Testing of a Freeze-proof Condenser for the Tracker Thermal Control System on AMS-02 2007-01-3238

The paper describes freezing and pressure tests required to develop a freeze-proof condenser for the Tracker Thermal Control System (TTCS). The TTCS is a mechanically pumped two-phase carbon-dioxide loop dedicated to control the temperature of the Tracker electronics. The TTCS is part of the Alpha Magnetic Spectrometer planned aboard the truss of the International Space Station (ISS). The TTCS collects the heat at two evaporators and rejects it at two radiators. In case of an accidental power-down of the AMS02 experiment, resulting in a loss of radiator heater control, the Tracker radiators and the connected TTCS-condensers may cool down as low as −120ºC, which is well below the CO₂-freezing point (−56ºC@3MPa). During uncontrolled radiator heat-up and thawing of the solid CO₂, liquid CO₂ can be trapped in between solid parts resulting in high pressures. To withstand these high pressures, a high-pressure resistant condenser has been developed. In order to verify the design it was needed to determine the maximum pressure inside the condenser during thawing. The pressure determination is performed by a dedicated test set-up with strain gauges.

The paper describes the test and the implications on the condenser design. After an introduction on AMS, a description of the test set-up is given, followed by details on the calibration of the pressure sensors. Subsequently the test and test results are described.

It is concluded that the pressure build up during thawing follows the CO₂ melting line found in the CO₂ 3-phase diagram. Therefore the condenser maximum design pressure directly follows from this diagram when the maximum unloaded condenser temperature is known. From thermal analyses this temperature was found to be −5 ºC leading to a condenser maximum design pressur e of 300 MPa. The condenser, comprising small diameter Inconel 718 tubing attached to a grooved aluminium plate (d_in = 1.0mm, d_out = 3.0mm) is shown -by accepted stress calculation methods- to withstand this pressure within applicable safety margins.