The paper describes the development and the experimental validation of a cryogenic magnetic shielding system for transition edge sensor based space detector arrays. The system consists of an outer mu-metal shield and an inner superconducting niobium shield. First, a basic comparison is made between thin-walled mu-metal and superconducting shields, giving an off-axis expression for the field inside a cup-shaped superconductor as a function of the transverse external field. Starting from these preliminary analytical considerations, the design of an adequate and realistic shielding configuration for future space flight applications (either X-IFU [D. Barret et al., e-print arXiv:1308.6784 [astro-ph.IM] (2013)] or SAFARI [B. Jackson et al., IEEE Trans. Terahertz Sci. Technol. 2, 12 (2012)]) is described in more detail. The numerical design and verification tools (static and dynamic finite element method (FEM) models) are discussed together with their required input, i.e., the magnetic-field dependent permeability data. Next, the actual manufacturing of the shields is described, including a method to create a superconducting joint between the two superconducting shield elements that avoid flux penetration through the seam. The final part of the paper presents the experimental verification of the model predictions and the validation of the shield's performance. The shields were cooled through the superconducting transition temperature of niobium in zero applied magnetic field (<10 nT) or in a DC field with magnitude ∼100 μT, applied either along the system's symmetry axis or perpendicular to it. After cool-down, DC trapped flux profiles were measured along the shield axis with a flux-gate magnetometer and the attenuation of externally applied AC fields (100 μT, 0.1 Hz, both axial and transverse) was verified along this axis with superconducting quantum interference device magnetometers. The system's measured on-axis shielding factor is greater than 10, well exceeding the requirement of the envisaged missions. Following field-cooling in an axial field of 85 μT, the residual internal DC field normal to the detector plane is less than 1 μT. The trapped field patterns are compared to the predictions of the dynamic FEM model, which describes them well in the region where the internal field exceeds 6 μT.

SRON, Netherlands Institute for Space Research, is developing a Focal Plane Assembly (FPA) for future missions [1][2] requiring large-format arrays of Transition Edge Sensors (TES), read-out with Frequency Domain Multiplexing (FDM) and operating at 50 mK. The FPA is mechanically suspended from a temperature level of 1.7 K to 2 K, with an additional thermal interface at an intermediate temperature of 0.3K. The up-scaling of the amount of pixels together with the mass and volume limitations for a space instrument in general requires technology development activities in several areas. A dedicated program has been initiated for the development of a magnetic shield to provide enough attenuation over the full detector surface, to develop high density electrical wiring and interconnects and to provide a thermal insulating suspension capable to meet the mechanical requirements for launch. This with the goal of demonstrating Technology Readiness Level 4-5 (TRL) for each of these key-technologies before the end of 2015. This paper presents the status of the key-technology developments for the FPA, focusing on the following 3 subjects: I.The development and verification of a superconducting Niobium and high permeability magnetic shield combination.II. Development of high density superconducting interconnects, between the detector and 50 mK FDM electronics and between the 50 mK FDM electronics and the 1.7-2 K interface. III.Mechanical and thermal characterization of a double-layered thermal insulating Kevlar suspension required to mount the 550 g 50 mK mass with a first resonance frequency larger than 300 Hz.

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