Theoretical foundations for on-ground tests of LISA PathFinder thermal diagnostics

TL;DR

This paper presents a theoretical analysis to design an insulator for testing sensitive temperature sensors in the LISA PathFinder mission, ensuring thermal stability through material and structural optimization.

Contribution

It introduces a theoretical framework for designing a thermally quiet insulator for ground testing of LISA PathFinder sensors, including heat transfer and heat leakage assessments.

Findings

A sphere of about one meter diameter suffices for required stability.

Material and dimension choices meet the temperature stability requirements.

Heat leakage through wires is manageable within the design constraints.

Abstract

This paper reports on the methods and results of a theoretical analysis to design an insulator which must provide a thermally quiet environment to test on ground delicate temperature sensors and associated electronics. These will fly on board ESA's LISA PathFinder (LPF) mission as part of the thermal diagnostics subsystem of the LISA Test-flight Package (LTP). We evaluate the heat transfer function (in frequency domain) of a central body of good thermal conductivity surrounded by a layer of a very poorly conducting substrate. This is applied to assess the materials and dimensions necessary to meet temperature stability requirements in the metal core, where sensors will be implanted for test. The analysis is extended to evaluate the losses caused by heat leakage through connecting wires, linking the sensors with the electronics in a box outside the insulator. The results indicate that, in spite of the very demanding stability conditions, a sphere of outer diameter of the order one metre is sufficient.