chapter 4, Contamination Control

Excerpt

Once the cleanliness requirement for a surface has been quantified, the issue becomes, can this level of cleanliness be maintained and verified? If a surface can tolerate a large amount of contamination, no special procedures other than prelaunch visual inspection and cleaning may be warranted. In the other extreme, analysis may indicate that the required cleanliness level is too clean to be maintained on orbit. This would force the program to relax the contamination requirements by either a) redesigning the hardware, or b) altering the mission operations profile. In most cases, the required cleanliness level lies between these two extremes and can be maintained only through enforcement of the proper contamination control processes and procedures.

The sections that follow provide a discussion of the various methods that can be used to prevent, detect, and remove contamination from sensitive surfaces, as well as methods to help maintain surface cleanliness. These sections may be tailored to specific program objectives and utilized in a contamination control plan as part of the overall contamination control effort. The specific case of the Shuttle Orbiter is examined in order to provide the designer with a feel for the type of environment a spacecraft will be exposed to during launch processing and early on-orbit operations. Finally, lessons learned from the Midcourse Space Experiment, perhaps the most contamination-aware program of all time, are summarized.

4.1 Preventing Contamination

To be effective, the contamination control process must start with conceptual design and proceed through on-orbit operations. There are a variety of steps that the designer can take to minimize both the contamination generated by a subsystem and the effects of contamination on a subsystem. Often these steps impose no added effort to the program and can simplify problems during the later stages, when solutions are more costly and time consuming.