Table 6 3.  Service Availability as a Function of

 Specified Satellite Outage Conditions

Global Average

Worst Regional Service

Satellite Temporary Outage Condition

Service Availability

Availability

No Satellites Out:

100.00%

100.00%

ONE SATELLITE OUT FOR MAINTENANCE OR REPAIR

Least Impacting Satellite Out:

 99.98%

99.17%

Average Satellite Out:

 99.93%

97.79%

Most Impacting Satellite Out:

 99.83%

97.63%

TWO SATELLITES OUT FOR MAINTENANCE OR REPAIR

Least Impacting 2 Satellites Out:

 99.93%

 98.21%

Average 2 Satellites Out:

 99.64%

 95.71%

Most Impacting 2 Satellites Out:

 98.85%

 91.08%

THREE SATELLITES OUT FOR MAINTENANCE OR REPAIR

Least Impacting 3 Satellites Out:

 99.89%

 97.13%

Average 3 Satellites Out:

 99.03%

 93.38%

Most Impacting 3 Satellites Out:

 95.87%

 83.92%

Table 6 4.  Example of 3 Day Global Service Availability

 with Component Failure on Worst Day

Ops Scenario Condition

Best Case

Average Case

Worst Case

1 Day   3 Satellites Down

 99.89%

 99.03%

 95.87%

1 Day   1 Satellite Down

 99.98%

 99.93%

 99.83%

28 Days   No Satellites Down

100.00%

100.00%

100.00%

Average Daily Availability

 99.99%

 99.97%

 99.85%

experience downtime.  The service availability service standard was established based

upon this scenario, to ensure that the system can support standard compliance.

The second service availability scenario is shown in Table 6 5, and represents what

may be considered to be a more common 30 day interval.  In this scenario, three

satellites were removed from service for up to 24 hours, each on separate days.

Typical satellite maintenance  operations are conducted on one satellite at a time, which

means that the removal of two satellites for maintenance at the same time will be a rare

occurrence.

6 7