Mr. Randy J. Hedgeland Profile

Randy J. Hedgeland

Engineer at NASA Goddard Space Flight Ctr

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Publications (6)

Proceedings Article | 7 September 2006 Paper

Contamination control of space-based laser instruments

Philip Chen, Randy Hedgeland, Larry Ramsey, Rachel Rivera, Karrie Houston

Proceedings Volume 6291, 629104 (2006) https://doi.org/10.1117/12.681175

KEYWORDS: Contamination, Contamination control, Laser applications, Laser induced damage, Space based lasers, LIDAR, Space operations, Pulsed laser operation, Laser development, Semiconductor lasers

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Proceedings Article | 19 October 1994 Paper

Maintaining a Class M 5.5 environment in a Class M 6.5 cleanroom

David Hughes, Randy Hedgeland, Wayne Geer, Barry Greenberg

Proceedings Volume 2261, (1994) https://doi.org/10.1117/12.190157

KEYWORDS: Particles, Contamination, Silicon, Inspection, Contamination control, Space telescopes, Carbon, Video, Roads, Hubble Space Telescope

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Proceedings Article | 19 October 1994 Paper

Results of STS-51 orbiter crew compartment contamination generation and extravehicular activity (EVA) payload bay transfer experiment

Patricia Hansen, Randy Hedgeland, Carl Maag, Calvin Seaman

Proceedings Volume 2261, (1994) https://doi.org/10.1117/12.190131

KEYWORDS: Contamination, Particles, Hubble Space Telescope, Optical components, Silicon, Photometry, Observatories, Polishing, Adhesives, Statistical analysis

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Proceedings Article | 19 October 1994 Paper

Integrated approach for contamination control and verification for the Hubble Space Telescope first servicing mission

Randy Hedgeland, Patricia Hansen, David Hughes

Proceedings Volume 2261, (1994) https://doi.org/10.1117/12.190141

KEYWORDS: Contamination, Silicon, Particles, Mirrors, Contamination control, Hubble Space Telescope, Ultraviolet radiation, Charge-coupled devices, Space telescopes, Space operations

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Proceedings Article | 19 October 1994 Paper

Protective bag design for the Hubble Space Telescope servicing mission carriers

Randy Hedgeland, Barry Greenberg, Wayne Geer, Joe Hammerbacher, Leon Bailey, John DiBartolo, Don Gabbert

Proceedings Volume 2261, (1994) https://doi.org/10.1117/12.190152

KEYWORDS: Contamination, Particles, Hubble Space Telescope, Space operations, Silicon, Mirrors, Optical instrument design, Safety, Standards development, Inspection

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Proceedings Article | 1 November 1990 Paper

Surface accommodation of molecular contaminants

Philip Chen, Randy Hedgeland, Shaun Thomson

Proceedings Volume 1329, (1990) https://doi.org/10.1117/12.22614

KEYWORDS: Molecules, Contamination, Temperature metrology, Contamination control, Space operations, Receivers, Solids, Adsorption, Data centers, Control systems

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The transport of molecules, under vacuum conditions, from a source surface to a receiving surface is of major concern from the perspective of spacecraft contamination control. The transport phenomena involved is a complex mechanism comprising the physical characteristics of each surface, the properties of contaminant species participating, and the temperatures of both surfaces. Because of both the complex nature and the limited data available to describe such a phenomena, contamination modeling usually requires that a highly simplified engineering approach be undertaken. One area where this is particularly true is in the representation of the surface accommodation of incident molecules. When a molecule in the gas phase collides with the surface of a receiver it can either "stick" to that surface or be scattered away. Molecules accommodated by this surface become thermally equilibrated to the receiver temperature while the material that is not accommodated retains its original energy and undergoes specular reflection. The ratio of this thermally accommodated mass to the total incident mass is known as the "accommodation" or "sticking" coefficient. Most of the current theory and experimental work performed to date has been restricted to the accommodation coefficients of the rare gases in contact with metal surfaces3'10"1. UnfortUnately, the results generated by these studies cannot be made very useful to spacecraft contamination engineers who are predominantly interested in environments where contaminants are typically limited only to water and long-chain hydrocarbons. Because of this deficiency most current spacecraft contamination analyses are forced to rely on general mathematical expressions that consider the sticking coefficient to be only a direct function of the temperature gradient between the emitting and receiving surfaces. The major shortcoming of the simplified method presently in use is that it may provide an inadequate representation of the actual molecular transport occurring between surfaces. The purpose of this paper is, therefore, to study the nature of the transport mechanisms involved in the adsorption of high molecular weight gases on typical spacecraft surfaces, the overall concept of the sticking coefficient, and the quantitative and qualitative theory involved. In addition, this paper will examine some of the existing molecular accommodation data as it relates to spacecraft applications, as well as present new experimental data gathered by the Contamination Control Section of the Goddard Space Flight Center (GSFC). All this information will then be correlated and used to verify the accuracy of the most common sticking coefficient equations in use by contamination analyses.

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