CRYOGENIC TESTING OF THE HERSCHEL FLIGHT MODEL SPACECRAFT

Abstract

The ‘Herschel Space Observatory’ is the fourth cornerstone mission in the ‘Horizons 2000’ program of the European Space Agency (ESA), with the objectives to study the formation of galaxies in the early universe and the creation of stars. It will observe the chemical composition of surfaces and atmospheres of comets, planets and natural satellites, and examine the molecular chemistry of the universe. Herschel was launched into an operational Lissajous orbit around the Earth‐Sun L2 point by an Ariane 5 on May 14th 2009 to perform photometer and spectrometer measurements, covering the full far infrared to sub‐millimeter wavelength range from 60 to 670 micrometers during its operational lifetime of more than four years.This paper gives a short overview of the cryogenic system and summarises the cryogenic aspects of the different phases of the acceptance test campaign, including the launch preparation phase as well as the post‐launch transient cool‐down of the system, the verification of the Passive Phase Separator performance and the evaluation of pressure drop measurements performed on the helium venting system. The impact of thermo‐acoustic oscillations within the helium subsystem is described, which were present during the initial cool‐down test phase. A comparison of measurements to numerical analysis results is shown.