Design and in-orbit performance of EP-FXT thermal control

Purpose The follow-up X-ray telescope (FXT) is one of the two payloads of the Einstein Probe (EP), consisting of the upper composite with the X-ray mirror module as the core, the lower composite with the pnCCD module as the core, and the interface structure. The FXT thermal control subsystem is responsible for the thermal design, thermal implementations, and testing of the entire FXT payload thermal control.
Methods A design approach is adopted with passive thermal control technology as the main method and active thermal control technology as a supplement for common components. The X-ray mirror modules are high-precision optical components, utilizing active closed-loop temperature control to ensure high precision and stability. The pnCCD detectors operate at a stable low temperature, with refrigerators used to cool the detector houses, ensuring they can operate under stable low-temperature conditions. The hot ends of the refrigerators are connected to the external radiator panels through heat pipes for heat dissipation.
Results The thermal control subsystem of FXT is operating properly in-orbit. All component temperatures meet the design requirements.
Conclusion After multiple rounds of design and test verification, FXT was successfully launched with EP and completed in-orbit testing. During the in-orbit testing phase of EP, the function of the FXT thermal control subsystem works well. The temperatures of the components and units are normal. This paper introduces the design of FXT thermal control and the in-orbit performance of the thermal control subsystem.