OVERVIEW

The Neutral External Contamination Working Group (NECWG) develops and integrates technical activities associated with space contamination.

WHAT IS CONTAMINATION?

There are two primary categories of contamination: molecular and particulate. Both types of contamination come from a variety of sources (as described below). The accumulation of contaminants on spacecraft surfaces can present a threat to the desired performance of spacecraft systems (optical, thermal, attitude control, etc.). The photo shows metal particulates on a spacecraft wire harness.
 

Sources of contamination (both molecular and particulate) are present during all mission phases from ground handling, through the launch phase and up through the end of mission life. The figures depict some of the major sources of contamination during each of the main mission phases (click to load at full resolution). In addition, during the on-orbit phase, there are often combined or synergistic effects due to the interaction of contaminants with various space environments such as solar exposure, radiation, and ambient gases at spacecraft altitudes.

EXAMPLE OF MOLECULAR CONTAMINATION

The silicon wafer shown in the photo has been contaminated with a pump oil, and has resulted in a thin film deposit. The right hand side of the wafer has been cleaned using CO2 snow cleaning method. Once a contaminant has been deposited, there are a number of cleaning methods which may be employed including:

• Conventional solvent rinsing and wiping

• Vacuum bakeout

• Recoating

• New technology methods such as:

  • CO2 Snow cleaning

  • Laser cleaning

  • Ion cleaning

  • Jet spray cleaning

  • On-orbit exposure to ambient atomic oxygen

In addition, new preventive technology such as molecular absorbers have been utilized. The absorbers prevent outgassing materials from reaching sensitive surfaces by trapping contaminant molecules within the absorber. (Photo supplied by Hughes Aircraft Company, El Segundo, CA)

This photo depicts severe particulate contamination of a spacecraft radiator surface. The presence of white, fairly large particles is easily seen on the right side of the component. Due to the delicate nature of the surface, coventional cleaning methods may abrade the surface and reduce the radiator performance. Before launch, these particles were successfully removed using the CO2 snow cleaning method.  Particulate contamination cleaning methods include:

• Surface vacuuming and wiping

• Brushing

• Ultrasonic cleaning

• Particle charging method

• New technology methods such as:

  • CO2 Snow cleaning

  • Laser cleaning

  • Ion cleaning

  • Jet spray cleaning

  • On-orbit exposure to ambient atomic oxygen

(Photo supplied by Space System/Loral, Palo Alto, CA)

CONTAMINATION EFFECTS ON SPACECRAFT SYSTEMS

There have been many spacecraft missions whose goals and performance were jeopardized by contamination accumulations. Reported contamination incidents dated as early as Orbiting Geophysical Observatories (OGO-6) mission in 1969 and as late as recent Titan IV fairing problem in 1994. If a thermal control system is contaminated by either molecules or particles, the thermal properties may be changed. As a result, the spacecraft or instruments may be incapable of maintaining proper temperature control. Similarly, if an optical system is contaminated, it may result in serious mission performance problems such as improper data acquisition, reduction in throughput, or incorrect imaging. This photo shows molecular contamination from a unintentional vent on LDEF.

The basic goal of a contamination control program is to limit the amount of contamination both on the ground and on-orbit, thus helping to ensure that mission performance requirements are achieved.

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