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  • Author or Editor: James C. Barnes x
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William K. Widger Jr. and James C. Barnes


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Arnold H. Glaser, James C. Barnes, and Donald W. Beran


A Monte Carlo technique simulates the effects of cloudcover on the performance of the Apollo On-board Navigation System. For each of three simulated Apollo missions, the probability of sighting at least a specific number of landmarks within the first two and one-half revolutions is determined. Cloudcover over the landmarks is derived from meteorological satellite data. These cloud amounts were found to be generally less than ground observed; the difference is believed to be due to the existence of small cumulus cells not resolved by the satellite, and the overestimation of sky cover by ground observers. A discussion of these factors is included.

The results of the mission simulation program indicate that the number of sightings can be materially increased by a choice of landmarks that are distributed to conform to the operational characteristics of the On-board Navigation System as much as by choice for optimum climate.

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