Roger C. Linton

Earth albedo studies using Pegasus thermal data.

Earth albedo calculation using Pegasus 1 thermal data, discussing Rayleigh scattering, spacecraft position, atmospheric reflection effects, etc

Solar absorptance measurements in space on operational spacecraft

Spacecraft hardware such as radiators requires the maintenance of solar absorptance within tight bounds for their design life. Such hardware is sized in part based on the beginning- and end-of-life absorptance. It has been difficult to make accurate end-of-life determinations based on either ground based data or flight data. The synergistic effect of atomic oxygen, ultraviolet radiation, and contamination has made it difficult to duplicate space exposures in the laboratory. The absorptance of flight exposed samples brought back to earth are not representative of the conditions in space because of changes brought about by exposure to air. This paper proposes to augment the current in-space monitoring techniques with periodic, in- space, direct measurements of the solar absorptance on operational hardware. NASA funded AZ Technology to develop a portable, space-rated device similar to the LPSR-200 portable spectroreflectometer, a space portable spectroreflectometer (SPSR). This instrument is robotically compatible and can be run using spacecraft power or batteries. The instrument also has measurement storage capacity for later retrieval and evaluation. Although extensive development work has already been completed, authorization to build a unit for a flight experiment has not been received. The Russians have expressed an interest in having absorptance measurements made on their MIR I Space Station as part of the NASA/MIR flight experiments. Proposals are currently being made to obtain authorization for the construction and use of SPSR on NASA/MIR flight experiments, to help mitigate potential problems for the International Space Station Alpha (ISSA).

In Situ Measurements of Scattering from Contaminated Optics in the Vacuum Ultraviolet

NASAs In Situ Contamination Effects Facility has been used to measure the time dependence of the angular reflectance from molecularly contaminated optical surfaces in the vacuum ultraviolet. The light scattering measurements are accomplished in situ on optical surfaces in real time during deposition of molecular contaminants. The measurements are taken using noncoherent VUV sources with the predominant wavelengths being the krypton resonance lines at 1236 and 1600 angstroms. Detection of the scattered light is accomplished using a set of three solar blind VUV photomultipliers. An in-plane VUV BRDF (bidirectional reflectance distribution function) experiment is described and details of the on-going program to characterize optical materials exposed to the space environment is reported.

Vacuum-ultraviolet optical properties of single-crystal InBi

The optical constants (n, k) of single crystalline InBi have been determined using a two-angle method applying Fresnel’s equations. The complex dielectric constant was then calculated using the relation ∊* = ∊1 − i∊2, where ∊1 = n2 − k2 and ∊2 = 2nk. Assuming a free-electron model, the volume plasma resonance energy was found from the crossover position of the n and k curves to be 10.3 eV. The energy loss functions − Im[1/∊] and − Im[1/(∊ + 1)], which have been interpreted as having maxima at the volume and surface plasma frequencies, respectively, when interband transitions are not significant, were plotted using the n and k data. These values were in general agreement with those obtained from the crossover point on the n and k curves and from the Ritchie relation Es=Ev/2.