SIMBAD references

The interferometric system used for guidance of HST is sensitive to close binaries. Before the launch of HST it was believed that up to 25% of all guide star pairs would lead to guidance failure due to duplicity. After more than 3 years of operation the actual failure rate ascribable to duplicity is estimated to be just below 1%. A computer simulator has been developed to understand the causes of the discrepancy. The simulation indicates a failure rate of under 2% per guide-star pair, in much closer agreement with the observed performance of the guiding system. The failure criterion originally used, was based on the manufacturer's expectations, and was too conservative. The proportion of binary guide stars in the critical separation range had also been somewhat overestimated.