Operations and Performance of the PACS Instrument 3He Sorption Cooler on board of the Herschel Space Observatory

TL;DR

This paper details the operation, performance, and recycling procedures of the 3He sorption cooler on the Herschel Space Observatory's PACS instrument, including temperature stability, hold times, and innovative helium lifetime estimation methods.

Contribution

It provides a comprehensive overview of the cooler's operational performance and introduces an alternative helium lifetime measurement technique based on recycling temperature effects.

Findings

Stable temperature of 285mK maintained for 60-73 hours.

Established a reliable functional relation for hold time prediction.

Innovative use of recycling temperature effects for helium lifetime estimation.

Abstract

A 3He sorption cooler produced the operational temperature of 285mK for the bolometer arrays of the Photodetector Array Camera and Spectrometer (PACS) instrument of the Herschel Space Observatory. This cooler provided a stable hold time between 60 and 73h, depending on the operational conditions of the instrument. The respective hold time could be determined by a simple functional relation established early on in the mission and reliably applied by the scientific mission planning for the entire mission. After exhaustion of the liquid 3He due to the heat input by the detector arrays, the cooler was recycled for the next operational period following a well established automatic procedure. We give an overview of the cooler operations and performance over the entire mission and distinguishing in-between the start conditions for the cooler recycling and the two main modes of PACS photometer operations. As a spin-off, the cooler recycling temperature effects on the Herschel cryostat 4He bath were utilized as an alternative method to dedicated Direct Liquid Helium Content Measurements in determining the lifetime of the liquid Helium coolant.