What is Service Probability and how can I use it?
The Service Probability calculation in IONCAP and included in VOACAP is a place holder for a future model. It was a first attempt at computing a confidence factor for the reliability value. In other words it is the probability that the hourly reliability value will be achieved over the days of the month. For example, if the reliability for a given circuit at a specified frequency, hour, month and sunspot number is 90 percent and the service probability is 70 percent, then one would expect that the required signal-to-noise ratio will be equalled or exceeded on 27 days of the month on 70 percent of the possible monthly attempts over numerous sunspot cycles. Although the concept is well founded and useful in life-cycle management of a system, it was based on the best guesses as to what the standard error of estimate is on all of the variables used in calculating reliability. Since the estimates of error are SWAGS, one really can’t put much faith in the SERVICE PROBABILITY values. At this
