Standards are an important component of national and international trade. We depend upon standards to assure that manufactured parts will work together, wherever they are made, and that we speak the same technical language, no matter what language we speak. Understanding is important in order to know when to take exceptions to or tailor the standard to fit the job. Standards that are used in contamination control have increased in numbers over the years as more industries have had to improve their manufacturing processes to enhance reliability or yields of products. Some older standards have been revised to include new technologies, and many new standards have been developed. Some of the new standards were written for specific industries while others apply to many industries. Many government standards have been replaced with standards from nongovernmental standards organizations. This trend has been encouraged by U.S. law that requires the government to use commercial standards where possible. This paper reviews some of the more important standards for the aerospace industry, such as IEST-STD-CC1246 and ISO 14644-1, that have been published in recent years. Benefits, usage, and problems with some standards will be discussed. Some standards are referenced, and websites of some standards organizations are listed.
During the launch of a spacecraft, particles on the spacecraft, support structure, and the payload fairing may be removed from surfaces and move to other surfaces. Some particles may vent from the payload fairing. It is desirable to be able to predict the cleanliness of critical surfaces following launch based on hardware cleanliness before launch. Reliable prediction of post-launch contamination would help in setting hardware cleanliness and cleaning requirements during assembly and integration operation before launch. Particles are removed from surfaces by forces that result from vibro-acoustic, shock, acceleration, and aerodynamic actions. Acceleration and aerodynamic forces may transport the removed particles to other surfaces and out of the vents.
Manu U.S. government standards are being replaced with nongovernmental standards, both national and international. The use of international standards is increasing as the levels of international trade increase. Contamination control is critical for many industries and has resulted in greater numbers of national and international standards on this subject with more standards in development. Some standards relate to specific industries, and others are applicable to many industries. This paper review the status of the U.S., European, and ISO (International Organization for Standardization) that are of interest to optical systems, especially those related to space systems.. Items taht are discussed include the following: The revision to MIL-STD-1246 (Product Cleanliness Levels and Contamination Control Program) will be published by the IEST (Institute of Environmental Sciences and Technology) as a nongovernmental standard; ISO 14644-1 and 14644-2 will replace FED-STD-209 (Airborne Particle Cleanliness Classes in Cleanroom and Clean Zones); ISO 15388 (Space Systems - Contamination and cleanliness Control) is under development; IEST-RP-CC016 (The Rate of Deposition of Nonvolatile Residue in Cleanrooms) is now being revised; ASTM E 595 (outgassing screening test) is used internationally; the ASTM E 1559 outgassing test has been revised; and ASTM E 490 (Standard Solar Constant and Zero Air Mass Solar Spectral Irradiance Tables) has been revised. Other standards from ASTM, IEST, ECSS (European Cooperation for Space Standardization), and ISO are discussed. Lists of standards, points of contact, and information available on the Internet are included.
Monitoring of cleanroom and spacecraft cleanliness during ground processing operations is essential in order to verify performance requirements for optical systems prior to launch. The objective is to replace manual particle counting with automated particle counting in order to reduce the processing time for the witness plates and to improve precision and accuracy of the measurements. A modified silicon wafer inspection instrument, using a HeNe laser light source, was used to count and size particles deposited on wafers exposed in the cleanrooms. The previous paper discussed measuring particles on silicon wafer witness plates during operations cleanrooms and discussed analytical methods for calculating percent area coverage. This paper describes the optical performance of the ESTEK instrument and test on the instrument.
The orbiters undergo periodic maintenance during which extensive mechanical and electrical system inspection, upgrades and/or refurbishment are performed. For sensitive payloads, new materials added to the orbiter midbody (payload bay) area is of concern for the first flight after an orbiter maintenance down period (OMDP). Discovery, (OV- 103), recently underwent an OMDP, and the Hubble Space Telescope Servicing Mission 2 will be its first flight after OMDP. Due to the contamination sensitivity of the Hubble Space Telescope, a program was implemented to monitor the nonvolatile residue and particle levels of the midbody during the OMDP.
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