Engineering topics

Bellows, A. H.

Publications and source records attributed to Bellows, A. H..

6 records

NASA NTRS1992

A versatile get away special furnace for materials processing in space

A furnace suitable for performing a variety of high-temperature materials science experiments, including crystal growth in the microgravity of Shuttle orbit, has been developed by GTE Laboratories under the sponsorship of NASA Lewis Research Center. It has been designed for use in NASA's Get Away Special (GAS), small self-contained payload program. A prototype has been designed, built, installed in a simulated GAS container, purged with argon, and used for a series of characterization tests. Also, it was outfitted twice with high-temperature GaAs crystal growth charges and used to successfully grow both. Two different GAS payload configurations have been outlined; one is entirely self-contained and includes one furnace; the other requires external power but incorporates 3 furnaces and their control systems.

Bellows, A. H.↗

NASA NTRS1990

Interface demarcation in GaAs by current pulsing

GTE Laboratories is currently conducting a program to investigate the effect of convection in the melt on the properties of bulk grown gallium arsenide (GaAs). In addition to extensive ground based experimentation, a Get Away Special growth system has been developed to grow two GaAs crystals aboard the Space Shuttle, each with a one inch diameter. In order to perform a complete segregation analysis of the crystals grown in space, it is necessary to measure the interface shape and growth rate as well as the spatial distribution of the selenium dopant. The techniques for interface demarcation in selenium doped GaAs by current pulsing have been developed at GTE Laboratories and successful interface demarcation has been achieved for current pulses ranging from 20 to 90 amps, in both single crystal and polycrystalline regions.

Matthiesen, D. H.↗

NASA NTRS1990

Free float acceleration measurements aboard NASA's KC-135 Microgravity Research Aircraft

A three-axis accelerometer subsystem, developed as part of a get-away-special Ga-As crystal growth system for the Space Shuttle, is described. Each axis of this subsystem contains a quartz flexure accelerometer capable of dc measurements, custom-designed measurement circuitry, a programmable microcomputer for measurement control and data reduction, and memory for recording data. The subsystem was flown as a free float experiment aboard the NASA KC-135 microgravity research aircraft, yielding measurements of accelerations during free float at a resolution of 10 micro-g.

Bellows, A. H.↗

NASA NTRS1988

A comparative study of the influence of buoyancy driven fluid flow on GaAs crystal growth

A systematic investigation of the effect of gravity driven fluid flow on GaAs crystal growth was performed. It includes GaAs crystal growth in the microgravity environment aboard the Space Shuttle. The program involves a controlled comparative study of crystal growth under a variety of earth based conditions with variable orientation and applied magnetic field in addition to the microgravity growth. Earth based growth will be performed under stabilizing as well as destabilizing temperature gradients. The boules grown in space and on earth will be fully characterized to correlate the degree of convection with the distribution of impurities. Both macro- and micro-segregation will be determined. The space growth experiment will be flown in a self-contained payload container through NASA's Get Away Special program.

Kafalas, J. A.↗

NASA NTRS1987

A comparative study of the influence of buoyancy driven fluid flow on GaAs crystal growth

An experiment on the effect of gravity-driven fluid flow on GaAs crystal growth under a variety of Earth-based conditions and in microgravity aboard the space shuttle is described. Earth-based growth is performed under stabilizing and destabilizing temperature gradients, with and without applied magnetic fields. The space growth experiment is flown in a self-contained payload container through NASA's Get Away Special program. The scope of the experiment and the experimental apparatus are outlined. Results of the Earth-based portions of the experiment are presented.

Kafales, J. A.↗

NASA NTRS1984

Arc discharge convection studies: A Space Shuttle experiment

Three mercury vapor arc lamps were tested in the microgravity environment of one of NASA's small, self-contained payloads during STS-41B. A description of the payload structural design, photographic and optical systems, and electrical system is provided. Thermal control within the payload is discussed. Examination of digital film data indicates that the 175 watt arc lamp has a significant increase in light output when convection is removed in the gravity-free environment of space.

Bellows, A. H.↗