Ultraviolet radiation effects

Solar ultraviolet testing was not developed which will provide highly accelerated (20 to 50X) exposures that correlate to flight test data. Additional studies are required to develop an exposure methodology which will assure that accelerated testing can be used for qualification of materials and coatings for long duration space flight. Some conclusions are listed: Solar UV radiation is present in all orbital environments; Solar UV does not change in flux with orbital altitude; UV radiation can degrade most coatings and polymeric films; Laboratory UV simulation methodology is needed for accelerated testing to 20 UV solar constants; Simulation of extreme UV (below 200 nm) is needed to evaluate requirements for EUV in solar simulation

Working group written presentation: Solar radiation

The members of the Solar Radiation Working Group arrived at two major solar radiation technology needs: (1) generation of a long term flight data base; and (2) development of a standardized UV testing methodology. The flight data base should include 1 to 5 year exposure of optical filters, windows, thermal control coatings, hardened coatings, polymeric films, and structural composites. The UV flux and wavelength distribution, as well as particulate radiation flux and energy, should be measured during this flight exposure. A standard testing methodology is needed to establish techniques for highly accelerated UV exposure which will correlate well with flight test data. Currently, UV can only be accelerated to about 3 solar constants and can correlate well with flight exposure data. With space missions to 30 years, acceleration rates of 30 to 100X are needed for efficient laboratory testing

Solar radiation

The effects of solar radiation in aerospace environments on aerospace systems are examined. It was concluded that most materials degrade to solar radiation. The information available on short term effects on materials provides a limited data base. Flight data on coating degradation seems to be confused by contamination. Other conclusions of data examination are listed

An analysis of LDEF-exposed silvered FEP teflon thermal blanket material

The characterization of selected silvered fluorinated ethylene propylene (FEP) teflon thermal blanket material which received 5 years and 9 months of exposure to the LEO environment on the Long Duration Exposure Facility is reported. X-ray photoelectron spectroscopy, infrared, and thermal analyses did not detect a significant change at the molecular level as the result of this exposure. However, various microscopic analyses revealed a roughening of the coating surface due to atomic oxygen erosion which resulted in some materials changing from specular reflectors of visible radiation to diffuse reflectors. The potential effect of silicon-containing molecular contamination on these materials is addressed

A Method for Measuring the Spectral Normal Emittance in Air of A Variety of Materials Having Stable Emittance Characteristics

A method and apparatus is described for the measurement of spectral normal emittance in air of a variety of materials. The system permits measurements to be performed over a wavelength region of 1.0 through 15.0 microns and over a temperature range of 600F to 1,8000F with an accuracy of 5.0 percent. The advantages of this system are described. Results obtained by this system are compared with results reported by another observer using a different technique

LDEF thermal control coatings post-flight analysis

The NASA Long Duration Exposure Facility (LDEF) provided a unique flight opportunity for conducting experiments in space and return of these experiments to Earth for laboratory evaluation. The results of one of these experiments, S0010, Exposure of Spacecraft Coatings, in which selected spacecraft thermal control coatings were exposed to the low-Earth orbital (LEO) environment on LDEF are reported. The objective of the experiment is to evaluate the response of thermal control coatings to LEO exposure, which includes atomic oxygen, ultraviolet and particulate radiation, meteoroid and debris, vacuum, and temperature cycling

Spacecraft materials and coatings experiments

The 5.8-year exposure data from the Long Duration Experiment Facility (LDEF) has demonstrated the benefits of long-term exposure in low Earth orbit (LEO) for understanding the behavior of spacecraft materials and coatings for use in extended space missions. The Space Station Freedom represents the next large area spacecraft available in NASA planned missions for obtaining this long term space exposure data. The advantages of using the Space Station Freedom for these studies are presented. Discrepancies between short-term flight exposure result from Shuttle Orbiter experiments and the long-term LDEF results are shown. The major objectives and benefits of conducting materials and coatings experiments on Space Station Freedom are emphasized

LDEF polymeric materials: 10 months versus 5.8 years of exposure

The chemical characterization of several polymeric materials which received 10 months of exposure and 5.8 years of exposure on a Row 9 Long Duration Exposure Facility (LDEF) experiment (A0134) is reported. Specimens include fluorinated ethylene propylene (FEP) teflon film, polysulfone film, and graphite fiber reinforced epoxy amd polysulfone matrix composites. The responses of these materials to the two LEO exposures are compared. The results of infrared, thermal, x-ray photoelectron, and scanning electron microscope analyses are reported. Solution property measurements of various molecular weight parameters are presented for the thermoplastic polysulfone materials. Molecular level effects attributable to exposure that were present in 10-month exposed specimens were not found in 5.8-year exposed specimens. This result suggests that increased atomic oxygen fluence toward the end of the LDEF mission may have eroded away selected environmentally induced changes in surface chemistry for 5.8-year exposure specimens

A Materials Exposure Facility

The objective of the Materials Exposure Facility (MEF) is to provide a test bed in space for conducting long-term (greater than one year) materials experiments which require exposure to the low Earth orbit (LEO) space environment. The proposed MEF is planned to be an integral part of the agency's Space Environments and Effects Research Program. The facility will provide experiment trays similar to the Long Duration Exposure Facility (LDEF). Each tray location is planned to have a power and data interface and robotic installation and removal provisions. Space environmental monitoring for each side of the MEF will also be provided. Since routine access to MEF for specimen retrieval is extremely important to the materials research, Space Station Freedom has been chosen as the preferred MEF carrier

Evaluation of thermal control coatings for use on solar dynamic radiators in low Earth orbit

Thermal control coatings with high thermal emittance and low solar absorptance are needed for Space Station Freedom (SSF) solar dynamic power module radiator (SDR) surfaces for efficient heat rejection. Additionally, these coatings must be durable to low earth orbital (LEO) environmental effects of atomic oxygen, ultraviolet radiation and deep thermal cycles which occur as a result of start-up and shut-down of the solar dynamic power system. Eleven candidate coatings were characterized for their solar absorptance and emittance before and after exposure to ultraviolet (UV) radiation (200 to 400 nm), vacuum UV (VUV) radiation (100 to 200 nm) and atomic oxygen. Results indicated that the most durable and best performing coatings were white paint thermal control coatings Z-93, zinc oxide pigment in potassium silicate binder, and YB-71, zinc orthotitanate pigment in potassium silicate binder. Optical micrographs of these materials exposed to the individual environmental effects of atomic oxygen and vacuum thermal cycling showed that no surface cracking occurred