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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Development of a 13 kW Hall Thruster Propulsion System Performance Model for AEPS

The Advanced Electric Propulsion System (AEPS) program will develop a flight 13kW Hall thruster propulsion system based on NASA's HERMeS thruster. The AEPS system includes the Hall Thruster, the Power Processing Unit (PPU) and the Xenon Flow Controller (XFC). These three primary components must operate together to ensure that the system generates the required combinations of thrust and specific impulse at the required system efficiencies for the desired system lifetime. At the highest level, the AEPS system will be integrated into the spacecraft and will receive power, propellant, and commands from the spacecraft. Power and propellant flow rates will be determined by the throttle set points commanded by the spacecraft. Within the system, the major control loop is between the mass flow rate and thruster current, with time-dependencies required to handle all expected transients, and additional, much slower interactions between the thruster and cathode temperatures, flow controller and PPU. The internal system interactions generally occur on shorter timescales than the spacecraft interactions, though certain failure modes may require rapid responses from the spacecraft. The AEPS system performance model is designed to account for all these interactions in a way that allows evaluation of the sensitivity of the system to expected changes over the planned mission as well as to assess the impacts of normal component and assembly variability during the production phase of the program. This effort describes the plan for the system performance model development, correlation to NASA test data, and how the model will be used to evaluate the critical internal and external interactions. The results will ensure the component requirements do not unnecessarily drive the system cost or overly constrain the development program. Finally, the model will be available to quickly troubleshoot any future unforeseen development challenges.

Stanley, Steven↗
NASA NTRS2016

Transient Thermal Analysis of the 12.5 KW HERMeS Hall Thruster

NASA’s Dawn spacecraft entered orbit around the dwarf planet Ceres on March 6, 2015 thereby becoming the first mission to orbit two celestial bodies outside of the Earth-moon system. This feat was made possible due to the use of electric propulsion (EP) to provide the 11 km/s of delta-V that was necessary. This type of propulsion is also enabling for many of NASA’s future missions, such as the proposed Asteroid Redirect Robotic Mission (ARRM). Specifically, the Hall Effect Rocket with Magnetic Shielding (HERMeS) is the propulsive design baseline due to its long operational lifetime and high specific impulse. Extensive modeling is required to verify the thruster's predicted thermal performance and survival during the bounding mission phases. Since the thruster would constrain plasma on the order of tens of thousands of hours, components in the thruster must be able to accommodate much higher sustained temperatures than typical spacecraft hardware. Furthermore, the high temperatures necessitate care in analyzing thermal gradients within the thruster. In this paper, we describe a thermal model of the HERMeS thruster and focus upon the thruster's transient performance under different initial firing conditions. The thruster's transient thermal response is critical to verify margin in the thermal stresses inherent in the thruster and to determine safe start-up procedures to protect the thruster's critical components. This model is used to perform transient thermal analysis of the thruster during startup and shutdown, provide temperature maps for structural analysis, and plan for thermal cycle testing conducted at JPL. The thermal cycle testing includes thruster starts at the cold temperature limits and operation at maximum expected external heat flux. This work will support laboratory environmental testing of the HERMeS thruster, which is being conducted at JPL in 2016.

Reilly, Sean↗
NASA NTRS2019

A Kuiper Belt Object Orbiter Enabled By 10 kW Kilopower Electric Propulsion

Recently, the New Horizons spacecraft flew by the Kuiper Belt Object Ultima Thule 13 years after launch. While flybys are a necessary 'first look' at the object in question a more comprehensive evaluation of the object will require an orbiter. Due to these object’s low mass a chemical propulsion system is not a viable option for entering their shallow gravity wells. The Dawn mission showed that solar electric propulsion is significantly better at the task of reaching low mass objects, but at Kuiper belt distances solar power is not a viable choice. A small nuclear reactor based on the recent kilopower ground test could provide 1-10 kWe of power for an electric propulsion system. The NASA Compass Team developed a Nuclear Electric Propulsion Kuiper Belt Object Orbiter to explore what a vehicle would look like to orbit these deep space objects.

Kuiper belt Object↗
NASA NTRSDate not supplied

Initial Characterization of the 30 kW Miniature Arc Jet (mARC II) at NASA Ames Research Center

The second-generation Miniature Arc jet Research Chamber (mARC II) at NASA Ames is undergoing integrated systems testing. Once fully operational, this facility will be added to the range of available test facilities operated by the NASA Ames Thermophysics Facilities Branch, with primary focus on applications such as new arc jet flow diagnostics and new arc column diagnostics. Initial characterization of the mARC II is reported here, specifically, measured arc current, arc voltage, column and chamber pressures, mass flow rates, and initial emission measurements carried out at a range of conditions.

arc jet↗
NASA NTRSDate not supplied

12.5kW Advanced Electric Propulsion System Thruster Development Testing

Since 2012, NASA has been developing the12.5kW Hall Effect Rocket with Magnetic Shielding (HERMeS)thruster to serve the need for deep space propulsion. Aerojet Rocketdyne (AR)is developing the HERMeS Hall Current Thruster (HCT)into a flight capable design through the Advanced Electric Propulsion System (AEPS) program. In execution of this program, Aerojet Rocketdyne has designed, built and begun test of two Engineering Test Unit (ETU)HCTs, designated ETU-1 and ETU-2. This paper presents some of the preliminary results from theETU-1 thruster and draws comparisons to previous HERMeS Technology Demonstration Units (TDUs)and theETU-2 characterization unit. The ETU-1 thruster serves to evaluate the ETU design against dynamic and thermal environments while ETU-2 undergoes operational characterization and wear testing. The thruster has been exposed to acceptance and qualification-level vibration and shock testing and has undergone acceptance and characterization hot-firing to evaluate thruster performance after exposure to dynamic environments. The results have demonstrated that the dynamic environments have not had an adverse effect on performance and demonstrated that stability and operating characteristics remain unaffected. Together, ETU-1 and ETU-2 HCTs have demonstrated operating performance and characteristics in-family with each other and with the NASA HERMeS Technology Demonstration Units.

