Structural Analysis of Pyrolytic Graphite Optics for the HiPEP Ion Thruster

The long lifetime requirements of interplanetary exploration missions is driving the need to develop long-life components for the electric propulsion thrusters that are being targeted for these missions. One of the primary life-limiting components of ion thrusters are the optics, which are continuously eroded during the operation of the thruster. Pyrolytic graphite optics are being considered for the High Power Electric Propulsion (HiPEP) ion thruster because of their very high resistance to erosion. This paper describes the structural analysis of the HiPEP pyrolytic graphite. A description of the development of the grid model, as well as the development of the effective properties and stress concentrations in the apertured area of the grids is included. An evaluation of the use of curved grids shows that the increased stiffness (compared to flat grids) prevents intergrid impact during launch, however, the residual stresses introduced by curving the grids pushes the resulting peak stresses beyond the critical stress. As a result, flat grids are recommended as the design solution. Thermally induced grid displacements during normal thruster operation are also presented

A Performance Comparison of Pulsed Plasma Thruster Electrode Configurations

Pulsed plasma thrusters are currently planned on two small satellite missions and proposed for a third. In these missions, the pulsed plasma thruster's unique characteristics will be used variously to provide propulsive attitude control, orbit raising, translation, and precision positioning. Pulsed plasma thrusters are attractive for small satellite applications because they are essentially stand alone devices which eliminate the need for toxic and/or distributed propellant systems. Pulsed plasma thrusters also operate at low power and over a wide power range without loss of performance. As part of the technical development required for the noted missions, an experimental program to optimize performance with respect to electrode configuration was undertaken. One of the planned missions will use pulsed plasma thrusters for orbit raising requiring relatively high thrust and previously tested configurations did not provide this. Also, higher capacitor energies were tested than previously tried for this mission. Multiple configurations were tested and a final configuration was selected for flight hardware development. This paper describes the results of the electrode optimization in detail

Pulsed Plasma Thruster Technology for Small Satellite Missions

Pulsed plasma thrusters (PPT's) offer the combined benefits of extremely low average electric power requirements (1 to 150 W), high specific impulse (approximately 1000 s), and system simplicity derived from the use of an inert solid propellant. Potential applications range from orbit insertion and maintenance of small satellites to attitude control for large geostationary communications satellites. While PPT's have been used operationally on several spacecraft, there has been no new PPT technology development since the early 1970's. As result of the rapid growth in the small satellite community and the broad range of PPT applications, NASA has initiated a development program with the objective of dramatically reducing the PPT dry mass, increasing PPT performance, and demonstrating a flight ready system by October 1997. This paper presents the results of a series of near-Earth mission studies including both primary and auxiliary propulsion and attitude control functions and reviews the status of NASA's on-going development program

Fluid Flow Programming in Paper-Derived Silica–Polymer Hybrids

In paper-based devices, capillary fluid flow is based on length-scale selective functional control within a hierarchical porous system. The fluid flow can be tuned by altering the paper preparation process, which controls parameters such as the paper grammage. Interestingly, the fiber morphology and nanoporosity are often neglected. In this work, porous voids are incorporated into paper by the combination of dense or mesoporous ceramic silica coatings with hierarchically porous cotton linter paper. Varying the silica coating leads to significant changes in the fluid flow characteristics, up to the complete water exclusion without any further fiber surface hydrophobization, providing new approaches to control fluid flow. Additionally, functionalization with redox-responsive polymers leads to reversible, dynamic gating of fluid flow in these hybrid paper materials, demonstrating the potential of length scale specific, dynamic, and external transport control

Use of ED-Tethers for Orbit Maintenance and Deorbit - NASA GLAST Mission

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77325/1/AIAA-2002-4044-386.pd

Pulsed Plasma Thruster Technology for Small Satellite Missions

Pulsed plasma thrusters (PPTs) offer the combined benefits of extremely low average electric power requirements (1 to 150 W), high specific impulse (~ 1000 s), and system simplicity derived from the use of an inert solid propellant. Potential applications range from orbit insertion and maintenance of small satellites to attitude control for large geostationary communications satellites. While PPTs have been used operationally on several spacecraft, there has been no new PPT technology development since the early 1970\u27s. As a result of the rapid growth in the small satellite community and the broad range of PPT applications, NASA has initiated a development program with the objective of dramatically reducing the PPT dry mass, increasing PPT performance, and demonstrating a flight ready system by October 1997. This paper presents the results of a series of near-Earth mission studies including both primary and auxiliary propulsion and attitude control functions and reviews the status of NASA\u27s on-going development program

Janus‐Type Hybrid Paper Membranes

Functional paper-based materials and devices have been increasingly attractive to scientists in the recent past. In particular, the possibility to functionalize the surface of paper fibers with tailor-made coatings has broadened a possible scope of emerging application considerably. This work introduces novel functional paper membranes with adjustable gradient and Janus-type wettability based on gradient and Janus-type silica coating distribution along the paper cross-section. Correlation of CLSM (distribution), thermogravimetric analysis (silica amount), and Kr-BET (surface area; BET: Brunauer–Emmett–Teller) reveals an extremely low coating thickness, in the range of just a few nanometers, being sufficient to fully inverse paper wettability from hydrophilic to very hydrophobic excluding water. This asymmetric wettability, originating from an asymmetric silica distribution along the paper cross-section, is established by synchronizing silane hydrolysis and condensation reaction rates with silane transport rates in paper within a simple and scalable one-step drying process after having immersed a paper sheet into a tetraethoxysilane-containing precursor solution. As silica by itself, like paper, is a hydrophilic material, the observed hydrophobicity is related to a reduction in cellulose fiber nanoscale porosity controlling water imbibition. While being relevant in manifold applications, these ultrathin, Janus-type hybrid paper membranes are demonstrated to show directed gating and selective oil–water separation

Development of a PPT for the EO-1 Spacecraft

A Pulsed Plasma Thruster (PPT) has been developed for use in a technology demonstration flight experiment on the Earth Observing 1 (EO-1) New Millennium Program mission. The thruster replaces the spacecraft pitch axis momentum wheel for control and momentum management during an experiment of a minimum three-day duration. The EO-1 PPT configuration is a combination of new technology and design heritage from similar systems flown in the 1970's and 1980's. Acceptance testing of the protoflight unit has validated readiness for flight, and integration with the spacecraft, including initial combined testing, has been completed. The thruster provides a range of capability from 90 microN-sec impulse bit at 650 sec specific impulse for 12 W input power, through 860 microN-sec impulse bit at 1400 see specific impulse for 70 W input power. Development of this thruster reinitiates technology research and development and re-establishes an industry base for production of flight hardware. This paper reviews the EO-1 PPT development, including technology selection, design and fabrication, acceptance testing, and initial spacecraft integration and test