OLSG Report_Final_06_05_12 - Interagency Operations Advisory ...

Optical Link Study Group (OLSG) Final Report
IOAG.T.OLSG.2012.V1
PDT accumulated the total CFLOS during each day, ensuring a minimum elevation angle of
20° was met to assess performance. Since the satellite has three days of onboard storage,
the maximum performance for this scenario required at least nine hours of combined
(between sites) CFLOS every three days. Since ground sites visible to L2 orbit are only visible
at night, the PDT is expected to be quite high relative to daytime, when more clouds are
typically observed. The overall PDT was computed for three locations, including the Tenerife
OGS; Ascension Island; and Hartebeesthoek, S. Africa (see Figure 37 and Table 18 below).
The Tenerife OGS has the best performance, since it is both very clear at night and it sits 2.3
km above mean sea-level. However, when combined with an additional site, the effects of
geographic diversity become quite noticeable, increasing the PDT to greater than 99%. Using
two sites in different hemispheres mitigates not only the weather, but also variability within
the L2 orbit that produces different elevation angles throughout the mission.
Figure 37: Location of ground sites in the L2 Scenario.
Table 18: PDT (%) for L2 Scenario over the 2005-2010 period.
Tenerife OGS Ascension Is. Hartebeesthoek Tenerife OGS +
Ascension Is.
Tenerife OGS +
Hartebeesthoek
96.3% 89.6% 85.2% 99.8% 99.9%
Figure 38 shows the cumulative distribution of the monthly PDT for each site and the
combinations of sites. For single sites, there is a small probability that the PDT for a given
month could drop below 50%. However, when two sites are used, that probability is greatly
reduced. In fact, the Tenerife OGS + Hartebeesthoek combination rarely produces a PDT less
than 100%. The results of this scenario suggest there is a credible business case for
interoperability between the space agencies.
Page | 77