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Laboratory for Atmospheric and Space Physics


The Total and Spectral Solar Irradiance Sensor (TSIS-1), first selected in 1998 for the National Polar-orbiting Operational Environmental Satellite System (NPOESS), re-manifested in 2010 on the NOAA-NASA Joint Polar Satellite System (JPSS), then the NOAA Polar Free Flyer, but in the end launched to the International Space Station on December 8, 2017.

TSIS-1 acquires measurements of total and spectral solar irradiance (TSI and SSI, respectively). TSI is required for establishing Earth’s total energy input while SSI is needed to understand how the atmosphere responds to changes in the sun’s output. Solar irradiance is one of the longest and most fundamental of all climate data records derived from space-based observations.

TSIS-1 provides continuation of the Total Irradiance Monitor (TIM) and the Spectral Irradiance Monitor (SIM), currently flying on the NASA Solar Radiation and Climate Experiment (SORCE). Launched in 2003, SORCE is now more than ten years beyond its prime-mission lifetime. The launch failure of the NASA Glory mission in 2011, coupled with diminished battery capacity on SORCE and delays in the launch of TSIS-1 have put the continuous 38-year TSI record at risk. In 2012, a plan to maintain continuity of the TSI calibration scale between SORCE and TSIS-1 was rapidly implemented through the USAF Space Test Program STPSat-3 that launched in late 2013 as TCTE: the “Total solar irradiance Calibration Transfer Experiment” . TCTE has been taking TSI measurements at various cadences since. An overlap period is planned when both SORCE and TSIS measurements are taken to cross-calibrate the two data sets and extend the data records for TSI and SSI.

Mission Concept

TSIS-1 consists of the TIM and SIM instruments, TPS, microprocessor unit, fine sun sensors, and support equipment. Because the TIM and SIM are designed to operatenominally in a solar-viewing orientation they are mounted on a gimbaled platform  that accommodates targeting independent of the ISS attitude. The instruments and their associated supporting flight segment systems are depicted in Figure below.

Mission planning, routine state of health monitoring, and spacecraft commanding are accomplished by the TSIS-1 Science Operations Center (TSOC) in coordination with the ISS Payload Operations Integration Center (POIC). Raw science data are recorded by the ISS and regularly transmitted by way of TDRSS to the POIC and then routed to the TSOC. Once received at TSOC the data is transferred to the TSIS Science Data
System (TSDS) for calibration and data processing. After resulting data products are validated for accuracy and precision, they are made available to the science data users by the TSDS and also delivered to the Goddard Earth Science Data and Information Services Center (GES DISC) for archiving.