Development of mechanical cryocoolers for the cooling system of the Soft X-ray Spectrometer onboard Astro-H

Abstract

Astro-H is the Japanese X-ray astronomy satellite planned for launch in 2014. The Soft X-ray Spectrometer (SXS) onboard Astro-H, is a high energy resolution spectrometer utilizing an X-ray micro-calorimeter array, which is operated at 50mK by the ADR with the 30-L superfluid liquid helium (LHe). The mechanical cryocoolers, 4K-class Joule Thomson (JT) cooler and 20K-class double-staged Stirling (2ST) cooler are key components to achieve a LHe lifetime for over 3years in orbit (5years as a goal). Based on the existing cryocoolers onboard Akari (2006) and JEM/SMILES (2009), modifications for higher cooling power and reliability had been investigated. In the present development phase, the Engineering Models (EMs) of these upgraded cryocoolers are fabricated to carry out verification tests for cooling performance, mechanical performance and lifetime. Nominal cooling power of 200mW at 20K for the 2ST cooler and 40mW at 4.5K for the JT cooler were demonstrated with temperature and power margin. Mechanical performance test for the 2ST cooler units proves tolerability for pyro shock and vibration environment of the Astro-H criteria. Continuous running of the 4K-class JT cooler combined with the 2ST precooler for lifetime test has achieved over 5000h without any degradation of cooling performance.