Thermal Testing of the Herschel EPLM STM

The Herschel Extended Payload Module (H-EPLM) consists of the cryostat, the telescope, and the sunshield and solar generator. Within the cryostat, a 2367 l superfluid helium tank and its gas, evaporating via a passive phase separator, provide the required heat sinks at four staggered temperature levels from 1.7 to 15 K to the focal plane units of three scientific instruments. The helium gas is then used to cool three thermal radiation shields inside the cryostat vacuum vessel before being vented to space. In the frame of the EPLM qualification program, cryogenic / thermal tests were performed on EPLM Structural / Thermal Model (STM) level at ambient conditions and in the Large Space Simulator (LSS) facility in Noordwijk, NL. Mass and thermal dummies were integrated in the STM instead of the respective flight parts for the instruments’ focal plane and local oscillator units, the telescope and the sunshield / solar generator. This paper presents the test setup, measured data and evaluation results.