Randy J. Hedgeland

Contamination Effects on the Geostationary Operational Environmental Satellite Instrument Thermal Control System

The instrument thermal control system of the Geostationary Operational Environmental Satellite may have been affected by specie c contamination problems that arose because of the unique conditions and requirements of the spacecraft mission. This paper addresses some specie c contamination effects from the coatings used in the instrument cavities. Contamination control actions that were implemented during ground processing to ensure limited impact on the on-orbit temperature control are described. The selection of thermal coatings is an integral part of the overall spacecraft design. Molecular contamination accretion on thermal coatings may alter the design properties of the surface coatings. In an effort to quantify the molecular contamination effects from material outgassing, an assessment was conducted to address the concerns inside the instrument cavities. The study results prompted an extensive prelaunch vacuum bakeout effort and an on-orbit solar radiation avoidance exercise. In addition, the thermal performance of the instrument radiant coolers could have been detrimentally affected by scattered solar radiation from particulate contamination. To mitigate the impact of the particulate contamination the radiant cooler surfaces were cleaned to an established criteria prior to launch.

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

During Kennedy Space Center processing of the Hubble Space Telescope First Servicing Mission, critical optical components were integrated in a Class 100,000 (M 6.5 at 0.5 micrometers and 5.0 micrometers , per Fed-Std 209E) cleanroom. A Class 10,000 (M 5.5) environment was mandated by the 400B (per Mil-Std 1246B) surface cleanliness requirement of the Scientific Instruments. To maintain a Class M 5.5 environment, a contamination control plan was implemented which addressed personnel constraints, operations, and site management. This plan limited personnel access, imposed strict gowning requirements, and increased cleanroom janitorial operations, prohibited operations known to generate contamination while sensitive hardware was exposed to the environment, and controlled roadwork, insecticide spraying, and similar activities. Facility preparations included a ceiling to floor cleaning, sealing of vents and doors, and revising the garment change room entry patterns. The cleanroom was successfully run below Class 5000 while the instruments were present; certain operations, however, were observed to cause local contamination levels to increase above Class M 5.5.

Cleanliness Correlation By BRDF And PFO Instruments

At NASAs Goddard Space Flight Center (GSFC), Bi-Directional Reflectance Distribution Function (BRDF) is applied to characterize the scattering properties of optical and thermal surfaces. In addition, the Particle Fall Out (PFO) instrument (currently under evaluation) is used to determine the particulate contamination on surfaces. This paper describes both instruments and correlates the results from their empirical measurements. Both the BRDF and PFO instruments are located in a Class 1,000 cleanroom to minimize contamination. The BRDF instrument is completely automated and controlled by a personal computer. The FF0 is a scattering measurement instrument developed by SAAB and updated by Uramec (Bilthoven/The Netherlands) [1]. The PFO is used to determine the surface cleanliness level on a contaminated plate by measuring the scattered light due to particles on the plate. For this paper, black glass is used as the contaminated sample for both the optical measurements. The PFO and BRDF instruments are then utilized to measure the scattering of the contaminated sample. Results are compared and related to the surface cleanliness level as well as obscuration factor.

Optical cavity surface coatings for 1 micron laser missions

The particulate surface cleanliness level on several coatings for aluminum and beryllium substrates were examined for use in the optical cavities of high pulse energy Nd:YAG Q-switched, diode-pumped lasers for space flight applications. Because of the high intensity of the lasers, any contaminants in the laser beam path could damage optical components and limit the instrument mission objectives at the operating wavelength of 1 micron (/spl mu/m). Our goal was to achieve a Mil-Std 1246 level 100 particulate distribution or better to ensure that particulate redistribution during launch would not adversely affect the mission performance objectives. Tapelifts were performed to quantify the amount of particles using in-house developed procedures. The primary coatings included chromate conversion coated aluminum (Al), uncoated (bare) Al, electroless nickel (EN) on Al, gold (Au)/EN on Al, anodized Al, and Au/EN on Beryllium (Be). When considering applications that need to meet launch environments, the results indicate advantages in Au/EN coating applications for the two major substrates, Al and Be.

Contamination effects and resolutions on the GOES thermal control system

The Geostationary Operational Environmental Satellite (GOES) thermal control system could have been affected by specific contamination problems that arose due to the unique conditions and requirements of the specific space mission. This paper addresses some specific contamination effects from the coatings used in the GOES instrument cavity. In addition, the paper describes contamination control actions that were implemented during ground processing to ensure limited impact on the on-orbit temperature control. The selection of thermal coatings is an integral part of the overall spacecraft design. As a result of a higher contamination accretion, properties of the surface coatings may become altered. In an effort to quantify the molecular contamination effects from material outgassing, an assessment was conducted to address the concerns inside the GOES instrument cavities. The study results prompted an extensive prelaunch vacuum bakeout effort and an on-orbit decontamination exercise. In addition, the thermal performance of the instrument radiant coolers could have been detrimentally affected by scattered solar radiation from particulate contamination. In order to mitigate the impact of the particulate contamination, the radiant cooler surfaces were cleaned according to an established criterion prior to launch. (Author)

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

The Hubble Space Telescope is the first spacecraft designed from its conception to allow for Scientific Instrument upgrading and subsystem maintenance by using the Shuttle. Regular and contingency servicing missions preserve and broaden the scientific objectives of the HST through on-orbit maintenance. To achieve mission success for the Hubble Space Telescope First Servicing Mission, a contamination control methodology was developed and instituted by ensure that scientific instrument performance was not degraded or compromised during fabrication, build-up, ground integration and test activities, on-orbit servicing including Extravehicular Activities, or through on-orbit operational activities. The cleanliness methodology considered the effects of outgassing and surface contaminants on the degradation of the sensitive components. Through plans and procedures for handling sensitive components and the development of a detailed contamination budget extending from Goddard Space Flight Center processing through launch, the preservation of the science capabilities (as affected by contamination) was achieved.

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

Contamination witness plates were flown on STS-51 as part of a NASA Extravehicular Activity (EVA) Flight Test Experiment to quantify and identify particulate contamination generated in the Orbiter crew compartment which has the potential to contaminate the Extravehicular Mobility Units (EMUs) and transfer from the EMUs to mission critical hardware during EVAs. Particles, larger than 100 microns, were found on both witness plates, indicating transfer from the EMUs during EVAs. For missions such as the Hubble Space Telescope First Servicing Mission, where contamination critical optical elements were exposed during EVAs, the potential for particulate transfer from the crew compartment to these optical elements and the Hubble Space Telescope was evaluated.