Enhanced plasma current collection from weakly conducting solar array blankets

Among the solar cell technologies to be tested in space as part of the Solar Array Module Plasma Interactions Experiment (SAMPIE) will be the Advanced Photovoltaic Solar Array (APSA). Several prototype twelve cell coupons were built for NASA using different blanket materials and mounting techniques. The first conforms to the baseline design for APSA which calls for the cells to be mounted on a carbon loaded Kapton blanket to control charging in GEO. When deployed, this design has a flexible blanket supported around the edges. A second coupon was built with the cells mounted on Kapton-H, which was in turn cemented to a solid aluminum substrate. A final coupon was identical to the latter but used germanium coated Kapton to control atomic oxygen attack in LEO. Ground testing of these coupons in a plasma chamber showed considerable differences in plasma current collection. The Kapton-H coupon demonstrated current collection consistent with exposed interconnects and some degree of cell snapover. The other two coupons experienced anomalously large collection currents. This behavior is believed to be a consequence of enhanced plasma sheaths supported by the weakly conducting carbon and germanium used in these coupons. The results reported here are the first experimental evidence that the use of such materials can result in power losses to high voltage space power systems

The Solar Array Module Plasma Interactions Experiment (SAMPIE): A shuttle-based plasma interaction experiment

The SAMPIE flight experiment, tentatively scheduled to fly on a shuttle mission in mid 1992, will investigate plasma interactions of high voltage space power systems. Solar cells representing a number of technologies will be biased to high voltage to study both negative potential arching and positive potential current collection characteristics. Additionally, several idealized metal/insulator mockups will be flown to study the basic nature of these interactions. Described here is the basic rationale for a space experiment as well as the measurements to be made and the significance of the expected results. The current design status of the flight hardware is presented

The Solar Array Module Plasma Interactions Experiment (SAMPIE): Science and technology objectives

The Solar Array Module Plasma Interactions Experiment (SAMPIE) is an approved NASA Space Shuttle space flight experiment to be launched in Jul. 1993. The SAMPIE experiment is designed to investigate the interaction of high voltage space power systems with ionospheric plasma. To study the behavior of solar cells, a number of cell coupons, representing technologies of current interest, will be biased to high voltages to characterize both negative potential arcing and positive potential current collection. Additionally, various theories of arc suppression will be tested by including several specially modified cell coupons. Finally, SAMPIE will include experiments to study the basic nature of these interactions. The rationale for a space flight experiment, the measurements to be made, the significance of the expected results, and the current design status of the flight hardware are described

Acceptance testing of the prototype electrometer for the SAMPIE flight experiment

The Solar Array Module Plasma Interaction Experiment (SAMPIE) has two key instruments at the heart of its data acquisition capability. One of these, the electrometer, is designed to measure both ion and electron current from most of the samples included in the experiment. The accuracy requirement, specified by the project's Principal Investigator, is for agreement within 10 percent with a calibrated laboratory instrument. Plasma chamber testing was performed to assess the capabilities of the prototype design. Agreement was determined to be within 2 percent for electron collection and within 3 percent for ion collection

Plasma current collection of Z-93 thermal control paint as measured in the Lewis Research Center's plasma interaction facility

A sample of Z-93 thermal control paint was exposed to a simulated space environment in a plasma chamber. The sample was biased through a series of voltages ranging from -100 volts to +300 volts and electron and ion currents were measured. Currents were found to be in the micro-ampere range indicating that the material remains a reasonably good insulator under plasma conditions. As a second step, the sample was left in the chamber for six days and retested. Collected currents were reduced by from two to five times from the previous values indicating a substantial loss of conductivity. As a final test, the sample was removed, exposed to room conditions for two days, and returned to the chamber. Current measurements showed that the sample had partially recovered the lost conductivity. In addition to presenting these results, this report documents all of the experimental data as well as the statistical analyses performed

