Evaluation of particulate contamination under the storage environment of ADEOS-II

Abstract

Contamination monitoring of spacecrafts during ground processing operations is essential to maintain performance of optical systems. The cleanliness level of spacecrafts is usually evaluated by counting particles fall on collector plates, but the manual counting is taken a considerable time and subject to human errors. Computer-aided counting of particles was performed on silicon wafers with various cleanliness levels using a scanning laser microscope. It was possible to detect particles larger than 1μm. Number of deposited particles, μparticle size distribution, and area coverage were measured and the correlation between the surface cleanliness level and the area coverage was obtained within the range of cleanliness level from 250 to 800. Concurrently with laboratory measurement, the contamination monitoring of storage environment of ADEOS-II at Tanegashima Space Center was performed with collector plates. The area coverage of collector plates agreed very well with the results of the laboratory experiments. The chemical component analysis was also carried out to the particles accreted on the collector plates set in the ADEOS-II storage clean room by an electron probe micro-analyzer. It found that a maximum of 70% of the particles on collector plates were organic and these were thought to come from human sources. Fibrous particles accounted for 11% of measured particles. Moreover, the percentage of particles containing heavy metals was significantly higher than in outdoor environment.