Calibration of the SOLSPEC spectrometer to measure the solar irradiance from space

The SOLSPEC instrument has been built to carry out absolute solar spectral irradiance measurements from space. It was first flown in December 1983 on mission STS 9 (Spacelab 1), from August 1992 to June 1993 on board the free -flying EURECA platform with mission STS 46 (deployment) and STS 57 (retrie val), then flown three times more with the ATLAS missions STS 45, 56 and 66 . Further applications are foreseen in combination with the International S pace Station Alpha (ISSA). SOLSPEC covers a wavelength range from 180 nm to 3000 nm split into three separate spectrometer channels (ultraviolet, visi ble and infrared) and has been calibrated pre- and post-flight using a blac k body at the Landessternwarte Heidelberg with temperatures up to 3300 K. I n this paper the calibration concept is presented, together with a short in strument description and suggestions for improvements in order that higher black-body temperatures can be reached.