leading edge to augment lift at low speeds--bring to the aircraft performance in approach conditions. Recent changes to the regulations related to certifying small aircraft (14 CFR x23) and these new regulations' implications on the certification of aircraft with high-lift propellers are discussed. Recommendations about control systems for high-lift propeller systems are made, and performance estimates for the X-57 aircraft with high-lift propellers operating are presented

The evolutionary development of high specific impulse electric thruster technology

Electric propulsion flight and technology demonstrations conducted primarily by Europe, Japan, China, the U.S., and the USSR are reviewed. Evolutionary mission applications for high specific impulse electric thruster systems are discussed, and the status of arcjet, ion, and magnetoplasmadynamic thrusters and associated power processor technologies are summarized

Pressure vessel with improved impact resistance and method of making the same

A composite overwrapped pressure vessel is provided which includes a composite overwrapping material including fibers disposed in a resin matrix. At least first and second kinds of fibers are used. These fibers typically have characteristics of high strength and high toughness to provide impact resistance with increased pressure handling capability and low weight. The fibers are applied to form a pressure vessel using wrapping or winding techniques with winding angles varied for specific performance characteristics. The fibers of different kinds are dispersed in a single layer of winding or wound in distinct separate layers. Layers of fabric comprised of such fibers are interspersed between windings for added strength or impact resistance. The weight percentages of the high toughness and high strength materials are varied to provide specified impact resistance characteristics. The resin matrix is formed with prepregnated fibers or through wet winding. The vessels are formed with or without liners

Cost-Utility of Routine Endometrial Evaluation Prior to Le Fort Colpocleisis

Objective: Endometrial evaluation is routinely performed in elderly women undergoing Le Fort colpocleisis. There is little evidence to support this practice. We sought to investigate the cost-utility of routine evaluation of the uterine cavity prior to performing a Le Fort colpocleisis. Study Design: A decision analysis model was created to compare uterine evaluation, by either endometrial biopsy or transvaginal ultrasound, to no evaluation for a cohort of women \u3e 80 years old undergoing Le Fort colpocleisis. Baseline assumptions for our model were made to reflect women who did not carry significant risk for the development of endometrial cancer, such as history of postmenopausal bleeding, abnormal uterine pathology, obesity, diabetes, and tamoxifen use. Decision paths included no screening, ultrasound evaluation, and biopsy. The horizon was five years until the endpoint of survival, death, or the development of cancer. Those pathways in which cancer was diagnosed were carried out to the endpoint of either five-year survival or death. Treatment arms for endometrial cancer were based on management methods used at our institution. Probabilities and utilities for health outcomes were estimated through literature review or, when unavailable, by expert opinion. Costs were obtained from US Medicare charges for the appropriate CPT and DRG codes and are reported in 2012 US Dollars. Cost-utility analysis was performed using US recommendations from a societal perspective. Sensitivity analysis using Monte Carlo simulation was performed to test the validity of our model. Results: Analysis of our decision tree demonstrates that a strategy of no evaluation is superior to that of either biopsy or ultrasound. Univariate sensitivity analysis demonstrates that at a 0.55 probability of cancer, biopsy surpasses both no evaluation and ultrasound as the dominant strategy. Using Monte Carlo simulation, at willingness-to-pay thresholds of $50,000 and$100,000, no evaluation was superior to both biopsy and ultrasound from the patient, health-plan, and societal perspectives. Biopsy appears to be a more effective strategy than ultrasound when uterine evaluation is needed. Conclusions: Our model shows that a practice of not evaluating the endometrial cavity prior to performing Le Fort colpocleisis is superior to either biopsy or ultrasound. These results are likely being driven by the low incidence of endometrial cancer in this population. It may not be necessary to perform uterine evaluation prior to Le Fort colpocleisis in a low-risk population. If uterine evaluation is needed, biopsy appears to be the preferred strategy over ultrasound. More studies are needed to determine utility values for health states experienced by women with pelvic organ prolapse and with endometrial cancer. This will enhance our ability to develop more accurate cost-utility models for treating these women

Ion Thruster Development at NASA Lewis Research Center

Recent ion propulsion technology efforts at NASA's Lewis Research Center including development of kW-class xenon ion thrusters, high power xenon and krypton ion thrusters, and power processors are reviewed. Thruster physical characteristics, performance data, life projections, and power processor component technology are summarized. The ion propulsion technology program is structured to address a broad set of mission applications from satellite stationkeeping and repositioning to primary propulsion using solar or nuclear power systems

Hybrid Wound Filaments for Greater Resistance to Impacts

A hybrid material containing wound filaments made of a hybrid of high-strength carbon fibers and poly(phenylene benzobisoxazole) [PBO] fibers is discussed. This hybrid material is chosen in an effort to increase the ability of the pressure vessel to resist damage by low-speed impacts (e.g., dropping of tools on the vessel or bumping of the vessel against hard objects during installation and use) without significantly increasing the weight of the vessel. While the basic concept of hybridizing fibers in filament-wound structures is not new, the use of hybridization to increase resistance to impacts is an innovation, and can be expected to be of interest in the composite-pressure-vessel industry. The precise types and the proportions of the high-strength carbon fibers and the PBO fibers in the hybrid are chosen, along with the filament-winding pattern, to maximize the advantageous effects and minimize the disadvantageous effects of each material. In particular, one seeks to (1) take advantage of the ability of the carbon fibers to resist stress rupture while minimizing their contribution to vulnerability of the vessel to impact damage and (2) take advantage of the toughness of the PBO fibers while minimizing their contribution to vulnerability of the vessel to stress rupture. Experiments on prototype vessels fabricated according to this concept have shown promising results. At the time of reporting the information for this article, research toward understanding and optimizing the performances of PBO fibers so as to minimize their contribution to vulnerability of the pressure vessel to stress rupture had yet to be performed

An Exploration of the Performance and Acoustic Characteristics of UAV-Scale Stacked Rotor Configurations

As interest grows in rotor- and propeller-driven electric vertical takeoff and landing (eVTOL) aircraft for the Urban Air Mobility market, there is a potential for previously studied concepts to reemerge due to the opportunities afforded by novel technologies and operating modes. One such concept is the stacked rotor, which consists of multiple co-rotating rotors positioned co-axially with a small axial offset. The goal of the work presented in this paper is to determine whether stacked rotors offer a compelling advantage for eVTOL aircraft in terms of both performance and acoustic characteristics. Results are presented for new experimental tests and computational modeling of multiple stacked rotor configurations, and comparisons are made with conventional rotor configurations. Testing of thirteen separate configurations each using the same blade shaperevealed a configuration that resulted in an increase in the rotor power loading efficiency by more than 7% and reduced noise by more than 3 dBA when compared with a conventional rotor with all blades located in the same rotational plane