In collaboration with the PMOD Institute (Physikalisch-Meteorologisches Observatorium Davos) and under an ESA contract, a novel type of radiometer for space application has been developed for the PROBA 3 mission. The objective of the instrument is the continues and precise Total Solar Measurement (TSI) to monitor the short and long-term solar radiative activity.

The method to measure the sun’s irradiation is based on digitally controlled cavity power substitution. The instrument features three independently controllable cavities, which allows backup measurement in case of a defect cavity; furthermore, cavity aging effects can be measured.

The instrument software runs on the well-known 68k microprocessor where a multi-tasking operating system solves the real time issues and manages the flash memory access. On top of that, the radiometer can be accessed by a serial interface which is extended by a robust communication protocol.