Long-term radiometric accuracy is a fundamental requirement for the measurement of solar, terrestrial, and/or planetary atmospheric EUV emissions from space. Due to non-traceable changes of the numerous spectrometric efficiency parameters with time, long-term stability of satellite instrumentation has not been achieved in the past. One possibility to overcome these shortcomings is the use of absolute standard detectors in combination with spectrometers to recalibrate EUV spectrometers in space. The system ACES takes advantage of this approach in the wavelength range from about 1 to 180 nm at 0.4 nm to 2 nm spectral resolution. ACES is based on a combination of three spectrometers, four special double ion chambers, and one proportional counter. Specific features and experimental details are presented. The expected radiometric accuracy is better than 10 percent.