Engineering topics

He, Charles C.

Publications and source records attributed to He, Charles C..

4 records

NASA NTRS2010

Micrometeoroid Impacts and Optical Surface Scatter in Space Environment

This presentation will discuss the results of an attempt to use laboratory test data and empirically derived models to quantify the degree of surface damage and associated light scattering that might be expected from hypervelocity particle impacts in space environment. Micrometeoroid sizes are predicted to be predominantly in the mass range 10(exp -5) g or less, with most having diameters near 1 micrometer, but some larger than 120 micrometers, with velocities near 20 km/s. In a laboratory test, latex (p = 1.1 g/cu cm) and iron (7.9 g/cu cm) particles with sizes ranging from 0.75 micrometer to 1.60 micrometer and with velocities ranging from 2.0 km/s to 18.5 km/s, were shot at a dielectric coated gold mirror. Scanning electron and atomic force microscopy were used to measure crater dimensions that were then associated with particle impact energies. These data were then fitted to empirical models derived from solar cell and other spacecraft surface components returned from orbit, as well as studies of impact craters studied on glassy materials returned from the lunar surface, to establish a link between particle energy and impact crater dimension. Published estimates of the Martian and Saturnian meteoroid environments were used as the sources of particle flux estimates. From these data, an estimate of total expected damaged area was computed and this result produced an estimate of expected surface scatter from the modeled environment.

Heaney, James B.↗

NASA NTRS2010

Micrometeoroid Impacts and Optical Scatter in Space Environment

This paper discusses the results of an attempt to use laboratory test data and empirically derived models to quantify the degree of surface damage and associated light scattering that might be expected from hypervelocity particle impacts in space environment. Published descriptions of the interplanetary dust environment were used as the sources of particle mass, size, and velocity estimates. Micrometeoroid sizes are predicted to be predominantly in the mass range 10(exp -5) g or less, with most having diameters near 1 micrometer, but some larger than I20 micrometers, with velocities near 20 kilometers per second. In a laboratory test, latex ( p = 1.1. grams per cubic centimeter) and iron (7.9 grams per cubic centimeter) particles with diameters ranging from 0.75 micrometers to 1.60 micrometers and with velocities ranging from 2.0 kilometers per second to 18.5 kilometers per second, were shot at a Be substrate mirror that had a dielectric coated gold reflecting surface. Scanning electron and atomic force microscopy were used to measure crater dimensions that were then associated with particle impact energies. These data were then fitted to empirical models derived from solar cell and other spacecraft surface components returned from orbit, as well as studies of impact craters studied on glassy materials returned from the lunar surface, to establish a link between particle energy and impact crater dimension. From these data, an estimate of total expected damaged area was computed and this result produced an estimate of expected surface scatter from the modeled environment.

Heaney, James B.↗

NASA NTRS2002

Physical and Thermal Properties Evaluated of Teflon FEP Retrieved From the Hubble Space Telescope During Three Servicing Missions

Mechanical properties of aluminized Teflon fluorinated ethylene propylene (FEP) thermal control materials on the Hubble Space Telescope (HST) exposed to low Earth orbit for up to 9.7 years have significantly degraded, with extensive cracking occurring on orbit. The NASA Glenn Research Center and the NASA Goddard Space Flight Center have collaborated on analyzing the physical and thermal properties of aluminized FEP (FEP-Al, DuPont) materials retrieved in December 1999 during HST's third servicing mission (SM3A). Comparisons have been made to properties of FEP-Al retrieved during the first and second HST servicing missions, SM1 and SM2, in order to determine degradation processes for FEP on HST.

Dever, Joyce A.↗

NASA NTRS1995

Preventing Cracking of Anodized Coatings

Anodized coatings have been used as optical and thermal surfaces in spacecraft. Particulate contamination from cracked coatings is a concern for many applications. The major cause for the cracking is the difference in the coefficient of thermal expansion between the oxide coatings and the aluminum substrate. The loss of water when the coating is exposed to a vacuum also could induce cracking of the coating. Hot-water sealing was identified as the major cause for the cracking of the coatings because of the large temperature change when the parts were immersed in boiling water and the water was absorbed in the coating. when the hot-water sealing process was eliminated, the cracking resistance of the anodized coatings was greatly improved. Also, it was found that dyed black coatings were more susceptible than clear coatings to cracking during thermo-vacuum cyclings.

He, Charles C.↗