DARA instrument

Proba-3's shoebox-sized Davos Absolute Radiometer, DARA, fitted to the Sunward face of the mission's Occulter spacecraft, will maintain a continuous measurement of the Sun’s total energy output, known as the total solar irradiance, which is a vital variable for climate studies. DARA's silver front end includes a 5-mm diameter cavity made from black-painted silver, possessing low temperature emissivity. For 15 seconds at a time sunlight warms the interior of the cavity, then a shutter blade automatically closes at its entrance. For the next 15 seconds electric heat maintains the cavity’s previous temperature – and the energy needed to maintain this temperature is extrapolated to the unit of total solar irradiance which is watts per metre squared. This process continues for the entire lifetime of the instrument – the actuated shutter design employed in DARA has been tested for millions of opening and closings in PMOD’s vacuum chamber.