Plasma chamber testing of APSA coupons for the SAMPIE flight experiment

Among the solar cell technologies to be tested in space as part of the Solar Array Module Plasma Interactions Experiment (SAMPIE) will be the Advanced Photovoltaic Solar Array (APSA). Several prototype twelve cell coupons were built for NASA using different blanket materials and mounting techniques. The first conforms to the baseline design for APSA which calls for the cells to be mounted on a carbon loaded Kapton blanket to control charging in GEO. When deployed, this design has a flexible blanket supported around the edges. A second coupon was built with the cells mounted on Kapton-H, which was in turn cemented to a solid aluminum substrate. A final coupon was identical to the latter but used germanium coated Kapton to control atomic oxygen attack in LEO. Ground testing of these coupons in a plasma chamber showed considerable differences in plasma current collection. The Kapton-H coupon demonstrated current collection consistent with exposed interconnects and some degree of cell snapover. The other two coupons experienced anomalously large collection currents. This behavior is believed to a consequence of enhanced plasma sheaths supported by the weakly conducting carbon and germanium used in these coupons. The results reported here are the first experimental evidence that the use of such materials can result in power losses to high voltage space power systems

Research at the UWC: Understanding the Diversity of Student's Experiences

A pilot study redesigns data collection to reflect increasing diversity in student populations and to improve writing center consultations and campus outreach efforts. The Undergraduate Writing Center (UWC) at The University of Texas at Austin (UT) performs roughly 11,500 writing consultations each year. In addition to providing one-on-one consultations with undergraduate students, a considerable amount of activity happens behind the scenes. For example, project groups are a mainstay of the UWC and are an integral aspect of work we do beyond consulting. Up until now, the Research & Publications Project Group has primarily analyzed data the UWC collects from students’ Intake Forms. The Intake Form asks students to report basic information regarding their course prefix, their instructor’s information, their assignment, their writing process, and their ESL status. While these forms lend valuable information about the classes for which students request to receive help and the types of problems students encounter with their writing, there is a tremendous amount of information we do not collect (and therefore do not know) about the students who walk through our doors.University Writing Cente

Top-down and bottom-up research in biodemography

The most efficient way to make scientific progress in biodemography is to encourage bi-directional exchange between ‘top-down’ and ‘bottom-up’ research. This will entail exchange along the continuum of research from microscopic intracellular processes to population-level consequences. In addition, our understanding of the biology of aging and its demographic consequences will be enriched by mutual influence between studies of mechanistic or ‘proximate’ causal processes and investigations of the evolutionary processes underlying the same phenomena. Researchers working at these different levels of explanation could be more productive if they were informed by research at other levels and interacted with scientists with complementary expertise. Such collaborations could be encouraged both through interdisciplinary workshops, research projects, program projects and training programs.aging, biodemography, evolution, life history

Environmental interactions in Space Exploration: Announcement of the formation of an Environmental Interactions Working Group

With the advent of the Space Exploration Initiative, the possibility of designing and using systems on scales not heretofore attempted presents exciting new challenges in systems design and space science. The environments addressed by the Space Exploration Initiative include the surfaces of the Moon and Mars, as well as the varied plasma and field environments which will be encountered by humans and cargo enroute to these destinations. Systems designers will need to understand environmental interactions and be able to model these mechanisms from the earliest conceptual design stages through design completion. To the end of understanding environmental interactions and establishing robotic precursor mission requirements, an Environmental Interactions Working Group has been established as part of the Robotic Missions Working Group. The current paper describes the working group and gives an update of its current activities. Working group charter and operation are reviewed, background information on the environmental interactions and their characteristics is offered, and the current status of the group's activities is presented along with anticipations for the future

Spacecraft control/flexible structures interaction study

An initial study to begin development of a flight experiment to measure spacecraft control/flexible structure interactions was completed. The approach consisted of developing the equations of motion for a vehicle possessing a flexible solar array, then linearizing about some nominal motion of the craft. A set of solutions is assumed for array deflection using a continuous normal mode method and important parameters are identified. Interrelationships between these parameters, measurement techniques, and input requirements are discussed which assure minimization of special vehicle maneuvers and optimization of data to be obtained during the normal flight sequence. Limited consideration is given to flight data retrieval and processing techniques as correlated with the requirements imposed by the measurement system. Results indicate that inflight measurement of the bending and torsional mode shapes and respective frequencies, and damping ratios, is necessary. Other parameters may be measured from design data