currently being provided by the SORCE/SOLSTICE, is likely the largest single factor that will degrade the TSI variability model capability (long-term stability) below that assessed in this analysis.

6. Summary

Neither alternate currently on-orbit TSI instruments nor solar models can fill and expected SORCE-to-TSIS TIM measurement gap with the required solar climate data record stability. With a TSIS launch late in 2016 and a 1-year baseline TCTE mission duration beginning in late 2013, as analyzed in this report, TCTE will maintain the record’s current level of stability for the duration of the STP-Sat3 mission if it overlaps with SORCE, but will otherwise provide only marginal stability improvement to the TSI record across a SORCE-to-TSIS gap because of its short duration and lack of direct connectivity to the SORCE/TIM record. Only if the TCTE overlaps with both SORCE and TSIS are the CDR stability requirements maintained until TSIS launches.

Although they fail to meet the TSIS CDR requirements by a factor of three, we show that VIRGO data provide the best TSI values in both stability and noise for filling TIM measurement gaps of the anticipated durations, The NRL model provides the next best alternative should the VIRGO data not be available.

We find that the planned TCTE low observing cadence does not limit the TSI record long-term stability provided that the TCTE overlaps with each of the surrounding instruments for two months.

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