AEPS↗
NASA NTRS2018

Investigations of Pole Erosion Mechanisms in the 12.5 kW HERMeS Hall Thruster Using Numerical Simulations and Ion Velocity Measurements

When the Hall Effect Rocket with Magnetic Shielding (HERMeS) was tested at the NASA GRC’s VF-5 the erosion rate on the pole covers was found to be at least a factor of two higher at 300 V and 20.8 A than at other operating conditions in the 400 V to 600 V range. Simulations using our hydrodynamics code Hall2De do not predict increased erosion rates at 300 V but accurately compute erosion rates similar to the measurements at the other operating conditions. We investigate the source of the discrepancy between measurements and simulations at 300 V using a combination of numerical simulations and experimental measurements of the ion velocity fields in the acceleration region of the thruster. By examining previous simulations that predicted the measured erosion rates for other thrusters and operating conditions, we determine that sputtering of the pole surfaces by high energy ions is the most likely mechanism behind the erosion rates at 300 V. High energy ions sputter the pole surfaces when the acceleration region of the thruster is downstream of the pole surface plane. When the latter occurs, the curvature of the plasma potential contours at the edges of the channel accelerates a small fraction of the high energy ions radially. We find that neither our Hall2De simulations nor the experimental measurements produce ions of sufficiently high energy and flux to the inner pole cover to explain the measured erosion there. Only at the outer edge of the cover is where we find the ions needed to yield simulation results that are comparable to the erosion measurements. We argue that one possible mechanism for the higher erosion is high energy ions that graze the channel corner of the pole and become trapped in a sheath that develops downstream. Within the sheath, we find that the electric field is large enough to turn the ions towards the surface of the pole. A simplified calculation shows that the erosion rates produced by sputtering of trapped ions are similar to the measurements. We also propose that the presence of local oscillations and high-energy cathode ions may be sources of the enhanced erosion We conclude this article by proposing a combination of analysis, simulation, and experimental measurements that can be used to address the validity of these hypotheses.

Mikellides, Ioannis G.↗
NASA NTRSDate not supplied

Optimization, Design, and Demonstration of 1 kW Stirling Controller Using Capacitor-based Power Factor Correction

Free-piston Stirling convertors provide efficient, reliable thermal to electric power conversion, provided they are paired with a reliable controller. This paper outlines work underway on design concepts for kilowatt-class controllers. Using passive power factor correction (PFC) this design explores the possibility of reducing programmatic risk through system simplification. Efficiency is maximized through incorporating wide-bandgap gallium nitride (GaN) switches, and passive PFC volume is minimized through the use of polymer multi-layer capacitors. This work is aimed at exploring new approaches for future Stirling controllers.

Christopher Barth↗
NASA NTRS2020

Anomalous Ion Heating and Pole Erosion in the 12.5-kW Hall Effect Rocket with Magnetic Shielding (HERMeS)

Wear measurements of the inner pole cover in HERMeS have shown as much as ten times higher erosion rates than past numerical simulations predicted. Also, measurements of ion velocity distribution functions (IVDF) suggest that ion heating occurs near the chamfered regions of the acceleration channel and around the inner pole surface. In our companion paper we present theoretical evidence that the plasma conditions in this region can excite instabilities in the lower hybrid frequency. Here, we provide further evidence of their presence through comparisons between numerical simulations and measurements. After including in the 2-D axisymmetric hydrodynamic-PIC code Hall2De an idealized model of the ion temperature based on a scaling with the lower hybrid frequency, we find the agreement between the computed and measured IVDF is significantly improved. In addition, the computed erosion rates at the inner pole surface are now in close agreement with wear test measurements.

Frieman, Jason↗
DOE OSTI2020

Analysis and Validation of Spectral Irradiance Simulations for 75 kW Bifacial Solar Test Field

This work investigates how the spectrum of irradiance incident on the rear of bifacial modules impacts their performance. Light incident on the rear of bifacial modules can be reflected from the ground, mounting structures, and other nearby objects, causing both the intensity and spectrum to be modified. As a result, PV cells and sensors with different spectral responses report different values for the rear irradiance, leading to increased uncertainty when modeling performance. Here, we calculate the spectral irradiance incident on the rear of modules through raytrace simulations and validate with measured field data collected from a 75kW single-axis-tracked bifacial test site. Spectral responses for different sensors and PV cells are applied and compared with field measurements for four days. Based on these results, a method for improving non-spectral simulations is proposed. In addition, a linear regression is applied to the modeled spectral results as a method to gain insight into the contributions of ground reflected light to total rear irradiance.

bifacial photovoltaics↗